[nwiswell]

For an airship of the size proposed in that post, I don't think I agree. Presumably there would be some measure of compartmentalization, ventilation, and fire suppression so that even if a portion of the craft was stricken, the entire vessel would not be doomed.

But even so, there's going to be a point where there's just too much fuel to keep the fire under control despite best efforts, and the fire-resistant magnesium could certainly contribute to reaching that threshold once you cross a certain temperature. And you cannot simply vent combusting magnesium the way you can vent combusting hydrogen (hypothetically, anyway).