STATIC SPARK IGNITES FLAMMABLE ATMOSPHERE IN CHEMICAL DISTRIBUTION FACILITY

On October 29th, 2007 a fire and series of explosions caused the destruction of a chemical distributor’s warehousing facility in Des Moines, Iowa, resulting in the evacuation of local businesses and significant business interruption costs for the company involved.

The fire originated in the packaging area of the facility and was caused by an uncontrolled discharge of static electricity when a 300 gallon (1100 litre) Intermediate Bulk Container (IBC) was being filled with ethyl acetate.

An investigation carried out by the Chemical Safety Board concludes that an incendive spark discharge ignited the vapours emanating from the IBC. According to investigation report the IBC, pump and weighing scales on which the IBC had been situated were all grounded. However, the nozzle that was filling the IBC contained isolated conductive parts that accumulated static electricity during the filling operation. A metal weight suspended from the nozzle is also thought to have a potential source for the static discharge.

During the filling operation static electricity accumulated to such a level on the isolated components that it discharged to the grounded IBC igniting the flammable ethyl ether atmosphere. The operator heard a ‘popping’ noise just before the fire began which is likely to have been some of the energy released by the spark.

The ignition of the flammable atmosphere caused the filling nozzle to dislodge from the IBC and it continued discharging the ethyl ether into the fire, which spread to the rest of the storage area containing flammable and combustible materials.

In order to reduce the risk of incendive spark discharges igniting potentially flammable and combustible atmospheres:

• ensure that all conductive parts of the system including the container being filled, pipes, pumps, nozzles are properly grounded to international guidelines (NFPA 77 & Cenelec CLC/TR:50404).

• wherever possible only use material that is defined as conductive or static dissipative within potentially flammable or explosive atmospheres.

• control filling flow rates and avoid splash filling (Guidance Notice 51a issued by the Solvent Industry Association provides advice in this regard).

• only use equipment that is certified for use within flammable / explosive atmospheres, e.g. ATEX / FM / CSA.

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