Gas release at the bulk terminals complex, Chicago, Illinois. 26th April
Bulk Terminals was a storage tank farm with 78 tanks ranging in size up
to 4900 m3. At about 12:30 hours on Friday 26 April 1974 a dull
thud was heard and fumes were seen rising from the bund surrounding a 3300 m3
tank of silicon tetrachloride. It was discovered that a pressure relief
valve on a 6-inch line leading to the tank had been inadvertently closed.
The pressure in the system was sufficient to burst a flexible coupling in
the line, shifting the piping system and cracking a 3-inch line on the tank
wall. Liquid silicon tetrachloride escaped forming an irritant cloud
containing hydrogen chloride gas.
The terminal management waited for the owners of the chemical to take
emergency action and the fire service did not respond, as there was no fire.
The EPA sent lime trucks to neutralise the chemical, but these were refused
entry to the site. By 15:00 hours the cloud was 400 m wide, 300-450 m high
and 1600 m long.
At 04:10 hours on Saturday 27 April, foam was added to blanket the liquid
in the bund but this failed. At 09:00 hours fuel oil was added along with
eight truck loads of lime. The vaporisation reduced dramatically and
operations began to transfer the liquid from the damaged tank. At 08:00
hours on Sunday 28th April, it began to rain. Power lines were corroded by
the hydrochloric acid in the rain, and four pumps became inoperable due to
corrosion before a general power failure stopped all pumping.
The materials added into it had reduced the capacity of the bund, and a
further pit had to be dug to take the overflow in the event of a full tank
failure. It was attempted to seal the leak on the tank using quick drying
cement. The first attempt failed and it wasn’t until 23:30 hours on Monday
29 April that the leak was sealed. It took until 3 May to empty the tank and
until 15 May before emissions had reduced to tolerable levels. One person
was killed, 160 hospitalised and 16,000 people were evacuated during this
Failures in technical measures
- Inadvertent closure of a pressure relief valve allowed the pressure to
rise causing the failure of a flexible connection.
- Relief Systems / Vent Systems:
relief valves, bursting discs
- Design Codes - Pipework: use of
- The site emergency plan was not developed, leading to a situation
where no-one knew whose responsibility it was to take action.
- Emergency Response / Spill Control:
site emergency plan
- The secondary containment was inadequate considering that blanketing
and absorbent materials would need to be added in the event of a major
- Secondary Containment: Bunds
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.