Safety Digest
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Case 11
Explosion in Gas Compressor

Narrative

Location mapLinda Kosan was a 2,223gt liquid gas carrier, registered in Denmark, which suffered an explosion and fire while on passage down the English Channel. The Danish authorities investigated the incident and this article is based on their report.

The vessel had loaded 320 tonnes of propane initially, followed by 640 tonnes of butane, at Fawley near Southampton. During loading, the vessel’s cargo cooling system was in operation. After loading, the vessel sailed for Douglas, Isle of Man.

On passage west down the English Channel, the mate began a planned leak test on the condenser of the starboard cargo-cooling unit. He had previously drained the condenser of liquid butane, which was the last cargo to be loaded.

The intended test method was to pressurise the condenser with air to 15 bar using the system’s compressor, and measure any drop in pressure.

To remove butane from the system, he closed the gas outlet from the condenser, opened the inlet of the compressor to atmosphere, and ran the compressor to pump air into the condenser to a pressure of 3 bar. This was enough to allow butane to condense and be drained. The procedure was repeated several times.

Judging the unit to be gas free, the mate ran the compressor and gradually raised the condenser’s pressure to 15 bar. He then stopped the compressor, and began to close the inlet valve to the condenser. Just as he did so, there was a powerful explosion followed by a fire breaking out in the compressor room, which was on deck.

Seeing these events from the wheelhouse, the master immediately activated the deck sprinkler system. The mate and chief engineer began to tackle the fire using hoses. The remainder of the crew was mustered to assist them, and Brixham Coastguard was alerted.

Fire and medical personnel were airlifted to the vessel, but the crew had successfully controlled the fire. One person needed slight medical treatment.

After the fire was extinguished, the starboard compressor and associated piping were found to be badly damaged by the explosion. However, damage did not extend outside the compressor room.

The Lessons

1. By compressing air to 15 bar, a temperature above the auto-ignition temperature of butane was generated. With traces of butane still in the system such as that remaining in the compressor’s lubricating oil, an explosive mixture was generated in the compressor.

2. This procedure did not comply with the owner’s instructions for leak testing, which specified that propane should be the medium used to pressurise the condenser, not air.

3. This explosion resulted from incorrect procedures being followed, and could have caused serious injury or loss of life. Changes to well-established system operating procedures should always be very carefully considered where the consequences of a system failure could be serious.

4. Once the fire had started, the crew acted extremely quickly and resourcefully to contain and extinguish it, so preventing it from developing into a major accident. Prompt and disciplined action paid off.