Explosion on an Ammonia Reactor of a Fertilizers Plant
The explosion, accompanied by abundant black smoke, occurred at 8:50. An ignited leak of hydrogen (H2) in the ammonia production unit (NH3) had spread to the pressure circuit carrying synthesis gas (mixture of nitrogen N2, H2 and NH3 already synthesized). The 7 operators operated the emergency stop and evacuated the unit (risk of toxic leak) to the fall-back zone (reinforced control room). The plant operator triggered the emergency plan around 9:15, alerted the public rescue service and the crisis unit of the prefecture. Firefighters took over from the in-house firefighters who were watering the accident unit with three water spears to prevent the spread of the fire. In the control room, the production team flushed the synthesis gas circuit with nitrogen in order to remove the hydrogen and stopped the machines in the workshop while a lower secondary explosion was noticeable. The operator closed the water networks of the site to avoid pollution of the river Seine by the extinction water. For lack of fuel, the fire goes down gradually around 9:55.Toxicity measurements (NH3) were performed in the unit and around the site by fixed and mobile sensors. While downwind around the site the measurements did not reveal any dangerous concentration; 200 ppm was measured in the machine room of the accident unit (the toxicity threshold is at of 345 ppm for a 1 hour exposure). Characteristic NH3 odours were perceptible off site. the NH3 concentrations were zero at the level of the accident unit which was put in cold stop. Half hour later toxicity was back to zero. The first elements of the investigation showed that the rupture of a pipe near a valve carrying synthesis gas at 200 bar near a compressor of the unit, could have caused a high pressure burst at the origin of the perceived explosion. Another hypothesis is the formation of a unconfined vapour cloud explosion after gas release. The leaking synthesis gas, containing highly flammable H2, ignited on contact with air and spread around the pipe.
Event Date
September 29, 2011
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Causes
Cause Comments
Unclear if immediate cause is:1. rupture of a pipe near a valve carrying synthesis gas at 200 bar near a compressor of the unit, causing a high pressure burst 2. formation of a unconfined vapor cloud explosion after gas release. The leaking synthesis gas, containing highly flammable H2, ignited on contact with air and spread around the pipe.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
ammonia production unit
Storage/Process Medium
Location Type
Location description
Industrial Area
Pre-event Summary
The first elements of the investigation showed that the rupture of a pipe at a tap (D 1 ") carrying synthesis gas at 200 bar near a compressor of the unit, would have caused a pneumatic burst at the origin of the perceived explosion. Another hypothesis would be the formation of a UVCE following the leak. The leaking synthesis gas, containing highly flammable H2, ignited on contact with air and spread around the pipe. The site was the subject of a July surprise exercise triggered by the prefecture simulating an NH3 leak and an accident due to pneumatic bursting on a pressure steam pipe had occurred on the same unit in June 2010 (ARIA 38831).
Consequences
Number of Injured Persons
1
Currency
Lessons Learned
Lessons Learned
Unknown
Event Nature
Emergency Action
8:50 Explosion, accompanied by abundant black smoke. The seven-men operation team on the site activates the emergency stop and evacuates the unit because of the risk of toxic leak, moving to the fall-back zone (reinforced control room). Some employees of neighbouring units ran to hide in their vehicles while others attend calmly to the subsequent fire. 9:15 The plant operator triggers the emergency plan around, alerts the public rescue service and the crisis unit of the prefecture, which was already operational, thanks to an ongoing emergency drill. The Firefighters mobilise 70 men, 25 vehicles and a mobile chemical intervention cell (CMIC).). They take over from the in-house firefighters who water the accident unit with 3 spears to prevent the spread of the fire. In the control room, the production team flushes the synthesis gas circuit with nitrogen in order to remove the H2 and stops the machines in the workshop while a lower secondary explosion is heard.The plant operator closes the water networks of the site to avoid pollution of the river Seine by the extinction water. 9:55 the fire dies out due to lack of fuel9:50 The gendarmerie and the inspection of IC arrived on the site. Toxicity measurements are performed in the unit and around the site by fixed and mobile sensors. Measurements carried downwind (10 km/h) around the site did not reveal a dangerous concentration; however, 200 ppm was measured at 10:07 to the machine room of the accident unit (toxicity threshold of 345 ppm for a 1 hour exposure). Characteristic NH3 odours were perceptible off site. 10:40 A press release from the prefecture announcing the smells, the absence of toxic effects and the control of the accident is sent, while an automatic telephone message informed the mayors of local communities. 10:55 the emergency plan is called off. 11:25, the NH3 concentrations are zero at the level of the accident unit, which has been put in cold stop. The operator holds a press conference with the prefecture for the benefit of the numerous local and national media who visited the site; information and photos of the accident taken by local residents were circulating on the Internet since 10 am. The management of the site apologized to the residents for the inconvenience caused by the accident. 11:50.Firefighters leave the site
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
ARIA data base
event no. 41025