CA2521389A1 - Energy absorber for personal fall arrestor - Google Patents

Abstract

An energy absorber for use in a personal fall arresting system. The absorber contains upper and lower webbings which are each two ply members. The back ply of the upper webbing is mounted adjacent to the face ply of the lower webbing with said webbing being of about equal length and width. Exterior tear elements run back and forth sinusoidally between attachment points on the face ply of the upper webbing and the back ply of the lower webbing. Interior tear elements run back and forth sinusoidally between attachment points on the back ply of the upper webbing and the top ply of the lower webbing.

Description

ENERGY ABSORBER FOR PERSONAL FALL ARRESTOR
Field of the Invention [0001) This invention relates to an energy absorbing device suitable for use in a personal fall arresting system.
Background of the Invention [0002] Workers who are obligated to work in high places such as on scaffolding, window ledges, and the like typically wear a body harness and/or a safety belt which is secured by a lanyard to some type of available anchorage. In the event the worker falls from a relatively high perch, he or she can reach a very high velocity in a matter of seconds.
Depending upon the length of the lanyard, a falling worker's descent can be abruptly terminated causing serious bodily harm to the worker. Various shock absorbing devices have been developed over the years to decelerate a worker's fall, and thus cushion the resulting impact shock. The shock absorber is typically made part of the lanyard connecting the worker's body harness or belt to an anchorage. One prevalent type of shock absorber is disclosed in U.S. Patent No. 3,444,957 to Ervin, Jr. that involves a length of high strength webbing that is folded over itself a number of times with the adjacent folds being stitched together. The stitching is adapted to tear apart when placed under a given dynamic load to absorb the energy generated by the fall. This type of absorber is relatively lightweight, compact, and thus easily portable as well as being easily retrofitted into existing safety systems. This type of shock absorber will herein be referred to as a tear away type of energy ab sorb er.

[0003] A Canadian National Standard 2259.11-OS relating to Energy Absorbers and Lanyards was issued in 2005 and superseded the previous edition published in 1992 and reaffirmed in 1998. The Standard addresses different safety system and methods for arresting the fall of a worker from a high place. The Standard is consistent in many important features with many of the standards in other countries, but is more stringent than most in that the requirement for dynamic drop testing must be performed upon test specimens that have been conditioned by heat and moisture. Most tear away energy absorbers that are tested cannot consistently pass the dynamic drop test set out in the National Standard for Canada.

Summary of the Invention [0004] It is therefore an obj ect of the present invention to improve personal fall arrest systems.

[0005] It is a further object to improve tear away shock absorbers used in personal fall arrest systems.

[0006] It is still a further obj ect of the present invention to provide a web type tear away shock absorber that can pass the dynamic drop tests set out in the American and Canadian National Standards covering safety requirements for personal fall arrest systems.

[0007] Another object of the present invention is to provide a tear away shock absorber for use in a personal fall arrest system that is simple in design, lightweight, flexible, and easily integrated into existing systems.

[0008] These and other objects of the present invention are attained by an energy absorber suitable for use in a personal fall arresting system that includes upper and lower two-ply webbings. Each webbing has a face ply and a back ply extending along the length of the webbing. The webbings are mounted one over the other with the back ply of the upper webbing being adjacent to and aligned with the face ply of the lower webbing.
Exterior tear elements are arranged to run back and forth sinusoidally between attaching points located on the face ply of the upper webbing and the back ply of the lower webbing.
Interior tear elements are arranged to run back and forth sinusoidially between attachment points Located on the back ply of the upper webbing and the face ply of the lower webbing.
The tear elements are coated with a material for reducing yarn on yarn abrasion especially after exposure to moisture which was seen to be effective over a range of temperatures from ultra cold to elevated. The tear elements are designed to tear away decelerating the worker's rate of fall and thus reduce the shock at impact.
Brief Description of the Drawings [0009] For a better understanding of these and other objects of the subject invention, reference will be made in the disclosure below to the accompanying drawings, wherein:

(00010] Figure 1 is a partial perspective view illustrating a tear away web type shock absorber that embodies the teachings of the present invention;

[00011] Figure 2 is a perspective view of the shock absorber shown in Figure l, further illustrating the upper and lower webbings starting to separate under load;

[00012] Figure 3 is an enlarged partial sectional view taken along lines 3-3 in Figure 1 further showing the construction of the shock absorber; and [00013] Figure 4 is a partial front elevation of a test strand for performing dynamic drop tests upon specimens of shock absorbers embodying the teachings of the present invention.
Detailed Description of the Invention [00014] Turning now to Figures 1-3, there is illustrated a tear away type energy absorber, generally referenced 10, that embodies the teachings of the present invention. The absorber contains a pair of two ply webbings that includes an upper webbing 12 and lower webbing 13. The two webbings are woven from high tenacity polyester yarns with each ply including a series of longitudinally extended ends having a series of warps 16 spaced along its length and filling yarn or wefts 17 that pass laterally throughout the warps to transverse the width of the yarn.

[00015] The upper webbing contains a face ply 20 and a back ply 21. The lower webbing similarly includes a face ply 23 and a back ply 24. The wefts contained in the back ply of each webbing are arranged in assembly so that they are located about midway between the wefts contained in the face ply of each webbing. The upper and lower webbings are of the same length and width. In assembly, the two webbings are superimposed in alignment one over the other with the back ply of the upper webbing being mounted adjacent to the face ply of the lower webbing. As illustrated in Figure 3, the wefts in the two face plys are placed in commonly shared vertical rows and the.wefts in the two back plys are also placed in commonly shared vertical rows with the rows containing the back ply wefts being located about midway with respect to the rows containing the face ply rows.

[00016] The two pieces of webbing are woven together using a series of binders that are formed by continuous strands of tear elements. The tear elements include what will herein be referred to as an exterior tear element 30 and interior tear element 31. The tear elements in this embodiment are fabricated of high tenacity polyester yarns, although other suitable yarns such as nylon or the like having similar properties may be used without departing from the teachings of the present invention. The exterior binder runs back and forth in a sinusoidal manner between attachment points on the face ply of the upper webbing and the back face of the lower webbing. The interior binding runs back and forth in a sinusoidal configuration between attachment points on the back ply of the upper webbing and the face ply of the lower webbing. As illustrated in Figure 3, the laterally extended wefts in each of the ply serve as the attachment points for both binders. The tensile strength of the two binders is less than that of the wefts and as will be explained in greater detail below, the binders will tear out under load before the wefts will rupture. A lock stitch 33 (Figure 2) is included along the longitudinal knitted edge of each webbing.

[00017] The two opposing ends 38 and 39 ofthe energy absorber 10 will typically be provided with connectors for attaching the energy absorber to a personal fall arrest system.
In assembly, the energy absorber will be placed in series with a lanyard for coupling the worker harness or safety belt to a suitable anchorage such as a stationary structural element having sufficient strength to arrest a worker's descent in the event of a fall. The lanyard provides sufficient length to permit the worker to move about with a reasonable amount of freedom. In the event of a fall, the lanyard will play out until it becomes taut at which time the dynamic load of the falling worker is taken up by the energy absorber whereupon the binders begin to tear away absorbing the kinetic energy generated by the fall.
The rate of the fall is thus decelerated, lowering the force acting upon the worker's body as the fall is being arrested.

[00018] Applicant, in order to insure that it is in compliance with the National Standards of Canada, has constructed a test stand for dynamically testing sample absorber specimens of the type described above. As illustrated in Figures 1 and 2, the test specimens were equipped at each end with high strength non-elastic loop connectors 40 and 41 that are sewn into the ends of the absorber. The connectors will not pull out or elongate when experiencing dynamic load well in excess of one thousand pounds.

[00019] With further reference to Figure 4, the test stand contains an anchorage consisting of a horizontal cross beam 50 supported upon a pair of spaced apart vertical columns, one of which is depicted at 51. Although not shown, the cross beam is suspended above a drop pit containing a deep layer of sand. During a test, the two loops of the energy absorber are initially provided with shackles and the shackle of one loop connected to an anchorage point. A ten pound weight is suspended from the other loop and the distance between the two loop fold over points recorded. A load cell 53 is securely mounted upon the center of the crosspiece and one of the energy absorber loops is attached to the load cell by a suitable eyebolt.

(00020] An air activated release mechanism 55 is connected to a 100 kilogram weight 52 by means of a suitable shackle. The weight is connected to a hoist 60 which is used to raise the weight to a desired height. A 2,440 millimeter long wire rope lanyard equipped at each end by snap hooks is employed to attach the weight to the other loop of the energy absorber. The distance between the two snap hooks when the lanyard is placed under a 44N
load is measured and recorded prior to attaching the test lanyard between the weight and the energy absorber. The test weight is hoisted to a height such that the weight can free fall a distance of 1.8 meters before the test lanyard becomes taut and the energy absorber becomes active. The 1.8 meter distance includes the loop to loop fold over distance that was previously recorded.

[00021] At this time, the quick disconnect mechanism is released and the weight allowed to drop, thereby activating the energy absorber, whereupon the tear element breaks away, decelerating the falling weight and bringing the weight to a controlled halt. The distance between the foldover points of the two loops upon the played out energy absorber is then measured and the elongation of the absorber is calculated by subtracting the initially recorded foldover distance prior to the absorber being activated and the final foldover distance measurement. The elongation tear length of the energy absorber is recorded and the peak load and average load data are graphically provided by the load cell readout.

[00022] In order to meet the requirements of the Canadian Standard, test specimens of a given energy absorber design must pass a number of dynamic drop tests that are carried out under different conditions. These drop tests include:

(00023] 1) Ambient testing of specimens at 20°C, ~ 2°C, wherein the arresting force does not exceed 4.0 kN and the elongation of the energy absorber shall not exceed 1.2 meters;

(00024] 2) Elevated temperature testing of a specimen that has been conditioned at 45°C, ~ 2°C, for a minimum of eight hours. The test is carried out within five minutes after conditioning is completed wherein the arresting force shall not exceed 6.0 kN
and the permanent elongation of the energy absorber shall not exceed 1.2 meters.

[00025] 3) Wet testing of a specimen that has been immersed in water at 20°C, ~ 2°C, for a minimum of eight hours. Under this test, the specimen shall not exceed an arresting force of 5.0 kN and its permanent elongation shall not exceed 1.2 meters.

[00026] 4) Cold testing of a specimen is also carried out wherein the specimen is conditioned at a temperature of -3 5°C, ~ 2°C, for eight hours and tested within five minutes upon completion of the conditioning. The energy absorber shall limit the maximum arrest force to 5.0 kN and its permanent elongation shall not exceed 1.2 meters.

[00027] 5) Lastly, testing of a specimen that has been exposed to both water and a low temperature is carried out. Initially, the specimen is immersed in water at 20°C, ~ 2°C, for a minimum of eight hours. The specimen may be allowed to drain for up to fifteen minutes and is then conditioned at -35°C, ~ 2°C, for a minimum of eight hours. Within five minutes after the completion of conditioning, the specimen is tested and shall limit the arresting force to 6.0 kN or less and the permanent elongation shall not exceed 1.2 meters.

[00028] A number of test specimens were constructed which contain the double two-ply webbing arrangement with the two webbings being woven together using both exterior and interior bindings that were configured as described above. The specimens were tested in the above noted test stand to determine the maximum arresting force and permanent elongation of the absorber reached during testing. One configuration was identified which consistently met or exceeded all the dynamic drop test requirements set out in the published Canadian National Standard. The specimen webbing each had a length of 609 millimeters and a width of 44 millimeters. The face ply and back ply of both webbings contained fifty-two ends of 1,300 denier two-ply high tenacity yarn. The wefts located in each webbing were fabricated of 1,300 denier high tenacity yarns. Each webbing further included twenty-five ends of exterior binders and twenty-five ends of interior binders fabricated of 1,000 denier high tenacity polyester yarns. Minimally, the.binder yarns are coated with a material for improving the binder's yarn on yarn abrasion resistance as well as protecting the binder against moisture. One such coating material that greatly enhanced the absorber's performance is a siloxane-based material that forms a durable polymeric network over the surface of the binders which is marketed by Performance Fibers, Inc. under the trademark SEAGARD. In a further embodiment of the invention, the performance absorber is further enhanced by also coating the webbing wefts with the above noted siloxane-based material.

[00029] While this invention has been particularly shown and described with reference to the preferred embodiment in the drawings, it will be understood by one skilled in the art that various changes in its details may be effected therein without departing from the teachings of the invention.

Claims (12)

1. An energy absorber for use as part of a personal fall arresting system that includes:

upper and lower two-ply webbings, each having a face ply and a back ply extending along the length of the webbing, said webbings mounted one over the other with the back ply of the upper webbing being adjacent to the face ply of the lower webbing;

exterior tear elements running back and forth sinusoidally between attachment points on the face plys of the upper webbing and the back plys of the lower webbing;

interior tear elements running back and forth sinusoidally between attachment points on the back plys of the upper webbing and the face plys of the lower webbing; and each tear element being fabricated of a continuous high tenacity polyester yarn that is coated with a material for protecting the tear elements against yarn on yarn abrasion at extreme temperatures, either dry or after exposure to moisture.

2. The energy absorber of claim 1, wherein the attachment points are evenly distributed along the width of selected ends of each ply.

3. The energy absorber of claim 1, wherein said coating is a siloxane-based material that forms a polymeric network over the surface of the tear elements.

4. The energy absorber of claim 1, wherein each tear yarn is looped around wefts that pass laterally through warps ends contained in said face plys and said back plys of the upper and lower webbings.

5. The energy absorber of claim 4, wherein the tear elements are fabricated of a material that will rupture before the face weft and back weft of the upper and lower webbings when the absorber is placed under load.

6. The energy absorber of claim 5, wherein a lock stitch is included along the knitted edges of the webbings.

7. An energy absorber for use as a component part of a personal fall arresting system that includes:

a two-ply upper webbing having face ply and back ply each containing uniformly spaced wefts that pass laterally through warps located in the plys of said upper webbing;

a two-ply lower webbing having face ply and back ply each containing uniformly spaced wefts that pass laterally through warps located in the plys of the said lower webbing;

said webbing being mounted one over the other with the back ply of the upper webbing located adjacent to and in alignment with the face ply of the lower webbing with the wefts in the two back ply being spaced about midway between the wefts in the two face plys;

a number of continuous exterior tear yarns, each of which runs back and forth over the wefts contained in the face ply of the upper webbing and adjacent wefts contained in the back ply of the lower webbing to establish a sinusoidal-shaped exterior binder;

a number of continuous interior tear yarns, each of which runs back and forth over the wefts contained in the back ply of the upper webbing and adjacent wefts contained in the face ply of the lower webbing to establish a sinusoidal-shaped interior binder; and each tear yarn being fabricated of a continuous high tenacity polyester that is coated with a material for protecting the yarn against yarn on yarn abrasion at extreme temperatures either while dry or after exposure to moisture.

8. The energy absorber of claim 7, wherein said yarn coating is a siloxane-based material that forms a durable polymeric coating over the surface of the binders.

9. The energy absorber of claim 7, wherein each ply contains about fifty-two face ends and about fifty-two back ends.

10. The energy absorber of claim 9, wherein each ply further contains about twenty-five exterior tear yarns and about twenty-five interior tear yarns.

11. The energy absorber of claim 7, wherein said warps are fabricated from 1,300 denier two-ply high tenacity polyester yarns, wefts are 1,300 denier single ply high tenacity polyester yarn, and tear yarns are fabricated of 1,000 denier high tenacity polyester yarns.

12. The energy absorber of claim 11, wherein said wefts are coated with a material for protecting the wefts against yarn on yarn abrasion at extreme temperatures either while dry or after exposure to moisture.