Air fresher + cigarette lighter = No ******* way?!

Soldato
Joined
9 Mar 2003
Posts
14,058
The propellant used in aerosol air fresheners is normally some kind of hydrocarbon (propane/butane) and highly flammable.

The air volume inside a car isn’t that much and you only need a few % fuel to air ratio to cause an explosion. You also have to remember the air isn’t likely to be well mixed and the fuel will be localised to where the person was spraying and the lighting up.

If I remember correctly from watching myth busters I think the optimum was around 7% but you’ll get an explosion at as low as 3%. Fairly sure there was a whole episode on this topic alone.

It will only take a few PSI pressure differential over a split second of the explosion to cause that kind of damage and could be below whats needed to hurt a human.

edit: here you go
https://www.cdc.gov/niosh/docket/archive/pdfs/niosh-125/125-explosionsandrefugechambers.pdf

1 PSI over pressure will smash glass
5 PSI... will only cause the eardrums to burst in 1% of people
15 PSI... for internal injuries
35 PSI... is where you start to get fatalities.

3 PSI... will take down a house.
 
Last edited:

alx

alx

Soldato
Joined
10 Aug 2003
Posts
6,066
Location
Dubai, UAE
The propellant used in aerosol air fresheners is normally some kind of hydrocarbon (propane/butane) and highly flammable.

The air volume inside a car isn’t that much and you only need a few % fuel to air ratio to cause an explosion. You also have to remember the air isn’t likely to be well mixed and the fuel will be localised to where the person was spraying and the lighting up.

If I remember correctly from watching myth busters I think the optimum was around 7% but you’ll get an explosion at as low as 3%. Fairly sure there was a whole episode on this topic alone.

It will only take a few PSI pressure differential over a split second of the explosion to cause that kind of damage and could be below whats needed to hurt a human.

edit: here you go
https://www.cdc.gov/niosh/docket/archive/pdfs/niosh-125/125-explosionsandrefugechambers.pdf

1 PSI over pressure will smash glass
5 PSI... will only cause the eardrums to burst in 1% of people
15 PSI... for internal injuries
35 PSI... is where you start to get fatalities.

3 PSI... will take down a house.

Yes, typically the propellant in an aerosol can is often LPG, and in spraying the air freshener within the car the driver created a vapour cloud without any path for the gases to naturally vent (the car is essentially a sealed box, thus zero dimension confinement). A small source of ignition (lighting the cigarette) then resulted in a vapour cloud explosion with an incredibly high flame speed, potentially even reaching detonation conditions.

This mechanism is sometimes refered to as the ‘bang box’ effect. A small ignition source within a confined space (the ‘bang box’) can cause a disproportionally powerful explosion.
 
Caporegime
Joined
11 Mar 2005
Posts
32,197
Location
Leafy Cheshire
Yes, typically the propellant in an aerosol can is often LPG, and in spraying the air freshener within the car the driver created a vapour cloud without any path for the gases to naturally vent (the car is essentially a sealed box, thus zero dimension confinement). A small source of ignition (lighting the cigarette) then resulted in a vapour cloud explosion with an incredibly high flame speed, potentially even reaching detonation conditions.

This mechanism is sometimes refered to as the ‘bang box’ effect. A small ignition source within a confined space (the ‘bang box’) can cause a disproportionally powerful explosion.

Spot the Safety / Risk Consultant :p

I would model the over-pressure using a simple Shell software simulation if i was at work.
 
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