Suspension Trauma Prevention: Fall arrest harnesses

Fall arrest harnesses

Users of industrial full-body fall arrest harnesses can have a problem with preventing suspension trauma, should they fall and become suspended by their harness. The difficulty arises from the position of the attachment point, and the various national laws on how they may be used.

Dorsal and sternal attachment points

A fall arrest harness is designed to catch someone if they fall, but will only do so after they have travelled a certain distance. As such they will be moving at some speed, and so must be stopped gradually to avoid causing injuries. Fall arrest equipment typically uses an energy absorber to limit the force applied to the user to a value specified in law (6kN for the EU, 8kN for the USA, etc.) - being as low as possible helps prevent injuries from deceleration, but the smaller the force, the longer the distance required to slow the person down. There's a compromise between killing you by G-force, or killing you by letting you hit the ground!

Because of the relatively high forces in the standard harness designs, the only safe way to apply the force is along the line of your spine (mimicking the way a parachute harness works). Applying 6kN to a belt will snap you in half. So, fall arrest harnesses have a foll-body design, and the attachment points are as high as possible above your center of gravity. The two options we have, given the shape of a human and the need to avoid strangling you with your own harness, are:-

Dorsal attachment point - on your back between the shoulder blades.
Sternal attachment point - on your chest between your nipples.

When arresting a fall, both work equally well. It's argued by some people that the sternal point is better (because it allows you to attach yourself and check things are still connected, plus it pushes your face away from things as you're falling) but others argue it's the dorsal point which is best.

For suspension trauma, both are equally likely to cause it. Only one allows you to prevent it.

If you are suspended from a sternal point, you can often lift your knees into a sitting position with very little effort, and the harness webbing is less restrictive on the ribcage and diaphragm. Suspended from a dorsal point your body is tilted forwards, and it is impossible to life your legs. Many harnesses will also tighten around your chest, making breathing labored and increasing the risks of fainting.

The law on attachment points

Within Europe and countries which use the EN standards system, both a dorsal and sternal point are equally legal. The very cheapest harnesses may only have a dorsal point, but the laws and product specifications say "either or both". In those countries we strongly advise that the sternal point is always used where there is a risk of suspension.

Within the USA and countries which use the OSHA/ANSI system, only the dorsal point can be used for full fall arrest duties [29 CFR 1926.502(d)17] and [29 CFR 1910.66.C.I]. The ANSI Z359.1 product standard permits a sternal point to be fitted to a harness only as a limited-duty fall arrest point which can for example be used when climbing a ladder using a fixed lifeline, but cannot be used with lanyards. Until OSHA revise the prohibitions in 29 CFR, it is not legal under the 1926/1910 schemes to use what we consider is the safest system of work, and so you must connect your fall arrest lanyards to the dorsal attachment point. This means that post-fall you will be unable to lift your knees, and so will require immediate rescue in every possible situation.

STIS is of the opinion, based on extensive trials of both attachment points and review of the research behind each national policy, that the OSHA prohibitions on use of the sternal point are incorrect and lead to an increased risk to users post-fall.

Suspension Trauma

Fall arrest harnesses

Dorsal and sternal attachment points

The law on attachment points

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