Fire in the electrical transformer of a metallurgical plant

A fire broke out on a transformer transforming 225 kV into 15 kV in a metallurgical plant. This transformer supplies electrical power the site and to a neighbouring factory.
In the following three hours, staff brought the fire under control with CO2 extinguishers, the internal emergency plan was activated, and the firefighters ventilated the premises and took readings of the flames using a thermal camera.
Meanwhile, however, the shutdown of the electrical installation caused the stop of the operation of an electrolysis unit using zinc sulphate. This unplanned stop of the process caused the generation of hydrogen at slow rate: a change from 0 to 8% LEL in 3 hours was detected.
For more than an hour, the staff, assisted by a specialised company, was busy in empting 82 tanks of 25 m³ each with the company's pump truck. After that, the electrical installation was put back into service and all the plant processes were checked.

The presence of a cat in the transformer caused the fire to start.
The formation of hydrogen was due to the unplanned stop of the electrolyser.
The root cause can only be guessed, in between design or management shortcoming for not having foresees the risk of the possibility of sudden stop to zinc production facility.

transformator, zinc electrolysis

A lack of power supply from the transformer on fire was at the basis of the incident.

DESCRIPTION OF THE PROCESS
The process involved in this incident was an industrial process called electrowinning, used for extracting metals from their ore by means of electrolysis.
In the electrolysis of zinc sulphate (ZnSO4), Zn+ ions in the electrolyte are reduced to metallic Zn at the cathode, while oxygen forms at the anode, with H2SO4 (and hydrogen) as by-product.

An internal firefighter, slightly inconvenienced by the fumes during his intervention, was taken to hospital as a precaution.
No technical unemployment, only production losses in the two metallurgical plants.

10:00 - Fire on the transformer transforming
Fire under control by means of CO2 extinguishers. The internal emergency plan was activated. The firefighters ventilated the premises and took readings of the flames using a thermal camera.
From 12.45 to 14:00, the staff, assisted by a specialized company, worked to eliminate the causes of the hydrogen production from the zinc electrolysers by empting the supply tanks.
14:15 - Electrical installation put back into service and all the plant processes checked.
14:30 - Firefighters left the site.