Sounds like it was indeed a
Sounds like it was indeed a lead-acid battery. Sulfuric is the acid in the electrolyte of lead acid batteries and hydgrogen (or sulfides of hydrogen) are off-gassed normally. The problem starts when they are not vented. Rookie error. Weird this can happen in a GM lab. An inexpensive combustible gas sensor could have ben used to shut this process down and vent before the LEL level was reached. Perhaps it was inside a reactor vessel and something failed that was supposed to open.