The Story

Shipboard emergency systems may depend on other ship's systems for their proper operation. For example, fire protection systems may require external power sources, piping systems, or control networks. Failure of these "support" systems can reduce the fire protection system's efficiency or even render it useless. A fire onboard a U.S. Naval vessel illustrates this clearly.

In October 1972, the research vessel USNS SILAS BENT was standing at anchor in the Pacific when an explosion and fire occurred in a space housing a gas turbine. The fire reportedly was caused by a leak in the pressure regulating diaphragm on the turbine generator fuel boost pump.

The leaking diesel fuel sprayed onto the lagging about the turbine exhaust lines which in turn ignited, and caused the combustible mixture within the space to explode.

At the time of the fire, the vessel had been operating with the emergency standby generator out of service.

At the outbreak of the fire, the ship's crew attempted to use the installed total flooding carbon dioxide system. Because of a failure in the control linkage, the remote release would not activate the system. The system could have been operated from the carbon dioxide storage room; but the ship's crew were not totally familiar with the system and could not activate it. Additional efforts were made to gain control of the fire using the portable extinguishers located throughout the machinery space. These were without success.

They attempted to control the fire using water spray. However, the power drive for the fire pumps was not operable. The fire pumps are powered by electric motors, and because of the fire, no electric current was available aboard the vessel. Normally the emergency standby generator would have been put into operation, but it had been out of service for some time. When the fire occurred, the turbine generator was being operated in parallel with the No. 1 diesel generator. The fire caused the turbine generator to shut down, which in turn caused an excessive load to be placed upon the diesel generator which tripped off the line shutting both generators down.

The electrical distribution panel had been so arranged as to prevent the inadvertent simultaneous operation of the main generator with the auxiliary generator. Because of this arrangement, the auxiliary generator could not be used to operate the fire pumps, so the electrical distribution panel was rewired and the No. 1 diesel generator restarted and switched onto the line. The fire pumps were started and control of the fire was gained using water.

Lesson Learned

Two systems failures are evident in this incident. Not only did the mechanical system fail, the people failed as well. When a fire protection or other emergency system is designed, it is intended to be highly dependable under expected operating conditions. Unfortunately, the unexpected is often encountered during emergencies. The crew who operate the system must therefore have a basic understanding of how the system works so that improvised modes of operation come readily to their minds under emergency conditions. Should an emergency system fail, existing alternate systems should be tried. Should the alternate systems fail, resort must be had to improvised methods of averting disaster. In the casualty described above, the carbon dioxide system did not operate because the remote release mechanism failed. The alternate method of releasing the agent existed, but was not known by the crew. Instructions which would have explained the existence and operation of this alternative were not posted on the ship. The fire pumps could not be operated because a generator was not available to supply current. A standby source of current should have been maintained while the emergency generator was out of service.