If it were to be closed WITHOUT first testing the combo at least three times you may be hosed.
Here is the "How to" just for the experience of reliving it!
I worked as a military radioman for 20 years, consequently at least twice a day two of us (Danged John Walker) - Two Person Integrity - would open "our" side of the safe. I have spent literally hundreds of hours working on safes that have "Jumped" the combo.
Modern safes, contrary to their size and looks are precision devices and any little "timing" issue can render them "Locked" , shall we say ...permanently...
They normally have two ratings, a "brute force" rating and a "Surreptitious" rating. One is "No rules any tools" entry, the other is doing it rather "Quietly" , that is , using the dial "Cracking it" or some other method of less than "Brutal" entry.
I remember when Plasma cutters hit the market! Woo hoo! I thought...We had a big Mosler that "Jumped" the combo, 2- 12 hour watch sections of 8 people each tried the "Combo" , 1-2-3 numbers ahead and behind of each of the original "Combo" digits..Sometimes you get lucky and this will work, sometimes not...We got some riggers and we "Escorted" the safe to a aircraft maintenance shop where they had the latest and greatest , super sized, government purchased plasma cutter. After a quick lesson I suited up and tore into the safe with it. Well, it cut through the "Skin" of the safe like a tin can, just beautiful cuts with no slag and little extra heat to burn up the contents like a torch cut can sometimes do. Well, when I to to the "Hardened" locking lugs all the plasma cutter did was discolor them and create a hella lot of sparks. Barely even dinged them, this obviously was not the technological breakthrough that the tired radiomen had hoped for. I asked if the had a 10" grinder and some cut-off wheels, yes...
This is the BEST option for getting in the "hard" way. It creates major sparks but if you are careful the contents will be undamaged and there is not nearly the heat that a torch creates. Believe me, I have cut into three of these things in my career, NOTHING, I mean NOTHING, beats the tried and tested abrasive cut off wheel on a big arsed grinder. I havent tried a carbon torch but I have tried the smaller version that can be run on a big AC/DC welder. they work good on regular carbon steel, but the Hardened locking lugs on a safe....Nah, give me back that grinder would ya...I dont have all day....If you cant get it out easily just throw down some blue tarps, have your wife give you 2 old blankets and wet them down with a hose to contain the sparks the grinder will give off. Wear a dust mask, eye protection and gloves...Come on in,...the waters fine...
Brute force advice;
Find out where the locking lugs are from the mfgr. and rent a plasma cutter to remove the "Skin" of the safe door to expose the hardened locking lugs. this is what you will be trying to defeat with the 10 or 12" grinder and abrasive cut-off wheels....Tent it off with tarps and wet blankets, have a couple of beers and put two more in the fridge. You will need them after an hour or so on that grinder and 4-6, 1"-2" hardened locking through lugs and 10 grinding discs later...The good news is that it only takes an hour or so to get in. the bad news is that it will ruin the safe and make a helluva mess....This method however WILL not hurt the contents of the safe if your is like most , that is having a thick external skin and a thinner internal skin that will "protect" the contents from your efforts...
