If there is air stuck it will be a big pop.
Make sure you take out the air valve just to be safe.
Then get an allen key or wrench one that fits through the eye lets and warp it with a rag.
So when it pops off the rag will stop it from fly off as 120psi is a lot of pressure.
Also as you unscrew it push down on the can so it comes off slowly!
But it might be jolting!

 I have seen this go wrong. Advice above is sound.