Do engine fires happen? Naturally aspirated, small diesels.

[Jeff on Aurora]

Does anyone have first hand knowledge of an engine compartment fire caused by a small (say under 100-ish hp) non-turbo diesel on a sailboat?

I'm about to replace the the 20 y/o Fireboy automatic halon extinguisher in my engine compartment. Wow! Talk about sticker shock!! A new extinguisher and cable are almost $1k. I will spend the money to have a safe vessel, but there may be other issues to address where the money is better spent. I'm not feeling a huge risk of engine compartment fire.


Personally, I have first-hand knowledge of two engine room fires, but both were on large hp diesels (approx 45' sport fish boats) and turbocharger failure was the suspected source of ignition. One of these boats went from "Hey, do you guys smell smoke?" to a completely engulfed vessel in less than five minutes.

I have been around diesel powered sailboats for three decades and have yet to hear of a serious engine compartment fire. Sure, there have been plenty of fuel system leaks that resulted in a complete mess and the engine stopping, but none led to a fire. How would one ignite diesel anyway unless 1) fuel or compressed fuel vapor was spilling and 2) there was some very hot ignition source like an electrical fire?



Thanks in advance,


Jeff

[Calif.Ted]

During training for flammable liquid fires we had a large concrete "wading" pool filled with diesel. To ignite 5 gallons of gasoline were floated on top and lit. As the gas burned it got the diesel up to ignition temperature. I have seen an inch of diesel filling the area below a running engine on a sailboat without ignition.

[chrisr]

there have been many cases onboard ships where high pressure diesel is sprayed onto a hot exhaust and catches fires, however i don't think this is possible on a yacht engine (??)

we once had a major diesel leak on one engine, and the only problem was the auto bilge pump pumping 200L of diesel overboard and the engine stopping

can certainly imagine an electrical fire in an engine bay, but without petrol it may take some time to get hot enough to ignite liquid diesel (210 deg C)

cheers,

[diverd]

An electrical fire in the engine bay is the most likely ignition source, and it would need to be very hot for a while to get the diesel fuel going. Regardless of the fuel the electrics are generally the issue.

Though the extinguisher is ideal to knock a fire back / down, an electrical kill will often stop the fire and i went for both, a battery kill in a place i can get to it without being in the engine bay and and extinguisher.

To answer your question, 30 years in the fire service and i dont remember a singler fire in small diesel engines. I expect they will happen, but in the 3 harbours and 2 marinas i covered in my career i dont remember any.

hope this helps

[Kettlewell]

So, I've wondered this ever since I had a small leak in an injector return line that was spraying atomized diesel into the engine compartment while the engine was quite hot. I only noticed it because of the smell. No fire.

[Iron E]

Originally Posted by Calif.Ted

During training for flammable liquid fires we had a large concrete "wading" pool filled with diesel. To ignite 5 gallons of gasoline were floated on top and lit. As the gas burned it got the diesel up to ignition temperature.

Yeah, that was a blast... Cape May?

Also, to OP... Electrical fires may be of concern

[thinwater]

Yes. A starter wire ignited the fiberglass. They were on board, saw the smoke, and also saw the sparking that was causing it.

[Lepke]

Even black old NS bunker oil will ignite when sprayed on a hot object. The auto ignition point for #2 diesel is 410°F to 536°F. Measure the exhaust ports on your engine during a long run and it's probably that temp, even higher with a turbo.
If an injector tube were to split, it makes a nice spray.

[rslifkin]

With a fuel leak under high pressure, whether you get a fire or just a mess is all a bit of luck in what the fuel spray hits. Any engine can cause a fire if things fail in the right way.

[Tin Tin]

Runaways look bad

https://www.youtube.com/watch?v=k_wPMQJ_nNI

[boatpoker]

Installing a fire port (about $15) rather than an automatic system in the engine compartment meets ABYC Standard A-4 Fire Fighting Equipment.

[GordMay]

Diesel is used in a high-compression engine. Air is compressed, until it is heated above the autoignition temperature of diesel. Then, the fuel is injected, as a high pressure spray. There is no ignition source. As a result, diesel is required to have a high flash point, and a low autoignition temperature.

The flashpoint of a fuel is the lowest temperature, at which it can form an ignitable mix with air. The high flash point in diesel fuel means that it does not burn as easily as gasoline, which is a safety factor. Too low of a flash point is a fire hazard, because ignition may continue, and lead to explosion.

Autoignition temperature is the temperature at which a substance can be brought to flames, without any sort of external force, such as a flame or spark.

[Tin Tin]

Having just re-watched that video about runaways and then some more research I have just ordered a CO2 extinguisher. My engines rooms have fire ports so probably no need to open the hatch (catamaran)

[Hope123]

You should be careful about safety because diesel requires high pressure or temperature to ignite and in most cases fuel system leaks and that can lead you towards a mess rather then a fire. So be careful.

[Grattaway]

Boat poker has your answer
Fire port is a better solution
it is both much cheaper and unlimited in what you can use to suppress/extinguish a fire

FWIW -here in NZ they have reduced the "life" of extinguishers where required in business premises as problems have arisen with "clumping" of ingredients in the bottom of the extinguishers. It has also been recommended by our Wormald service agent that we remove them from their mounts every year, invert and "tap" the bottoms with a plastic or rubber mallet to avoid this.