Breath Tests with Deployed Air Bags

In today’s times when nearly all cars have airbags, the question arises as to whether a deployed airbag will affect the reliability of a breath sample. This is known as the Tyndall Effect. The Tyndall Effect, discovered by John Tyndall, a British physicist in the 1800s, is the suspension of insoluble particles (colloidal suspension) in liquid or gases. The effect is a dispersion of light. Like headlights in the fog, the light emitted from the headlight is not shown directly through the fog to a road sign. Instead, the fog (colloid) disperses the light. In relation to airbags and breath alcohol testing, a person exposed to airbag deployment can produce an erroneously high breath alcohol reading using infrared technology machines.

The airbag is deployed at 200 m.p.h. using a nitrogen gas to fill the airbag in about 30 milliseconds. The powdery substance seen during deployment and on an individual’s clothing is talc and/or cornstarch packed with the bag to maintain the bag’s integrity while stored in place. When the talc and cornstarch are deployed into the air with the airbag inflation, the particles are inhaled and will be expelled in the breath for several hours. Individuals have reported regurgitating and spitting out the powdery substance for two to three hours and more. Andreas Madlung, The Chemistry behind the Airbag: High Tech in First-Year Chemistry, 73 J.Chem.Educ. 347 (1996).

When an individual then blows into a breath machine using infrared analysis like the Intoxilyzer Model 5000 we use here in Texas, the talc and/or cornstarch is blown into the Intoxilyzer’s sample chamber. When the infrared light is shown through the chamber, the light is then dispersed because of the Tyndall Effect. Consequently, this can lead to an erroneous high reading of ethyl alcohol. When Texas first started using the Intoxilyzer Model 5000, the airbag/Tyndall Effect was not as big of a deal since most cars didn’t have airbags. However, with the mandates for airbags and expansion of their usage within the vehicle, the Tyndall Effect is a major factor in determining the reliability of a breath test result, when the airbag has been deployed.