Chapter 1 SOME ASPECTS OF FALL PROTECTION EQUIPMENT EMPLOYED IN CONSTRUCTION AND PUBLIC WORKS INDUSTRIES

Georges Noel, M. Gilbert A rdo u in, Pierre Archer, Maurice Amphoux, Andre Sevin

Editor's Preface This paper, translated and re-printed here with minor editorial changes, was originally

published ill the Annales de l'Institut Technique du Batiment et des Travaux Publics No. 362 Juin 1978. The original title was: "Le materiel de securite dnns Ie batiment et les travaux publics. La legerete et l'ergonomie apparantes d'un materiel individuel ne sont pas toujours synonymes de vie sal/vee apres une chute dans Ie vide". The publisher of the Annales is the Institut Technique du Batiment et des Travaux Publics located at 6, rue Paul-Valery, 75116 Paris, France.

The experimental part of the study reported on in this paper was performed at the Centre Experimental du Batiment et des Travaux Publics in collaboration with Organisme Professionnel de Prevention du Batiment et des Travaux Publics (O.P.P.B.T.P.) and Association Paritaire d'Action Societe, Medecine du Travail du Batiment et des Travaux Publics de la Region Parisicnne (A.P A.S.-M.T.) in France.

1

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TOLERANCE TO INDIVIDUAL FALL PROTECTION SYSTEMS DURING PROLONGED SUSPENSION Quite randomly, as a result of falls by stunt-men, it became evident that prolonged

suspension in a variety of diverse harnessing systems could rapidly become painful or intolerable, indeed even dangerous. This is notably the case when using the system in the photograph in Fig. 1. This is a light thoracic belt which proved to have serious disadvantages. In effect, it is not always possible, for a variety of different reasons, to rescue immediately a worker who has fallen from a height; and his rescue may sometimes require a rather significant interval of time. Furthermore, the problem may be exacerbated if the victim is not capable of participating in his own rescue.

It is therefore necessary that the victim be able to tolcrate a prolonged suspension without ill effects. Now, with the belt given in Fig. 1, the tolerance tests rapidly showcd that, due to the respiratory trouble it causes, loss of consciousness results very quickly and, very soon thereafter, a fatality may result. The problem is unfortunately identical with certain traditional belts currently in use and still available on the market.

It is necessary to say that, up to the present day, the aspects of this prob lem have not concerned us: it seemed more important to us to arrive at fall-arrest without physical harm.

On the other hand, the difficulties of rescuing the victim could, in retrospect, be rather significant. It is not necessarily easy for untrained personnel to organize--without the risk to others--th~ rescue of a worker suspended at the end of a lanyard and at a distance from any kind of easily accessible support. It is even to be fcared that, in the event there is loss of consciousness, the occurrence of complete muscular rc1axation would reduce tolerance time in the suspended position.

The first attempts to prolong the time of suspension made us suspect that the effort of the individual to adjust himself in his equipment was one of the causes of good tolerance relative to the system. It thus appeared necessary to us, in order to orient our research and to respond to certain objections justly raised elsewhere, to effect a series of tests on prolonged suspension up to the appearance of serious physica l troubles.

1.1 EQUIPMENT AND MEfHOD The testing of prolonged suspension was undertaken at the Faculty of Medicine,

located at Rue des Saints-Peres in Paris. It was a matter of suspending a living subject by the use of a manual hoist, which provided for a slow elevation without shock, and of maintaining him in a stationery position a foot or so above the ground until the appearance of difficulties.

The physiological condition of the subject was monitored partially by his own comments an partially by the transmission of cardiac and muscular signals to multi-scan recorder, detected by the use of five electrodes distributed in the following fashion:

2

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three thoracic electrodes (electrocardiogram); lwu cervical electrodes (electromyogram) .

Figure 1. Light Thoracic Belt

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Due to the potential risks of such operations, doctors Amphoux and Sevin con-tinuously monitored the experiments as they occurred without any difficulty, although some of them were continued up to the point of nausea.

The individuals participating in this experiment demonstrated no exceptional ath-letic abilities and thereby constituted a test group reasonably close to reality. Their ages and weights varied thus:

59 years, 82 kg 32 years, 72 kg 31 years, 63 kg 28 years, 72 kg 18 years, 59 kg

During the tests, the subjects were dressed normally or had overalls over their clothes. The test equipment was composed of a certain number of possible suspension systems: from the traditional waist belt to recently manufactured harnesses, all the way up to the full parachute harness and even an alpine belt.

The tests were undertaken in random order, and we will present the results in the order in which they were obtained. In any case, we would like to make the following clear: the tests thus executed have above all a strictly scientific character--this is the reason why the designation of the equipment was undertaken as follows, without any indication of the commercial brands.

4

recently manufactured harnesses, types A,B,C, (these different types are presented in Fig. 5,6, & 7);

parachute harness (Fig. 8); thoracic belt (alpine belt); traditional waist belt with shoulder straps.

Fig. A. A typical sub-pelvic design harness without a waist strap (Note: this illustration is not a part of the original G. Noel's paper. Edit)

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Figure 5. Suspension with Type A Harness

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Figure 6. Suspension with Type II Harness

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Figure 7. Suspension with TJpe C lIarness

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Figure 8. Suspension with Parachute Harness

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Figure 9. Suspension with waist belt equipped with shoulder straps; it is seen that the subject has added several layers of cushioning on his stomach and kidneys in an attempt to withstand better the pressure of the waist belt during the prolonged suspension test.

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1.2. PRESENfA TION OF OBSERVATIONS

Harness Type A Duration of suspension Cardiac frequency (before) Cardiac frequency (during)

Harness Type B

SUBJECT 59 YEARS, 82 KG

31 minutes 90 pulses per minute 125 pulses per minute (maximum value observed during suspension)

Duration of suspension 12 minutes 15 seconds Cardiac frequency (before) 92 pulses per minute Cardiac frequency (during) 125 pulses per minute (maximum value) After 12 minutes and 15 seconds, suspension became intolerable.

Harness Type C Duration of suspension 29 Minutes 13 seconds Cardiac frequency (before) 90 pulses per minute Cardiac frequency (after) 125 pulses per minute (max imum value) After 29 minutes and 13 seconds, suspension became painful

Parachute Harness Duration of suspension 28 minutes 10 seconds Cardiac frequency (before) 92 pulses per minute Cardiac freq uency (during) 125 pulses per minute (maximum value) After 28 minutes and 10 seconds, suspension became painful.

In summary: Very good tolerance with type A, 31 minutes without any probem; With type B, tolerance is very average; With type C and the parachute harness, good tolerance.

Harness Type A Duration of suspension Cardiac frequency (before) Cardiac frequency (during) End of suspension

Harness Type B Duration of suspension Cardiac frequency (before) Cardiac frequency (during) End of suspension

10

SUBJECT 32 YEARS, 72 KG

36 minutes 46 seconds 60 pulses per minute 70 pulses per minute (maximum value) No problem

8 minutes 60 pulses per minute 80 pulses per minute (maximum value) Nausea

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Harness Type C Duration of suspension Cardiac frequency (before) Cardiac frequency (during) End of suspension

Parachute Harness Duration of suspension Cardiac frequency (before) Cardiac frequency (during) After 17 minutes, suspension intolerable.

Waist Belt with Shoulder Strap

27 Minutes 55 seconds 53 pulses per minute 120 pulses per minute (maximum value) Abdominal compression, nausea

17 minutes 37 seconds 60 pulses per minute 80 pulses per minute (maximum value)

Duration of suspension 3 minutes Cardiac frequency (before) 65 pulses per minute Cardiac frequency (during) 130 pulses per minute (maximum value) Slippage of the belt, compression under the arms, compression of the waist buckle, beginning of nausea.

In summary: Very good tolerance with type A, 36 minutes 46 seconds without

any problems Parachute harness (17 minutes), beginning of nausea; Average tolerance with types Band C; Very poor tolerance with waist belt. It is to be noted that, for the subject 32 yearls old and 72 kg,

nausea was reached with type C, the parachute harness and the waist belt.

Harness Type A Duration of suspension Cardiac frequency (before) Cardiac frequency (during) End of suspension

Harness Type B Duration of suspension Cardiac frequency (before) Cardiac frequ ency (during) End of suspension

SUBJECT 31 YEARS, 63 KG

27 minutes 90 pulses per minute 100 pulses per minute (maximum value No problem

23 minutes 5 seconds 65 pulses per minute 120 pulses per minute (maximum value) Slight pain in the hips

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Harness Type C Duration of suspension Cardiac frequency (before) Cardiac frequency (during) End of suspension

In summary:

14 minutes 28 seconds 110 pulses per minute 160 pulses per minute (maximum value) Nausea

Very good tolerance with types A and B, nausea with type C. SUBJECT 28 YEARS, 72 KG

Harness Type A Duration of suspension Cardiac frequency (before) Suspension intolerable after 14 minutes.

Harness Type B Duration of suspension Cardiac frequency (before) Cardiac Frequency (during) Suspension intolerable.

Harness Type C Duration of suspension Cardiac frequency (before) Cardiac frequency (during) End of suspension

Thoracic Belt Duration of suspension Cardiac frequency (before) Cardiac frequency (during) Pain unbearable in the stomach.

In summary:

14 minutes 20 seconds 80 pulses per minute

24 minutes 55 seconds 60 pulses per minute 160 pulses per minure (maximum value)

45 Minutes 85 pulses per minute 120 pulses per minute (maximum value) No problem

1 minute 35 seconds 70 pulses per minute 270 pulses per mihute (max imum va lue)

very good tolerance with type C (45 minutes); good tolerance with type B (25 minutes); average tolerance with type A; no tolerance with the thoracic belt.

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SUBJECT 18 YEARS, 59 KG Harness Type A

Duration of suspension Cardiac frequency (before) Cardiac frequency (during) After 23 minutes, suspension intolerable

Harness Type B Duration of suspension End of suspension

Harness Type C Duration of suspension Cardiac frequency (before) Cardiac frequency (during) End of suspension

Thoracic Belt Duration of suspension

Parachute Harness Duration of suspension Cardiac frequency (before) Cardiac frequency (during) After 18 minutes

Waist Belt with Shoulder straps Duration of suspension Cardiac frequency (before) Cardiac frequency (during) Suspension intolerable.

In summary:

23 minutes 65 pulses per minute 180 pulses per minute (maximum value)

28 minutes 39 seconds Very painful

22 Minutes 70 pulses per minute 120 pulses per minute (maximum value) Nausea

1 minute 20 seconds Nausea

18 minutes 70 pulses per minute 125 pulses per minute (maximum value)

Respiratory problems, nausea

1 minute 21 seconds 75 pulses per minute 120 pulses per minute (maximum value)

good tol.erance with type B despite some irritation at the end or suspensIOn;

average tolerance using types A and C, with nausea after 22 minutes of suspension for type C;

poor tolerance with parachute harness, nausea reached at the con-clusion of 18 minutes; no tolerance with the thoracic and waist belts (despite cushioning between belt and body).

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1.3. RESULTS There is now no longer any doubt that the waist and thoracic belts should be

prohibited. Of the five subjects presented, none tolerated them for more than two minutes. It is thus evident under these conditions that, if the rescue of the victim is delayed for some reason, a fatal result may ensue.

Table 1 summarizes the suspension times and the average values of the tolerance as a function of the subjects and the harnesses tested.

We mentioned above that the physiological condition of the subjects had been monitored with an electrocardiograph, we will now thus present some of the diagrams obtained in the course of these experiments. The behavior of each of the subjects during the suspension tests is summarized on each of the diagrams presented. *

A typical electrocardiogram results are shown in Fig. 10

14

1 seconde E.C.G.

~~~~~~r~~r s s

Figure 10. Typical Electrocardiogram

(*) It is thus evident that all information has not been included in the present text. In any case, it may be obtained on request from Doctors Amphoux and Sevin at the A.PA.S.

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,..,.. SubJt: 11 )'MIl Sublt 51 )'MIl SubltJl,.. Sublt2l)'MII SubltJ2,.. A""", SuI. 7Jme ~ ~ ~

Type A DIlation: 23 mil 311Tin. 10 aec. 21 nin. 27 aec. 14 ni". 20 aec. 361Tin. 46 aec. 25nin.21118C. P~02-1al 1!8-11~2B-12O l00aw2.al 96-1CX)'OO-102 94-74,00-102 AIy1t1nia, rurrbness 1hcradc compressial i" Iowef' imbs

paili'lPl Pai1i'lSlWdn

TypeB 21 ni". 20 S9C'J 29 mil. 13 sec 14 nin. 2B aec. 43 ni". 15 aec. 271Tin. 55 aec. 27 nin. 14 aec. 102-88114-124 10Da1/126-102 ~ llB-1Q2J114-1al ~ NIXllboess i'l upper Imbs, ~a/epIga- raspiaIay ciIOOJtias Arytrnia A.IJdorrWIj CQ,.,assIoi " feeling at sufWIion stnlJTl, runb In upper imbs nausea

TypeC 28 ni". 39 sec. 12 ni". 15 aec. 23 min. 5 sec. 26 ni". 55 sec. 8min. 19 ni". 47 aec. 84-92J8B-96 1!8-112}136-124 ~ 100-92134-96 5B-62'64-70 Nausea abdominal pain Nausea

P8I8CIxJte 18min. 2B ni". 10 aec. 17 nin. 37 sec. 21 nin. 15 sec. - -92-881144-138 112-114/1:Jl ~

respiraby pain, TllorQ; ~., SLdden dizziness we9iI on che6t

Waist. Belt with ShoJIder 1 min. 21 sec. 3 min. - - - -sraps 100-11&'114-102 83-78184-72

Tha'act Belt 1 min. 20 sec. 1 mil. 35aec. - - - -9Q.96I120-96 7~104-S2

Average T oIenn:e 22 nin. 45 sec. 25 nin. 12 aec. 19 nin. 40 sec. 2B min. 10 sec. 36 nin. 46 sec. \

-toHamess

Order ot T eOOJ 1 28 nin. 39 sec. 29 nin. 13 sec. 14 nin. 2B sec. 26 min. 55 sec. 27 nin. 55 sec. 25 min. 2B sec.

2 23 min. 31 mil.l0 aec. 23 min. 5 sec. 14 min. 20 aec. 36 nin. 46 sec. 25 nin. 40 aec.

3 21 min. 20 sec. 12 nin. 15 sec. 21 nin. 27 sec. 43 min. 15 aec. 8 nin. 21 nin. 15 aec.

4 18min. 2B nin. 10 sec. 17 min. 37 sec. 21 min. 16 sec. - -

....

U1

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16

Sor~E DIAGRAHS OBTAINED IN THE COURSE OF THE EXPERI:IENTS

SUBJECT 18 YEARS, HARNESS TYPE C , , , , , __ J., " E,.", ... ,~ , .. ,"' ... "', ..... l!.q , ..... , . , , .. ' .

,,/lllI/l/"I'IJIJ//""'TI' HI 11M /~'I! . ' II{"I!/J ''t-J} . l' !11Im\f!I 'lilll'\\~lll~l'lnlil I\'n l \1 Illli\i~\\l\'}JJttH~'iilh~'{) '11111 ) rflHil~H\ii1i Hl:~m,~ \\'\\\i!l\\\Ih~\\\\it "\\\' II '\\ \ '\' .\\\\ .1\ 11\\\ \\\\\il\ I\i\ ,\ \ I

After 21 min., 35 sec. of suspension, the subject felt a sensation of suffocation, his pulse was rapid (114), but returned to 72 a minute later.

-----------------------------------.---------------------

ECG very inconstant: T and, above all. S I~aves are very large. Sand T rapidly diminish after descent. but the ECG remains irregular for about one minute. as does also the pulse.

_____ ..................... ~"'"'~~.~~I,;. " ' .. '''''J..."..,__=____ ... ~._;y;\ ~~ ..... J.~ ... ~..., 0;::"": ' ............. ~-r'"" ....-. ...........f'" . "'-~-r- -.---- -r-- .... -..-. ....... ,,~ I . End of sus~ension _" A .A A, __ u

SUBJECT 28 YEARS, HARNESS TYPE A

, , .. , .. ;;, .... , , .......... 'W,i,l., , .. '1' .... '," , ", ', '~' .... , " . ,,!i 1/ I . ,'II!!!/ I fi,II" ", ii;ji\l~\ \ \ il\\ It I i\iii1 11111 \~i,~~~1\\ \1\ I \\\\Wl\ \\W\~\\\ \\\\\\ \ \{\{{{\\\\\\W~\\\\~ \\~

Fro", the beginning of suspension, Sigllll}fcant increase of T and S occurred--an increase which remained the same throughout the duration of suspension.

___ --__________ ~/r------------------__________ __

-------

,"

~,.~~:~=~::::=:==;;=:-~=:::===o>C~~~I'~-~'-'-~~"')~ /\ Suspension A~{\ _ .. .. lr CD II

. _ t .. ,_ .-..,.1\ 1\

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SUBJECT 28 YEARS. HARNESS TY PE A

'" 11-; """ " " ". " """""",,2

. ~\\\\\\ \ \i~\\\ \\\ \\\ \ \\\Wii" ;~~i \\~\\ \,\,i; i; ;iii iii i\l{W i11iiiiiiiil{\(I {Ii l (j il {iI/ii Hr] \

End of suspension: immediate diminishing of Sand T--ra pi d respiration abates. The pulse slows progressively (102 at th e moment of tennination to 78 after one minute).

4 i . , -.> ~'-----~.~--=..,..."....~- -'t7-r;---a....-I .. _" ..... .J ;=>0..,....;\::;=-::::. ... >-1

. : . , '" 11 , r .,....r-' . . . y-.,--r 1 ..,.-~

End of suspens\on ,,/\

SUBJECT 18 YEARS. PARACHUTE IIAR NESS

-LLL' , 1 1 , , , 1 , i....L..L.1....ULL' , I I , , I , , I ~ I I , 1 " I I , I 1 1 , , , I I , , I , I t I '" , , , I I 1t

(l\ \\i\I[\(( (\1\(((((( ((i( ((((ill\ III \ ((Ill \[ ((((((((((((((((((((((i~l@ jIllIl1 min ~ ~ ii) jl i iii I jl im 11 (, J n Ii lI li ii j! mOIlif'; i i ~ (; ECG during suspension: small R and large Sand T waves. J\t tlte point of descent (due to feelings of dizziness) a t 18 min utes . Sand T diminished. R did not begin to increase until 30 s econds . lite pulse slowed but was irregular for more than 2 minutes.

I End of Suspension

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SUBJECT 28 YEARS, THORACIC HARNESS

t w , , , , , , I , , I , , , , , I , l , , ~_: ' t!. A ' I , , , , , , , , , , , ,

From the start of suspension: significant increase of T and Sand ca rd i ac frequency

. tS ~~ . ~ .. '\ 001 .~. ~~y~~~------,~. ----~---------~---~ suspe,\s i on

SUBJECT 28 YEARS, 1llORACIC IIARtlESS , ~

I I I I I I , , I , , , I , I , , , I J,..J,.....L.J. _'....L-J....,..LJL..LJ.....I-l-J~.-L.L-L.L..J.- I I I I I,

\\~\\\\\Ii\iW\\\ \\\\\\i\ \ii\l\ \\\\\\\\1 iil~ \ttit\ i \ i Hili ~1 Hi I iHi i4J WI i1 HI] i 11 \ I i 11111-

At descent: more or less inillediate return to the ECG of rest and to a cardiac frequency of rest.

L ;:.-" , ,,,,,--"-.J . ~-...----: .~l~:-"'~"'~ .J.~ ______ ..... __ _ -.:.-.~-c-- .-: ........ ~ . - ,.-"":-r-t~.-... _'l--r.. ..... V1~""f '. I I' .

End of Lspension "--'" ~"- /V'Y. .

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SUBJECT 28 YEARS, HARNESS TYPE B

;'~~I:~~'~~~~~~~~ Soon after beginning of suspension, a significant increase of the Sand T waves was noticed--the cardiac frequency increased slightly.

Cardiac frequency ~----------------------~----------------------------------

Integrated

(: ."'-, ln~t-e-gr~a~t-e~a------~-~~----------~~-'~~~~---------------

(i) Suspension

SUBJECT 28 YEARS, HARNESS TYPE B

N

_.~-" I----J---A-I---'--J--I--J--t_'" .. '---A-I .... ,~~~

After 5 minutes, Sand T waves are still large. R is diminished.

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20

SUBJECT 28 YEARS, HARNESS TYPE B

(Speed ' of trace divided by two) The subject could no longer tolerate suspension, started moving. (irregularities of base line of ECG, R wave still small, Sand T waves large--descent at 24 min. 55 sec. ECG remains irregular for a certain interval.) ------ -.-.- _ ..

,

. -.=:. I ". ,'.", .'.!;~ ....... :;::; ~

:~~?i.:. =e~""""", , A. 1\ End of Suspension ~ (sitting position)

SUBJECT 31 YEARS, ItARNESS TYPE C

t '" ,~ """,""""'"""",',,',, " ~i{;,":"~" " ',','" ;It'~iIJ~'''' "lJ.II~!'uDJllIJJjJilUJJJJUIJJUHUIJIJUHlll.illltll '\ rriWI\ \\~~\\W\\~ \\~\\ . r 1:\W~i h Ilr1\l \II \I \ 1\1 Ii il\1I1I1I11i i fi 11111" I \II II Ii n IIi r It

Electrodes inverted, whence Rand T are toward the bottom and S waves toward the top. From the beginning of suspension, an increase of the allipl i tude of wave T is noted, as well as a slight increase of A and a slight diminution of R.

------------------------------

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SUBJECT 31 YEARS, HARNESS TYPE C

.1 . J J' I L'~ , I ___ ..L_ ~-----.t:.----'-L.t..-.:..,A___._ , ..... ~ .... ~ ~.~-'"'"'~_ ., -,. ,.r--r--.r...?" =,.........,.....- . ---.,.~...",..--.-. '("' '"'i'-~ ~J ' .

o ~ ~ /\ End of Suspension ".,J.. _ . ..... ~._ . _ -J ,JL-.-.J\~

------------

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SUBJECT 32 YEARS, HARNESS TYPE C OJ

; , , , , , , , , , , 1 .,, 1 1 1 II. 1 1 1 1 , 1 , , , 1 1 , , , 1 ':1' 1 1 1 , 1 1 , 1"', 1 , ,

4U~~WWmmuU~~~w~~~~~~~~~~~~~~~~W~~J~~~~~~~~~, Suspension: EeG increase of the amplitude of wave T.

---------------------

--~----+'--~----'~~---~~--,~-----

SUBJECT 32 YEARS, PARACHUTE HARNESS

t L~' I I ,. I L L."""--'L;;: " , o.J... .J'.J.'..1.' .1..' .1-' U' 'U'.J,'..1.' ,l...' Wi 'L.I"~-~ --~~ , , I I , I I , , 'l ..

--------~'-'----~---------------------------------From the beginning of suspension, waves Sand T increased, whl?reas R diminished.

.";:-;,...------...... - ~~--------------~-

SUOJECT 32 YEI\RS, PAP-I\CHUTE III\IHlESS , ~

., I " It" It'll" II" J" , II II I" l~' I" 11""" It 11"" J,"",.", '1

End of suspellsion at 17 min. 37 sec.--sudden weight on chest, pulse accelerated--soon waves Sand T reassume their rest values.

End of sJspension ------------------

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1.4. CONCLUSION This series of exploratory tests leads us to pose questions rather than announce

definitive conclusions. In effect, the results confirm the hypothesis which was too often neglected during

our earlier work, according to which the problems of maintaining a fall victim in a state of suspension may be as critical as those of fall arrest. It is possible that deaths attributed to shock were, in fact, due to asphyxiation--and this problem should not be neglected in any way. Results obtained elsewhere point in the same direction, although the experimental conditions have been rather different.

Due to the ease of the tests, all prototypes should be tested in simple suspension, even before the drop tests; but here, an unknown exists: in effect, judging from the results given above, it is evident that, whichever harness is presented, tolerance in suspension varies with the subjects in considerable measure, which witnesses not only to the important unforeseen differences of individual capacities, but also to differences in the use of the equipment.

It is not easy to see, under these conditions, how one should propose a reasonable test standard--for example, thirty minutes without noticeable irritation--since, depend-ing on the individual tested, each one of the tested harnesses could have been accepted or rejected--and this situation seems normal.

Furthermore, the tests were purely static. I could be asked what would happen during a brutal fall arrest, and above all, if the victim is unconscious and must undergo prolonged suspension (this new aspect in our research will be undertaken persistently).

Nonetheless, it is no less true that the problem is still with us and that all efforts should now be directed toward the implementation of equipment sufficiently sophis-ticated to satisfy all needs--not only in fall arrest, but also in waiting for the rescue of the victim.

There is no doubt that individual protection should be oriented toward complete harnesses which, however, are equipped with features that allow the victim, on the one hand, to position himself correctly and, on the other hand, do not cause asphyxiation if the victim is unconscious or if rescue is delayed in arriving at the scene.

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INFLUENCE OF SHOCK ABSORBING DEVICES ON G-FORCES AND ON PENDULAR DISTANCES DURING FALL ARREST 2.1 PRESENTATION Although undertaken before the static suspension tests that we have presented in

the first part of this articJe, the study which we are now going to see more or less constitutes a logical follow-up, permitting us to learn of the parameters which a fall victim must endure (as seen in the photograph in Fig. 11).

Knowledge of all these parameters will allow for the evolution of positive solutions concerning the implementation of equipment which, to assure absolute safety, must be universal, yet also effective in all areas.

It is known that significant forces impact the human body during severe fall arrest. These forces have been limited by the incJusion of shock absorbers in the individual fall equipment, which reduce the forces to approximately 600 daN, regardless of the height of the fall.

The effect of different commercial shock absorbers on G-forces and on the pendular distances which they may cause at the moment of fall arrest is not clearly known.

It is in an attempt to resolve this problem that this second part of the research has been undertaken.

2.2 STUDY OF G-FORCES AND PENDULAR EFFECfS The parameters considered in this study are: different types of shock absorbers and

different fall heights. The pendular effect at the moment of severe fall arrest is perhaps one of the most

neglected parameters-- and yet it is of too much importance to ignore. It is the most calculable, yet its interest is not apparent at first sight.

It occurs frequently that a worker operating at a height and comfortably strapped into his fall protection equipment finds himself relatively far away from the vertical of his point of suspension. If, for some reason, a fall occurs and no one has taken account of the pendular distances at the moment of fall arrest, the consequences could be very serious. In effect, if an obstacle is placed on the pendular trajectory, the worker will collide with it. This trajectory can be made even worse if the individual has any initial velocity resulting, for example, from the effect of an impact.

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26

Figure 11. Demonstration jump from the test tower at Saint-Remy-Ies Chevreuse

1991 International Society for Fall Protection. All rights reserved. No part of this publication may be reproduced in any form without written permission from the publisher.

The mechanics of the pendular effect are reproduced in the diagram in Fig. 12. By way of example, we have cited two falls, one with shock absorber, and the other without shock absorber. The distance between the point of suspension and the point of work was 0.80 m for both falls. In the first case, the trajectory reached 3 meters, and in the second case, 4 meters, even though the worker was no more than 0.80 m from his point of anchorage.

In order to study this very important parameter and to draw the attention of the users to it, numerous experimental falls performed with an anthropomorphic dummy were reproduced using a distance of 0.80 m and 1.60 m, respectively, between the point of anchorage and the individual. The observations made are summarized in Table II. The importance of the remarks we have made above should be evident. Moreover, it is imperative not to forget that the amount of free space necessary, vertically as well as horizontally, is a function of the size of the individual. Therefore, the values in the table have been normalized to 2 meters.

Parallel to the pendular effects, the G-forces were also determined, since the two parameters are related. Let us specify, in any case, that these two phenomena which impact a fall victim are a function of the energy acquired during fall-arrest; this is the reason why we have considered several configurations:

without shock absorber with shock absorber with different types of shock absorbers

with different incorporations and positions of the shock absorbers in the harness, this latter variation having a favorable effect on the pendular phenomenon. In any case, the latter experiments should be performed again since the first results were obtained with models which were not wholly suitable.

The two types of shock absorbers considered were: 1) textile shock absorber with controlled tearing (A and C); 2) rubber shock absorber (ellipsoidal body passing through a series of rubber

plates). In order to preserve the purely scientific character of this study, we have marked

them with A, B, C, and 0, thereby eliminating any public interpretation, which was not the intent of this research.

Naturally, several different fall heights were studied, varying from 1 to 5.63 m. A part of the results obtained are logged in Table II.

Moreover, we thereafter present some diagrams of the G-forccs recorded in the course of the experiment. These diagrams show the positive influence of the shock absorbers not only on the G-forces, but also on the pendular effects as evidenced in values of Table II.

It is known that the human body can endure rather high G-forces, but only for a short time. The research objective was thus to verify this parameter and the size of the G-forces. It is seen in the diagrams that the times and amplitudes vary according to the absence or presence of a shock absorber--and this is the case for all heights considered.

27 1991 International Society for Fall Protection. All rights reserved. No part of this publication may be reproduced in any form without written permission from the publisher.

It is also seen that certain types of shock absorbers have a more marked effect on the G-forces than others, which means that the systems can still be improved; but, on the whole, the types of shock absorbers demonstrated their effectiveness.

Let us again specify that the fall tests performed were free falls without initial velocity. It is to be seen how the fall victim and the system respond when there is initial velocity and when the fall occurs head first. This will be the next stage of testing.

28

POINT Or IlTTIlCIIMENr -

O. {JO .. -OlsrANCE--~ _POINTOF

--

I 'YORK I

, I , ,

, '"

""

I~

_ ....

,.:. I

" I

.,./ ...,"

"i ~-FALL. A,{',f'ESr ,,-

1+--- f'EtYOULAR DISTANCE ---..j

fixa'tPles: IS ance O.80m--Fall 4m, with shock absorber,

Pendular distance 2.5UIII

Distance O.80m-- Fall 4m, without shock absorber,

Pendular distance 3.8Jm

Figure 12. Pendulum Effect

1991 International Society for Fall Protection. All rights reserved. No part of this publication may be reproduced in any form without written permission from the publisher.

T E S T ,

I 2 3 4 5 6 7 a

9 10 II 12 13 14 15 16 17 II 19 20 21

22

23

2A 2S 26

27

28

29 30

31

32

33

34

3S

36

DETERMINATION OF ACCELERATIONS (POSITIVE AND NEGATIVE) AND THE PENDULAR DISTANCE AS A FUNCTION OF FALL DISTANCES AND DIFFERENT SHOCK ABSORBERS. mORACIC BELT.

FALLIN METERS

1.00 I.SO 1.75 3.SO 1.00 1.00 1.00 1.00 1.00 1.00 2 .00 2.00 2.00 2.00 2.00 3.00 3.00 3 .00 4 .00 4 .00 4 .00

4 .00

2.00

1.00 1.00 1.00

1.00

1.00

2.00 2.00

2 .00

2 .00

2 .00

2 .00

2.00

2.00

TABLED

ACCELEROMETER PLACED VERTICALLY ON THE THORAX DISTANCE BETWEEN POINT OF ATTACHMENT AND POINT OF WORK: O.8m

LENGTH OF ABSORBER PENDULAR AMPLITUDES

TOTAL SHOCK ABSORBER BEFORE AFTER FORCE

FALLIN FALL FALL IN

Mt>11>lQ (em) (em) daN G+ G- OUT BACK OUT BACK

I NO ABSORBER - - 680 - - 0.90 1.2A 1.19 1.11 t.S NO ABSORBER - - 900 - - 1.00 ua 1.78 1.78

1.75 NO ABSORBER - - TJi) - - 0 .90 1.93 1.67 1.S6 3.5 NO ABSORBER - - 940 II 15 1.00 4 .48 4 .2S HrT 2 .2 TYPE A - - 404 I 12 - - - -

1.98 TYPE A - - 400 7 9 0 .60 0 .80 0 .80 0 .12 1.S6 TYPE A 28 84 360 5 10 0 .60 0 .81 0 .81 0 .87 1.35 TYPE B 78 108 S48 2 9 0 .60 O.al 0.11 0.11 1.28 TYPEC 43 71 448 7 9 O.SO 0 .11 0 .60 0 .43

I NO ABSORBER - - 680 7 12 0 .70 0 .90 0 .81 -2 NO ABSORBER - - 6SO 6 14 1.92 2 .33 2.20 2 .20

2.61 TYPEA 28 89 312 8 10 1.45 1.92 1.13 -2 .47 TYPE B 68 115 512 2 II 1.26 1.44 1.2S -3 .06 TYPE D 2A 130 364 8 12 1.26 1.44 1.2S 1.2S 2.S6 TYPEC 44 100 420 9 10 0.a7 1.01 1.01 1.2A

3 NO ABSORBER - - 932 6 17 2. 14 3.21 3.21 3.OS 4 .3S TYPE A 21 162 392 5 10 1.60 U7 U7 1.60 3.75 TYPEC 40 115 404 6 10 1.S9 2 . 13 2 .13 2.13

4 NO ABSORBER - - 916 9 13 2.OS 3.13 3.45 3.4S 5.63 TYPE A 27 190 400 7 II 1.12 2 .48 2 .48 -4.7S TYPEC 43 - 616 S II 1.12 2 .48 2 .48 1.12

NO ABSORBER 4 MANNEQUIN-DYNAMOME - 118 600 3 9 4 .41 4.1S 4 .SS 4.SS

DISTANCE: 1.6Om TYPE A - MANNEQUIN

2.61 DYNAMOMETER DlSTANC 27 88 376 7 II 1.79 2.08 2.08 1.94 1.6Om

SHOULDER STRAPS WfO ABSORBER 416 2.S 6.S 0 .7S 0.80 0 .17 0 .7S SHOULDER STRAPS WfO ABSORBERS S04

10 I G-

30

[)etennination of G-forces . Test 10, no absorber, fall: 1 m

I~~,~ D.,.,.;n";on 0' G-'o',., 11~~~1~\....~ Test 8, absorber 8( 1), fa 11:

W 1 m

Determination of G-forces Test 11, no absorber, fall: 2 m

1 .. 11/'0.

Determination of G-forces Test 12, absorber A(2), fall: 2 /II

, ." I r",

1991 International Society for Fall Protection. All rights reserved. No part of this publication may be reproduced in any form without written permission from the publisher.

Uetennination of G-forces Test 23, absorber A(S), fall: 2 m

1.21/10,

Determination of G-forces f Test 14, absorber D, fall: 2 m

121 G-.~-------

Oetennination of G-forces Test 15, absorber C(2), fall: 2 m

t.11/10.

Determination of G-forces 101 G- Test JO, absorber C(3), fall: J m

31 1991 International Society for Fall Protection. All rights reserved. No part of this publication may be reproduced in any form without written permission from the publisher.

32

Determination of G-forces Test 17, absorber A(3), fall: 3 m

101G-

Determination of G-forces Test 22, without absorber, fall: 4

Detennination of G- forces Test 21, absorber C(4), fall : 4 m

Edited by the S.A. LE BATII-lENT, 6, rue Paul-Valery, 75116 Paris Nouvelles Presses Du Centre, 87-Limoges--Depot legal: 2e trilliestre 1978--

COlilnission Paritaire no. 59 460 Ann. I.T.B.T.P The Director: J.C. Maldague

1991 International Society for Fall Protection. All rights reserved. No part of this publication may be reproduced in any form without written permission from the publisher.