Pedantry Warning
Trevor, here is the definition, as given in the Yahoo on-line dictionary
" Historically, flammable and inflammable mean the same thing. However, the presence of the prefix in– has misled many people into assuming that inflammable means "not flammable" or "noncombustible." The prefix –in in inflammable is not, however, the Latin negative prefix –in, which is related to the English –un and appears in such words as indecent and inglorious. Rather, this –in is an intensive prefix derived from the Latin preposition in. This prefix also appears in the word enflame. But many people are not aware of this derivation, and for clarity's sake it is advisable to use only flammable to give warnings. "