ALL certified co2 bottles that are correctly filled are perfectly safe .... A standard rupture disc is set to blow @ approx 2,200 psi .. On a correctly filled bottle this shouldnt happen until its temperature exceeds 120 degrees F ...... squeezing a little extra into the bottle e.g. 1/2 a kilo on a std 2kg bottle brings the temperature/burst disc threshold down to around 80 degrees F.
Note that bottles are/should be ONLY turned on in the Arena.