Although fall protection harnesses have saved many lives, the human body is not designed to hang in a harness for any length of time.
The problem is the design of our bodies, specifically our legs. Our circulatory system does not have the ability to pump blood all the way down into our legs and back to our torso. Our bodies, however, developed a unique way to deal with this; we have one-way valves in our leg veins. When we move our leg muscles, the contractions push the blood through these one-way valves and up into our torsos.
But when you are hanging in a harness the leg straps cut off this return flow. Blood pools in the legs where the tissues scrub out all the oxygen and load it up with metabolic waste products. With this reduction of blood circulating in the body, the heart compensates by speeding up the heart rate to maintain blood flow to the brain.
How long does this process take? It depends on many factors, including:
- The type of harness (padding and how it's adjusted).
- Injuries suffered during the fall including blood loss and shock.
- Overall health (cardiovascular disease, dehydration, hypothermia, etc.)
- Fatigue and the person't mental state.
- Nausea and dizziness
- Unusually low or increased heart rate
- Low blood pressure
- Hot flashes
If the worker is conscious rescuers can assess whether the worker is experiencing these conditions. In addition, there are a variety of techniques and equipment (suspension trauma straps) that can greatly increase the amount of time a worker can remain suspended.
First Aid Considerations
When a fallen worker has been retrieved, rescuers should be trained to not lay a worker down and immediately remove or loosen the leg straps. This can result in a large volume of de-oxygenated blood moving to the heart which may cause cardiac arrest. Rather, they should place the worker in an upright position and gradually loosen the leg straps.