Do engine fires happen? Naturally aspirated, small diesels.

[stormalong]

Don't throw away your Halon extinguisher. Weigh it. Check if the weight is right. Write the date and weight on the extinguisher. You are good to go.

Repeat every couple of years, don't erase the prior weight record - just write the new date and weight beneath it. That shows a record of your diligence.

I have four Halon extinguishers on my boat that are over 35 years old. I have been boarded by the USCG twice. Both times they looked at the extinguishers, saw the date record and said nothing.

If you must throw it away send it to me instead. I'll pay shipping.

[SailingHarmonie]

Originally Posted by 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.

What is quoted here is a mix of half truths, that are not clearly presented, and quite out of context. Quoting from a google search is not the same as actually understanding the issues here.

The "Flash point" of any liquid is that temperature at which the VAPORS are ignitable. It actually has nothing to do with the liquid. Vapors of gasoline are much more dangerous than diesel at room temperature. Granted. BUT... the flash point of diesel fuel can be as low as 125F. That's not so very much higher than the temperatures in a typical engine room when the engine has been running for a few hours, so counting on the high flash point of diesel is not always a get out of jail free card. And there is more...

What is missing here is the most significant danger of diesel fuel. If you have ever seen the microscopic mist of diesel fuel that sprays from a cracked high pressure fuel line of a diesel engine, you have seen something that is every bit as dangerous as gasoline fumes. ANY spark or high temperature can ignite this mist of fuel in an explosive way, even if the temperature is far below the flash point.

Since diesel is handled at very high pressures in the fuel gallery (especially true with common rail engines, but not exclusively so) this danger is real. The fact that it is rare, does not mean it does not exist. Diesel dripping on a hot engine, evaporates and makes a flammable mix with air, even if the air temperature is below the flash point.

If you ignite an airborne mist of diesel fuel, it will explode with the violence of a gasoline fume explosion. Likely not something that an engine room fire suppression system can handle. But the idea that diesel is somehow so safe that fires are impossible is just wrong. They are LESS LIKELY, but most surely not impossible.

Soak a diesel spill into insulation, rag, foam, or paper and it can be lit just like any candle, and the fire will spread fast and furious. Try it. Soak a paper towel in diesel fuel, and touch a match to it. See what happens. Respect it.

I have taken those firefighting classes. We did not need any gasoline to ignite the diesel fuel pool. We just soaked a rag in diesel, lit it with a match and tossed it on the pool. The flames quickly spread across the surface, in a dense, yellow, sooty, smokey fire.

So, if you never spill diesel fuel, and never have electrical sparks, or hot spots, you will never have a fire. Are you taking bets on that?

Now, it's up to you if you want an automatic fire suppression system, or a fire port and a properly sized CO2 extinguisher. But it you do go the fire port route, be SURE that the CO2 extinguisher is large enough. Many of the ones I have seen on boats are criminally undersized and unlikely to actually extinguish a fire.

[chrisr]

Originally Posted by SailingHarmonie

...What is missing here is the most significant danger of diesel fuel. If you have ever seen the microscopic mist of diesel fuel that sprays from a cracked high pressure fuel line of a diesel engine, you have seen something that is every bit as dangerous as gasoline fumes. ANY spark or high temperature can ignite this mist of fuel in an explosive way, even if the temperature is far below the flash point...

agree with this point completely (i referred to it in another post)

however

it is my understanding that this is much more a problem on large marine diesels (> 1000bhp) as on these engines they will continue to run with a cracked HP line on one unit. thus fuel continues to spray and ignite (ask me how i know...)

on the small diesels we are talking about here, a leaking HP line on one cylinder will almost certainly stop the engine. you might be unlucky enough to get a flash, but there won't be a continuous stream of fuel so (probably) no ongoing fire

as said : my understanding from 60 years seagoing experience...but no mechanic and may be i'm wrong

cheers,

[Pete7]

Originally Posted by stormalong

Don't throw away your Halon extinguisher. Weigh it. Check if the weight is right. Write the date and weight on the extinguisher. You are good to go.

You are aware of the Montreal Protocol which the US signed up to? There is no legitimate reason why you need to keep Halon on board a leisure yacht, nice yacht btw :thumb when they can be be replaced with far more environmentally safe agents today. Don't get me wrong, I am not an all out tree hugger, but do try to do my bit for the environment. Removal and proper disposal of Halon is an easy win for anyone in a first world country that can afford a yacht.

Originally Posted by Jeff on Aurora

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. Jeff

Jeff, no idea why you need to install $1k worth of extinguisher in the engine compartment. We have one of these:

https://www.marinesuperstore.com/fir...e-extinguisher

In addition we have a good selection of AFFF and CO2 extinguishers on board, plus a bucket and a liferaft.

[GordMay]

Originally Posted by GordMay

... The flashpoint of a fuel is the lowest temperature, at which it can form an ignitable mix with air. ....

Originally Posted by SailingHarmonie

...
The "Flash point" of any liquid is that temperature at which the VAPORS are ignitable. It actually has nothing to do with the liquid ...

Thanks for the supplemental contribution.
I’m sorry, if I was unclear.
A “mixture with air” implies a “Vapour”.

A better [but not scientifically complete] definition, than I previously offered:
“The flash point is the lowest temperature, at which the vapour, formed above a pool of liquid, can be ignited [external ignition source] in air, at atmospheric pressure [101.3 kPa/760 mm Hg], under specified test conditions.”

The flash point temperature determines the tendency, of the test specimen [liquid diesel fuel], to form a flammable mixture with air [vapour], when under these controlled laboratory conditions.

Several ASTM standards, for the determination of the flash point [flammability] of petroleum and petroleum products exist. An important method is ASTM D 93 [Pensky-Martens Method], because it is used for the specification of Diesel and aviation turbine fuels.

ASTM D93-20
Standard Test Methods for Flash Point by Pensky-Martens Closed Cup Tester

”The flash point temperature is one measure of the tendency of the test specimen to form a flammable mixture with air under controlled laboratory conditions. It is only one of a number of properties which must be considered in assessing the overall flammability hazard of a material ... “

ASTM D93 ➥ https://www.astm.org/d0093-20.html
ASTM D93 ➥ https://www.astm.org/d6450-16ar21.html

See also ➥ The MSDS HyperGlossary: Flash Point


The enthalpy change, for a combustion reaction, is always negative.
In other words, fire is hot.

Q: What do you call a sacred, flammable piece of wood?
A: A match, made in Heaven.

[stormalong]

Originally Posted by Pete7

You are aware of the Montreal Protocol which the US signed up to? There is no legitimate reason why you need to keep Halon on board a leisure yacht, nice yacht btw :thumb when they can be be replaced with far more environmentally safe agents today. Don't get me wrong, I am not an all out tree hugger, but do try to do my bit for the environment. Removal and proper disposal of Halon is an easy win for anyone in a first world country that can afford a yacht.

There is no legal requirement to replace a Halon fire extinguisher. No ban on the use of an old one. And no environmental impact of an unused extinguisher. New Halon manufacture is banned.

So you can keep your old extinguisher in case you need it. Just be sure it is in working condition. Once used throw away the thing.

https://www.kauffmanco.net/blog/when...-halon-system/

[chrisr]

another thought that comes to mind when considering a diesel fire

we have a pair of 3JH yanmars, which flat out use about 3L per hour. this equates to about 50ml per minute, or say 17ml per cylinder per minute (remember this is flat stick...usual cruising will be less)

so in the event of a leakage on the HP fuel line on one cylinder, there will be about 17ml spraying out per minute

(have a look at a syringe or similar to remind how small is 17ml !)

now i'm not certain but i'm reasonably sure that if one cylinder is not firing my engines would stop. perhaps somebody can comment ? certainly a twin would stop ??

at the very least the different engine note and vibration is going to attract immediate attention, but lets say you are asleep and it takes 30 mins to notice. in my 3 cylinder engines, this would mean say 500ml of fuel sprayed out

but this fuel is not going to stay atomised...it will revert to fully liquid state quickly and may not ignite easily in this state

bottom line is that imho while a cracked HP line can spray out some atomised fuel that will be easily ignited, the quantity involved is going to be very very small. this is going to have a big affect on any resultant fire and what needs to be done to put it out

cheers,

[skipperpete]

Engine room fires aboard yachts rarely occur due to cracked high pressure injector pipes or fuel leaks because the wet exhaust system and water cooled exhaust manifold and turbo jacket remove the most significant source of ignition. I’m more concerned about the rarely discussed collateral damage from using Halon and Co2 on yachts. I was witness to an uncommanded Halon release on a large charter cat here in Australia that left the vessel dead in the water with a full complement of guests and crew.... unable to be restarted by the engineer and more recently there was a report and video of a Viking 92 sports fisherman that reportedly had the same accidental discharge and loss of all engine power that resulted in the vessel being stranded on a beach.... the poor guys on board could not only NOT restore power by restarting the engines and generators, they also were unable to release an anchor. If an engine is instantly stopped under full power by an engine room snuffer the turbo is unlikely to escape undamaged (it’s why we use turbo timers) and that’s just the most obvious side effect. I dislike working in machinery spaces where an accidental activation of the fire fighting system FOR ANY REASON is possible and especially dislike the off the shelf automatic systems installed by amateurs on yachts.
Electrical fires are far more likely than diesel and of these I’ve seen a few, one with total loss of the vessel, another with flames as high as the first spreaders.

[Cheechako]

I think batteries/cables are the much higher risk than the engine itself. But if you lose your impellor, the exhaust can get hot enough to ignite the rubber exhaust hose I imagine. Put a "snap disc" heat switch on your exhaust with an audible alarm. Cheap and easy.

And, you can throw a lighted stick match into a bucket of diesel and it wont ignite....

[Kettlewell]

If you stop the diesel engine with its normal shutoff what's going to sustain the fire? No fuel will be pumped, and presumably the tanks are located well away from the engine. It would have to be other stuff burning, which means ordinary fire extinguishers would do the trick. In other words, fire detected, shut the engine down, switch off the main battery switch to cut off electrics, and then fight the fire with ordinary fire extinguishers.

[stormalong]

Originally Posted by Kettlewell

If you stop the diesel engine with its normal shutoff what's going to sustain the fire? No fuel will be pumped, and presumably the tanks are located well away from the engine. It would have to be other stuff burning, which means ordinary fire extinguishers would do the trick. In other words, fire detected, shut the engine down, switch off the main battery switch to cut off electrics, and then fight the fire with ordinary fire extinguishers.

Many automatic fire extinguishers have a switch that can shut down the engine when they discharge. By the time a person recognizes that there is a fire and shut down the engine the fire could be too far advanced to risk opening the engine space. My battery switches are in the engine space and I'll bet many other boats are the same way.

Some boats have a fire port to discharge an extinguisher into the engine space in case of fire. Mine does not. Does yours?

Yes, of course I could add a fire port but with an automatic engine shutdown and extinguisher discharge the fire could be out before anyone even knew there was a fire.

[boatpoker]

Originally Posted by stormalong

My battery switches are in the engine space and I'll bet many other boats are the same way.

Poor, incorrect and illegal battery installations are by far the most common cause of recommendations in my survey reports over the last 30 years.

The vast majority of boat fires start in the DC wiring in the engine compartment. Shutting down the engine will have no effect on these.

Transport Canada TP1332E and ABYC “AC & DC Electrical Systems” require that battery disconnect switch be readily accessible. TP1332E defines readily accessible as “means capable of being reached for inspection, maintenance or usage under emergency conditions”. US CFR's are silent on the issue.

In case of engine compartment fire, one of the first actions recommended is to turn off the battery switches. Opening the engine compartment to turn off the batteries is the last thing you want to do.

[Bowdrie]

Originally Posted by Pete7

You are aware of the Montreal Protocol which the US signed up to? There is no legitimate reason why you need to keep Halon on board a leisure yacht, nice yacht btw :thumb when they can be be replaced with far more environmentally safe agents today. Don't get me wrong, I am not an all out tree hugger, but do try to do my bit for the environment. Removal and proper disposal of Halon is an easy win for anyone in a first world country that can afford a yacht.

I've a couple of the Halon units that are still usable, and no, I'll not get rid of them.
If there's a fire my first consideration is for the "environment" on the boat.
Even with very little fire damage you'll be heartbroken over the mess that the dry chemical stuff leaves.
I do like CO2.

[boatpoker]

Originally Posted by Pete7

Removal and proper disposal of Halon is an easy win for anyone in a first world country that can afford a yacht.

You do realize I'm sure that "properly disposed halon" is sold back into the market place right ?

[chrisr]

regarding turning off battery switches : if you want to shut down all current in the system these days it will also be necessary to disconnect the solar panels

cheers,