What fire extinguisher in my engine bay?

[mucklestone]

I am rebuilding an old fletcher speedboat which has a Mercruiser sterndrive 3.0 petrol engine.

I would like to add an automatic fire extinguisher in the engine bay for obvious reasons.

What type of fire extinguisher do I need and where should I mount it?

Most seem to be powder type. Do they need to be mounted above the engine? Like most installations there is little space above the engine. Would mounting it on the bulkhead in front of the engine be ok?

 

[harvey38]

An auto powder extinguisher will do the job but will also kill the engine once it has ingested the powder. If you do a Google search for clean agent fire extinguisher, they seem to be the way to go these days.

 

[Jamie Dundee]

Something like this

 

[geem]

Dry powder won't do any harm to an engine assuming you have proper filtration on the carb intake. The most important thing is to put the fire out.
If you use an automatic extinguisher, they are heat activated so need to be above the fire and therefore probably above the engine.
The spray pattern from the exstingisher head is hemispherical so any thing in the way will reduce its effectiveness. If you can't fit one above the engine it may be better to carry a handheld exstingisher mounted elsewhere

 

[Stemar]

Another tip I've seen is to have a small hole into the engine compartment where you can squirt a hand held extinguisher. Cover it with a keyhole cover. The last thing you want to do in the event of a fire in an enclosed space is open a hatch - google flashover

 

[mucklestone]

So looks like I need a clean agent one or risk the engine if it accidentally went off. Guarantee if I go for a cheaper standard one it will go off accidentally and if I pay the extra it never will lol

Still confused as to the location. Looks like they generally have to be vertically mounted. How do people every get the output nozzle above the engine? It's a typical sterndrive installation with a sun pad above.

 

[Jamie Dundee]

So looks like I need a clean agent one or risk the engine if it accidentally went off. Guarantee if I go for a cheaper standard one it will go off accidentally and if I pay the extra it never will lol

Still confused as to the location. Looks like they generally have to be vertically mounted. How do people every get the output nozzle above the engine? It's a typical sterndrive installation with a sun pad above.

A clean agent extinguisher doesn’t need to be mounted above the engine. It works by depriving fire and engine with oxygen so needs to be sized with regard to the size of your engine room. Mine is mounted alongside the engine, it is also a requirement of my insurance that I have an auto extinguisher fitted.

 

[geem]

So looks like I need a clean agent one or risk the engine if it accidentally went off. Guarantee if I go for a cheaper standard one it will go off accidentally and if I pay the extra it never will lol

Still confused as to the location. Looks like they generally have to be vertically mounted. How do people every get the output nozzle above the engine? It's a typical sterndrive installation with a sun pad above.

This is what I have.

 

[mucklestone]

That looks more like it, thanks for the photo. Mine would have to be a similar location.

Nice clean engine bay you have there.

 

[penberth3]

An auto powder extinguisher will do the job but will also kill the engine once it has ingested the powder.......

The old wives tale again! If you have an engine fire, first thing to do is shut down the engine. Then it doesn't ingest powder or anything else.

 

[harvey38]

The old wives tale again! If you have an engine fire, first thing to do is shut down the engine. Then it doesn't ingest powder or anything else.

If you know you have a fire!

 

[srm]

If you have an engine fire, first thing to do is shut down the engine. Then it doesn't ingest powder or anything else.

How will you know there is a fire? Once you see smoke or flames from around a petrol engine bay its probably time to abandon ship, even if you have shut off the engine.

An automatic extinguisher may well detect the fire and and flood the compartment before you realise that there is a problem. Any ventilation fans should also be turned off to prevent venting the extinguishing medium as otherwise there is a risk of reignition.

As to mounting an extinguisher, the instructions with my conventionally shaped automatic extinguisher was for the head to be 20 degrees or more below the horizontal. I would suggest on the carb side of the engine bay as being the higher risk area for a petrol engine.

 

[mucklestone]

My feeling was for the carb side of the engine but looking at pictures many seem to be the other side near the fuel pump

 

[srm]

My feeling was for the carb side of the engine but looking at pictures many seem to be the other side near the fuel pump

In a tight engine bay it will probably come down to where there is sufficient space and the configuration. I would try to keep the sensor away from the exhaust manifold as this will normally be the hottest area. A fire will cause a quick build up of heat so near the top of the bay should do. You also need to consider the volume of the engine bay and ensure the extinguisher has capacity to fill the bay with some to spare.

 

[colind3782]

I've fitted one of these which looks a lot nicer than just a drilled hole with a plywood cover:

Fire Port - Stainless Steel or White - Float Your Boat

 

[srm]

I've fitted one of these which looks a lot nicer than just a drilled hole with a plywood cover:

Fire Port - Stainless Steel or White - Float Your Boat

Which is possibly just about sufficient for a small diesel installation provided a suitable portable extinguisher is kept next to the engine box. With a big petrol engine, such as quoted by the OP, by the time you first notice the smell/smoke/flames it's probably already too late .

Incidentally, a few years ago my insurers added a new clause: they would only cover a claim for fire if an automatic powder extinguisher was fitted inside the engine bay. (Moderate sized diesel engine) Personally, I would have preferred to fit CO2 as I have a fair bit of experience using both. Even if the engine is stopped a powder extinguisher will make one hell of a mess and won't do the electrical components any good.

 

[geem]

Which is possibly just about sufficient for a small diesel installation provided a suitable portable extinguisher is kept next to the engine box. With a big petrol engine, such as quoted by the OP, by the time you first notice the smell/smoke/flames it's probably already too late .

Incidentally, a few years ago my insurers added a new clause: they would only cover a claim for fire if an automatic powder extinguisher was fitted inside the engine bay. (Moderate sized diesel engine) Personally, I would have preferred to fit CO2 as I have a fair bit of experience using both. Even if the engine is stopped a powder extinguisher will make one hell of a mess and won't do the electrical components any good.

On a boat you need to be careful with CO2. It can be pretty lethal in large quantities and no way to remove it.

 

[Farmer Piles]

Which is possibly just about sufficient for a small diesel installation provided a suitable portable extinguisher is kept next to the engine box. With a big petrol engine, such as quoted by the OP, by the time you first notice the smell/smoke/flames it's probably already too late .

Incidentally, a few years ago my insurers added a new clause: they would only cover a claim for fire if an automatic powder extinguisher was fitted inside the engine bay. (Moderate sized diesel engine) Personally, I would have preferred to fit CO2 as I have a fair bit of experience using both. Even if the engine is stopped a powder extinguisher will make one hell of a mess and won't do the electrical components any good.

I'm with you on the horrible mess that a powder extinguisher makes and leaves behind having had to empty two 25kg ones into the guts of a flaming diesel powered grain dryer. That said, if you have a fire in your engine bay that kicks one of these extinguishers into action then it will almost certainly be an insurance claim, and given that they insisted on a powder unit then let them deal with it.

 

[Tamar]

My engine bay has two small steel pipes drilled through the walls where I can poke a nozzle of an extinguisher through. They were originally plastic pipes but the surveyor wasn't happy as they could melt. I guess he ignored the fact that the engine housing is made of wood.

 

[PetiteFleur]

I've fitted a 'halon replacement' auto fire extinguisher in my engine bay - not sure what it's filled with but definitely not powder which is terrible stuff to clean up afterwards.