A fall protection system did its job. The harness caught the worker. The lanyard absorbed the shock. The anchor held. The worker is alive, hanging in midair. And now the clock starts ticking — because the very equipment that saved this worker's life can kill them if rescue does not happen quickly enough.
This is suspension trauma, also known as harness-induced pathology or orthostatic intolerance. It is one of the least understood and most underestimated hazards in fall protection, and it is the reason a fall protection plan in Ontario needs a written rescue procedure: O. Reg. 213/91 requires one before anyone uses a fall arrest system or safety net.
What Is Suspension Trauma?
Suspension trauma occurs when a person hangs motionless in a full-body harness for an extended period. The harness leg straps compress the femoral veins in the upper thighs, restricting blood flow from the legs back to the heart. Blood begins to pool in the lower extremities. With less blood returning to the heart, cardiac output drops. Blood pressure falls. The brain and vital organs receive less oxygen.
The medical term for this is orthostatic intolerance — the body's inability to maintain adequate blood circulation in an upright, motionless position. It is the same mechanism that causes soldiers to faint during prolonged standing on parade grounds, but in a suspended harness, the consequences are far more severe because the worker cannot collapse to a horizontal position where circulation would naturally recover.
If the worker is unconscious — from the fall impact, from pain, or from the suspension itself — they cannot pump their legs or shift their weight to promote blood flow. The condition accelerates rapidly.
The Timeline — How Fast Can It Kill?
Research and case studies indicate that suspension trauma can become life-threatening in as little as 10 to 30 minutes. The progression follows a predictable pattern:
0-5 minutes — the worker may feel relatively stable, especially if conscious and able to move their legs. Discomfort in the groin area from the leg straps is common. The worker should immediately attempt to relieve pressure by standing in suspension relief straps (if equipped) or pushing against a structure.
5-15 minutes — blood pooling intensifies. The worker begins to feel lightheaded, dizzy, and nauseous. Vision may narrow or blur. Sweating increases. Heart rate may initially rise as the body compensates, then begin to slow as the heart struggles to pump against the reduced blood volume.
15-30 minutes — without intervention, the worker may lose consciousness. Once unconscious, all compensatory movements stop, and the condition accelerates. Renal failure can begin as the kidneys are deprived of adequate blood flow.
Beyond 30 minutes — the risk of cardiac arrest and death is significant. Get the worker down and give standard first aid without delay (see post-rescue positioning below).
These timelines are approximate and vary based on the worker's physical condition, ambient temperature, the severity of any injuries sustained during the fall, and whether the worker is conscious and able to move.
Recognizing the Symptoms
Workers and rescuers need to recognize the signs of suspension trauma before the situation becomes critical:
Paleness or grey skin colour — particularly in the face, indicating reduced blood flow to the head
Excessive sweating — a sign of cardiovascular distress
Dizziness and disorientation — the worker may report feeling faint or confused
Nausea — a common early symptom of reduced blood pressure
Breathlessness — difficulty breathing even without chest injuries
Unresponsiveness — if the worker stops responding to voice commands or radio contact, the situation is critical and rescue must be immediate
Ontario Rescue Plan Requirements
Under Ontario Regulation 213/91 (Construction Projects), before any worker uses a fall arrest system or safety net, the employer must develop written procedures for rescuing the worker after a fall has been arrested. This is not optional. A fall protection system without a rescue plan is an incomplete system.
The rescue plan must address:
Method of rescue — how the suspended worker will be reached and lowered to a safe surface. This could involve self-rescue equipment, co-worker assisted rescue, or mechanical rescue devices.
Equipment required — all rescue equipment must be identified, available on site, and maintained in working condition. This includes rescue kits, descent devices, aerial work platforms, or ladders, depending on the rescue method.
Trained personnel — workers designated to perform rescue must be trained in the rescue procedure and in recognizing the symptoms of suspension trauma. They must practice the procedure regularly — not just read about it.
Time to rescue — the plan must be designed to achieve rescue within minutes, not hours. Some people hanging still are close to fainting within 10 minutes, so aim to reach the worker as fast as possible; the ANSI Z359.2 rescue standard sets a goal of making contact within 6 minutes.
Communication — how the fallen worker will signal for help, how rescuers will be alerted, and how emergency medical services will be contacted.
Types of Rescue
There are three primary categories of rescue after a fall arrest, and your plan should identify which method applies to each work location on your project.
Self-rescue — the worker uses their own equipment and ability to reach a safe surface. This is only viable if the worker is conscious, uninjured, and has access to a structure or self-rescue device. Self-rescue equipment includes suspension relief straps (loops that attach to the harness and allow the worker to stand, reducing pressure on the leg straps) and retractable rescue devices that allow the worker to lower themselves.
Assisted rescue (co-worker) — a trained co-worker on site uses rescue equipment to reach the suspended worker and lower them. This may involve a rescue kit mounted near the anchor point, a manual descent device, or positioning the worker to reach a ladder or platform. This method requires advance training and practice.
Mechanical rescue — an aerial work platform (boom lift or scissor lift), crane with a man basket, or other mechanical device is used to reach the worker and bring them to ground level. This is often the fastest method on sites where aerial equipment is available, but it requires that the equipment be accessible, operational, and operated by a competent person.
Calling 911 is not a rescue plan. Even when the fire department arrives quickly, accessing a worker suspended at height can take significantly longer. By the time external rescuers arrive, set up, and reach the worker, 30 minutes or more may have passed. Your site must have the capability to initiate rescue immediately.
Trauma Straps (Suspension Relief Straps)
Trauma straps are simple, inexpensive devices that can significantly extend the survival window for a suspended worker. They are loops of webbing that attach to the harness and deploy after a fall, allowing the worker to stand in them and periodically push against the straps with their legs. This muscle contraction pumps blood out of the lower extremities and back toward the heart, counteracting the pooling effect.
Every full-body harness used on an Ontario construction site should be equipped with trauma straps or an equivalent suspension relief device. Workers must be trained in how to deploy and use them — it is not intuitive, especially under the stress of hanging after a fall.
Post-Rescue Positioning — The Hidden Danger
One of the most counterintuitive aspects of suspension trauma is what happens after the rescue. Older guidance said never to lay the rescued worker flat. The current evidence says the opposite.
That older advice rested on the idea that blood pooled in the legs would rush back to the heart and cause a fatal "rescue death" or "reflow syndrome". An evidence review for the UK Health and Safety Executive found no reported cases of reflow syndrome after harness suspension, and called the advice to keep a rescued person sitting up unsupported and potentially dangerous.
Correct positioning — lay the rescued worker flat and give standard first aid, as you would for anyone who has fainted or collapsed. Do not keep them sitting up.
Monitor continuously — even a worker who appears alert and stable after rescue should be monitored closely. Symptoms can deteriorate rapidly. Call emergency medical services for any worker who has been suspended for more than 5 minutes.
Do not leave them alone — assign a worker to stay with the rescued person until paramedics arrive and assume care.
Suspension trauma turns the equipment that saves lives into a ticking clock. The harness stops the fall — but only a rescue plan stops the harness from becoming the next hazard. Every site, every shift, every worker at height must know the plan before they clip in.
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