Suspension Trauma: A Lethal Cascade of Events

(This is part one in a series on Suspension Trauma.)

In 2009, the Bureau of Labor Statistics estimated that there were over 212,000 industrial related falls that resulted in serious injury, 605 fatalities. That averages 48 falls per hour if considering a 12-hour work day and a work year of 365 days. Occupational Safety and Health Administration (OSHA) has stated that falls are the leading cause of construction death and the second leading cause of workplace injuries. The Consumer Product Safety Commission, CPSC, estimates that there are approximately 6000 treestand related injuries each year to hunters.


After a successful fall stop with a full body harness, a person will feel the obvious elation of still being alive. But if immediate recovery back to a standing position is not possible, another less known lethal danger must be responded to very quickly; and it is called Suspension Trauma.

OSHA requires that a suspended worker be rescued “as quickly as possible,” presumably within 10 minutes. They further state, “Suspension in a fall arrest system can result in unconsciousness, followed by death, in less than 30 minutes.” ANSI Z359.2 states that contact with a suspended worker must be within six minutes.

In 2009, the Consumer Product Safety Commission (CPSC) stated in a letter to the Treestand Manufactures Association (TMA) that the use of a Suspension Relief Strap is not self-rescue. These decisions and rulings are not haphazardly determined; they are based on 40 years of research and studies conducted on harness safety and suspension trauma.

In 1972, during the Second International Conference of Mountain Rescue Doctors, an Austrian report was discussed in which 10 climbers had become suspended and had to be rescued. Some were using foot loops for suspension relief straps.

The rescues took anywhere from 30 minutes to eight hours. Two climbers died before help arrived, three died shortly after being rescued and the other five died over the next 11 days. None had any external signs of significant injury. They all died from suspension trauma but from different mechanisms of pathophysiology, which will be explained shortly.              

The Innsbruck Mountain Rescue Service in Austria decided to do additional circulatory and renal testing after a review of the Austrian Report. They took 10 experienced rescue personnel and suspended all of them in their Sit harnesses and foot slings (suspension relief straps). They were instructed not to move.

The test was to proceed for a minimum of 30 minutes. Three test subjects passed out before reaching 30 minutes and had to be revived. The test was stopped shortly after 30 minutes for the other seven test subjects. All these test subjects survived without long term injury.

Tilt Table Testing

In concluding remarks on the papers of the Second International Conference of Mountain Rescue Doctors it was stated by the authors; “Orthostatic shock and typical respiratory obstruction may lead to death when hanging on a rope; the probability of survival after hanging two hours is small; death may occur during or after detachment from the rope when rescued.”             

In 1987, at the request of OSHA, the United State Air Force conducted extensive harness suspension testing at the Wright Patterson Air Force Base, Ohio. Thirteen test subjects were given a comprehensive medical evaluation and screening before entry into the test group. Final test results showed that an immobile person suspended in a full body harness has an average physical tolerance limit of 14.5 minutes before exhibiting presyncopal or near fainting symptoms at which time the test was terminated.

Presyncopal symptoms included nausea, light headedness, peripheral vision loss, flushing and paresthesia of the extremities. The range of tolerance limits from five to 30 minutes was observed before testing was terminated. It was also noted that a person suspended in a vertical position is in danger of brain damage and eventual death within four to six minutes of fainting.

In 1997, NASA conducted a study on orthostatic intolerance in astronauts. During the study, one test subject became unconscious in three minutes. This study was the foundation for the article “Will Your Safety Harness Kill You?” by Dr. Bill Weems and Dr. Phil Bishop, OHS, March 2003.

Gravity and Immobility is all that is required for Blood Pooling to occur.

For over 2000 years, man has known that being suspended in a vertical position with the legs immobile can cause death. In the Bible, references to the death of Jesus Christ indicate that he died between three and six hours. Crucifixion victims ultimately died of suspension trauma induced pathology, the customary breaking of the legs, only hastened the outcome.

Tilt table testing has confirmed that even in the absence of being suspended in a harness, hypotension, bradycardia and presyncopal symptoms can occur in 80 percent of healthy adults in less than one hour. These same symptoms have been recorded in EMS training exercises where a healthy subject was immobilized on a backboard and carried feet first down flights of stairs. It is very common for military personnel to pass out while standing at attention. Gravity and immobility is all that is required for a syncopal event to occur in a vertically positioned person; being suspended in a harness allows fainting to occur quicker and it can be lethal.

It is very evident that body posture, health of the individual, immobility, gravity, body weight, vasovagal responses to pain, emotional stress, hypovolemia, hypotension, bradycardia, cerebral hypoxia, dehydration, exhaustion, confusion, panic, hypoglycemia, restrictive respiration and obstruction to blood circulation all play important roles in the Suspension Trauma Cascade of injury and death.

Over the past 40 years, study after study has confirmed that being suspended in certain types of harnesses accelerate the onset of syncopal events and suspension trauma. A full body harness can allow for a life-saving experience, but immediately upon suspension, time can quickly run out in a matter of minutes due to the rapid activation of the suspension trauma cascade of events. If this cascade is allowed to progress, a suspended person will experience each and every one of these events, including death.

In an overall view of suspension trauma, one must mention the liability aspects of training, equipment and the personal safety of employees and consumers. “Failure To Warn” litigation has been a very costly endeavor for companies in the past. Failure To Warn has been ruled negligence by the courts and multimillion dollar settlements have been common.

“During your official capacity and in the course of instructing or advocating the use of any product, you MUST provide complete information and inform of ANY potential dangers in using that product if there is ANY possibility of it causing injuries.” This description of Failure To Warn, lays out the heart of the matter; there are moral, ethical and legal responsibilities that must be adhered to for personal safety, and if not stringently followed, the cost of litigation will only be outweighed by the cost in human life.

Harness Type and Suspension Trauma Factors

A distinction needs to be made between a front-attached work harness similar to an Alpine, Climbing or an Arborist Sit harness, and a rear-attached safety harness that is used in construction and hunting from treestands.

A front-attached Alpine, Climbing or Sit work harness is designed for the user to be suspended in them while they work; the very design of these harnesses causes very little pressure against the femoral vein in the legs, the main vessel that returns blood from the legs. Also, while suspended in this type of harness, the upper sections of both legs are in more of a horizontal position helping to negate the gravitational pull on the blood.

Both of these qualities in conjunction with active movement of the legs and body allow for a comfortable suspension with less incidence of blood pooling and suspension trauma injury or death. Even though blood pooling can occur, the length of time that one can be safely suspended without injury is greatly increased as long as there is active movement. The Hybrid Sit Harness while using the sternal-attachment does not provide the same level of safety as the waist-attachment location. A sternal-attachment is not intended for prolonged suspension and presents similar hazards to a rear-attached harness.

Front-attached sit harness design ensures very little pressure placed on the femoral vein.

A rear-attached safety harness commonly used in construction and by treestand hunters is not intended to provide long term suspension. Its sole purpose is to provide a fall stop and then one must remove themselves from the harness as soon as possible. When suspended in a rear-attached harness, the Suspension Trauma Cascade begins immediately. With this type of harness, there is direct pressure placed on the femoral vein and nerve from the leg straps, and the legs are hanging in a vertical position allowing for an increased effect of the gravitational pull on the blood.

While suspended, a restrictive force is also placed against the abdominal and thoracic areas increasing the difficulty in breathing and discomfort. A rear-attached harness is very difficult to move in and will drain all your energy to exhaustion very quickly. In personal testing and harness development over the past 10 years involving thousands of suspensions, my personal exhaustion limit in trying to recover to a standing position is reached in less than five minutes, and the presyncopal or Suspension Trauma symptoms of tachycardia, nausea, shortness of breath and a feeling of increasing anxiety are felt in less than 10 minutes. I do not believe that I could remain conscious for more than 20 minutes while suspended in a rear-attached harness.

All of these factors result in immediate pooling of blood in the legs, a very rapid deterioration of overall blood circulation, decrease oxygenation of visceral organs, heart and brain and an increasing level of physical discomfort and emotional stress. These immediately combined factors support the progression of the Suspension Trauma Cascade which is responsible for a suspended victim becoming symptomatic very quickly and losing consciousness.

Suspension Trauma Cascade

While suspended in a safety harness, the leg straps cause a tourniquet effect on the femoral vein and pressure on the femoral nerve, causing blood to pool in the lower extremities, and considerable discomfort and pain. The venous return from the legs has very little pressure behind it, approximately one-fifth of the arterial pressure going into the legs. During ambulation, the normal venous pressure in the feet of 25 mm Hg can be increased to 90 mm Hg in just a few minutes due to gravitational pull on the blood and immobility.

To assist the body in movement of blood against gravity, the venous return from the legs has one-way valves to help the transfer of blood back to the heart. To provide the pressure needed to overcome the gravitational pull on the blood, active leg muscle contractions must be used. As the leg muscles contract, pressure is exerted on the veins in the legs forcing the blood through the one-way valves and back to the heart.

Unfortunately, while suspended in a harness, the “muscle pumps” of the legs may be inadequate to overcome the compressive forces placed on the femoral veins by the leg straps and blood pooling occurs. Even with active leg movements, which can prolong the onset of presyncopal symptoms, they ultimately may be ineffective against the rapidly progressing chain of events that cause increasing immobility and unconsciousness.

There are many reasons why a suspended person would become immobile; a lack of understanding of Suspension Trauma, injury, confusion, physical and emotional exhaustion, pain, hypoglycemia, muscle failure due to hypoxia and aesthesia of the legs or the Suspension Trauma Cascade has progressed to the point of unconsciousness. The longer the suspension, the less mobile a person will become and the Suspension Trauma Cascade of events will begin to proceed at an ever-progressive rate.

The average human body contains 10 pints of blood with two pints normally in the legs at any one time. As soon as a person is suspended in a rear-attached harness, those two pints of blood are trapped in the legs and the body has a decrease of 20 percent of its total circulating blood volume and Class II Hypovolemic Shock is present. The heart is powerful enough to push the blood past the leg straps via the arteries and as long as the heart continues to beat, more blood will be pushed into the legs where it will be trapped.

The lower extremities can hold 60 percent (six pints) of a body’s total blood volume. As soon as the heart has pumped over 40 percent (four pints) of blood into the legs, the victim is now in Class IV Hypovolemic Shock, the most severe level of Hypovolemic Shock with impending death if no immediate medical care is rendered. There is no Class V.

This is the same as cutting both wrists and bleeding out half of the body’s blood. Blood pressure and oxygen levels drop to a critical point where it causes unconsciousness and then death. If the body is placed in a horizontal position, survival is possible; however, being suspended by a harness in a vertical position, there is little chance of survival without immediate suspension relief.

Normal Circulation

A Vasovagal syncopal event, fainting, while suspended in a vertical posture can end in the same catastrophic result. The Autonomic Nervous System (ANS) controls our “Fight or Flight” responses as well as our “Normal Relaxation State.” In an emergency, similar to having a harness fall stop, the sympathetic or “Fight or Flight” component of the ANS quickly prepares us to physically respond by increasing the heart rate, breathing and blood pressure through catecholamine release and blood vessel constriction.

This sympathetic control will remain dominate in an emergency unless reduced by an increasing parasympathetic tone. The parasympathetic or “Normal Relaxation State” component of the ANS creates the opposite effect on the body by decreasing the heart rate and blood pressure. The 10th Cranial Nerve, the Vagus Nerve is part of the parasympathetic ANS.

Blood Pooling

The vagus nerve can be stimulated by pain, emotional stress and hypovolemia. While suspended in a harness the body can be experiencing all three stimulants and the longer the suspension, the more intense the vagal tone will become. Contributing to this vasovagal event is the Bezold-Jarisch Reflex which is initiated when ischemic hypoperfusion or hypovolemia is sensed by chemoreceptors and mechanoreceptors in the left ventricle of the heart. This reflex causes a marked increase in vagal tone causing immediate bradycardia and dilatation of blood vessels by decreasing the sympathetic input.

Rear-attached safety harness leg straps exert direct compression of the femoral vein.

When the vagal tone becomes significant enough, a vasovagal syncopal event will occur due to the rapidly decreasing heart rate, blood pressure and cerebral perfusion. This can take a minute or two where the victim feels the symptoms of presyncope, or it can be instantaneous as in a person fainting over the sight of blood or being stuck by a needle. A victim will never know how soon this event will occur, but it will be very rapid.

Elements of the Suspension Trauma Cascade can present so suddenly that the suspended victim may have little opportunity to respond in an effective manner. One of the earliest symptoms of suspension trauma is cognitive impairment or confusion which makes the suspended victim much less likely to be able to assist in their own self rescue.

Vasovagal Event (Fainting)

As soon as the Suspension Trauma Cascade progresses to the victim’s limits of physical or emotional tolerance, unconsciousness will occur by hypovolemic shock, vasovagal event or both. During unconsciousness, the respiratory rate will slow, oxygenation of the brain and heart will diminish, thus causing a greater drop in respiration and blood pressure which causes a further drop in oxygenation and the cascade spirals downward. There will be permanent brain damage in a few minutes. The heart will stop shortly after that when it sustains a global myocardial infarction, a “massive heart attack” from the lack of oxygen and death occurs. All of this can happen in “less than 30 minutes.”

(Next issue will discuss more about the 10 victims from the Austrian report.)

Dr. Wood was a member of the West Virginia WV State Police in 1985 and became a Special Agent for the Organized Crime Drug Enforcement Task Force, US Customs Service, San Francisco, CA. He later attended the West Virginia School of Osteopathic Medicine, after 16 years in law enforcement. He graduated with honors. In 1998 during his residency training, he fell 20 feet out of a tree while trimming a limb. He was not wearing a fall arrest harness.Dr. Wood had to drag himself 100 yards, crawl onto his 4-wheeler and drive to his cabin to call for help. He was transported to the Trauma Center where he worked and was placed in the Intensive Care Unit for the first week. He broke his pelvis in two places, left hand and had internal bleeding. As Dr. Wood states, “when you cannot walk for almost four months it gives you a lot of time to think”.During his recovery and up to the present time, Dr. Wood has been working on safety products that make elevated work and treestand hunting safer. He has been awarded four U.S. Patents for fall safety equipment and is the owner of several U. S. Patent Pendings.In 2010, Dr. Wood finished his long term project, The Rescue One CDS (Controlled Descent System) harness, a new revolutionary full body safety harness that eliminates serious injury or death from suspension trauma.Dr. Wood is currently the lead physician for Kittitas Valley Healthcare Medical Clinic, Cle Elum WA.

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