Explosion on a storage vessel of a chemical plant

The accident occurred when a welder of a sub-contractor company was working on a tank roof. The zeolite crystallisation tank was being cleaned out with approx. 20% sulphuric acid. It was not pressurised and was vented to atmosphere. The worker had been asked to cut a larger inspection hole in tank top. He had not yet begun to cut, but possibly had already lit up the oxy-acetylene equipment, when a loud explosion was heard by many.

Hydrogen evolution due to acid action on steel vessel walls was suspected to be the cause of the accident.

The HSE communication does not give indications useful for drawing a root cause.

zeolite crystallisation tank, H2SO4, welding gear

The accident occurred when the tank was being cleaned. An additional intervention was planned, consisting in cutting a large inspection hole on the tank top. .

1. Oxy acetylene equipment and sample from tank taken for analysis.

2. FCG contacted.

3. Hydrogen evolution due to acid action on steel vessel walls
suspected to be the cause of the accident.

The fire was fought by means of water and cement. The smoke triggered a request of home-confinement to few neighbouring houses.
EMERGENCY ACTIONS SEQUENCE
9:30 The fire started.
At 9:34 - Fire department was called and the shut-off valves were closed. While awaiting the arrival of emergency services, site personnel sprayed the fire with a fire hose reel and a fire hose.
10:00 - The firefighters deployed two fire hoses, one of which was mounted on an aerial ladder. 10:45 - Cement, already on site due to ongoing construction work, was used to smother the fire. A new supply had to be requested from a local provider.
12:45 - The fire was brought under control around.
From 12:45 p.m. to 16:00 - The waste was removed from the building and then sprayed with foam to ensure complete extinguishment. Atmospheric readings were taken by emergency services, and the results showed no significant impact.
16:30 - The operation concluded. The firefighting water (approximately 5 m³) was contained on site. It was analysed to determine its discharge point. The waste removed from the building was secured, and the exterior surfaces were cleaned.