At 11:15 pm, an explosion followed by fire occurred in the vicinity of the measurement transformer on an isolated 90,000 V electrical oil transformer at a plant manufacturing technical polymers. Plant personnel placed the installations in safe operating mode, while the backup line and 15,000 V transformer were activated, in coordination with the electric grid operator to keep the site’s supply lines open. The risk of falling electrical cables led to closing the adjacent departmental highway, and the emergency crew installed a protective fire hose. A certified plant employee isolated the transformer in order to allow the site’s responders to put out the fire using a powder extinguisher. The response was concluded at 2:30 am, with plant production resuming by the end of the night. The plant operator issued a press release. The cause of this accident was a hydrogen release and explosion, most likely triggered by entry of humidity into the transformer oil. Two hypotheses were forwarded to explain this humidity inflow: a poor quality steaming of absorbent paper, and/or a flawed oil replacement procedure.