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Subject: Pressurized Vessels on Vehicles - Part 2
Topic: Catastrophic Failure of Pressurized Cylinders During Vehicle Fires
Objective: Review real-world incidents of firefighter injuries due to failure of energy-absorbing bumper struts and compressed gas hood struts during vehicle fires
Task: Establish procedural guidelines for operating at vehicle fires, including engine compartment fires, to ensure maximum safety for suppression personnel from the hazard of compressed gas strut failures.
From California to New York State, from Connecticut to Kansas City, incidents of firefighters being struck by objects exploding and flying off vehicles during fires are increasing in frequency.
In a 1997 Kansas City, KS, incident, for example, a firefighter at a car fire was hit in the stomach by an exploding hood hinge strut, forcing the removal of quite a bit of the firefighter's abdomen in later surgery.
During a vehicle fire attack in Wichita, KS, the outer housing from a gas/spring strut hood hinge assembly propelled the entire strut unit out of the front headlight opening. The housing impaled a fire lieutenant's hand. The second strut exploded and rocketed out the front headlight assembly as well, although no firefighters were struck by the second unit.
It isn't just hood hinge struts that can be dangerous during fire incidents. In August 1998, a Los Angeles County Fire Department engine company responded to a vehicle fire where the passenger compartment was well involved on arrival. Both pressurized struts for the rear hatchback window assembly exploded. One strut traveled at a right angle about 50 to 75 feet from the vehicle. No firefighters were injured.
Only a month before, a Los Angeles County firefighter assigned to Engine 43 was injured at a car fire. The firefighter was prying open the hood of a 1992 Oldsmobile Achieva to allow access to the burning engine compartment fire. Both gas hood hinge struts exploded from the hood area. One flew almost 60 feet and bounced off the wall of a nearby building. The other strut entered the front side of the firefighter's lower leg below the knee and passed through his calf. One end of the strut stuck out the opposite side of his leg.
Design and Function Of Hood Hinge Struts
The strut device that fails when heated is a two-piece telescoping unit. It is a pressurized and sealed vessel that comes in various diameters and lengths. One portion of the strut is a solid rod while the other section is a sealed hollow tube. This larger portion contains a pressurized inert gas, typically nitrogen, and a small amount of oil.
These struts may assist with lifting and holding a tailgate or liftgate in the open position. On a sedan, small size struts may serve as trunk hinges. Inside a vehicle, pressurized struts may help tilt a front seat so passengers can get into the rear seat area.
Most importantly for firefighters, struts are increasingly being used to replace the conventional hood hinge. One will be located on each side of the rear corner of the hood along the firewall area.
According to the strut manufacturers, these sealed and pressurized struts are designed to operate at temperatures ranging from 40 degrees Fahrenheit to 284 degrees Fahrenheit. No manufacturer could provide any evidence that any testing at temperatures above 284 degrees Fahrenheit had ever been conducted.
During a vehicle fire, especially an engine compartment fire, the two hood hinge struts will be exposed to high heat levels. Since there is no pressure relief "valve" on any of these sealed and pressurized struts, the units can fail violently when overheated.
Unfortunately for firefighters, this failure can actually "launch" the entire strut or just one part of the unit a significant distance off the vehicle like an unguided missile. It is the launching of the heated strut that in several incidents across the United States, has caused serious injury to firefighters.