The effects of differential pressure are seen most commonly in areas that have rapidly moving water, such as near storm drains, sewer accesses, dam spillways and submerged culverts. The danger arises when a rescuer or victim enters a high-pressure zone, only to be pinned by the force of the water. In many cases, the strength of the suction is too powerful to overcome without mechanical assistance.
Real-life tragedies
There have been numerous tragic incidents in which rescuers fell victim to differential pressure. One common scenario involves a person being pulled toward a storm drain. Even in just a few feet of water, the pressure differential can generate hundreds of pounds of force, to render escape nearly impossible.
One heartbreaking example of this occurred in May 2015. Claremore, OK, Fire Department Capt. Jason Farley lost his life when he became trapped by differential pressure while walking near a flooded stormwater catch basin. For one hour prior to his death, Farley and his crew operated in varying floodwater depths, assisting at least 10 civilians to safety. At one point, the force of the water was too much to escape, and Farley drowned before his crew could free him.
How to stay safe
Rescuers and flood response teams must be aware of differential pressure dangers and take precautions to avoid falling victim to its deadly grip. Here are key safety measures:
- Recognize high-risk areas. Identify locations where water flow is strong and obstacles, such as pipes, drains and openings, might create suction hazards.
- Avoid direct contact. Never approach submerged openings or areas that have visible turbulence without proper equipment and risk assessment.
- Use safety gear. Wear a drysuit and use personal flotation devices, throw ropes and probe poles for walking in flooded areas. Avoid wearing structural turnout gear near any body of water.
- Train for water rescues. First responders should undergo specialized training in swiftwater and flood rescue operations to recognize and mitigate the risks of differential pressure.
- Utilize proper equipment. Mechanical tools, such as hydraulic spreaders, cutting torches and air lifting bags, might be needed to free individuals who are trapped by differential pressure.
- Preplan. Preplanning isn’t just for building fires. Get out and plan your response area. With flood events on the rise, areas that don’t commonly flood now might be prone to flooding.
These key safety measures can help to keep members safe while they operate in the floodwater environment. Being aware of such dangers can help to avoid a tragedy from occurring.
Know your enemy
Even with all safety measures in place, bad things still can happen. Knowing your enemy allows you to rescue a rescuer who becomes trapped by differential pressure.
Consult with the department that handles your storm sewer system and ask for maps of the system. Knowing the system will give you an idea of where a victim might come out when caught within the system. Getting these maps ahead of the emergency makes things easier when the pressure is on. This also allows you to understand how the system functions in the event of a catastrophically bad day.
Often overlooked hazard
Flood rescues are high-risk/low-frequency incidents that can be inherently dangerous, but differential pressure presents a unique and often overlooked hazard. Education, awareness, and proper training can mean the difference between life and death. Understanding the deadly effects of differential pressure can prevent tragic losses and save lives.
