After the drum failed, its contents were examined, sorted, and set out to dry. An aqueous layer was present. Samples of the water were taken for analysis. Pressurization was therefore caused by a different mechanism. Sampling results documented that the water phase was saturated with carbon dioxide, and had high ammonia content concluding the storage conditions were favorable to aerobic and anaerobic bacterial growth.
Aerobic bacteria prefer acid environments.
The PCB cleaner, Techstract PCB Clean, is acidic and is suspected of favoring initial aerobic bacterial growth resulting in carbon dioxide pressure. As the oxygen was consumed, the aerobic population would be expected to decline and be replaced by anaerobic bacteria which produce methane, more carbon dioxide and ammonia. The added methane and carbon dioxide would increase the drum pressure. The sampling results support this conclusion. The contributing cause was determined to be Procedure Problem, defective or inadequate procedure.