Sorry, a little off-topic, and maybe discussed before:
once I was thinking of buying one of those heavy-ish plaster/gypsum-filled vinyl outside fire and waterproof safe boxes at Staples (I think it was the Sentry brand)--the kind with the key lock in front. Anyway, I was looking at one of the small-to-medium sized box models. Someone before me had thoughtfully conducted a little demo on the unit on the shelf. They had ripped the top off the safe from the back (hinge) side. I had always thought there must be a very strong metal rod or somesuch hinge on the back, however I was amazed to see that the "hinge" is composed only of two smallish plastic nubbins (for lack of a better word) that also appeared to be filled with the plaster material. Each nubbin fit in a corresponding socket that composed the other part of the hinge on the lower portion of the box. As I recall, the nubbins didn't appear to be more than a half to three-quarters of an inch long, and they had been completely fractured and bent when the top had been ripped off the safe from the hinge side. I was amazed to see such an apparently flimsy "hinge" for a box that supposedly was supposed to be somewhat difficult to open.

Again, sorry to drag this off the fireproof subject, but I thought those considering purchasing one of these units might be interested.