Methods of extinguishing Scavenge Fires
Once a scavenge fire starts, hit the engine room emergency button, reduce the engine to its slowest possible revolutions this will limit the amount of fuel oil being admitted to the cylinders. It will also reduce the amount of combustion air to the cylinders, lowering the oxygen content being supplied to the scavenge fire.
The fuel must be isolated to the cylinder in which the fire is occurring by lifting the relative fuel pump plunger clear of the operating cam. The bridge should be informed and the engine room telegraph put to dead slow ahead, recording the times and the movements in the log book for future reference.
This may seem a lot to do at once, but I have had some serious scavenge fires while senior watch keeper on Sulzer two-stroke main engines and it can be done with a little help from the recently startled off-duty engineers (we have all been awakened by the banshee wail of the engine emergency siren and subsequent slowing down of the engine beat)
The watch keepers The senior engineer should remain at the controls, junior engineer adjusts the seawater to the lube oil and jacket coolers maintaining operating temperatures.
Other Engineers The rest of engineers should operate scavenge CO2 or mist sprays if fitted, Isolate the fuel by lifting the pump piston rod of the offending cylinders fuel pump cam, increases lube oil to that cylinder by hand operating the lubricator to prevent the piston seizing and, keep an eye on the exhaust condition out of the flu, scavenge door temperature and drains to sludge tank. Once the greasers have cleaned out the scavenge space, the senior engineer should inspect the piston rod and gland for signs of excessive scorching. The gland may need stripping if the springs holding the scraping rings have lost their tension through heat from the burning oil; excessive oil usually accumulating around this area. Excessive scorching will be evident by the blue color of the gland top keep ring and set screws.
Engine room Greasers - Once it has been determined that the fire has been extinguished, and the scavenge space has cooled enough for cleaning, the scavenge inspection doors should be slowly and carefully removed. The resultant carbon residue and fuel oil can now scraped away then cleaned using rags leaving the space dry and clean. The exhaust gas boiler should be fired up to maintain boiler steam pressure and the offending cylinder lube oil reservoir kept topped up.
Note: It is many, many years since I was a seagoing engineer, so please allow for a bit of age and alcohol related brain damage to this old retired Irish marine engineer, I would be pleased to answer any relevant queries through the comments section at the end of the article.