bro airbags do not sit "compressed", they have chemicals inside that react instantaneously upon an impact to release gases that inflate the airbag. it all happens in a split seond, ofcourse, as we all know.
here's a source if you don't believe me:
http://en.wikipedia.org/wiki/Airbag :
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Inflation
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When the frontal airbags are to deploy, a signal is sent to the inflator unit within the airbag control unit. An igniter starts a rapid chemical reaction generating primarily nitrogen gas (Nsub2/sub) to fill the airbag making it deploy through the module cover. Some airbag technologies use compressed nitrogen or argon gas with a pyrotechnic operated valve ("hybrid gas generator"), while other technologies use various energeticpropellants. Propellants containing the highly toxic sodium azide (NaNsub3/sub) were common in early inflator designs. However, propellants containing sodium azide were widely phased out during the 1990s in pursuit of more efficient, less expensive and less toxic alternatives.sup[citation needed]/sup
The azide-containing pyrotechnic gas generators contain a substantial amount of the propellant. The driver-side airbag would contain a canister containing about 50 grams of sodium azide. The passenger side container holds about 200 grams of sodium azide.sup[
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]/sup The incomplete combustion of the charge due to rapid cooling leads to production of carbon monoxide (CO) and nitrogen(II) oxide as reaction by-products.sup[
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]/sup
The alternative propellants may incorporate, for example, a combination of nitroguanidine, phase-stabilized ammonium nitrate (NHsub4/subNOsub3/sub) or other nonmetallic oxidizer, and a nitrogen-rich fuel different than azide (eg.tetrazoles, triazoles, and their salts). The burn rate modifiers in the mixture may be an alkaline metal nitrate (NOsub3/sub-) or nitrite (NOsub2/sub-), dicyanamide or its salts, sodium borohydride (NaBHsub4/sub), etc. The coolants and slagformers may be eg. clay, silica, alumina, glass, etc.sup[
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]/sup Other alternatives are eg. nitrocellulose based propellants (which have high gas yield but bad storage stability, and their oxygen balance requires secondary oxidation of the reaction products to avoid buildup of carbon monoxide), or high-oxygen nitrogen-free organic compounds with inorganic oxidizers (e.g., di or tricarboxylic acids with chlorates (ClOsub3/sub-) or perchlorates(HClOsub4/sub) and eventually metallic oxides; the nitrogen-free formulation avoids formation of toxic nitrogen oxides).
From the onset of the crash, the entire deployment and inflation process is about 0.04 seconds — faster than the blink of an eye (about 0.2 seconds). Because vehicles change speed so quickly in a crash, airbags must inflate rapidly to reduce the risk of the occupant hitting the vehicle's interior.