Case 8
Air Compressor Blows UpNarrative
A watchkeeping engineer had completed some maintenance tasks on the outboard air start compressor on RFA Fort Austin. He then prepared it for use as the duty machine and shut down the other, inboard compressor.
Initially he had some difficulty starting the outboard compressor, but eventually did so locally on manual control.
With the outboard compressor running, he had further difficulty closing its second stage drain valve, but another engineer managed to do so. No sooner had he done this, than the compressor’s second stage cooler burst to pressurise the water jacket. This then ruptured, throwing debris across the engine room.
The compressor’s second stage safety valve did not operate.
The largest piece of flying debris was from the water jacket and measured approximately 500mm x 250mm. One engineer was slightly injured by another, smaller piece.
On examination, it was found that the outlet valve from the compressor’s second stage was closed, and the safety valve on it was fouled with carbon deposits. It could not, however, be established whether these had prevented the valve lifting.
The Lessons
1. Both engineers were experienced in preparing a compressor for duty. The operation had probably become so routine that limited thought was applied to the task; as shown by the outlet valve being left closed. The potential consequences of allowing simple routine tasks to be performed on ‘autopilot’ are demonstrated by this incident.
2. The safety valve was fitted to the compressor as protection against the consequences of operator errors such as this. Its failure gave the engineers no warning of its over-pressurisation. Had it done so, it is probable that they would have discovered the closed outlet valve and quickly corrected the situation. The importance of routinely testing and properly maintaining safety devices of this type is clear.