Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
21:~q.8~8
FALL-ARRESI- SI RAP AND FALL PREVEN~ON MEIHOD
Field of ~e Invention
This invention relates to a fall-arrest strap and, more particularly,
relates to a fall-arrest strap having an intPrmP~ ry folded-over stitched portion
which acts as a shock absorber when the strap is employed, and to a mPthntl for
~tt~rhing the strap to a wooden beam at a workcitP-
Ba~u~d of the IllVt~ iUIl
Fall-arrest straps used as safety devices to protect workers from risk
of injury or death from a fall when working at elevated workcitPs or on uneven or
unb~l~nce~l work surfaces are well known.
Fall-arrest straps may be secured to workcitPc at various lor~honc to
enable workers to be secure at all times. They may be attached to a safety belt or
h~rnPcs around a worker's waist or to a tether ~tt~rh~l to a worker's safety belt or
h~rnPcs to secure the worker.
C~n~ n Patent No. 1,182,435 which issued February 12, 1985 to
Sulowski et al shows a ladder climbers' safety device which ~tt~rhPs to the climber's
safety belt. The device has a pair of handle members which colltain l~trhing means
for engaging the rungs of a ladder. The handle members are interconnPctP-l with
a climber's safety belt and with one another by a flexible cable. The cable is freely
threaded through a co~nPctor ring ~tt~rhP-1 to the climber's safety belt. The support
further co.. 'l" ;cec a flP~ihl~ wire rope fastened to the handle members and passing
through ~e cr)nnPctor ring. When using the device, the handle members are
~kPrn~tPly moved to engage successive rungs of a ladder. rn the event of a fall, the
wire rope absorbs the shock load.
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C~n~ n Patent No. 1,182,435 relates to a safety device which
utilizes a wire rope for absorbing the shock load of a fall rather than the
interconnPchng fle~nble cable.
Su~ of the Invention
The disadvantages of the prior art may be ov~:rcol~e by providing a
relatively light weight fall-arrest strap which itself su~L~ S a large amount of force
and provides a means for re~llleing the amount of force initially felt by a fallen
worker.
Accorlingly, in one broad aspect, the fall-arrest strap of the present
invention comprises:
~tt~rhmPnt means at one end thereof to allow ~tt~hmPnt to a support
structure;
handle means at the other end of said strap for attaching said strap
to the safety belt or h~rnP~s worn by the worker or a tether secured thereto;
fl~rihle support means intPrmP~i~te said handle me~ns and said
atta~hmPnt means, said fle~ible support means having an intPrmPrli~ry folded-over
portion secured by stitches, said sht~hPs having less tensile strength than saidflexible support means, whereby when the worker falls, said stitches break upon
application of a force less than the breakage strength of said strap, thereby
absorbing shock load. The fall-arrest strap may be used to secure a worker working
at elevated job sites or may be used to st~hili7e such structures as l~ldPr~ from
lateral movement.
Accur~ g to another embo-Iim~nt of the invention, the flexible
support means interconnPcting said ~tt~rhmPnt means with said handle means and
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~tt~chmPnt means has an int~rmP~i~ry folded-over portion which has a plurality of
folds secured by stitches, said stitches having less tensile strength than said fle~nble
support mP~n~, whereby when the worker falls, said stitches break upon application
of a force less than the breakage strength of said strap, thereby absorbing shock
load.
In a further preferred embo~limPnt, the ~tt~rhmPnt means simply
comprises a portion of strap that is of a weave sl-ffl~iPntly fl~ihle or porous enough
to allow nails to be h~mmPred or inserted the,elh~ough, to allow one end of the
strap to be nailed to a wooden beam. ~ltprn~tply~ such ~tt~chm~nt means at said
one end of the strap may con,~l;se ferrules located within said strap, to allow nails
to be inserted thel~ough to allow said one end of strap to be secured to a
wooden beam.
The invention also relates to a fall prevention method to secure
workers to a support structure, c-)mpri~ing:
p~Csing se~ur~llent means, which in the plert:lled embodiment are
nails, through one end of a fl~ihle fall arrest strap to thereby attach one end of said
strap to a wooden beam or truss, sd wrapping said strap at least once around said
beam and securing said other end of said strap to said worker.
Advantageously, the above method of attaching a fall arrest strap to
a wooden beam allows easy and rapid securement of the strap to a beam and by
wrapping the strap at least once around the beam allows any force on the strap and
nails to be applied perpendicularly to the direction of insertion of the nails in the
beam. By having the force exerted perpendicular to the direction of insertion ofnails into the beam, a greater cross-section of strap m~tPri~l is able to resist the
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applied force than would otherwise be the case if there was no wrapping of the
strap about the beam and any applied force was thus applied in an axial direction
(i.e. in a direction parallel to the direction of insertion of the nails), in which case
the entire force is only resisted by the portion of the strap underlying the head of
the inserted nails.
Brief Description of the Drawings
The present invention will now be described in detail with reference
to the accompanying drawings, in which:
Figure 1 is a perspective view of a worksite with devices of the
invention secured at various positions at the worksite and a workman attached to
a tether which is attached to the fall-arrest strap of the invention.
Figure 2 is a perspective view of the strap of the present invention.
Figure 3 is a perspective view of the strap of the present invention.
Figures 4 and 5 are fr~gmPnt~ry perspective views illustrating two
embollimPn~ of the anchor bracket of the strap of the invention.
Figure 6 is a fr~gmPnt~ry side elevation view of another embodiment
of the anchor bracket of the strap of the invention.
Figure 7 is a perspective view of the embodiment of the strap shown
in Figure 6.
Figure 8 is a side view of the strap of the invention attached to a
wood beam.
Des~ ion of the Prefem~d Embodimf~n~
Referring first to Figure 1, the fall-arrest strap 12 of the present
invention may be placed at numerous positions around worksite 10 or support
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structures such as walls, etc. Strap 12iS~tt~chptl to tether 14 which is ~tt~rhPti to
safety belt 16 worn by worker 11. Strap 12 may also be ~tt~rhPrl dir~.lly to safety
belt 16. Worker 11 may move about wo~ e 10 by simply securing tether 14 to
a strap 12 which is closest to the position of worker 11 at worksite 10. Tether 14
may be of different lengths and it, in comhin~tion with the various pl~cPmPntc of
straps 12 about worksite 10, Pn~hlPc worker 11 to be secure at all times. Worker11 may wear a h~rnPss in place of safety belt 16 for attarhmPnt to tether 14 or for
hmPnt di~ ;Lly to strap 12.
Figure 2 shows strap 12 in detail. Strap 12isplt:rE:ldbly a flP~riblP
m~tPri~l, such as nylon webbing, having one end where nails may be h~mmPred
thele:lhLough, and has D-ring 18 which attaches to safety belt 16 or a h~rnPss worn
by worker 11. Anchor bracket 20is located at the other end of strap 12. Anchor
bracket 20 has aperture 24 formed therein. Loops 26 are formed at both ends of
strap 12 and are stitched in place by collvelllional thread. Loops 26 are formedaround D-ring 18 or similar handle members and anchor bracket 20, to allow the
flexible strap to be aff~xed to Ring 18 and bracket 20. A nail or a bolt and nutcombination is placed through aperture 24 to join strap 12 to a truss at a work~ite.
In a preferred embo-limPnt, anchor bracket 20is not llhli7P~, and the
strap 12 at one end thereof is of a weave sllmriPntly flexible to allow nails to be
h~mmPred th~LLough to attach one end of strap 12 to a wooden beam or truss.
rmpolL~lLly, the nylon webbing of strap 12 has an intPrmP~
folded-over portion 22. The folded-over portion 22 of strap 12is stitched in place
with collv~lLion thread similar to the stitching forrr~ing loops 26. The stitches have
less tensile strength than the nylon webbing. When a worker falls, stitches of
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folded-over portion 22 break, thereby abso.l,i-~g shock load. The amount of force
initially felt by the worker is, therefore, reduced, to lessen the lik.qliht~od of injury
to a falling worker.
Figure 3 illustrates an ~mho~im~nt of strap 12 wherein the webbing
has been folded to give a plurality of folded-over portions 22. The folds are stitched
in place with col.v~l~ional thread. The stitches have less tensile strength than the
nylon webbing. When a worker falls, the stitches of the two folds succe~ivt:ly
break, thereby absorbing shock load and providing a gradual "braking" to the fall
of the worker. Stitches are placed through each of the folds and ~l(lit~on~l stitches
of thread are used to join the first fold of the webbing to the second fold, etc. The
shock load may then be absorbed in a two or more step fashion.
Figures 4, 5 and 6 illustrate further embo~lim.ont~ of anchor brackets
for secllring strap 12 to a workcite.
~n Figure 4, the anchor bracket is metal ring 28 which is large enough
to be placed over the top of a pole. Since most poles are tapered, ring 28 wouldform a frictio~ fit, thus securing strap 12 in place.
~n Figure 5, the ~tt~rhmPnt means of the strap at one end thereof is
a plate 30, having a number of apertures therein. Plate 30 may then be ~ rh~tl
to a beam at a worksite by il~ ing fasteners, such as nails, screws, or bolts,
through the apertures to secure such end to a structure. ~lt~ hvely~ the web maybe provided with ferrules (not shown) to allow nails, screws, or bolts to be inserted
the~ ough to allow the strap 12 at its one end to be secured to a beam or truss,with the other end of the strap having secured to the worker's safety h~rn~s or belt
via D-ring 18.
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In Figure 6, the anchor bracket is split-ring clamp 32 which allows
strap 12 to be ~tt~rhP~l to such structures as pipe 40. F~tPncion 44 of strap 12 is
welded to clamping member 34 and is Pnr~ce-l by clasp 42. Clamping member 36
is pivotally ~tt~rhP~l to rl~mping member 34 by pin 38. Pin 38 allows for
articulation of rl~mping member 36 around pipe 40. ln operation, clasp 42 is
spring loaded and is slidably moved towards strap 12, thus, allowing clamping
member 36 to be pivoted away from rl~mping member 34. Clamping member 36
is then placed around pipe 40. ~l~mping member 36 is returned to its at-rest
position as shown in Figure 6 and clasp 40 is moved towards strap 12. Clasp 40
clasps clamping members 34 and 36 together, thus ~tt~hing strap 12 to pipe 40.
The method of the invention for ~tt~rhing a fall-arrest strap to a
wooden beam is illustrated in Figure 8. Strap 12 for l1hli7.~hon in accordance with
this method does not have an anchor bracket 20. lnstead, nails or screws 48 secure
strap 12 at one end thereof to a wooden beam or truss 46. Nails 48 are either
driven through the nylon webbing, or through ferrules in the webbing located at
one end thereof. Strap 12 is preferably wrapped one or more times around a 2" x
4" or 2" x 6" piece of wood 44. Nails 50 may further then be driven through bothlayers of webbing. By Wld~illg strap 12 to wood 44, strap 12 is ripped
perpendicular to the pull of strap 12 when a worker falls.
The following tensile shrength test examples are included to further
illushrate the invention herein described and rl~imPtl The examples are not
int~n~le~ as limit~hons of the present invention.
The sample shraps tested were 2" wide x 3/8" thick nylon webbing
with a 2l/2" wide D-ring. The D-ring was attached to the strap by a stitched loop
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formed on the webbing. The other end of the strap was overlapped and stitched
forming a double layer of webbing and this end was nailed to a 2" x 4' or a 2" x 6"
spruce board with 3" ARDOX~ nails. ~n ~Y~mple 7, a pine board was used.
Example 1
The first strap was wrapped once around two 2" x 6" boards. Two
ARDOX~ nails were used to fasten the strap to the boards. A third nail was used
to fasten the end of the first loop to the boards. The load was applied parallel to
the 6" face.
Example 2
The second strap was wrapped one and a half times around one 2" by
6" board. Two ARDOX~ nails were used to fasten the strap to the board; the
protruding ends of the nails were bent over. A third nail was used to fasten the end
of the first loop to the board and the protruding end of the nail was bent over. The
load was applied parallel to the 6" face.
Example 3
The third strap was wrapped one and a quarter times around two 2"
by 4" boards. Two ARDOX~ nails were used to fasten the strap to the wood. Two
nails were used to fasten the end of the first loop to the wood. The load was
applied parallel to the 2" edges.
Example 4
The fourth strap was wrapped one and a half times around one 2" by
6" board. Two ARDOX~ nails were used to fasten the strap to the wood. The
protruding ends of the nails were bent over. A third nail was used to fasten the end
2 1 ~ 8
g
of the first loop to the wood and the protruding end of the nail was bent over. The
load was applied parallel to the 6" face.
Example 5
The fifth strap was wrapped one and a half times around one 2" by
4" board. Two ARDOX~ nails were used to fasten the strap to the board. The
protruding ends of the nails were bent over. A third nail was used to fasten the end
of the first loop to the wood and the protruding end of the nail was bent over. The
load was applied parallel to the 4" face.
Example 6
The sixth strap was wrapped one time around one 2" by 4" board.
Two ARDOX~ nails were used to fasten the strap to the wood and the protruding
end of the nails were bent over. A third nail was used to fasten the end of the first
loop to the wood and the protruding end of the nail was bent over. The load was
applied parallel to the 4" face.
Example 7
The seventh strap was wrapped once around one 2" by 6" pine board.
Two ARDOX~ nails were used to fasten the strap to the wood. A third nail was
used to fasten the end of the first loop to the wood. The load was applied parallel
to the 6" face.
The results are shown in the following table:
Number of M;.x;......... Failure
Example Loops Applied Load Mode
(lbf)
1 1 2,750 Nail heads pulled
through webbing
2 ll/z 3,830 "D" ring stitching
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failed
3 ll/4 3,150 Wood crushed, and
webbing failed
4 ll/2 3,500 "D" ring stitching
failed
ll/2 3,640 Wood crushed, and
fractured
6 1 3,280 Wood crushed
7 1 3,380 Webbingfailed at
nail hole
The prese~lt invention provides a mlmh~r of important advantages.
The fall-arrest strap permits workers to move freely along elevated surfaces and to
be secure at all times. The use of an int~rm~ ry folded-over portion in the strap
as a means for absorbing shock load obviates the need for a second cable to be used
for that purpose.
Although the disclosure describes and illustrates plef~,ed
embo-lim~ntc of the invention, many variations and mo~lific~tions will now occurto those skilled in the art. For a full tl~finifiion of the invention, refelellce is to be
made to the appended claims.
