The effectiveness of stationary automobiles as shelters in accidental releases of toxic materials

The protection offered to occupants of stationary automobiles against airborne gases and respirable particles, such as might result from an accident release, was measured and found to be substantial. For the four autos tested with the air conditioning (AC) system on and in recirculate position, the equilibrium ratios of inside/outside concentrations (I/O) for 2-μm diameter particles were less than 0.2, and some ratios were as small as 0.014. With both the AC compressor and the system fan off, the I/O for five autos ranged from 0.04 to 0.18. These low ratios are primarily a result of deposition within the autos. However, three of the five autos had substantially higher I/O ratios when the AC fan was on than when off, indicating that for some autos the AC caused significant added intake of outside air. Air exchange rates for the five stationary autos were on the order of 0.5h-1 with AC off, and 2.5h-1 with AC on. (Author)