Explosion inside Tank from welding Incident Info Sharing

Explosion inside Tank from welding Incident Info Sharing

Location:- This incident was occurred in large, responsible international company but in a distance plant- thousand miles away from the US and Europe.

 

Task :- Pipework connected to a tank that had contained a flammable liquid was being modified.

Preparation for the JOB – The tank was “washed clean with water” to quote(fill in) the report. Forman checked that the tank looked clean and that there was no smell. The valves on the tank and the manway cover were all closed, or so it was thought, and a permit was issued for welding on the pipework.

One of the pip[e was cut with the hacksaw and removed. When a welder started to weld the replacement section an explosion occurred in the tank.

Consequences :- The welder was hit by the manway cover and hurled 5m(16ft) to the ground and died from his injuries. Huge loss of property was occurred and few persons died.

Probable reasons leading this

·         Water washing may remove all the liquid from the tank but it cannot remove all the vapor. Tests for flammable vapor should have been carried out INSIDE AND OUTSIDE the tank before work started, and its recommended to place a portable gas detector alarm near the welding site in case condition change.

·         Two of the valves on the tank were found to be open to atmosphere. One of them, on the top of the tank, probably provided the flame to ignition path as the welder was working several meters away. The foreman should have checked these valves before issuing the permit-to-work.

·         It is possible that the valve between the tank and the line being welded was leaking. The lines between the tank and the welding operations should have been blinded.

·         The job was completed by removing  all the pipework and modifying it in the workshop. That could been done before the explosion.

·         The procedures for preparing equipment for maintenance were grossly inadequate or ignored. It is most unlikely that this was the first time that a job had been prepared in such a slipshod way, and more senior and professional staff should have noticed what was going on.

 

Lesson Learned:- A SMALL QUANTITY OF FLAMMABLE GAS OR VAPOR CAN CAUSE A LARGE EXPLOSION WITH SEVERE CONSEQUENCES – especially when the fuel is confined. A little as 5-25 KG of methane could cause the damage as its not necessary to fill it fully.