How combustible is gas in a clear container?

If gasoline was placed in a open container and the vapor filled the container before it was sealed, no explosion would occur because no oxygen was present. If the container also had liquid gasoline, gasoline vapor and air, no explosion would occur at ambient temperatures unless an ignition source was present. Heating the sealed container with all three components present would eventually explode but at which temperature that would occur at is difficult to say.

Not enough activation energy to start combustion of gasoline under 'normal' conditions.

(Note: A stoichiometric mixture of hydrogen might be initiated by strong blue light.)

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