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ACCIDENTS AND FINDINGS

FIONA (31 August 1988)

The forward cargo tank of the FIONA exploded while a surveyor measured cargo temperature prior to unloading, resulting in one death. The National Transportation Safety Board (NTSB) concluded that

• A steam leak in the tank caused static charge to be generated
• The charge accumulated on an ungrounded temperature probe and discharged as the probe was withdrawn from the tank,
• The resulting sparks ignited explosive vapors from the residue of the tank's previous cargo [9].

NTSB's recommendations addressed the foregoing items and other contributory factors:

• FIONA's cargo tanks should have been inerted.
• Inert gas system (IGS) should be used with all cargoes unless tanks are gas free.
• The main source of the explosive vapors was contamination of the cargo by previous condensate cargo, while release of light hydrocarbons by the fuel oil in the tank may have been contributory.
• Masters of vessels carrying Grade E cargoes should certify that explosive vapors are not present prior to sampling or measuring cargoes with a combustible gas indicator device.
• The static charge was generated by a steam leak in the cargo heating pipes and accumulated on an ungrounded temperature probe. Better maintenance might have prevented the casualty. · The probe lacked a precautionary nameplate stating the, need for grounding the instrument during use. Underwriters Laboratory UL) should adopt the Canadian Standards Association requirement for such a nameplate. The internal grounding wiring on these probes should also be checked periodically.

AMERICAN EAGLE (26, 27 February 1984)

The AMERICAN EAGLE, sailing in ballast, exploded and sank in the Gulf of Mexico with the loss of four lives. The NTSB concluded that the most probable cause of the explosion was the use of a steam powered air ventilator fitted with a long plastic sleeve in a non-gas free tank

The ship had been carrying fuel oil and gasoline. The tank in question had been washed, but not gas freed; an explosive mixture in the tank was possible.

The probable cause of ignition was an incentive spark between the tank structure and charged steam condensate falling from the plastic sleeve through which the air was being driven.

The crew was unaware of the clear warning against the introduction of steam into potentially explosive atmospheres. The use of non-conductive material contributed to the accumulation of static charge.

As a result of the accident, NTSB recommended that "A Manual for the Safe Handling of Flammable and Combustible Liquids and Other Hazardous Products", be revised to thoroughly address static electricity hazards on tank vessels.