: Some forms of napalm still burn under water after they have ignighted(sp?),
: the yhave there own o2 scource.
Liquid oxidisers (Solids won't do for napalm) are quite hard to use because many oxidisers are either based on a salt (eg. potassium chlorate) or burn at a dangerous rate, which may cause an explosion. However a vacuum would only be a few degrees in temperature, at which point oxygen would certainly be liquefied or even solidified - but the vacuum temperature would make it extreeeeeemely difficult to get the fuel to a temperature whereupon it would ignite. Perhaps some air would be trapped in the flamer, which would allow it to burn for a little while in a vacuum, but unless it was by design, it would not be a useful amount.
