Flammable and inflammable

These two words mean exactly the same thing: liable to burst into flames.

Often the prefix in- indicates a negative, as in invulnerable, incapable, ineluctable, inorganic, inactive. But just as often, perhaps even  more often,  it does not: inculcate, inflatable, incubate, influence, insert.

For health and safety reasons, manufacturers have started using flammable rather than inflammable, lest some genius decide that a bottle of  inflammable lighting fluid could not possibly explode and then sues them for his blistered face and incurable illiteracy.