Explosion and fire at DSM, Beek. 7th November 1975

Accident summary

Early on 7 November 1975, start-up of the Naphtha cracker commenced on the ethylene plant at the Dutch State Mines (DSM) works at Beek. At 06:00 hours compressed gas was sent to the low temperature system. At 09:48 hours an escape of vapour occurred from the depropaniser which ignited, resulting in a massive vapour cloud explosion. The explosion caused significant damage and started numerous fires around the plant. 14 people were killed and a total of 107 people injured, three of whom were outside of the site.

The investigation was hampered by the destruction of instrument records in the incident but evidence suggested that the release was due to low temperature embrittlement at the depropaniser feed drum. It was thought that the initial fracture had occurred on a 40 mm pipe connecting the feed drum to its relief valve. The normal operating temperature of the drum was 65°C, however, due to a process upset in the de-ethaniser column, the stream feeding into the depropaniser drum was a liquid at about 0°C(or lower) with a high C2 content. This would flash within the drum resulting in a temperature which could be as low as -10°C. The feed drum material could normally be used at temperatures as low as -20°C, however the fracture occurred at a weld, which with ageing may fail at up to 0°C.

The raising of the alarm was also flawed. The first operator to enter the control room to report the gas release was distressed and shocked. A second operator left the room to investigate, leaving orders for the fire alarm to be sounded. This did not occur. Some witnesses stated that the alarm system failed, but the investigation found that the system was in good working order before the explosion, and that none of the button switches had been operated.

Failures in technical measures

• The large deviation in process temperature from the normal operating conditions experienced in this instance meant that the structural integrity of the vessel was compromised at its weakest point.
• Design Codes - Plant: Suitability to withstand foreseeable temperature and pressure over whole life of plant
• The emergency response failed on so far as raising the alarm efficiently. Phone lines to DSM were also overloaded, however fortunately the rescue services had their own channels of communication.
• Emergency Response / Spill Control: site emergency plan, emergency operating procedures, training

References

FP Lees, 'Loss prevention in the process industries – Hazard identification, assessment and control', Volume 3, Appendix 1, Butterworth Heinemann, ISBN 0 7506 1547 8, 1996.