How do you think they died? It seemed they were the most careful as compared to crazy Mario and cowardly Jo, and the road they traveled didnt seem rough.
Was it a bump on the road or do you think it was something else?
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DIE, FANBOY, DIE share
It isn't explained in the film what specifically caused their truck to blow up. Something went wrong for them, and that's all the information we're given. The fact that they were careful just serves to emphasize how inherently dangerous the job is.
It's ironic that Bimba had been so concerned with appearances, saying that he wanted to be a "presentable" corpse, when, after that accident with the nitro, there wouldn't have been much of him left (intact).