Ladders

Ladder Slide Out - First Order Analysis
Triodyne Safety Brief Volume 12 No. 1, November 1996
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.


Extension Ladders - Going Out on a Limb
Triodyne Safety Bulletin Volume 3 No. 1
Ralph L. Barnett and Andrew H. Tudor

Sawing off a limb in back of you - this image has become cartoon cliche. On the other hand, sawing off a limb in front of you does not conjure up the slightest portent of danger. Nevertheless, when this activity is combined with an extension ladder, it can lead to the telescoping collapse of the ladder.


Ladder Rung vs. Siderail Hand Grip Strategies
Triodyne Safety Brief Volume 16 No. 4, April 2000
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.


How To Climb An Unsafe Ladder
Triodyne Safety Bulletin Volume 9 No. 4, January 2001
Ralph L. Barnett

Weaknesses in a ladder structure are not always self revealing. Furthermore, a momentary loss of foot or hand control or even a patch of ice or grease may compromise a climber's safety. The proposed climbing strategy optimizes the safety profile. On the other hand, climbers must continue to follow the "classical ladder rules" dealing with ladder angle, overreaching, etc.


Anti-Slide Out Devices for Straight And Extension Ladders
US Patent 6,405,829, June 18, 2002
Ralph L. Barnett

A non-self-supporting ladder having an anti-slide-out device which enables a user to set up the ladder at the specified minimum ladder set-up angle Θ or greater angles for precluding the base of the ladder from sliding away from a structure against which the ladder is leaning upon application of a weight on the ladder, but prevents the ladder to be set up at angles smaller than Θ. The device includes an inboard roller assembly having a bracket connected to each side rail of the ladder and a roller connected to each bracket oriented and disposed so as to impose a specified ladder inclination angle Θ, when the lower end of the ladder and the roller simultaneously rest on a substantially flat horizontal surface. At set-up angles smaller than the specified minimum angle Θ, only the rollers rest on the horizontal surface, preventing the ladder from being set up.


Auto-Setting Ladder Inclination
Triodyne Safety Brief Volume 24 No. 1, July 2003
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.


Anti-Slide Out Devices for Straight And Extension Ladders
US Patent 6,629,582, October 7, 2003
Ralph L. Barnett

A non-self-supporting ladder having an anti-slide-out device which enables a user to set up the ladder at the specified minimum ladder set-up angle (Θ) or greater angles for precluding the base of the ladder from sliding away from a structure against which the ladder is leaning upon application of a weight on the ladder, but prevents the ladder to be set up at angles smaller than (Θ). The device includes an inboard roller assembly having a bracket connected to each side rail of the ladder and a roller connected to each bracket oriented and disposed so as to impose a specified ladder inclination angle (Θ), when the lower end of the ladder and the rollers simultaneously rest on a substantially flat horizontal surface. At set-up angles smaller than the specified minimum angle (Θ), only the rollers rest on the horizontal surface, preventing the ladder from being set-up.


Sloped Surfaces - Ladder Slide Out
Triodyne Safety Brief Volume 25 No. 1, January 2004
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.


Ladder Cages
Triodyne Safety Brief Volume 25 No. 4, April 2004
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.


Ladders
Center of Excellence
Ralph L. Barnett

Review of the subject of ladders as a safety topic.


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