Will Your Safety Harness Kill You?
(Taken from Occupational Health & Safety magazine,
Vol. 27, No. 3, pages 86-90, March 2003)
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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 lucky.
Harness-Induced Death
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 dead 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
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 heart is 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, so 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.
Fall arrest
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.
Suspension
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 trauma.
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
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 position.
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 comfortable.
Recommendations
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).
- It the 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:
- The victim 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.
- Front (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 closely supervised.
- 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.
- 5) Workers should get supervised (because this is dangerous)
experience at hanging in the harness they will be using. [OHS
endbug]
Bill Weems (bweems@ccs.ua.edu)
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 performance.
Reference
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 fatal.
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