|Will Your Safety Harness Kill You?
|(Taken from Occupational Health & Safety magazine, Vol. 27, No. 3, pages 86-90, March 2003) [PDF file]:
Bill Weems and Phil Bishop
Occupational Health & Safety magazine:
Workers and emergency response personnel must be trained to recognize the risks
of suspension trauma.
I was surprisingly comfortable with my legs
dangling relaxed beneath me, and my arms outstretched in a posture that must
have resembled a crucifixion. I had no feeling of stress and mused as to why
this was considered dangerous. I felt I could stay in this position for a long
time. Three minutes later, maybe less, I wondered why I suddenly felt so hot.
The next thing I knew, they were reviving me from unconsciousness. I had just
experienced what could be deadly for your workers who use safety harnesses.
Fortunately for me, my suspension trauma occurred in the safe environment of the
research ward of University of Texas Medical Branch Hospital at Galveston,
Texas, where I was the first subject in a NASA experiment studying orthostatic
intolerance in astronauts. Your workers won't be so
Wide ranges of situations require
safety harnesses of various types. Workers requiring fall protection, workers
entering many confined spaces, mountain climbers, deer hunters in elevated
stands, and cave explorers all try to protect themselves through the use of
safety harnesses, belts, and seats. What is little known however, is that these
harnesses can also kill. Harnesses can become deadly whenever a worker is
suspended for duration over five minutes in an upright posture, with the legs
relaxed straight beneath the body. This can occur in many different situations
in industry. A carpenter working alone is caught in mid-fall by his safety
harness, only to die 15 minutes later from suspension trauma. An electrical
worker is lowered into a shaft after testing for toxic gases. He is lowered on a
cable and is positioned at the right level to repair a junction box. After five
minutes he is unconscious--but his buddies tending the line don't realize it,
and 15 minutes later a dea
d body is hauled out. The cause of this problem is
called "suspension trauma." Fall protection researchers have recognized this
phenomenon for decades. Despite this, data have not been collected on the extent
of the problem; most users of fall protection equipment, rescue personnel, and
safety and health professionals remain unaware of the hazard.
Suspension trauma death is caused by orthostatic incompetence
(also called orthostatic intolerance). Orthostatic incompetence can occur any
time a person is required to stand quietly for prolonged periods and may be
worsened by heat and dehydration. It is most commonly encountered in military
parades where soldiers must stand at attention for prolonged periods.
Supervisors can prevent it by training soldiers to keep their knees slightly
bent so the leg muscles are engaged in maintaining posture. What happens in
orthostatic incompetence is that the legs are immobile with a worker in an
upright posture. Gravity pulls blood into the lower legs, which have a very
large storage capacity. Enough blood eventually accumulates so that return blood
flow to the right chamber of the heart is reduced. The heart can only pump the
blood available, so the heart's output begins to fall. The heart speeds up to
maintain sufficient blood flow to the brain, but if the blood supply to the
restricted enough, beating faster is ineffective, and the body
abruptly slows the heart. In most instances this solves the problem by causing
the worker to faint, which typically results in slumping to the ground where the
legs, the heart, and the brain are on the same level. Blood is now returned to
the heart and the worker typically recovers quickly. In a harness, however, the
worker can't fall into a horizontal posture, so the reduced heart rate causes
the brain's blood supply to fall below the critical level. Orthostatic
incompetence doesn't occur to us very often because it requires that the legs
remain relaxed, straight, and below heart level. If the leg muscles are
contracting in order to maintain balance and support the body, the muscles press
against the leg veins. This compression, together with well-placed one-way
valves, helps pump blood back to the heart. If the upper-legs are horizontal, as
when we sit quietly, the vertical pumping distance is greatly reduced,!
there are no problems. In suspension trauma, several unfortunate things occur
that aggravate the problem. First, the worker is suspended in an upright posture
with legs dangling. Second, the safety harness straps exert pressure on leg
veins, compressing them and reducing blood flow back to the heart. Third, the
harness keeps the worker in an upright position, regardless of loss of
consciousness, which is what kills workers.
Phases of Fall Protection
There are four phases of fall protection: Before the fall, at fall
arrest, suspension, and post-fall rescue. Each phase presents unique safety
challenges. Suspension trauma can be influenced by all aspects of the fall, so
they are all important. As with many aspects of safety, increasing the safety in
one phase can compromise the safety of the others. Whatever training workers
have received will determine how they respond to different phases. Here is a
brief discussion of each aspect of fall protection.
Before the fall
The key issue of fall protection before the fall is compliance. If a harness
is too uncomfortable, too inconvenient, or interferes too much with task
completion, workers may not use the equipment or may modify it (illegally) to
make it more tolerable. A second major point is the length of the attachment
lanyard, or, how far can a worker fall before his fall is arrested? The longer
the fall, the greater the stress on the body will be when the fall is arrested.
The shorter the lanyard, the more often it will have to be repositioned when
workers are mobile. A moveable safe anchor is one solution, but this situation
is only occasionally available.
The whole concept of
fall protection is that workers who fall will be stopped by the tethering
system. The longer the attachment lanyard, the greater the acceleration time
during the fall and the greater the stress on the body at arrest. Unfortunately,
the posture of the falling worker is unpredictable. Depending on the harness
attachment point and the position of the worker's body at arrest, different
harness attachments offer different advantages. An attachment near the shoulders
means that any drag from the lanyard will serve to position the worker's body in
an upright position so the forces are distributed from head to foot. The head is
somewhat protected if the legs and body precede it in the fall, but this offers
some disadvantages after the fall arrest is completed.
Many safety professionals naturally assume that, once a fall has been
arrested, the fall protection system has successfully completed its job.
Unfortunately, this is not the case. A worker suspended in an upright position
with the legs dangling in a harness of any type is subject to suspension
Fall victims can slow the onset of suspension trauma by pushing
down vigorously with the legs, by positioning their body in a horizontal or
slight leg-high position, or by standing up. Harness design and fall injuries
may prevent these actions, however.
Rescue must come rapidly
to minimize the dangers of suspension trauma. The circumstances together with
the lanyard attachment point will determine the possibilities of self-rescue. In
situations where self-rescue is not likely to be possible, workers must be
supervised at all times. Regardless of whether a worker can self-rescue or must
rely upon others, time is of the essence because a worker may lose consciousness
in only a few minutes. If a worker is suspended long enough to lose
consciousness, rescue personnel must be careful in handling such a person or the
rescued worker may die anyway. This post-rescue death is apparently caused by
the heart's inability to tolerate the abrupt increase in blood flow to the right
heart after removal from the harness. Current recommended procedures are to take
from 30 to 40 minutes to move the victim from kneeling to a sitting to a supine
Interference Among Phases
An arrest harness attachment
on the front of the body facilitates self-rescue after a fall. However, a front
attachment means the arresting lanyard may be in the way for many work tasks. An
attachment point near the center of gravity (CG) makes post-fall body
positioning much easier and increases the likelihood that a fallen worker will
not be suspended in an upright vertical position.
Yet a front near-CG
attachment point can greatly increase the bending stress on the spine at the
instant of arrest, raising the possibility that the arrest itself results in
serious injury. The most protective harnesses for suspension can be the least
Safety harnesses save many lives
and injuries. However, continual vigilance is needed to train and supervise
workers to ensure harnesses are used safely. All phases of fall protection need
to be examined for each particular application. Workers and emergency response
personnel must be trained to recognize the risks of suspension trauma.
Before the potential fall:
Workers should never be permitted to
work alone in a harness.
Rope/cable tenders must make certain the harness
user is conscious at all times.
Time in suspension should be limited to
under five minutes. Longer suspensions must have foothold straps or means for
putting weight on the legs.
Harnesses should be selected for specific
applications and must consider: compliance (convenience), potential arrest
injury, and suspension trauma.
Tie-off lanyards should be anchored as high
and tight as work permits.
After a fall:
Workers should be trained
to try to move their legs in the harness and try to push against any footholds.
Workers hanging in a harness should be trained to try to get their legs as
high as possible and their heads as close to horizontal as possible (this is
nearly impossible with many commercial harnesses in use today).
worker is suspended upright, emergency measures must be taken to remove the
worker from suspension or move the fallen worker into a horizontal posture, or
at least to a sitting position.
For harness rescues:
should not be suspended in a vertical (upright) posture with the legs dangling
straight. Victims should be kept as nearly horizontal as possible, or at least
in a sitting position.
Rescuers should be trained that victims who are
suspended vertically before rescue are in a potentially fatal situation.
Rescuers must be aware that post-rescue death may occur if victims are moved
to a horizontal position too rapidly.
Recommendations on harnesses:
It may be advantageous in some circumstances to locate the lanyard or
tie-off attachment of the harness as near to the body's center of gravity as
possible to reduce the whiplash and other trauma when a fall is arrested. This
also facilitates moving legs upward and head downward while suspended.
(stomach or chest) rather than rear (back) harness lanyard attachment points
will aid uninjured workers in self-rescue. This is crucial if workers are not
Any time a worker must spend time hanging in a harness,
a harness with a seat rather than straps alone should be used to help position
the upper legs horizontally.
A gradual arrest device should be employed to
lessen deceleration injuries.
Workers should get supervised (because this is
dangerous) experience at hanging in the harness they will be using. [OHS endbug]
Bill Weems and Phil Bishop are at the University of Alabama, in Tuscaloosa, Ala. Dr. Weems
is an industrial hygienist. He directs Safe State, the OSHA consultation agency
for small business in Alabama. Dr. Bishop is an ergonomist. He teaches and
conducts research in the physiology of human
Seddon, Paul. Harness Suspension: review
and evaluation of existing information. Health and Safety Executive. Research
Report 451/2002. 104 pp.
Pull quotes: All personnel should be trained
that suspension in an upright condition for longer than five minutes can be
This paper appears in the eLCOSH website with the permission
of the author and/or copyright holder and may not be reproduced without their
consent. eLCOSH is an information clearinghouse. eLCOSH and its sponsors are not
responsible for the accuracy of information provided on this web site, nor for
its use or misuse.
Copyright © 2004 Mike Holt Enterprises,Inc.