Explosion and fire in a fertiliser production plant

A syngas leak (hydrogen + methane) occurred at exit of the ammonia production reactor and led to an explosion followed by a fire.
The start point of the sequence of events was the syngas at the reactor outlet reaching an abnormal pressure of 150 bar and a temperature of 300°C. This caused a flange seal to move, causing the gases to leak.
The accident caused a pressure waves and fire observed on the installations over a distance of 450 metres.

The INITIATING cause was an overpressure on a flange, causing its loss of confinement. The sources do not mention the reason(s) for the unexpectedly high-pressure value. It could be assumed that it was an exceptional event, but not completely unexpected.

From the corrective actions adopted it appears an absence of a risk assessment based on the possibility of ignition of flammable gases at the ammonia reactor, the usage of a inadequate component (flange) and the lack of effective communication of an alarm to personnel. These points hint at ROOT CAUSES related to inadequate (safety) design and risk management.

ammonia reactor

DESCRIPTION OF THE COMPONENTS
The pipe diameter at the exit of the ammonia reactor had a diameter of 300 mm (DN300). The flange used on this pipe was a model with a lenticular seal between the clamp and the tube, screwed to the flange by bolts.

The accident caused 5 injuries. Material damage due to the pressure waves and fire was observed on the installations over a distance of 450 metres. The consequences for the site were estimated at €12,000,000.

The plant and local firebrigades intervened, with a total of 28 men. They monitored air concentration of after-combustion gases
During the mergency, the operator ensured the closing of all gas valves nad monitored reactor activities to prevent temperature changes of catalisator.

After the accident, the operator considered the following measures:
1) to conduct an explosion risk study in areas where ammonia or flammable gases are handled and in areas where an explosion has already occurred;
2) the installation of an personnel alert system and an evacuation procedure in the event of a process failure that could lead to an explosion;
3) the replacement of the flanges by a model more adapted to over-pressure hazard.