Extrication A-Pillar Stored Gas Inflator Modules

SUBJECT: Roof Airbag Systems
TOPIC: Identifying A-Pillar Stored Gas Inflator Modules
OBJECTIVE: Develop procedures for determining the presence of stored gas inflator modules mounted on or near vehicle A-pillars.
TASK: Given a crash-damaged late model vehicle, determine if the vehicle has stored gas inflator modules for a roof airbag system mounted on or near the A-pillar.

It is now common knowledge among rescue personnel that if a vehicle is equipped with a roof-mounted airbag system, there will be stored gas inflator modules present somewhere on the vehicle. The most common location for the inflators is mounted to the rearmost roof pillars; typically the C- or D-pillar.

There are several recent models of vehicles, however, that have pressurized inflator modules mounted on or near the front A-pillars. To assure safety during extrication, the location of cylinders in this new location must be identified prior to any roof removal evolutions or dash and firewall assignments being undertaken.

Image courtesy of Mercedes-Benz USA
The 2003 Mercedes E-class sedan has the stored gas inflator module for the roof airbag system mounted directly to the A-pillar; right in our "cut zone."

A typical stored gas inflator module for a roof airbag system contains a small, pressurized cylinder inside of a slightly larger inflator housing. There are various designs, but all designs use stored gas pressures ranging from 1,400 psi to 3,000 psi.

When activated due to a collision, the pressurized gases inside the inner cylinder are vented into a "burn chamber" inside the inflator housing. As they pass through this small chamber, the special liquid fuel that is present there burns in a hot flash fire, heating the gases. Hot gases expand to better fill the volume of the airbag. The nylon-coated rubber fill hose secured to the A-pillar then directs the gases into the various chambers of the airbag itself.

Image courtesy of Mercedes-Benz USA
Close-up view of inflator module shows its location on the front A-pillar of this E-320 sedan.

Engineers who designed the roof airbag system for the new E-class sedan from Mercedes-Benz chose to secure the pressurized inflator modules directly on the A-pillars, exactly in our roof removal "cut zone." The inflator module is only visible by stripping away the trim along the inside of the A-pillar. This will expose the airbag fill hose and the inflator at dashboard level.

Photo by Ron Moore
With the trim removed from the A-pillar of this BMW, the white hose can be seen leading down to the small black inflator module. (Cover of instrument panel and dashboard is removed in this photo taken in a body shop)

BMW has positioned the airbag inflator module for its roof-mounted HPS system near the front A-pillar, underneath the instrument panel cover. The cylinder resembles an old-time ink bottle with a white hose attached to its top. The short and stubby design of the inflator fits neatly into place within a bracket inside the dashboard and below the instrument panel. The inflator actually bolts to the inside of the A-pillar, just below dash level. When in place, although the cylinder cannot be seen normally because the dash covers it, it is even with the level of the top door hinge.

Once again, the presence of these inflators can be identified only by stripping away the trim along the A-pillar. If you observe a white nylon fill hose, it indicates that the inflator module is underneath the instrument panel.

Photo by Ron Moore
From a rescuer's point of view, the stored gas inflator won't be seen at a crash scene because it is below the instrument panel (which is missing in this photo). The cylinder’s position in relation to the top door hinge can be determined.

Standard Operating Procedure for Determining the Presence of Stored Gas Inflator Modules Mounted On or Near the A-Pillar

1. Scan vehicle for airbag ID for a roof-mounted airbag system

  • Middle of A-pillar
  • Top of A-pillar
  • Top of B-pillar
  • Top of C-pillar

2. Pry or strip interior trim off A-pillar

  • Inspect for presence of actual stored gas inflator module
  • Inspect for presence of rubber hose covered with white nylon

3. Determine location of stored gas inflator module

  • On A-pillar at dashboard level
  • Beneath instrument panel at level of top door hinge

4. Report findings to command or rescue sector officer

Ronald E. Moore, a Firehouse® contributing editor, serves as the Forum Moderator of the University of Extrication section of the Firehouse.com website. Moore is the author of the text Vehicle and Extrication Rescue (2nd edition), published by Mosby/JEMS. He can be contacted directly at Rmoore@firehouse.com.