Expert: Dr. Henry Boyter, Jr. - 6/26/2004

Question
which object is more combustible in a pure oxygen environment, pure hydrogen or gasoline?

Answer
First we have to look at some definitions.  Gasoline and hydrogen VAPOR will be flammable.  That is they have a flash point where the vapors of gasoline or hydrogen gas can be ignited.  LEL and UEL are the lower and upper explosive limits.  Outside of this range, vapors will not ignite.  LEL and UEL are also dependent on temperature.  Liquid nitrogen frozen gasoline probably will not ignite because there will be no vapor.  Hydrogen can not be frozen.  These also depend on pressure also.

Gasoline is flammable at standard temps between 1.3 and 8% vapor.  It is flammable above -45C  Hydrogen is flammable between 4% and 75%.  It is flammable above -253C.  Based on this, hydrogen is more flammable.  Note that at 80% gasoline or hydrogen, no burning at all takes place.


Based on this data, hydrogen is flammable in a wider range and starting at a lower temperature.  Note that the amount of oxygen makes no difference as long as there is enough.  Pure oxygen makes burning more efficient and possibly faster, but really makes no difference in when it starts.


On enote: if you have a pure oxygen atmosphere, there will be no hydrogen or gasoline present.  Can't have both.  It really is hydrogen is mixed with pure oxygen.