It looks more like a fire safe for protecting documents in a fire rather than a safe for valuables to me.
Which means torching it from the bottom will take a lot of time and gas, and will likely destroy any interesting contents.
Dropping it a few times from a great height onto concrete or similar, or running a forklift into it, may break the Ming vase or anything else breakable inside, but should not burn any bearer bonds, diamonds (yes, they burn), money etc..
You pays your money and you takes your chances ...
Shouldn't be too hard to crack though.
I think there is also a very quick technique with a forklift which crooks use, but I can't remember it.
Richard Feynmann, in his memoirs, has a very amusing chapter about safe- cracking (he was the unofficial safe-cracker for the Manhattan Project at Los Alamos, which he started mostly by playing jokes on his buddies).
The VERY FIRST thing you do is call the manufacturer and ask them if they have a default combination when they ship the safe. Most safes with combinations that can be changed ship with the factory combination, and many people (particularly if it's a fire safe) don't bother with changing it.
Try it. If it works, I'm a freaking genius. If it doesn't -- well, then I'm no worse off than I am now, right?
Wyatt, 51, is a man with time on his hands. He defines himself as a marginally employed computer repairman, a tinkerer in all things mechanical and an unrepentant coffee-shop slacker. He learned everything he knows about safecracking from a 34-page PDF document he found while doing a Google search on "safecracking for the computer scientist."
Rodgers recently bought a mid-century home in the Upper Castro neighborhood, which came complete with a 1-ton antique safe that prevented him from parking his car in the garage. He was offering 25 percent of the unknown contents to any person who could open the safe. The only catch was that the safecracker had to haul away the cracked safe when the job was done.
At 10:22 a.m., Wyatt cried out, "I got it!" Rodgers came running over just as the several-hundred-pound door fell off the safe - a contractor had removed the hinges in a previously failed attempt to get in.
Wyatt's reward was indeed 25 percent of the air in the safe. Apart from that, nothing was inside.
Still, Wyatt had a giant grin on his face as he held the inner workings of a lock like a shiny piece of gold. His curiosity had been quenched.
------ no word how Wyatt, on his bicycle, was getting the safe out of there
First off I would try forcing a large, 6 ft or so pry bar in between the door and side. Maybe use a small sledge and some cold chisels along the same edge to gain some room for the big pry. It really depends on how many bolts are in the door, how long they are, how well anchored... But I think a big pry bar will bend/spring the side away for you to gain entry :)
I guy I know used to work in a quarry and they had been using an old safe that was around as an anvil for years. At some point it eventually got opened and it was found to be full of sweating dynamite, seems it was the safe for storing it in safely and that had been forgotten. The bomb squad got called and the stuff was safely disposed of and all that had used it thought what if it had gone up, of course if it had they wouldn't have known about it.
I remember an old OU IIRC film and it showed the burning of diamond but they said the activation energy was so high the diamond needed to be heated white hot with the likes of an OA torch and then placed in liquid oxygen where it did burn. I know you're a chemist so maybe you know if there's more to it.
Carbon in any form will burn in air at above 800C or so, which is within normal flame temperatures.
Above about 650C diamond actually burns at a slightly lower activation energy than graphite or amorphous carbon, though the difference is very small and temperature-dependent.
However diamond and graphite present nearly atomically-smooth surfaces to the air, and amorphous carbon doesn't. In the middle of these smooth surfaces the activation energy is quite a bit higher, and the temperature has to be above about 800C - while at the edges, and for the larger surface areas of amorphous carbons, the required temperatures are lower, perhaps 450-500C.
And of course the hotter it is, the faster it burns. LOX is cold, and it will cool the carbon as well as reacting with it, so it helps to have the diamond red-hot when it enters the LOX. Not so important with a large diamond, but people don't burn large diamonds in LOX very often.
Also diamond conducts heat better than anything else (except graphene) - and by quite a lot, it has about 5 times the thermal conductivity of the next contender, pure silver - so burning small lumps of it in LOX is a bit atypical.
If it's a "fire safe", and not a security safe, it's easy as heck to get into. Just peel off the sheet metal, crush the gypsum insulation, and cut with anything you like to get the box inside open.
There's nothing 'secure' about a fire safe, because they aren't designed for that.
Even if it's a security safe, unless it's a high-end one, the door bolts can be cut pretty easily. It's unusual to find heat-sinking bolts in an inexpensive safe. (and even then, oxy-acetylene can cut the copper inserts, with some time and gas)
The whole idea of a 'hardened' safe is to make it take too long for a crook to feel comfortable staying on the job. Someone who has time and no fear of cops or discovery can get into almost any safe with common tools.