Pressurized Vessels on Vehicles - Part 3 Stored-gas Inflators

Oct. 1, 2005

Subject: Pressurized Vessels on Vehicles - Part 3

Topic: Airbag System Stored-Gas Inflators: Catastrophic Failure of Airbag System Stored-Gas Inflators During Vehicle Fires

Objective: Review real-world incidents of airbag system stored-gas inflators exposed to high heat levels during vehicle fires

Task: Establish procedural guidelines for operating at vehicle fires, including engine compartment fires, to ensure maximum safety for personnel from the hazard of airbag system stored-gas inflator 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.

Our series on pressurized vessels on vehicles continues with a look at the stored-gas inflator modules used to inflate supplemental restraint airbag systems. These pressurized vessels are used primarily to deploy roof-mounted airbags, but can also be found connected to seat- or door-mounted airbags as well as the passenger frontal airbag. The inflator is a cigar-shaped unit that contains argon and helium gas. The gases are pressurized at up to 4,000 psi. During a crash sequence, the gases are released from the inflator and flow into the airbag.

Responders already know that pressurized vessels on vehicles can fail violently during vehicle fires. But the stored-gas inflators are a new challenge for fire suppression crews and bring up the question of how they hold up during a fire.

An interesting vehicle fire occurred in Flagler County, FL, involving a 2001 Nissan Altima sedan that was stolen and then torched. The post-fire investigation revealed a hole in the roof above the front passenger-side seat area. A closer examination of the burned-out vehicle revealed that the stored-gas inflator from the side-impact airbag mounted in the front passenger seat had failed during the fire. Investigators determined that the top portion of it flew upward, making the hole in the roof.

In a similar incident in McKinney, TX, firefighters arrived at the scene of a fully involved 2002 Dodge vehicle. The stolen vehicle had been torched and was well involved when the firefighters arrived. After extinguishment, the crew found two large pieces of the passenger frontal airbag unit lying in the roadway approximately 120 feet ahead of the vehicle.

The passenger frontal airbag on an Altima uses a stored-gas inflator unit for deployment. The large unit, which resembles a Thermos bottle in size, is pressurized to 4,000 psi. During the fire, the pressurized stored-gas inflator cylinder had failed violently prior to the arrival of the engine company. The heat from the fire caused the vessel to rupture with enough force that the vessel broke free of its mounting and flew into the air.

Captain Lee Junkins, training officer of the Sansom Park, TX, Fire Department, has developed an entire training program based on the hazards of burning vehicles. As part of his research for that project, Captain Junkins obtained 100 identical stored-gas inflator units from automobile airbag systems. Using a homemade field-testing assembly, he exposed each of the pressurized inflators to the flame from a standard highway flare. In 93 out of the 100 tests he conducted, the inflator simply heated and deployed the airbag. In seven of the 100 tests, however, the stored-gas inflator failed violently, resulting in an uncontrolled explosion of shrapnel as the vessel disintegrated.

What's the bottom line on stored-gas inflator units and fires? The reality is that these 4,000-psi cylinders have no relief valve built into them. Any vehicle today can contain several of these airbag inflator units, two for the roof airbags, two for the front-seat airbags and another one for the front passenger airbag, for example. In most cases, nothing out of the ordinary will happen as the vehicle burns. The fire will heat the inflator and once a certain amount of heat is built up inside the inflator, it will "vent" by firing off the airbag. The nylon bag will deploy into the flashover conditions that exist inside the vehicle and the bag melts away.

The "real world" also tells us that things can and will go wrong as a vehicle burns. Our airbag fire case studies verify this. Stored-gas inflators for airbag systems can be heated to the point that the cylinder itself fails violently. That failure may result in a small projectile being shot out through a window or roof as with the 2001 Altima incident. In a worst-case scenario, the rupture of the cylinder may send large chunks of hot metal flying out in all directions, as in the McKinney, TX, incident. Either way, it is a dangerous situation for fire suppression personnel.

As firefighters, we cannot predict what will happen but we must anticipate what can happen. Any vehicle with open flame upon arrival must be thought of as a "total loss" vehicle. It's a loser already and that's not your fault. But it is your fault if a member of your crew is injured during the fire fight. The burning vehicle is worth nothing; your safety is worth everything.

Ensure that your department's guidelines for attacking vehicle fires require full protective clothing with self-contained breathing apparatus (SCBA). Emphasize an initial attack from a safe approach angle with an adequate-size handline that can initially sweep water beneath the vehicle to cool the undercarriage. Encourage crews to begin hitting the fire from a distance as they move in to cool the vehicle, especially if it is a well-involved interior fire.

TASK: Establish procedural guidelines for operating at vehicle fires, including engine compartment fires, to ensure maximum safety for suppression personnel from the hazard of airbag system stored-gas inflator failures.

Ron Moore, a Firehouse contributing editor, is a battalion chief and the training officer for the McKinney, TX, Fire Department. He also authors a monthly online article in the "MembersZone" and serves as the Forum Moderator for the extrication section of the website. Moore can be contacted directly at [email protected].

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