Explosion of a chemicals storage tank

In a chemical plant, a 1750 m³ tank containing an ammoniac solution exploded.
The anchorage of the tank was ripped, the tank lifted on one side and crashed against the retention wall, which was partially destroyed. 1000 m³ of solution (10-20% NH3) was discharged; the stream destroyed another part of the retaining wall at the opposite side and contaminated the surroundings.

The presence of an explosive atmosphere consisting of an air-NH3 / H2 / CH4 mixture was strongly suspected. The source of ignition was unknown (electrostatic, pyrophoric sulphides?).
Four people were slightly intoxicated (inhalations).

Preventive measures were adopted (inerting, grounding, etc.).

The INITIATING cause is the formation and ignition of an flammable atmosphere, probably a mixture consisting of air-NH3 / H2 / CH4.
The source of ignition is unknown (electrostatic, pyrophoric sulphides?)
ROOT CAUSE analysis is no given.

tank containing an ammoniac solution

4 people were slightly intoxicated (inhalations).

Following the incident, measures aiming at preventing the incident were adopted: among which inertisation of the atmosphere and electrical grounding of the tank.