Explosion in a Polyethylene Manufacturing Plant
In a polyethylene manufacturing plant, the explosion of a flammable cloud (isobutane, ethylene, hexane and hydrogen) escaped from a reactor during maintenance caused 23 fatalities and 314 injured workers. The explosion is equivalent to that of 2.4 t TNT and comparable to an earthquake of 3.5 on the Richter scale.The main explosion was followed by multiple other explosions (including those of 2 isobutane tanks) and fires which will only be under control after 10 hrs of emergency response. This long time was due to water supply difficulties, from not availability of power to too low pressure in the line. The accident occurred while a maintenance operation, carried out by a specialized subcontracting company, had started since the previous day: the aim was to clean up settling branches connected to the manufacturing reactor during operation. These branches allow the polymer deposits to be recovered so that they do not clog the reactor. A specific procedure has been defined for this operation, specifying in particular that the branches must be isolated by ball valves (actuated by compressed air) placed between them and the reactor.The investigation carried have shown that the accident resulted from the rejection of 40 tonnes of process gas to the atmosphere (99% of the reactor content) via an isolation valve of a settling branch that remained open, and which ignited within 90 to 120 sec on contact with one of the multiple sources of ignition nearby. The opening of the valve is due to the reversal of the connections of the compressed air pipes actuating it (error prior to the operation in progress): the valve was open while the actuator in the control room indicated that it was closed. However, safety standards require that in the event of an intervention on an operating reactor, the isolation device consists of a double valve or a closed flange, which was not provided for in the intervention procedure. The workshop was devoid of gas detectors.
Event Date
October 23, 1989
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Cause Comments
Immediate cause was the release of process gas during maintenance on a blocked reaction loop line. The instrument line to a shut valve was being connected when the valve opened and the massive release occurred. The valve actuating hoses were found connected the wrong way round.Root cause is an inadequate maintenance Contributing cause is the malfunctioning of the fire-extinction water system
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
Reaction vessel, line and valve
Storage/Process Medium
Location Type
Location description
Industrial Area
Pre-event Summary
The accident resulted from a release of process gas during maintenance on a blocked reaction loop line. The instrument line to a shut valve was being connected when the valve opened and the massive release occurred.
Lessons Learned
Lessons Learned
Lessons:1. The company had made no use of hazard analysis or an equivalent method to identify and assess the hazards of the installation.2. Separation distances between process equipment plant did not accord with accepted engineering practice and did not allow time for personnel to leave the plant safely during the initial vapour release and that the separation distance between the control room and the reactors was insufficient to allow emergency shut down procedures to be carried out.3. The ventilation intakes of buildings close to or downwind of the hydrocarbon processing plants were not arranged so as to prevent intake of gas in the event of a release.4. There was a failure to minimize the exposure of personnel.5. The plant had no fixed flammable gas detection system despite the fact that the plant had a large inventory of flammable materials held at high pressure and temperature.6. An effective permit system was not enforced for the control of the maintenance activities.7. The sole isolation was a ball valve which was meant to be closed but was in fact open. There was no double block system or blind flange. The practice of not providing positive isolation was a local one and violated corporate procedures. 8. The practice of relying for fire water on the process water system and the failure to provide a dedicated fire water system meant that the fire water system was vulnerable to an explosion.
Event Nature
Emergency Action
fires which will only be under control after 10 hrs of emergency response. This long time was due to water supply difficulties: the water line for fire was not separate from that of process water which was destroyed by the explosion. On top of that, the pressure was insufficient and the shut-off valves inaccessible due to the multiple fires. Since the fire had destroyed the electric cables supplying power to the water pumps, these remained inoperative. Out of the 3 diesel backup pumps, one was out of service and a second broke down after 1 hour of operation.
Release Type
Release Substance
Ignition Source
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
U.S. Fire Administration/Technical Report Series
USFA-TR-035/October 1989
ARIA event 891
https://www.aria.developpement-durable.gouv.fr/accident/891/
(accessed 2020)