Apr 162014

fireextWill your handheld fire extinguisher go off with a satisfying, throaty whoosh when it’s needed or will you be greeted by a rather disappointing, geriatric dribble? It might if the fire extinguisher is getting on a bit and has been serviced with the wrong components suggests a United States Coastguard safety alert.

Issued this month the alert says: During a fire-fighting event, a crewmember attempted to use a 15 lb CO2 extinguisher,
but the extinguisher failed to properly discharge and only seeped from the neck of the extinguisher.
The fire was extinguished by another crewmember using a dry-chemical fire extinguisher.”

The investigators had the extinguisher examined at a fire-fighting equipment service center. They found that the hose and discharge horn had been replaced at an earlier time. The end of the hose screws on to a diffuser on the side of the discharge valve/handle assembly of the extinguisher.

The diffuser is a ported protrusion on the male end of a ninety degree fitting. On the side of the protrusion are orifices through which the CO2 flows. The examination revealed that the spherical end of the protrusion, which contains no orifices, bottomed out against the orifice in the connection fitting that leads to the hose and horn assembly. The flow of CO2 was thus completely blocked.

They also noted that the male threads of the diffuser were tapered US national pipe threads, while the female threads of the hose connection were straight. This difference likely allowed the hose connection to be tightened further than intended on the diffuser threads, permitting the spherical end of the diffuser to bottom out against the orifice in the tube. This may have also resulted in the reported leakage from the neck of the extinguisher due to back pressure.

Newer types of diffusers exist in which the orifice follows the length of the protrusion and the end is not spherical. However, the issues regarding the tightening of the two components and the importance of ensuring proper lengths and compatibility of the threaded and machined surfaces remain. Binding or bottoming out should not occur except at the threaded surfaces. Replacement parts should be as specified by the original manufacturer of the extinguisher.

No-one knows how common the problem actually is and the USCG concedes that this might be a one-off. It says: “It involved an older CO2 extinguisher with a hose and horn assembly that had been replaced. We do not advise owners/operators or vessel personnel to take apart or disassemble their extinguishers. Only technicians from fire equipment service companies should work on this equipment.

“The Coast Guard only advises that if owners/operators, based on visual examination of their equipment, believe there is a possibility of potential blockage of flow due to conditions as described above, they should contact a qualified fire equipment service company for more thorough examination, testing, and repair, if needed.

Find the USCG Safety Alert here

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