persulfate pressurization leading to burst bottle

Incident Overview: 
On October 14th, 2014 at approximately 4:30pm a student who was working in N37 heard a loud sound, like a glass bottle being dropped to the floor from N40. However there was no one at that time at N40, so after opening the chemical storage cabinets, he found that a bottle had burst in the Acid storage cabinet (yellow) in N40.  The bottle that had burst had an orange waste tag clearly mentioning sodium persulfate (Na2S2O8). The bottle could not be opened and was bubbling inside. Also to be noted, there was a distinctive smell of acetic acid (C2H5COOH) in the cabinet. (Note that sodium persulfate is odorless.)
 
Sarah took the broken glass pieces and dumped them into the broken glass waste disposal container. At that moment I saw that we had one more Na2S2O8 container, which was almost completely full. We then decided to phone EH&S. EH&S came in at 5:30 and tried, but also could not open the other persulfate container. It was kept in a bucket in the fume hood (large), and was removed the next morning.
Root Cause: 
Pressurization caused the bottle to burst, however we do not know how long the pressure had been building. Also persulfate is an oxidizer, and is not very stable in an aqueous solution. Over time it degrades to form sulfate radicals and hydrogen peroxide. The hydrogen peroxide itself degrades to form oxygen and water.
 
Thus the pressurization could have happened from three sources:
 
1. Oxygen built up due to persulfate decomposition
 
2. CO2 build up due to mixing of organic stuff like acetone/IPA with persulfate solution
 
3. H2 and CO2 build up due to degradation of acetic acid with persulfate (Note: I mentioned there was a vinegar smell when the cabinet was opened so
acetic acid and persulfate may well have been mixed)
 
This would have not happened if we had used vented caps. I did not know about vented caps, which are always used in Prof. Redwing’s labs. I will be using them from now on.
 
 
Preventative Actions: 
1. Use of vented caps
 
2. Bi-weekly disposal of persulfate waste
 
3. Only pour persulfate waste in the bottle as marked! (This applies to all waste!)