Phillips 66, Pasadena, USA. 23rd October 1989

Accident summary

At approximately 1:00 p.m. on the 23rd October 1989 Phillips' 66 chemical complex at Pasadena, near Houston (USA) experienced a chemical release on the polyethylene plant. A flammable vapour cloud formed which subsequently ignited resulting in a massive vapour cloud explosion. Following this initial explosion there was a series of further explosions and fires.

The consequences of the explosions resulted in 23 fatalities and between 130 – 300 people were injured. Extensive damage to the plant facilities occurred.

The day before the incident scheduled maintenance work had begun to clear three of the six settling legs on a reactor. A specialist maintenance contractor was employed to carry out the work. A procedure was in place to isolate the leg to be worked on. During the clearing of No.2 settling leg part of the plug remained lodged in the pipework. A member of the team went to the control room to seek assistance. Shortly afterwards the release occurred. Approximately 2 minutes later the vapour cloud ignited.

Failings in technical measures

Both the company and industry safety required isolation by means of a double-block system or the use of blind flange. However, at a plant level a procedure had been adopted which did not comply with this.
Maintenance Procedures: isolation
The accident investigation established that the single isolating ball valve was actually open at the time of the release. The air hoses to the valve had been cross-connected so that the air supply that should have closed the valve actually opened it.
Maintenance Procedures: recommissioning
Site procedures laid down details that air hoses to valves were to be disconnected prior to maintenance work. This task was not carried out.
Maintenance Procedures: training/competence, management/supervision
The site held a large inventory of flammable materials under high pressure yet it had no fixed gas detection system.
Leak / Gas Detection: positioning of detectors
Ventilation intakes of buildings close to or downwind of the process plant were not arranged so as to prevent the intake of gas in the event of a release.
Plant Layout: positioning of occupied buildings
An effective permit to work (PTW) for both company employees and contractors was not enforced by the company.
Permit to Work Systems: working in hazardous areas
There was no dedicated fire water system. Firewater was drawn off from the process water system. This system was severely damaged in the explosions resulting in a loss of water pressure. The fire water pumps failed when the raging fires attacked their electrical supply cables. Of the three standby diesel pumps units, one was under maintenance and another ran out of fuel.
Active / Passive Fire Protection: testing and inspection
Some concern was expressed as to the audible level of the emergency alarm. It was likely that individuals in certain parts of the plant were unable to hear the siren.
Warning Signs: human factors
The intended control centre was damaged beyond use and telephone communications disrupted.
Emergency Response / Spill Control: site emergency plan
The location of the control room, separation distances between plant and escape routes (particularly for administrative staff) were all criticised.
Plant Layout: position of occupied buildings

References

Lees, F.P., 'Loss Prevention in the Process Industries – Hazard Identification, Assessment and Control', Volume 3, Appendix 1, Butterworth Heinemann, ISBN 0 7506 1547 8, 1996.