A massive explosion destroyed a large storage tank
containing a mixture of sulphuric acid and flammable hydrocarbons at an oil
refinery. One contract worker was killed, eight others were injured, and
sulphuric acid from collapsed and damage tanks polluted the local river. The
explosion occurred during welding operations to repair a catwalk above the
sulphuric acid tank, when flammable hydrocarbon vapour was ignited by welding
sparks. This resulted in a powerful explosion inside the tank.
Key learning points
On the day of the accident, flammable gas testing was performed only at the
start of the hot work, but monitoring was not conducted for the duration of the
repair activities. It is also important as to where the explosive atmosphere
measurements were made. Through the five hours between the last gas test and the
explosion, the ambient temperature raised significantly. This warming caused
the hydrocarbons inside the tank to vapourise. The resulting flammable vapour
leaked out from corrosion holes in the tank into the work area. The company had
a hot work program that included written permits, but the program was inadequate.
Hot work was allowed near tanks that contained flammable materials without
continuous atmospheric monitoring and the control of welding sparks was not
required.
Source:IChemE
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