DESIGN AND CALIBRATION OF AN EXPOSURE SYSTEM FOR SUPPLEMENTAL INFLATABLE RESTRAINT (SIR) AEROSOL (PARTICLES FROM AUTOMOTIVE AIRBAGS) INHALATION STUDY

The supplemental inflatable restraint (SIR) system, commonly known as the air bag, is expected to be standard equipment in many U.S.-built passenger cars in the 1990s. Although more than 99% of the combustion products after an air bag deployment is nitrogen, a complex aerosol of respirable size, consisting primarily of sodium carbonate, with lesser amounts of sodium hydroxide and metallic oxides, is also present in the passenger compartment. Since the effects of a short-term exposure to these aerosols in man is unknown, there is a need to establish a safe, no-effect exposure level to prevent any discomfort that might be experienced by the occupants.An exposure system has been designed and calibrated for a short-term inhalation study of SIR aerosols in humans. The system consists of a 200-L primary aerosol containment tank, a 1-m3 mixing chamber and several manually operated control valves. A sodium azide-based SIR module, mounted inside the aerosol containment tank, is used to generate the aerosols. After deployment, the aerosols are conditioned for approximately 3 min to allow for particle coagulation and pyrolysis of some of the deflated air bag fabric material in contact with the hot inflators. The delivery of SIR aerosols to the 1-m3 chamber is accomplished by proper aspiration at negative pressures up to 3.75 kPa (15 in. of waterThe exposure atmosphere is then diluted to the desired concentrations of 5–120 mg/m3, and the actual chamber concentrations are usually within 10% of the target values. The loss of SIR aerosols during inhalation through the two-way non-rebreathing valve was experimentally determined, and the aspiration coefficients were used to calculate the actual inhaled dose for each subject. The mass median aerodynamic diameter of the SIR aerosols in the mixing chamber determined by cascade impactors is 0.65 μm with a geometric standard deviation (σg) of 2.1. © 1990 Elsevier Science Publishing Co., Inc.