SAFETY BRIEFS

Drawing upon years of experience in safety consulting, Triodyne's engineers and scientists have published research papers which appear in the Triodyne Safety Briefs. These publications cover a variety of topics of interest to academics, manufacturers, and safety professionals.

Volume 1 No. 1, April 1981
On Classification of Safeguard Devices (Part I).
Ralph L. Barnett and Peter Barroso, Jr.

Engineers cannot change the law but we can provide guidelines to help the courts make more reasonable decisions. The first step is to stop looking at safety devices as a homogeneous lump. Safety devices differ in the amount of safety they provide and the amount of harm they can do. This article presents a classification system that makes it possible to evaluate the efficacy of safeguarding devices, breaking down devices into mutually exclusive and jointly exhaustive categories.

Volume 1 No. 2, September 1981
On Classification of Safeguard Devices (Part II).
Ralph L. Barnett and Peter Barroso, Jr.

Part I of this article described an intrinsic classification system focusing on characteristics of individual safeguarding devices. In Part II we are concerned with the relationships among such devices. This requires the introduction of a category which deals with those safety characteristics inherent in a system. These are ranked under Zero Order Systems in the article's functional hierarchy of safety devices and concepts.

Volume 1 No. 3, October 1982
Zero Obstruction Repair Overpass
Ralph L. Barnett

The Zero Obstruction Repair Overpass (Z.O.R.O.) is a new concept enabling roadways to be repaired without interrupting normal traffic flow. Z.O.R.O. is a movable prefabricated hill which cars drive over while construction proceeds underneath. Its lightweight, reusable modular design incorporates techniques developed for military bridge construction.

Volume 1 No. 4, December 1982
Philosophical Aspects of Dangerous Safety Systems.
Ralph L. Barnett and Beth A. Hamilton

One of the unfortunate trends developing in the product liability movement is the promotion of dangerous safeguarding devices. Such devices arise principally from insufficient research, judicial coercion, and liability proofing. The safety literature presents an unequivocal mandate against the use of safeguarding systems that sometimes present hazards themselves.

Volume 2 No. 1, July 1983
On Safety Codes and Standards.
Ralph L. Barnett

This article posits that 1) compliance, or non-compliance, with safety codes is presently the only rational way to judge whether a design is safe or defective, and 2) safety codes cannot properly protect the public interest unless they define both the lower and upper bounds, or limits, on the conduct of designers. Engineers are introduced to the doctrine of "rebuttable presumption" relative to safety standards and a semantic problem concerning the use of the term "minimum safety standards" is addressed.

Volume 2 No. 3, November 1983
Dependency Hypothesis (Part I).
Ralph L. Barnett, Gene D. Litwin and Peter Barroso,Jr.

This article discusses the types of changes in the man/machine interface which accompany the incorporation of safety systems into a machine. Safety systems introduced to meet narrowly defined safety objectives may give rise to broad secondary effects that subtly or profoundly influence the machine's overall safety and function. Some new criteria are described to aid in the evaluation of proposed safeguards.

Volume 2 No. 4, September 1984
On the Safety of Motorcycle Side Stands.
Dror Kopernik.

When a motorcycle is banked to the left with its kickstand in the down, or park position, the contact between the kickstand and the pavement can cause the driver to loose control. This paper explores the design parameters affecting kickstand retraction.

Volume 2 No. 4, September 1984
Drill Press Guards.
William G. Switalski and Ralph L. Barnett

An investigation into the safety of drilling reveals a number of shortcomings in drill press safety guards.

Volume 3 No. 1, December 1984
Dependency Hypothesis (Part II): Expected Use.
Ralph L. Barnett, Gene D. Litwin and Peter Barroso,Jr.

Safeguarding systems may be introduced to perform specific safety tasks, to comply with some code or standard, or to liability-proof a machine. Whatever the case, the device itself may be perceived to define a safety function and users will expect the device to perform that function.

Volume 3 No. 2, June 1985
Safety Hierarchy.
Ralph L. Barnett and Dennis B. Brickman

A popular litany heard in a product liability trial is "the safety hierarchy." It is associated with a number of misconceptions which are explored in this paper.

Volume 3 No. 3, July 1985
Trailer Hitches and Towbars.
William G. Switalski and Ralph L. Barnett

A survey of trailer hitch requirements in the 50 States has highlighted problems of uniformity, communication, suitability and design specificity.

Volume 3 No. 4, September 1985
Meat Grinder Safety Throat.
Ralph L. Barnett, Gene D. Litwin and Gary M. Hutter

Every engineered system represents a tradeoff among at least three criteria: cost, safety, and function. For a meat grinder with a safety feed throat and stomper, common sense tells us that operator safety will increase as the throat diameter gets smaller and its length gets longer. It is just as apparent that the feed throat capacity will decrease accordingly. This paper quantifies the relationship among the throat parameters, the capacity and the stomper force.

Volume 4 No. 1, April 1986
Mechanical Power Press Safety Bibliography.
Beth A. Hamilton, Joyce E. Courtois and Cheryl A. Hansen

The safety literature on mechanical power presses (punch presses) is characterized by publications more practical than scholarly and has not been subjected to the more exact bibliographic control of other technical literature, thereby inhibiting research on safety matters relating to power presses. The aim of this bibliography is to promote better control of, and to facilitate access to, the literature on mechanical power press safety.

Volume 4 No. 2, June 1986
On Rubber Augers -- Failure Modes and Effects.
Dennis B. Brickman and Ralph L. Barnett

The flexible flight auger gives rise to a new set of hazards and risks without fulfilling its promise of eliminating the amputation hazard. Failure modes of the auger are discussed.

Volume 4 No. 3, November 1986
Mandatory Seat-Belt Usage Laws: Exemptions to the Rule.
Gary M. Hutter and Cheryl A. Hansen

By 1986 twenty-seven states had passed mandatory seat-belt usage laws, all of which provide a variety of exemptions to mandatory usage. The categories and distribution of these exemptions are examined.

Volume 4 No. 4, December 1986
Proposed National Strategy for the Prevention of Severe Occupational Traumatic Injuries.
Association of Schools of Public Health

This position paper by the Association of Schools of Public Health outlines a proposal for minimizing workplace injury and advancing workplace safety.

Volume 5 No. 1, February 1988
Principles of Human Safety.
Ralph L. Barnett and William G. Switalski

This paper describes selected concepts from safety and human factors engineering. Important philosophical tools that affect designs are summarized.

Volume 5 No. 2, July 1988
Deadman Controls on Lawn Mowers and Snowblowers.
Ralph L. Barnett and Dennis B. Brickman

Consumer Product Safety Commission injury data are examined, and associated failure modes and effects verify the predictions contained in the literature. All failure modes involved ergonomic considerations. Zero mechanical state and its relationship with the current approach to lawn mower and snowblower maintenance are discussed.

Volume 5 No. 3, October 1989
Reliability and Safety of Medical Devices: Introduction.
James R. Wingfield

Medical devices are regulated by the Food and Drug Administration. Companies involved in this specialized area must conduct their business in an atmosphere of formality not present in other areas of commercial product development. Past FDA emphasis has been on manufacturing compliance. However, recent indications are that the design phase of product development will receive greater attention.

Volume 5 No. 4, January 1990
Status of Standards of Practice in Pharmacy
James T. O'Donnell

Forces affecting standards, including laws and regulations, accrediting agencies, legal opinions, and professional organizations, are discussed, and compliance is evaluated. Promulgation of standards is examined from positive and negative viewpoints.

Volume 6 No. 1, March 1990
Changing World of Products Liability Law
Kenneth W. Clarkson and Francisco O. Loriga

This paper highlights changes in products liability law in the fifty states over the last decade.

Volume 6 No. 2, June 1990
Ergonomic Studies of Grip Strength -- Literature Review.
Dennis B. Brickman

A thorough study of literature on human strength reveals the need for a single data source which could be easily accessible to many researchers. Published data on one subset of this topic, ergonomic grip strength, is summarized under sixteen factors. Available data has been charted and documented in a way that will facilitate future reference and use.

Volume 6 No. 3, March 1991
Introduction to Fracture Mechanics, Part 1.
E.J. Ripling

Until recently, blaming all fracture on discontinuities was expedient since there was no quantitative way of identifying the major contributing factors to service fractures. With the advent of fracture mechanics, fractures can now be analyzed with a certainty never before possible. The concepts of this new discipline are described.

Volume 6 No. 4, May 1991
Photographic Documentation and Analysis in Vehicle Accident Reconstruction.
Dror Kopernik and Crispin Hales

The use of the camera is increasingly important in vehicle accident reconstruction work. This paper reviews photographic methods currently in use in accident reconstruction.

Volume 7 No. 1, August 1991
Airborne Contaminants in the Machine Tool Industry.
Gary M. Hutter

This paper addresses some basic aspects of occupational exposure to toxic and hazardous substances in the machine tool industry.

Volume 7 No. 2, December 1991
Fire and Explosion Investigations: A Historical and Hysterical Perspective.
John A. Campbell and Kim R. Mniszewski

A large body of cause-and-effect mythology has developed in fire investigation. The lack of validity of common myths is reviewed, and new forensic engineering analysis techniques discussed.

Volume 7 No. 3, June 1992
Safety Interlocks -- The Dark Side.
Frank B. Hall

Interlock applications bring their own risks, which tend to offset the intended safety. The balancing of those risks against the safety afforded must always be considered in the ultimate decision on whether or not the safety device should be used at all. This paper enables readers to judge for themselves the effectiveness of interlocks and various alternative safety measures.

Volume 7 No. 4, August 1992
Small Agricultural Tractor ROPS: New Operator Protective Zone.
Edward A. Fritz and William G. Switalski

A literature search attempts to identify all Operator Protective Zones ever utilized in the world, in order to determine whether published information existed to define a more compact Operator Protective Zone than those of current SAE/ASAE standards. The researchers conclude that the Operator Protective Zone upon which the current standards are based is the only substantiated zone available for possible application to small agricultural tractors.

Volume 8 No. 1, September 1992
Doctrine of Manifest Danger and Its Relationship to Reliability, Preventive Maintenance and Fail-Safe Design.
Ralph L. Barnett

Doctrine of Manifest Danger is a design concept using direct cues or indicator devices to communicate to the community of users that the safety of a system has been compromised before injuries occur. The paper addresses a related legal issue by distinguishing between proximate cause and cause of action.

Volume 8 No. 2, February 1993
Electromagnetic Interference and Electrostatic Discharge Testing on Medical Products: An Introduction.
Richard M. Bilof

Electromagnetic Interference (EMI) and Electrostatic Discharge (ESD) testing are essential elements to the design of almost any new electronic or electromagnetic product. The effects of EMI and ESD are described. Several examples are presented of hospital equipment subject to EMI and ESD, and of mechanisms developed to eliminate them.

Volume 8 No. 2, February 1993
Understanding Adverse Drug Reactions.
James T. O'Donnell

As many as 1.5 million persons are hospitalized each year because of adverse drug reactions. This paper outlines the types of reactions, the importance of recognizing them, the elements involved in such reactions, and caregivers' countermeasures to prevent them.

Volume 8 No. 2, February 1993
Reliability and Safety of Medical Devices: Part II.
James R. Wingfield

The development of safe, reliable medical devices requires the implementation of a rigorous and disciplined approach throughout the product design phase. The monetary payback of program planning and design assurance activities expected to exceed the incremental cost of development. A rigorous design approach also fulfills the responsibility of manufacturers to exercise diligence in the design of critical medical devices.

Volume 8 No. 3, June 1993
Care and Feeding of PLC-Controlled Machinery.
Lawrence K. Bell

The history of the mass production-long run and mass production-short run concepts in American industry is reviewed, and the operation pf the tri-axis transfer machine is discussed.

Volume 8 No. 4, July 1993
Design Methodology for Predicting Ergonomic Grip Strength.
Dennis B. Brickman

A design methodology has been developed to assist bioengineering practitioners in effectively evaluating ergonomic grip strength data. The methodology employs a set of modifying factors to estimate the hand grip strength of a population in an explicit form. The introduced grip strength modification factor approach allows designers and researchers to predict the grip strength of individuals and collections of homogeneous distribution in various situations.

Volume 8 No. 4, July 1993
Under-the-Influence of Alcohol.
John P. Bederka

Factors in intoxication are reviewed, and methods of determining intoxication are discussed. A helpful guide for the expert witness/consultant involved in DUI litigation.

Volume 9 No. 1, November 1993
Mechanical Power Press Bibliography: Second Edition
Lucinda J. Fuller

Representing over two decades of engineering research, this is a comprehensive collection of literature on mechanical power press safety, 1902-1993.

Analysis of a fatal auger elevator accident reviews a number of fundamental failure modes in order to determine the cause of the accident. Analysis showed that the accident was caused by unusual misuse of the product. Known safety control concepts do not preclude such unforeseeable events.

Using universal guards developed by Bethlehem Steel and the U.S. Naval Academy, experiments were conducted which identify new hazards introduced by the proposed guards. The results support the ANSI B11.12 standard which states that "No universal method of safeguarding the point of operation for general-purpose roll benders is known at this time."

Continued discussion of mass production concepts in American industry, and operation of the tri-axis transfer machine, including questions of engineering documentation, record keeping and software considerations.

Volume 10 No. 1, August 1994
Principle of Uniform Safety.
Ralph L. Barnett

The expression of the Principle of Uniformity is generalized and focused on safety issues. Product designs which do not treat dangers uniformly, often cause human errors which arise from inductive inference and generalization of experience.

Volume 10 No. 2, November 1994
Care and Feeding of PLC-Controlled Machinery: Part 3.
Lawrence K. Bell

Part 3 concludes this series with a thorough analysis of the Product Liability aspects of the likely impact of the second industrial revolution, as described in this series of articles. Conclusions and recommendations are made for attorneys, insurance companies, and manufacturers.

Volume 10 No. 3, February 1995
The Pepcon Plant Fire / Explosion: A Rare Opportunity in Fire / Explosion Investigation.
Kim R. Mniszewski

Videotape of a fatal fire and explosion at a large ammonium perchlorate plant allowed advanced investigative fire reconstruction techniques. This and other engineering analyses were used to determine the complex sequence of events and to determine possible causes of the explosion.

Volume 10 No. 4, April 1995
Quantification versus Go / No-Go Criteria.
Dennis B. Brickman and Ralph L. Barnett

Compliance or noncompliance with a sound safety code or standard is currently the most rational way of judging whether a product or system is sufficiently safe. Many such codes specify minimum numerical criteria such as loading, tile angle and judgments based on quantitative test data as opposed to meeting minimum criteria. This paper illustrates the richness of quantification for a number of different products.

Volume 11 No. 1, April 1995
On the Safety of Stationary Buffing Machines.
Dennis B. Brickman and Ralph L. Barnett

When a workpiece locks onto the surface of a cloth buffing wheel, hazards associated with missiles, flailing, and entanglement are introduced. Classical barrier guards have been used; another approach is hooding the buffing wheel. A qualitative testing program indicated that the aggressiveness of the ensnarement and the compliant nature of the buffing wheel frustrate these proposed safeguards. New hazards are introduced by the safety devices themselves.

Volume 11 No. 2, May 1995
Safeguard Evaluation Protocol: A decision tree for standardizing, optionalizing, prohibiting, ignoring, enhancing or characterizing Safeguards.
Ralph L. Barnett and Steven R. Schmid

A decision protocol is presented for assessing whether a candidate safeguard should be offered as standard or optional equipment or whether it should be enhanced, prohibited, ignored or just characterized. Satisfaction of the protocol is a sufficient condition for satisfying the Code of Ethics for Engineers, extant codes and standards, the Intrinsic Classification of Safeguards and the Dangerous Safeguard Consensus. Decisions that do not satisfy the protocol violate one or more of these safety philosophies. The protocol transforms the decision making process into an engineering discipline.

Volume 11 No. 3, March 1996
On the Safety of a Portable Grinder Guard.
Dennis B. Brickman and Ralph L. Barnett

A rigid body mode of failure has been identified in two piece adjustable grinding wheel guards for portable grinders. Under the action of a fragment storm, the upper portion of the guard may tilt and allow an escape displacement to develop at the leading edge of the protective skirt. Three approaches for analyzing this behavior are described.

Volume 11 No. 4, March 1996
Three Wheeled vs. Four Wheeled Turf Work Trucks.
Kenneth L. d'Entremont and Ralph L. Barnett

The maneuverability, turning ability, traction performance, and lateral stability of three- and four-wheeled work trucks are evaluated.

Volume 12 No. 1, November 1996
Ladder Slide Out - First Order Analysis.
Ralph L. Barnett

One of the more important collapse modes for straight, combination, and extension ladders is base slide out; the top of the ladder slides down the support wall as the base slips away from it. Various fundamental models have been used to study this behavior. This paper revisits the analytical solutions associated with these models and describes their implications for the analysis, design, and testing of ladders.

Volume 12 No. 2, January 1997
Hand Trajectories Under Free Fall.
Ralph L. Barnett and Suzanne A. Glowiak

Can the hands elevate during a free fall scenario? This question arises in the design of fall intervention devices, during accident reconstruction and in the study of safe climbing strategies. This paper calculates the maximum simple reaction time that will enable the hands to elevate during a "drop" event.

Volume 12 No. 3, June 1997
Bungee Cord Danger Analysis.
Dennis B. Brickman, Ralph L. Barnett and Harry R. Smith

The utility of bungee cords is so persistently attractive that they continue to gain in popularity. Unfortunately, one of the characteristics of bungee cords is the sudden release of stored energy which results from opening of hooks, failure of the bungee cord and hook connection, inadvertent release of the bungee cord during application, and failure of the structure receiving the hook. The design of personal protection equipment and the evaluation of the danger level related to a released bungee cord require information on hook speed. This paper presents a first order analysis of the maximum attainable speed.

Volume 12 No. 4, January 2009
Foot Controls: Riding the Pedal
Ralph L. Barnett

The two predominant scenarios for accidentally tripping a foot control are stepping into the foot control and onto the pedal, i.e., "stepping contact" and keeping one foot on or just above the pedal at all times, i.e., "riding the pedal." This study shows that the various designs used to minimize "stepping contact" exacerbate inadvertent activation by "riding the pedal."

Volume 13 No. 1, August 1997
Forklift Safety Bibliography
Lucinda J. Fuller

This bibliography of forklift safety research encompasses a wealth of safety-related material, covering the years 1925 through 1997. The collection includes government and industry standards, research reports, periodical articles, accident statistics, and operator training materials.

Volume 13 No. 2, August 1997
Vehicle Lifts: The Hyperstatic Problem
Ralph L. Barnett and Peter J. Poczynok

Occasionally, vehicles topple off of structurally sound automobile lifts, even when they are properly supported at their lift points. This happens with a family of lifts that use four arms to position lifting pads under the vehicle chassis. There is a non-obvious structural phenomena called hyperstatic behavior that may easily lead to minimal, or even zero, pad loading with the attendant loss of resistance to horizontal pad movement. Unless otherwise restrained, the bumping and jostling associated with vehicle maintenance can produce random forces that will push a pad from beneath the vehicle. The resulting three-point support almost always leads to toppling of the vehicle from the lift.

Volume 13 No. 3, December 1997
Heavy Truck Wheel Separation: Failure Modes and Classifications
Christopher W. Ferrone and Dror Kopernik

The purpose of this paper is to illustrate the various wheel attachment systems and to define their components. Special failure modes and safety measures are discussed.

Volume 13 No. 4, June 1998
Design Defect: Doctrine of Alternative Design
Ralph L. Barnett

The American Law Institute has finalized its formulation of the Doctrine of Alternative Design which it adopted and promulgated on May 20, 1997 as Restatement of the Law Third; Torts: Products Liability. This paper is an attempt to characterize this doctrine from a technologist's viewpoint.

Volume 14 No. 1, August 1998
Patents: Restoring Safety
Ralph L. Barnett

The law punishes manufacturers who embrace safety innovation and product improvement. The "new" is literally the enemy of the "old" in the sense that a new safety design may be used by the law to show that all past and current designs are defective. On the other hand, if the new design is patented, a special attribute precludes its invocation as a remedial measure for a safety problem which predated the patent.

Volume 14 No. 2, September 1998
Foot Control Activation - Reciprocating vs. Pivoting
Ralph L. Barnett and Peter Barroso, Jr.

Discriminating between the two most widely used foot control concepts, open-sided and side-shielded, requires, among other things, an understanding of reciprocating and pivoting foot motions. In single cycle machine operations, it was found that the hands are steadier when foot controls are activated by pivoting about the heel as opposed to reciprocating. Furthermore, the study reveals the counterintuitive result that the reciprocating motion delivers slightly more activations per unit time than the pivoting action. If safety is not a consideration, stroke-rate, operator comfort and hand steadiness are maximized when foot controls are actuated by "riding the pedal" or "hold down/release."

Volume 14 No. 3, November 1998
Reasonably Foreseeable Use
Ralph L. Barnett

All technologists design products for an expected use; this use is the goal of the designer. Clearly, the actual use of products by their community of users is broader than the expected use; indeed, the original use contemplated by the designer may be expanded by marketers before the first prototype is finished. Tort law mandates that products be safely designed for their reasonably foreseeable use which includes not only their expected and expanded uses but also their reasonably foreseeable misuses. The concept of reasonably foreseeable use has a literal meaning in technology and this paper explores its impact as a design constraint.

Volume 14 No. 4, December 1998
Safety Analysis of Roller Compactors Exposed to Rollover
Dennis B. Brickman and Ralph L. Barnett

Roller compactors exhibit a high resistance to rollover which may be attributed to their low center of gravity, full width rollers, low speed, responsive braking system, high visibility, and operator profile. Tilt table testing of an Ingram pneumatic roller compactor demonstrates that its lateral stability normally exceeds or is comparable to other workplace vehicles. To eliminate or mitigate injuries resulting from roller compactor rollover excursions, a rollover protective structure (ROPS) and seat belt system has been widely debated as a proper countermeasure. Clearly, the roller compactor accident statistics demonstrate the potential of unbelted operators to suffer serious injuries inflicted by the ROPS safety device itself. In the face of reported low seat belt usage, the utilization of the ROPS and seat belt as standard equipment on a roller compactor is not straightforward and value systems are struggling with this dilemma.

Volume 15 No. 1, April 1999
The Float Scaffold
Peter J. Poczynok and Ralph L. Barnett

Unstable work platforms compromise the ability of workers to adjust their bodies to quickly react against the forces generated at their tool/workpiece interfaces. This paper focuses on the flexibility of work platforms with emphasis on the classical float scaffold used by iron workers. The ability to prestress the float gives rise to superior stiffness characteristics.

Volume 15 No. 2, October 1999
Commercial Walk-Behind Lawn Mower Failure Analysis Case Study
Dennis B. Brickman

A failure modes and effects testing program was conducted to analyze the cause of a mid-size commercial walk-behind lawn mower accident in which the operator's foot came into contact with the rotating blade. Systematic analysis showed that the accident was caused by improper mower service and operator misuse of the mower. Testing results reveal that an alternative design proposal does not preclude this random event. Accident prevention countermeasures are explored.

Volume 15 No. 3, October 1999
Trencher - Impingement on Buried Objects
Dennis B. Brickman and Ralph L. Barnett

There is a resemblance between the digging chain of a trencher and the folklore chain saw. The safety of trenchers requires that the similarities and differences between these two machines be understood so that appropriate warning signs can be formulated. There is a notion that the trencher can be suddenly thrust rearward in the direction of the digging chain in the manner associated with the chain saw. There is also a notion that the kickback characteristic of the chain saw is also characteristic of a trencher digging chain. This paper shows that these rearward thrust and kickback notions for the trencher are false. On the other hand, contact with moving teeth is hazardous on either machine.

Volume 15 No. 4, November 1999
Chipper/Shredder: The Pull-In Hypothesis
Ralph L. Barnett and Dennis B. Brickman

On rare occasions, a portion of an uncut fiber will exit the discharge chute of a consumer hammer mill type chipper/shredder and remain at rest with its inboard portion in the neighborhood of the rotating elements. Disturbing the fiber may cause it to commit to the rotating flails and be pulled instantaneously back into the machine. A number of investigators have postulated that an operator who grasps a fiber that subsequently experiences this pull-in phenomenon cannot release it fast enough to avoid being dragged into the flails. This hypothesis is discredited by both analytical and experimental analyses.

Volume 16 No. 1, January 2000
Snap-Lock Beads Danger Analysis
Dennis B. Brickman

A tragic accident occurred when a 16 month old child fell face down and an oblong plastic toy snap-lock bead lodged in his throat obstructing his airway. Approaches utilized in the danger analysis include safety and medical literature review, codes and standards research, accident statistics survey, and evaluation of alternative snap-lock beads designs. Results of the danger analysis indicate that there are technically and economically feasible design alternatives which prevent the snap-lock beads from blocking the user's airway.

Volume 16 No. 2, February 2000
Utilizing Electronic Control Module Data in Accident Reconstruction
John M. Goebelbecker and Christopher Ferrone

In November of 1998, Triodyne published a Safety Bulletin entitled "Electronic Control Module - The 'Flight Recorder' of Heavy Trucks," by John Goebelbecker and Christopher Ferrone. We have had so many requests for more information that we decided to reprint this longer article which John and Chris wrote for the Society of Automotive Engineers (Paper No. 2000-01-0466).

Volume 16 No. 3, February 2000
Power Transmission Safety Standards
Ralph L. Barnett and Peter J. Poczynok

The development of the Safety Standard for Mechanical Power Transmission Apparatus has been plagued by changing definitions and a penchant for expanding the scope of power transmission applications. The current code gives examples of devices which do not transmit power and, in some cases, represent points of operation. Power transmission hazards are increasingly being defined in terms of motion. The notion that mechanical hazards may be characterized as either point of operation or power transmission is a fundamental error that persistently plagues the "rule making" process.

Volume 16 No. 4, April 2000
Ladder Rung vs Siderail Hand Grip Strategies
Ralph L. Barnett and Peter J. Poczynok

When climbers lose their foothold on fixed, straight or extension ladders, the incipient fall may be arrested by gripping either the ladder rungs or siderails. Grasping the rungs provides an interference or power grip; squeezing the siderails provides a friction grip which is the primary focus of this paper. The falling scenario begins with free fall that lasts for the duration of the simple reaction time. Free fall is then decelerated by contravening friction forces derived from hand grip forces rapidly applied to the siderails. Using hand grip/time histories for various individuals, their fall distances were calculated for bare and gloved hands on a vertical steel fixed ladder. Sometimes the candidates could not arrest their falls; often their fall distance was too great to prevent ground impact. Under some circumstances, the vertical motion was brought under timely control. Although a rich literature is available for characterizing grip strength, data reflecting grip/time profiles does not appear. Grip strength/time diagrams were measured for fourteen test subjects.

Volume 16 No. 5, August 2000
Crash Data Retrieval Kit Recovers Reconstruction Data from GM Black Boxes
John M. Goebelbecker, P.E., Certified CDR Investigator

General Motors vehicles equipped with air bags and manufactured after 1990 utilize electronic modules to operate their air bag systems. These electronic modules are similar to "black boxes" used in the aviation and railroad industries in their ability to record data in the event an air bag deploys or nearly deploys. While General Motors has utilized these data in their accident investigations, they have not been accessible to the public. Breaking new ground in the area of automotive accident investigation, General Motors has entered into an agreement with an outside vendor to develop, manufacture and distribute a Crash Data Retrieval (CDR) kit for use by independent investigators to download crash data formerly considered to be proprietary information.

Volume 17 No. 2, September 2000
International Safety Alert Symbol
Ralph L. Barnett and Raymond Wambaja

With the adoption of the international safety alert symbol, the safety profession has lost an important weapon in the war against injury. The Symbol is not uniquely associated with safety, it does not have an optimum shape and it has no intrinsic pictorial to communicate danger to untrained people from every culture. The symbol represents a tragic "missed opportunity" for mobilizing personal vigilance.

Volume 17 No. 3, December 2000
Snowblower Failure Analysis Case Study
Dennis B. Brickman

A failure modes and effects analysis was conducted to analyze the cause of a snowblower accident in which the operator's hand came in contact with the rotating impeller. Systematic analysis showed that the accident was caused by multiple failures of the snowblower and improper snowblower service. Results of the analysis indicate that there are available design alternatives and countermeasures which would have prevented the accident.

Volume 17 No. 4, January 2001
Safety Potpourri
Ralph L. Barnett

The contents of this Safety Brief include the following: Child Resistant Closures; Poison Lookout Checklist; Railing Height - 42" Rule; Numbering Rules - Code of Federal Regulations.

Volume 18 No. 1, March 2001
Case Study: The Safety of Wood Railings
Ralph L. Barnett and William G. Switalski

When the handrail assembly broke away from a wooden deck attached to the rear of a private residence, the victim fell 12 feet to the lawn and sustained injuries rendering him a quadriplegic. Although the local building code required the handrail to withstand a 200 lb load applied in any direction at any point on the handrail, no guidance was given to the do-it-yourselfer who built the deck and railings to assure him that the final construction would produce an acceptable railing. The authors conducted testing and a statistical analysis of railing strength comparing the construction method used by the builder of the accident railing to another construction method utilizing a commercially available handrail bracket. The test program demonstrates that the strength of the wood used to build handrails can vary greatly and that a controlled method of building a handrail is necessary to ensure the integrity of a product intended to be consumer customized and assembled. It is necessary to have acceptable methods of railing construction because the failure of a railing joint can be life threatening. This is especially true in the consumer/do-it-yourself market where the designer/builder is not necessarily knowledgeable about building codes or construction methods.

Volume 18 No. 3, April 2001
Evaluating Driver Response to a Life-Threatening Emergency: Issues of Behavior, Chance and Hindsight
Michael A. Dilich and Dror Kopernik, P.E.

Imagine driving a truck on a major highway at 45 mph when you spot a car on your right stopped in a driveway and poised to cross the road. It doesn’t move until suddenly, when you are only seconds away, it accelerates into your lane. You react aggressively by swerving to the left to get around it to avoid a collision. But it doesn’t stop! It keeps accelerating and you strike it broadside in the median to the left, killing the driver and seriously injuring a passenger. After the investigators have studied the accident in detail, you are criticized for using bad judgment and over-reacting. It can be shown that if you had done nothing more than continue to go straight, the car would have just cleared your lane before you arrived.

Volume 18 No. 4, May 2001
Anti-Hair Snare Pool Drain Cover
Ralph L. Barnett and Peter J. Poczynok P. E.

A drain cover for swimming pools, spas and hot tubs has been designed which addresses eight hazards associated with conventional drain systems. This new drain cover, illustrated in Fig. 1, eliminates hair entanglement, child evisceration and finger entrapment as well as minimizing body entrapment. Furthermore, its design and construction provide effective countermeasures against vandalism, broken drain covers, missing drain covers and structural deterioration due to environmental antagonists. Additional features unrelated to safety include a universal fastening system which adapts the cover to all circular main drains available in the United States. Also the drain cover is an order of magnitude stronger than its competitors and has a safe flow rate that is 37% greater than its nearest competitor. This paper presents an anatomy of the product’s development.

Volume 19 No. 1, July 2001
Ten Critical Factors in the Design Process
Crispin Hales, PhD, CEng.

The engineering design process transforms a need or an idea into the information from which a product or system can be made. Possibilities and abstract thoughts are progressively developed into certainty and then brought into reality through manufacture of the product or system for service within an appropriate lifecycle. Careful management of multidisciplinary teams, precise communication, effective use of available design tools, appropriate application of materials and a professional respect for the legacy of previous designers all come into the development of a design which will meet user expectations and the environmental constraints within today’s aggressive and global markets. A failure in any aspect of the design process can spell disaster for a project immediately, and unforeseen circumstances can create havoc at any point in the lifecycle of the product or system. We must learn continually from past problems to help us with the task of successfully designing in the more complex web of the future.

Volume 19 No. 2, August 2001
On the Safety of Infeeding Vertical Garden Shredders
Dennis B. Brickman and Ralph L. Barnett

This paper addresses consumer garden shredders of the hammermill type with vertical hoppers that are manually fed. The purpose of this paper is to show that garden materials presented to a vertical garden shredder through the inlet hopper will not pull an erectly standing operator’s hand into the flails. In order for an erectly standing operator to contact the flails, it is necessary for the shoulder to move downward. Experiments demonstrate that the operator’s shoulder moves insignificantly downward during pull-in excursions using various garden materials that are attached to the operator’s hand through snagging mechanisms, hand friction, and entanglement.

Volume 19 No. 3, October 2001
Children’s Outerwear Drawstrings and Sliding Board SafetyAnalysis
Dennis B. Brickman

A two year old child strangled to death when the drawstrings of her jacket became lodged in a catch point hazard at the top of a residential sliding board. Approaches utilized in the safety analysis include accident reconstruction, safety literature review, standards research, an accident statistics survey, and an evaluation of alternative jacket and sliding board designs. Results of the analysis indicate there are technically and economically feasible design alternatives which prevent the child strangulation hazard associated with the jacket drawstrings and sliding board.

Volume 19 No. 4, February 2002
Critique: Drain Cover Standard ASME/ANSI - A112.19.8M-1987 (1996) Case Study: Steering Wheel
Ralph L. Barnett and Peter J. Poczynok P.E.

The current ASME/ANSI standard for pool/spa drain covers is relied upon as an effective guideline for drain system safety by pool industry practitioners, state building code commissions, the Consumer Product Safety Commission, the National Spa and Pool Institute, and a myriad of pool safety sophisticates. In fact, it is a license to kill. To demonstrate its shortcomings in the dawn of its next revision, an ordinary steering wheel is shown to satisfy the current standard while exposing bathers to every known fatal drain cover scenario. The paper raises a new issue: ASME, ANSI and pool professionals may all be in legal jeopardy.

Volume 20 No. 1, March 2002
Forklift Mounted Self-Dumping Hoppers: Counter Latch Invention
Ralph L. Barnett and Christopher Ferrone

A safety device is proposed that will enable the operator of a sit-down rider forklift to discharge a self-dumping hopper while seated at the control station. Dumping proceeds without ground personnel which removes them from traffic flow and protects them from impacting loads that overspill the hopper, roll, bounce, or are accidentally discharged from the hopper. Just the right amount of rearward mast tilt is normally required to overcome the latching resistance of heavily loaded forward biased hoppers without becoming relatched when the trip lever is released. The associated trial and error balancing procedure is eliminated together with any need for muscling the latch rod. Unlatching poles are no longer used for elevated dumping.

Volume 20 No. 2, April 2002
Forces and Injuries to the Human Body
Cheryl A. Pattin, Ph.D., P.E.

Biomechanics involves the application of mechanical engineering principles to describe forces associated with human movement and injury. The human body contains a number of tissues and organs, which respond in very specific ways to mechanical loading. Consequently, injury patterns observed following a trauma can provide important clues regarding the nature of the forces causing injury. Various aspects of applied forces and their relationship to injury patterns will be discussed including direction, severity, duration, and energetics.

Volume 20 No. 3, May 2002
Boiler Feedwater Pipe Failure by Flow-assisted Chelant Corrosion
Crispin Hales, Kelly J. Stevens, Phillip L. Daniel, Mehrooz Zamanzadeh and Albert D. Owens

On 22 April 1996, there was a catastrophic failure in a section of six-inch diameter feedwater line leading from the economizer to the steam drum on a boiler at a private industrial power plant in the Midwest. A full investigation into the cause of the failure was carried out over a period of 2 years, involving experts in mechanical design, metallurgy, water chemistry and fluid flow dynamics. The failure occurred due to progressive thinning of the pipe wall from the water side to the point where it could no longer tolerate the operating pressures and temperature. It was concluded that thinning of the carbon steel pipe wall had been caused by a specific mechanism, termed here "flow-assisted chelant corrosion". The difference between this and flow-accelerated corrosion (FAC) is presented and recommendations are offered to help avoid similar failures in the future.

Volume 20 No. 4, June 2002
Evaluating Driver Response to a Sudden Emergency: Issues of Expectancy, Emotional Arousal and Uncertainty
Michael A. Dilich, Dror Kopernik, P.E. and John M. Goebelbecker, P.E.

In April of 2001, Triodyne published a Safety Brief entitled "Evaluating Driver Response to a Life-Threatening Emergency: Issues of Behavior, Chance and Hindsight," by Michael A. Dilich and Dror Kopernik. We have had so many requests for more information that we decided to reprint this longer article which Michael and Dror along with John M. Goebelbecker wrote for the Society of Automotive Engineers. This paper is reprinted from SAE paper 2002-01-0089 ©2002 Society of Automotive Engineers, Inc. This paper was also presented to the Human Factors in Driving and Automotive Telematics Session on March 4, 2002 at the SAE World Congress in Detroit, MI.

Volume 21 No. 1, July 2002
Standard Infant Crib Testing Enhanced with Live Children Shaking
Dennis B. Brickman, P.E.

An infant asphyxiated when a machine screw detached from a crib, the headboard separated from the crib rod, and the infant's head stuck in the opening. The evaluation of infant cribs by inanimate standard test protocols is enhanced by live child crib shake testing. This live testing provides data for quantifying the horizontal push and pull forces that children actually apply to the sides of a crib. Comparisons are made between the live child shake test results and the inanimate test requirements contained in crib safety standards. Although the inanimate standard test protocols are inconsistent, the machine screw did not fail from normal use because the inanimate test requirements far exceed the maximum live results.

Volume 21 No. 2, August 2002
Commercial Tree Chipper: The Leg Pull-in Hypothesis
Dennis B. Brickman, P.E.

This paper addresses a commercial mobile tree chipper with a mechanical infeed system that is manually fed. The purpose of this paper is to show that tree branches and brush presented to a disc chipper through the infeed hopper will not pull an erectly standing operator's leg off the ground and into the feed wheels given the conditions set forth in this test program. In order for an erectly standing operator's leg to contact the feed wheels, it is necessary for the leg to be pulled off the ground and over the bottom leading edge of the infeed hopper. Experiments demonstrate that the operator's leg is pulled up against the lower leading edge of the infeed hopper and lodges there during pull-in scenarios using a winch, cable, and rope attached to the operator's ankle. Two safety devices, an infeed extension pan and a safety control bar, are explored in this paper.

Volume 21 No. 3, September 2002
"Slip and Fall" Theory - Extreme Order Statistics
Ralph Lipsey Barnett

Originally published in the International Journal of Occupational Safety and Ergonomics (JOSE) Volume 8, Number 2, 2002, this paper was the winner of the JOSE Best Paper Award for the years 2000 through 2002. Classical "slip and fall" analysis was reformulated in this paper to account for the stochastic nature of friction. As it turned out, the new theory, arising from this analysis, was a precise statement of the distribution function for the smallest value among n independent observations. This made it possible to invoke an important result from the asymptomatic theory of extreme order statistics that reduced the theory to a simple and elegant relationship among the probability of slipping, the critical friction criterion, the distance traveled by the walker, and the average, spread and asymmetry of the distribution of friction coefficients. This new theory reveals that short walks lead to fewer falls; low friction floors are sometimes better than high friction ones.

Volume 21 No. 4, October 2002
Tailgating - Rule of Three
Ralph L. Barnett

The safe following distance guidelines given in Illinois Rules of the Road are too complicated and/or unsafe. A safer guideline is proposed: measured in feet, the safe distance between vehicles is 3 times the speedometer reading. This is approximately the length of a fire truck (pumper) for every 10 mph.

Volume 22 No. 1, November 2002
Human Push Capability
Ralph L. Barnett and Theodore Liber

Use of unassisted human push capability arises from time to time in the areas of crowd and animal control, the security of locked doors, the integrity of railings, the removal of tree stumps and entrenched vehicles, the maneuvering of furniture, and athletic pursuits such as football or wrestling. Depending on the scenario, human push capability involves strength, weight, weight distribution, push angle, footwear/floor friction, and the friction between the upper body and the pushed object. Simple models are used to establish the relationships among these factors.

Volume 22 No. 2, December 2002
Gladhands - An Achilles Heel in Truck Air Brakes
Michael A. Dilich, John M. Goebelbecker, P.E. and Dror Kopernik, P.E.

The semi-trailer brakes on a tractor-trailer combination receive their air supply from the tractor's system via two hoses which are hanging between the tractor and the trailer. One of the hoses feeds the service brakes on the trailer and the other feeds the emergency/parking system. The hoses hang down from the back of the tractor where they are permanently connected. The ends of the hoses are coupled to the front of the trailer using quick-connect couplings called "gladhands." Without the use of tools, a truck driver can quickly connect and disconnect the gladhands whenever s/he needs to couple or uncouple a semi-trailer. The reliability of the gladhand connections is critical to the operation of the trailer's brake system.

Volume 22 No. 3, January 2003
Protecting Against Needle Sticks
James R. Wingfield, Ph.D., C.R.E.

This paper discusses the problem of needle sticks while disposing of sharps in the medical community, the current design of sharps disposal containers (SDC), and research trends in the design of these containers.

Volume 22 No. 4, February 2003
Stochastic Theory of Human Slipping
Ralph L. Barnett, Peter J. Poczynok, P.E., and Suzanne A. Glowiak

The conventional approach to human slipping is essentially deterministic; it states that no slipping will occur when the average friction coefficient is greater than some critical friction criterion. Under this condition, pedestrians will not slip when they encounter the average friction coefficient. On the other hand, to successfully negotiate a walk of n-steps they must not slip when they encounter the smallest of the n friction coefficients. Consequently, a new slip theory has been formulated as a problem in extreme value statistics. An elegant relationship is obtained among the probability of slipping, the critical friction criterion, the number of steps taken by the walker, and the central measure, scatter, and asymmetry of the distribution of friction coefficients. The new theory reveals the structure of human slipping in a startling way that introduces completely new concepts: the go/no go nature of classical slip predictions is replaced by a probability of slipping; low friction floor/footwear couples may lead to fewer slips than high friction ones; slipping can occur in any case where conventional theory predicts "no slip"; and the number of slips depends on the distance traveled by a pedestrian. Finally, this paper develops the idea that the slipperiness of a real floor must be evaluated for a duty-cycle. Duty-cycles can be represented as frequency histograms when a floor is homogeneous and isotropic.

Volume 23 No. 1, March 2003
Above Ground Swimming Pools - Safety Concepts
Ralph L. Barnett and Peter J. Poczynok, P.E.

The above-ground pool shown in this paper has been retrofitted with a perimeter safety barrier which consists of a fence, gate, ladder cage, water-side pool ladder, and an anti-grip/anti-foothold system. These safety concepts are combined to address the inadvertent and advertent foibles of bathers and bystanders who range from infants to adults, from uncoordinated to skillful, and from casual to mischievously determined. There are no proprietary devices used in the safety system; all of the concepts are well known and can therefore be applied by anyone skilled in the art. The prototype safety system eliminates every classic danger including diving, jumping, deck-side horseplay and unauthorized access. The system itself introduces new hazards that may be controlled using safeguards that are described in the paper.

Volume 23 No. 2, April 2003
Bumpers/Fenders Used for Low Speed Runover Protection
Dennis B. Brickman and Ralph L. Barnett

Because fenders, bumpers, and cowcatchers have been ubiquitous throughout our industrial history they are regularly proposed as safety intervention devices for runover accidents that occur with low speed industrial and construction vehicles. It has been alleged variously that they will protect pedestrians through the mechanisms of deflection, shielding, and tactile feedback. These notions are examined using straddle cranes, road grinders, and road wideners under low speed scenarios (4 mph). Anthropomorphic dummies and volunteers are used to simulate what actually happens to people when hit by various runover protection devices using different ground clearances. People think they are safe if a slow moving vehicle with a bumper, fender, or cowcatcher hits them because they expect to either bounce off of it or be moved out of the way. However, the tests in this paper show that these protection devices actually entrap people; and if the vehicle continues moving, the vehicle rolls right over them. Protection devices with only a few inches of clearance between the device and the ground may snare a person's shoe without entrapping his leg, but his hands and arms are not prevented from being entrapped and the run over.

Volume 23 No. 3, May 2003
Child Resistant Packaging - Regulations and Effectiveness, 1980-2002
Cheryl A. Pattin, Ph.D., P.E.

The Poison Prevention Packaging Act (PPPA) is a federally preemptive piece of legislation covering an ever expanding group of substances. The test methods used to establish compliance with the PPPA do not address the range of substances covered (e.g. liquids); the changing patterns of use of household substances such as increased use of liquid medications for children; or repeated access to and multiple reclosures of containers common in the home situation. To examine the effectiveness of the PPPA in addressing actual poisonings in children under 5, national databases from 1980 through March of 2002 were examined. The average age of children treated in hospitals was under 2, and fatalities due to Assisted access and Transfer of contents incidents were reported in children averaging under one year of age. These age ranges are below those of children used in child resistant packaging testing (3.5 to 4.25 years). More importantly, the average body weights -- directly related to the susceptibility to poisoning injury -- of children seen in hospitals is below the toxicity threshold set in the PPPA standard which is based on a 25 pound child. Training for children, the elderly, and parents would help increase awareness of Transfer of contents and assisted access poisonings, which are disproportionately represented in fatal poisoning incidents of young children.

Volume 23 No. 4, June 2003
On the Safety of Consumer Deep Fryers
Dennis B. Brickman

A 27 month old boy sustained burn injuries from a consumer electric cooker which was pulled off a kitchen countertop. Approaches utilized in the safety analysis include accident reconstruction, critical accident statistics analysis, UL 1083 standard research, and an evaluation of design alternatives. This paper investigates the safety implications of the new UL required break-away power cord for electric cookers/deep fryers.

Volume 24 No. 1, July 2003
Auto-Setting Ladder Inclination
William G. Switalski and Ralph L. Barnett

A straight or extension ladder maintains its equilibrium when placed against a wall or other structure by the friction resistance against sliding that is created between the side rail feet and the ground surface. When this friction force is not sufficient, the base of the ladder slides away from the wall dropping the climber. In the United States, ladders are designed and tested using an angle of 75.52° which is also used as the limiting ladder set-up angle to avoid slide-out. For the user to know that the ladder is properly set-up, a "rule-of-thumb" and on-product safety labels have been used. This safety strategy has room for improvement; over one-third of all ladder accidents are caused by ladder slide-out. A recent proposition involves a mechanical device using wheels attached at the bottom of the ladder at each side rail. This paper initially discusses the first generation of the proposed invention and its risks. Then, a second generation of the proposed invention is discussed and nine alternative designs are compared.

Volume 24 No. 2, August 2003
On the Safety of Infeeding Commercial Tree Chippers
Dennis B. Brickman, P.E.

This paper addresses a commercial mobile tree chipper with a mechanical infeed system that is manually fed. OSHA records associated with commercial tree chipper accidents indicate tree workers have alleged that their arms have been pulled into the chipper feed wheels by branches during the feeding process. An infeed extension pan has been proposed to prevent a tree worker's arm from being pulled into the chipper feed wheels if his gloved hand gets caught in the branches being fed into the infeed hopper. Experiments performed with human test subjects and an anthropomorphic dummy are presented under arm pull-in scenarios to study the safety implications of the proposed infeed extension pan.

Volume 24 No. 3, November 2003
Floor Reliability With Respect to "Slip and Fall"
Ralph Lipsey Barnett and Peter Joseph Poczynok

For a given community of walkers and a specific type of ambulation, force-plate studies have established the required level of horizontal resistance for stable locomotion. This stochastic floor loading is resisted by friction forces which must be great enough to prevent slipping. A statistical characterization of frictional resistance has recently been developed using extreme value statistics. Reliability theory provides a method for combining the floor loading and friction resistance which, for the first time, enables one to determine in a rational manner the probability of slipping. This paper presents a formula describing the "slip and fall" reliability of a floor/footwear couple.

Volume 24 No. 4, December 2003
Boogie Board Flexibility
Ralph Lipsey Barnett and Peter Joseph Poczynok

The flexibility of a closed cell polyethylene boogie board provides a man-machine interaction that differs qualitatively from the relatively rigid surfboard. Under the action of gravity and buoyancy forces, the closed cell polyethylene boogie board exhibits very large deflections that effect the shape of its bottom control surface. This paper demonstrates how hand placement provides an additional degree of freedom for the surfer.

Volume 25 No. 1, January 2004
Sloped Surfaces - Ladder Slide Out
Ralph Lipsey Barnett and Theodore Liber

Straight and extension ladders are designed to be operated on firm, level surfaces where resistance to ladder slide out is provided almost entirely by the friction resistance between the ladder foot and the base surface. The required friction resistance for a ladder on a sloped surface increases dramatically as the slope away from the vertical support structure becomes steeper. To maintain the current slide out resistance specified by ladder standards, the ladder inclination must be increased by the ground slope.

Volume 25 No. 2, February 2004
Pen Cap Failure Analysis and Prevention
Dennis B. Brickman

A tragic accident occurred when a young child swallowed the interior component of a two piece highlighter pen cap which obstructed his airway. Approaches utilized in the failure analysis include dynamic testing, accident statistics survey, safety literature research, and a review of alternative pen cap designs. Results of the analysis indicate that there are technically and economically feasible pen cap design alternatives on the market and in the literature which allow sufficient airflow to prevent asphyxiation if the cap enters the user's airway.

Volume 25 No. 3, March 2004
The Runaway Diesel - Part II: A Side by Side Mechanical Analysis
Christopher W. Ferrone and Charles Sinkovits

When a diesel engine is exposed to an external fuel source such as an airborne combustible hydrocarbon in the surrounding environment, it naturally ingests the mixture into the air intake system. Since diesel engines control fuel and not air, the engine can no longer maintain speed control.

Volume 25 No. 4, April 2004
Ladder Cages
Ralph L. Barnett and Christopher W. Ferrone

It is inexplicable that the literature on fixed ladders is silent on the topic of ladder cage function in spite of ubiquitous codes and standards that have specified their use for eight decades. Cages enable a climber to rest at any level by leaning backward against the cage structure. Fall protection is provided whenever a climber loses both hand grips while retaining a foothold.

Volume 26 No. 1, May 2004
Infant Pull Strength - Ability to Dislodge Crib Sheets
Ralph L. Barnett and Dennis B. Brickman

The suffocation of infants caused by crib sheet entanglement appears to be a nonproblem which has nevertheless resulted in a brouhaha that has incited remediation activities by the Good Housekeeping Institute (GHI), American Society for Testing Materials (ASTM), Consumer Product Safety Commission (CPSC), Juvenile Products Manufacturers Association (JPMA), crib sheet manufacturers, and product liability support professionals of different stripes. To show that the removal of crib sheets by infants is not a safety issue, one may establish that the problem is not reasonably foreseeable. Three approaches for doing this are described in this paper: anecdotal, simulation, and reliability. The reliability of a crib sheet is the probability that it will remain in situ when exposed to the community of infants. Application of the classical "load minus strength" analysis required new information on the pull strength of infants.

Volume 26 No. 2, June 2004
Slip and Fall Characterization of Floors
Ralph L. Barnett and Peter J. Poczynok

During ambulation, every maneuver causes the feet to impose tangential loading at each contact with the floor. If the frictional resistance at the contact point is less than the associated tangential loading, slipping occurs and sometimes falling. There are five disciplines, some recently developed, that enable one to develop the general theory for predicting the number of walkers who will slip within a given time period on a statistically homogeneous and isotropic floor. These include force-plate studies, floor duty cycles, tribometry, extreme value theory of slipperiness, and floor reliability theory. When used with some additional bookkeeping notions, the general theory will be extended to real floors traversed by walkers with multiple ambulation styles and wearing a variety of footwear.

Volume 26 No. 3, August 2004
Anti-Diving Safety Systems for Swimming Pools
Robert Kaplan and Ralph L. Barnett

This paper addresses new design concepts for the anti-diving system introduced in 2003 by Barnett and Poczynok.

Volume 26 No. 4, September 2004
Limited Movement Machinery Rollers
Ralph L. Barnett and Dennis B. Brickman

Ancient Egyptians allegedly moved large stone blocks by placing cylindrical rollers beneath them and manually urging them along. This rolling procedure required that the rollers emerging from the rear of the stone be manually lifted and replaced in front. This roller replacement protocol has been automated in commercially available roller units that allow continuous movement of heavy machinery under the action of pry bars, come-a-longs, winches, or manual push efforts. Unfortunately, when slopes or asperities are encountered these heavy loads may accelerate uncontrollably or steer themselves in unsafe directions when the roller units become reoriented. This paper describes two inventions that cause the locomotion of the machinery to proceed in inchmeal fashion by intermittently braking the system while the roller units are manually reset.

Volume 27 No. 1, October 2004
Driver Fatigue/Inattention Monitoring Device - An Integrated System for Heavy Trucks
Christopher W. Ferrone and Charles Sinkovits

The National Transportation Safety Board has reported statistics which indicate that 31% of all fatal-to-the-truck driver accidents occur due to fatigue/inattention and 58% of all single-vehicle large truck crashes were also fatigue related. If these numbers can be reduced, many lives can be saved. A Driver Fatigue Monitoring System has been designed and built to monitor whether a driver is sleeping or inattentive. This integrated system monitors the steering input behavior of the driver during a specified period of time. If the number of steering inputs is below the expected predetermined threshold, the system activates an audible alarm and light in the cab, waking the driver. Furthermore, this system can deactivate cruise control as well as activate various other preprogrammed truck systems or components to further aid in the control of the truck and to alert nearby motorists.

Volume 27 No. 2, November 2004
Standards - Impact and Impotence
Ralph L. Barnett and Suzanne A. Glowiak

Most of the technical works of humankind are designed without the guidance of safety codes and standards. Specific safety standards are generally developed when contrivances give rise to numerous accidents and liability actions. The salient features of such standards are briefly outlined in this article.

Volume 27 No. 3, April 2005
Back-Up Alarm System Design Using Smart Technology
Christopher W. Ferrone and Charles Sinkovits

Accidents occurring from trucks and equipment backing up and contacting workers and pedestrians remain a problem even with the use of back-up alarms which beep when trucks and heavy equipment are shifted into reverse. A new method, combining a warning when a vehicle is shifted into reverse with a separate and distinct warning to indicate that the vehicle is actually moving in reverse, has been developed.

Volume 27 No. 4, April 2005
Extreme Value Formulation of Human Slip: A Summary
Ralph L. Barnett and Suzanne A. Glowiak

Conventional "slip and fall" theory establishes a go-no-go criterion that indicates whether or not a given floor has satisfactory slip resistance. Specifically, the theory states that no slip, and hence no fall, will occur whenever the average coefficient of friction between a floor and some "worst case standard footwear material," e.g. leather, is greater than a threshold friction coefficient. This threshold friction is not selected by some rational protocol; it is often established by legislative fiat or consensus. Using extreme value statistics, this paper reformulates classical "slip theory" to explicitly account for the stochastic nature of friction coefficients. By abandoning the traditional deterministic approach to slip in favor of a statistical formulation, fully integrated protocols are able to be developed which predict the number of pedestrians who will slip or, alternatively, who will violate a threshold slip criterion. A new theory emerges that embraces everything from a simple floor with a single walker to very complicated real floors traversed by a throng of pedestrians with multiple ambulation styles and wearing a variety of footwear. It must be emphasized that the new slip protocol merely provides a mathematical framework that enables walkway professionals to make quantitative estimates of slip propensity. Like conventional theory, it also suffers from the "garbage in-garbage out" syndrome. Accu- rate tribometers, for example, are still required for precise predictions. On the other hand, the concept of threshold criterion and worst case footwear surrogates are replaced by force-plate data obtained by gait laboratories using various communities of walkers. Reliability determination for real floors requires the introduction of floor duty cycles.

Volume 28 No. 1, January 2015
On the Safety of Heating Pads
Ralph L. Barnett, James R. Wingfield

The electric heating pad represents one of the medical devices that escaped the FDA safety net by a “grandfather” exemption. An amazing number of philosophical safety issues are introduced by this relatively innocuous commodity. Pain relief is a major attribute of heating pads followed by a minor in actual medical efficacy associated with the improvement of local blood circulation. By contrast, the historic downside is very dramatic featuring electrocution, fire, and skin burns. This paper begins with a brief introduction to current protocol for placing new medical devices into the stream of commerce. In the case of heating pads, it is fortunate that the Underwriters Laboratories Inc. developed and promulgated design rules that effectively mitigated the dangers of shock/electrocution and promulgated design rules that effectively mitigated the dangers of shock/electrocution and fire. On the other hand, UL has not undertaken a technical program that addresses the skin burn problem that is the focus of this paper. Nevertheless, many heating pad manufacturers are under the impression that their compliance with UL 130 has ameliorated the skin burn propensity of their pads. Heating pad manufacturers have attempted to control skin burn injuries exclusively through the means of on-product and in-manual warnings that have been promulgated by UL, FDA, and CPSC. This approach has tenaciously maintained a burn rate of 1600 cases per year. A different approach to the skin burn problem is automatically orchestrated by invoking the “Safety Hierarchy.” For example, falling asleep and causing prolonged skin exposures to a heated pad can be eliminated by a dead-man control. Exposure to extreme temperatures that arise when both faces of the pad are concurrently covered is perhaps the most prevalent cause of skin burns. This paper exploits the notion of monitoring both face temperatures and shutting off the pad when they are almost the same. We also explored shutting down the pad when the cycle rate of the bang-bang controls was suffciently slow; higher heating rates are associated with an uncovered face.

Volume 28 No. 2, December 2015
Anti-Limb Entrapment Insert
Ralph L. Barnett

Access to the suction pipe in a main drain can occur whenever the sump cover is unfastened, broken, or missing. An arm or leg can be placed, sucked, or propelled into the pipe where the limb can be trapped by various mechanisms including suction, wedging, and tissue swelling. Although their success rate is unimpressive, there are a number of mitigation strategies for limb entrapment that are based on reduced pressure differential. These strategies are thoroughly examined in this paper. None of these compare however to the classic notion of preventing entrapment in the first instance. Restricting the pipe opening to small apertures through the use of permanent cross-members eliminates the limb entrapment hazard. Unfortunately, the cross-member solution used, for example, in tubs and slop sinks introduces new hazards that were not present in the open pipe; hair entrapment, finger entrapment, and mechanical entrapment (e.g. swimwear). This paper introduces a pipe insert at the entrance to the pipe that uses permanent fins to provide anti-limb entrapment. The fins are designed with an iso-friction profile to shed hair that may be entrained into the pipe. The equation for the profile is obtained in polar coordinates. The geometry of the fins minimizes finger and mechanical entrapment. Scallops are included around the edge of the pipe that inhibits body entrapment which can restrain a child with a suction force of 50 to 100 lbf (222 to 445 N). The use of an anti-limb entrapment insert together with a retrofittable anti-evisceration ring will achieve the same entrapment protection with or without a sump cover.

Volume 28 No. 3, January 2016
Fixed Enclosure Guards and the Safety of Screw Conveyors
Ralph L. Barnett

One cannot overstate the value and ever growing importance of the screw conveyor and one cannot overemphasize the intrinsic danger associated with this classic monster. This danger can be controlled using fixed enclosure guards that are not only compatible with the function of screw conveyors but are anecdotally acknowledged to be the most desirable type of guard. Nevertheless, the speciality conveyor standards promulgate dangerous guarding systems with features two levels below the fixed barrier guard. This paper revisits the system of conveyor safety standards to rout out equivocal notions, expose shortcomings, and generally demonstrate that a foolish inconsistency is not the hobgoblin of small minds. Finally, this paper challenges the notion that a fixed enclosure guard is an elementary concept whose parameters are settled; e.g. a machine inside of a welded steel box. The definition of fixity and the duality of operation and maintenance are both explored.

Volume 28 No. 4, February 2016
The Safety of Floor Mats on Flexible Foundations
Ralph L. Barnett

The ordinary floor mat is a ubiquitous Type V safety device; i.e. it sometimes protects you, sometimes hurts you, and sometimes makes no contribution. Its hazardous nature has been embraced by technical codes and standards and the courts have declared that an unremarkable ordinary floor mat is not unreasonably dangerous because reasonable lookout on the part of a pedestrian will abate its downside. As it turns out, these endorsements are all predicated on the notion that floor mats are supported on "rigid" surfaces such as concrete, tile, or wood. If the mat is placed on a flexible surface, such as a carpet, an unreasonably dangerous trip hazard may be formed by the carpet/mat combination. Furthermore, the hazard is open but not obvious.

Volume 29 No. 1, July 2007
Slipping on Concrete: A Case Study
Ralph L. Barnett, Adam A.E. Ziemba, and Theodore Liber

The ambulation of pedestrians claims more lives and produces more disabling injuries than warfare. Every year global statistics on Slip/Trip and Fall indicate that senior citizens and the general population have respectively achieved No. 1 and No. 2 status with respect to traumatic death and injury. The automobile is the only competition for this dubious distinction. This paper presents a forensic and safety study that focuses on slip and fall.

Volume 29 No. 2, January 2009
Auto Lifts - Unrestrained v. Restrained Swing Arms
Ralph L. Barnett, John B. Glauber

Various automotive lifts use four cantilevered arms to elevate and support vehicles on adapter pads positioned on their free ends. These arms, when raised, are supposed to be restrained against rotation in a horizontal plane. When restrained, the arms provide a robust structural system for resisting horizontal workplace forces that tend to slide vehicles off the pads. The arms maintain the horizontal locations of the adapters by developing bending and axial planar resistance. If, on the other hand, the arms are free to pivot through sloth or poor design, their structural behavior is dramatically transformed. The planar bending resistance of the arms completely disappears and they become direct stress diagonal truss members; the vehicle itself unwittingly becomes the truss’ tension chord. The appearance of the fixed and pivoting systems is the same; however, the truss action magnifies the horizontal forces acting on the adapter pads increasing the slip probability. Indeed, depending on the orientation of the pivoting swing arms, any finite horizontal force applied to a vehicle may lead to an unbounded tangential “slide-out” force. This is, of course, a theoretical possibility, not a practical reality.

Volume 29 No. 3, January 2009
Water Sport Tow Ropes
Ralph L. Barnett, Adam A.E. Ziemba

With the excption of tubing, towed water sports are afflicted by "wipeouts" that cause the athlete to release the handle of the tow rope. Once released, the resilience of the tow rope allows the rope and handle to spring toward the motorboat with the potential for overtaking the craft and impacting its crew. This paper examines this safety problem; specifically, it analyzes the wakeboard which subsumes water skiing, slaloming, kneeboarding and barefooting. A first order formulation is developed for describing the tow handle trajectory in terms of the system geometry, the skier's grip strength and the mechanical properties of the tow rope. A rope stiffness criterion is established that guarantees the release tow handle will fall harmlessly into the water as opposed to striking the motorboat. The handle flight time and maximum impact speed are predicted for a worst case scenario. Further, the formulation provides a guideline for refining its conservative predictions by testing rope candidates.

Volume 29 No. 4, April 2009
Safety of Fitness Equipment Cables
Ralph L. Barnett

There is a family of exercise machines that provides a manual workout task requiring the user to push or pull against a resistance provided by a stack of weight plates. The weight system is usually linked with a single cable to a gripping or user interface device to produce a constant resistance. A fracture of the tensioned cable along its length or at its end connectors causes a sudden acceleration of the grip or other interface device driven by the operator’s push or pull. The sudden loss of resistance often results in an exerciser pulling a heavy bar into his or her face. Because falling weights, accelerating grips and rapidly unloading muscles are all hazardous, manufacturers of exercise machines want to maintain the structural integrity of the cables. To accomplish this, manufacturers usually recommend “scheduled servicing” of their cables. This Preventive Maintenance (PM) strategy is frustrated by nylon sheathing that hides the cable failures. Further, the swedged or silver soldered connectors often fail covertly by internal fatigue fractures. A more effective PM strategy has been adopted by many manufacturers called “Scheduled Replacement”; they advocate annual cable replacement. Here the nemeses are sloth and greed, best expressed by the philosophy, “if it ain’t broke, don’t fix it.” As a first consideration of fault tolerant design, a redundant duplication of the cable system was added to a fitness machine; this is called “active redundancy.” This paper demonstrates the inadequacy of active redundancy for eliminating the catastrophic failure mode. Instead, the adoption of a “dormant/standby” redundancy is shown to provide the requisite safety. The proposed system not only eliminates the “fail-to-danger” mode, it provides the most economical use of the cable in the sense that it never discards a cable until its life is exhausted.

Volume 30 No. 1, November 2009
Force-Plate v. A-Frame Ladder
Ralph L. Barnett

Should a class of ladders be prohibited for certain aerial work tasks? The ladder industry does not address questions of this type; indeed, it seldom provides sufficient information for determining the apprpriateness of its products in a specific application. This paper proposes a methodology for establishing the safety of an A-Frame ladder for overhead ductwork installation. A force-place, normally used in gait testing, was used to support HVAC workers while they installed a typical ductwork detail. The force-plate output characterized the loading environment which was then compared to the resistance profile of a special duty A-Frame ladder. The applied forces sometimes exceeded the lateral resistance of the ladder. This is consistent with our field experience involving six death cases of sheet metal workers.

Volume 30 No. 2, February, 2012
Accidental Foot Control Actuation Equilibrium Bifurcation Method
Ralph L. Barnett

Acidental actuation of a foot controlled press brake causes a double amputation of a young woman's arms. The electric foot switch leading to this tragedy was protected by a barrier guarding on five sides and employed a pedal latch that had to be released before the pedal could be activated. The manufacturer of the foot switch also marketed the same design with the addition of a front gate that must be raised with the toe to gain access to the pedal and the pedal latch. To explore the different between these two advanced safety designs in a laboratory setting, a protocol was developed involving a bifurcation of equilibrium positions. One equilibrium posture naturally tended to engage an unprotected foot switch; a second stance balanced the operator after disengagement. Efforts to engage the foot pedal using bifurcation protocol does not involve cognition. The gate eliminated accidental actuation; the non-gated foot was actuated in 93% of the trials.

Volume 30 No. 3, November, 2012
Anti-Evisceration Rings - Proof of Concept
Ralph L. Barnett

Domed suction entrapment covers (grates) are generally mounted on cylindrical sumps or frames (mud rings) that are permanently installed in the bottoms or sidewalls of swimming or wading pools. These covers constitute a first-line-of-defense against the danger of evisceration by preventing children from sealing the sumps and drains with their buttock. When the covers are missing, loose, or broken, sealing a sump with their backsides exposes their bowels to dangerous levels of suction that cause disembowelment in a fraction of a second. There is an emerging paradigm shift in the aquatic’s industry that calls for equivalent protection for covered and uncovered sumps and frames. Using a simple concept patented by Barnett (2001) [1], the planar circle formed by the inside edge of a sump is replaced by a non-planar edge, e.g., scalloped or castellated. Edge geometry is chosen that will not conform to human body parts to preclude sealing. Testing inexpensive prototypes demonstrated that the proposed anti-evisceration rings reduce the body removal force from 324 lb. to 10 to 17 lb. Further, they lower the maximum pump vacuum from -14.3 psi to -1 to -2 psi.

Volume 30 No. 4, January, 2014
Standard Chain Lever Load Binder
Ralph L. Barnett, Theodore Liber

The standard chain lever load binder that is used for truck cargo securement operates on an over-center principle that has been used for over a century on suitcases, tool boxes and camera cases. The safety hazards associated with the uses and misuses of the load binder were identified decades ago and various inventors patented innovations that eliminated or mitigated the safety shortcomings. Furthermore, their ideas were not only effective, they were economical, versatile, and efficient. These patents are now in the public domain and many companies manufacture and/or distribute entire lines of securement that include not only the standard chain lever load binder but most of the alternative designs as well. This case study takes the position that the standard chain lever load binder should be banished. Since the appropriate bodies, after all these years, have not arranged for its demise, this paper appeals to the product liability system for safety relief. Engineering analysis and tests are provided to the legal profession to help them protect us by making the cost advantage of the standard binder too expensive. This paper explores some of the remarkable properties of the standard load binder.

Volume 31 No. 1, November, 2017
Auto-Deploying Vertical Band Saw Guard
Ralph L. Barnett

The origin of the band saw can be dated back to 1864. The safety of this 153 year old machine was first formalized in 1917 when the American Society of Mechanical Engineers first promulgated their safety standards for woodworking equipment. For the next 100 years, the safety of the vertical band saw has enjoyed a progress-free existence. Review of the ANSI standards indicate no significant change, in spite of the classical shortcomings that always subject workers to an unguarded saw blade during the band saw's idling, run-down, and stationary phases. During operation, most of the space between the table top and the upper guide rolls is filled with the workpiece. The portion of the blade above the guide rolls is required to be enclosed. This paper describes an invention that always guards the entire band saw blade unless cutting is called for. The guide rolls are constantly in contact with the table top until a foot control causes the guide roll to raise to a preset elevation exposing the band saw's "point-of-operation." A simple retrofit uses almost all of the original hardware and adds only a foot controlled "lifting/lowering" capability to the guide post or the attached blade guard. Examples of a retrofitted meat saw and a vertical wood/metal working band saw are explored.

Volume 31 No. 2, March, 2020
Overturning File Cabinet
Ralph L. Barnett

It is deceiving that an otherwise super-stable file cabinet can become critically unstable when it is unloaded or lightly loaded. This may expose office workers to the specter of a 200 lb. file cabinet striking the floor at 13 mph. File cabinet design is guided by standards that do not reflect "worst case scenarios," do not specify realistic safety loads, do not include snagging forces, and do not account for the effects of carpeting that may lower the tip resistance by 40%. This paper introduces three well known anti-tip concepts that radically improve the stability of file cabinets; elastic footprint extender, passively deployed outriggers, and rollers that trade off rotation for translation. These traditional concepts are added to the current arsenal of safety tip-over devices that include wall and floor bolting, ganging, under-mounting, counter-weighting, and single drawer deployment interlocks. The stability principles discussed are also applicable to such things as furniture, appliances, and tool cabinets.

Volume 31 No. 3, July, 2020
Safety Definitions: Colloquial, Standards, Regulatory, Torts, Heuristic, and Quantitative
Ralph L. Barnett

Scholars of every stripe have confessed that they cannot define pornography; but they know it when they see it. This unsatisfactory state-of-affairs is trivial compared to defining safety. Safety presents cascading levels of subjectiveness each of which defies definition. The current definitions of safety disguise our ignorance and deprive us of both certainty and objectivity. Indeed, as the field of safety continues to exist in a "research-free zone" we are all trying to be the one-eyed man in the valley of the blind. This paper considers colloquial, legal, and technical definitions of safety; all are useful, none are satisfactory. Even worse, none of the definitions pass the idiomatic "laugh test."

Volume 31 No. 4, August, 2020
On the Safety Theorem
Ralph L. Barnett

The contrivances of humankind come into existence through divine intervention, stealth, creative impulse, transformation, systematic design, evolutionary forces, and accidental benevolence. According to the safety theorem the elements of this cosmic stew have a common property, they can all cause harm. The safety theorem appears in many of the most important safety concepts, e.g., the colloquial definition of safety, the technical definition of safety, the control hierarchy, risk abatement, "safety through design" protocol, alternative design theory, and the classification of safety devices. According to the safety theorem, • The colloquial definition of safety, freedom from the occurrence of injury or loss, exists only as a concept not a reality. • A safe state does not exist, it may be approached asymptotically in the sense that a cup cannot be emptied by drinking half, followed by drinking half the remainder, etc. You may get as close to empty as you want; but, an infinite number of trials will not empty the cup. • Laypeople by and large mistakenly believe that products can be made perfectly safe if enough money and time were focused on their design. This paper offers a proof of the safety theorem together with some of its applications.

Volume 32 No. 1, October, 2020
On the Safety Hierarchy and Hierarchy of Controls
Ralph L. Barnett

History reveals an ever-increasing caboodle of protective measures for assuring an acceptable level of safety for both new product designs and for the remediation of man-made and natural hazards. Some seventy years ago, safety professionals began to functionally categorize these safety tools and rank the categories according to their perceived effectiveness. At first, the resulting hierarchies were designated Safety Hierarchies; later updated versions are now referred to as Hierarchies of Controls. To characterize Hierarchies, sixty-six references were surveyed that were published after 1952. Each of these design recipes begin with the admonition "Eliminate the hazards." All of the hierarchies were created using consensus or speculation, not research. We establish that the Safety Hierarchies and the Hierarchies of Controls are merely rules of thumb, not theorems. Generally, different hierarchies give rise to different designs. The principal strength of both Hierarchies is their replacement of the myth of colloquial safety as "freedom from harm" with a realistic technical definition of safety as an "acceptable level of risk" that is systematically achievable however tortuous.

Volume 32 No. 2, March, 2022
A Protocol Triumvirate - Risk Assessment and Risk Reduction
Ralph L. Barnett

Volume 32 No. 3, April, 2022
Standard Guardrails and Related Systems - Challenge and Opportunities
Ralph L. Barnett

Safety fences define safe from unsafe regions and safeguard against falls into such regions. Standards define their required strength and stiffness and specify critical aspects of their geometry. It is implicit that the community of users of safety fences are responsible adults with the further understanding that all ambulatory humans can willfully breach these structures. Despite their de minimis design constraints, technologists have not understood nor met the safety challenges posed by these simple, classical, and ubiquitous structures. The purpose of this paper is to identify a few of the safety shortcomings of fence technology which include the fundamental problem of anthropometric guarding, improperly written standards, the challenge of corrosion, dangerous testing protocols, and the creation of testing hardware.

Volume 32 No. 4, June, 2022
Friction Lock - "Falling Flat on One's Face"
Ralph L. Barnett

Normal ambulation and shuffling are both complex processes where a pedestrian is in a state of continuous forward falling. This is regularly interrupted when the walker's trailing leg is brought forward in a timely manner to prevent tumbling in the forward direction. Anything that blocks or sufficiently inhibits the swinging trailing leg leads to a subset of trip and fall onto one's face. In this paper, we call this unnamed phenomenon "Friction Lock." Here, premature interdiction of the trailing foot onto the walking surface at an arbitrary point in the gait cycle enables the walker to tumble onto a flat surface. Tripping proceeds without the usual "Change of Level" provided by visible asperities (stumbling blocks). In the shuffling mode where drag is present throughout the walking gait, premature transfer of the walker's full weight from the stationary forward leg onto the sliding rear leg gives rise to "Friction Lock" and its concomitant forward fall scenario. High levels of the coefficient of kinetic friction exacerbate the onset of "Friction Lock" which disproportionately affects senior citizens. Specialists in human ambulation are aware of the conundrum that low friction is counterproductive for slip and fall and high friction exacerbates the frequency of trip and fall; the problem is currently intractable.

Copyright © 2005 Triodyne Inc. All Rights Reserved

Copyright © 2005 Triodyne Inc. All Rights Reserved