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Old 11-23-2012, 07:51 PM   #1
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Engine Room Fire Suppression

Since the discussion over propane pretty much ended up a discussion about cooking (I eat chicken with my fingers so you know what side I am on), I thought I would relate my discussion with the insurance company on a survey of a recently purchased trawler. We got into the propane discussion and I agreed with them even before they told me to fix it. Something about a 10 lb propane bottle not tied down with 8 inches of regulators, valves, solenoid and piping hanging in the air in the enclosed area of the upper helm with an exposed DC distribution panel did not make me feel good.

The rest of the survey was little things here and there, but the one that got me was the recommendation for the engine room fire suppression system as "required by ABYC standards". I had already put on the potential list of things to consider something for engine room fire suppression, but I thought being instructed to comply with it as a condition of insurance was a reach. My response to the insurance company, "Not required by the USCG on this vessel" satisfied them and they dropped it.

I won't go into a long discussion of engine room fire suppression, but I thought the most important action I could take was preventing the fires in the first place. Since most engine room fires in diesel powered boats are electrical in origin, the first logical step is fusing the positive cable of the battery banks to prevent direct shorts or a seized starter motor in the engine room from starting a fire. It is not hard to do and not terribly expensive. I would have thought the surveyor would have mentioned that but he didn't. He didn't like the wooden box around the start battery bank and I can understand that since a fire caused by start battery bank problem would then have more to burn.

So the question is, what should I really do about engine room fire suppression?

Tom
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Old 11-24-2012, 06:32 AM   #2
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the first logical step is fusing the positive cable of the battery banks to prevent direct shorts or a seized starter motor in the engine room from starting a fire.

The amperage required to start a diesel, is easily enough to start an electrical fire , fuse or not.

A direct short on a alternator wire is far under what a starter feed will provide.

"So the question is, what should I really do about engine room fire suppression?"

The old system , where a cable is pulled , the exhaust blower is de-powered and the ER vents are closed ,
then massive CO2 is released seems reliable.
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Old 11-24-2012, 08:40 AM   #3
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"The old system , where a cable is pulled , the exhaust blower is de-powered and the ER vents are closed ,then massive CO2 is released seems reliable."

I haven't been around trawlers for very long, but I don't recall seeing engine room vent covers installed on any that I looked at before buying. I installed them myself on my previous boat. Anybody have photos of theirs or a place to purchase or designs to build?
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Old 11-24-2012, 09:24 AM   #4
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From a purely standards point of view ....

ABYC "Fire fighting Equipment" Standard A-4 and NFPA 302 “Fire Protection Standard for Pleasure and Commercial Motor Craft” require either an automatic extinguishing system in the engine compartment or a provision (fire port) for discharging a fire extinguisher directly into the engine compartment without opening the primary hatch.

ABYC "Storage Batteries" Standard E-10 requires in part that batteries be vented outside of accommodation spaces and that batteries be secured so as not to move more than one inch in any direction, be contained in boxes or trays resistant to electrolyte, that positive terminals be protected by dielectric material, prohibits wing nuts as a means of securing conductors 6AWG and larger and requires positive conductors be fused within 7” of the battery or 40” if the conductor is fully enclosed with the exception of the conductor running to the engine starter motor.
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Old 11-24-2012, 05:39 PM   #5
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A fuse or circuit breaker with a high enough trip or blow current rating to allow for enough current to operater the engine starter will be of little use in protecting against other electrical faults. That's why the starting circuit is an exception in the ABYC overcurrent protection requirements.

That doesn't mean you cannot install one, just that there is a small window between the current drawn by the starter attempting to start a very cold engine and the current of a short circuit from insulation failure or another fault.
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Old 11-25-2012, 07:58 AM   #6
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just that there is a small window between the current drawn by the starter attempting to start a very cold engine and the current of a short circuit from insulation failure or another fault. __________________

The point is a 10A fault can start a fire on a 500A start circuit .
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Old 11-25-2012, 08:31 AM   #7
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If you do not have a service disconnect on your engine cranking circuit then install one so that if a hung starter occurs you may go down and disconnect the batteries without tools. Leave it in the off position when you are not aboard in case your igniton switch or start bottom gets wet and decides to start the engine on its own while you are away.

On the subject of fire systems consider installing one even without a relay box and all the other knick knacks that end up doubling your installation cost. If you are aboard you will likely shut everything down yourself if you have a fire and if you are not aboard no machinery should be running anyway and you will be better protected than without a fire system. Install the system with a means to discharge it remotely manually. No point in waiting for the whole space to heat up before it discharges.

I have yet to see a fixed system that does everything ABYC standards require in the vessels I inspect typically up to 70' or so 5 years or more old. Most new vessels have a relay box to shut-down the machinery but none to close off the ventilation system except for shutting down electric blowers. That is not an argument not to do right just an observation...
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Old 11-25-2012, 09:09 AM   #8
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since most boat fires (boatUS stats) start in the wiring in the engine compartment I'd strongly suggest that battery switches not be in that compartment. One of the first things you want to do in a fire is turn off the batteries, One of the last things you want to do is open that compartment and supply more oxygen to the fire.
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Old 11-25-2012, 11:21 AM   #9
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just that there is a small window between the current drawn by the starter attempting to start a very cold engine and the current of a short circuit from insulation failure or another fault. __________________

The point is a 10A fault can start a fire on a 500A start circuit .
You're going to have to explain that statement.
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Old 11-27-2012, 06:43 AM   #10
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The point is a 10A fault can start a fire on a 500A start circuit .

You're going to have to explain that statement.

On many boats the alt output is simply fed to the starter cable , as it existys , is close , and can carry whatever output most alts create bacxk to the batts easily.

Really simple hookups will frequently have a "one wire" alt , where the V reg is turned on and operated by the Alt output.

The alt and regulator can start a heck of a fire being hooked to a starter cable , if fused to 500A , which will not blow.
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Old 11-27-2012, 07:20 AM   #11
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Some years back I owned a Jeaneau sailboat and it handled the issues being discussed here very nicely and at reasonable cost.

!. Each battery bank had a simple on/off switch on the negative lead and the switch was outside of the battery compartment.

2. There was a fire port on the engine room box behind the companionway. It was a simple hole covered with a plastic plug.

If a fire occurs in the engine compartment, turn all switches off, pull the plug and discharge a fire extinguisher inside.

David
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Old 11-27-2012, 08:24 AM   #12
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The alt and regulator can start a heck of a fire being hooked to a starter cable , if fused to 500A , which will not blow.
Ah well, then why not put a shunt in the alternator output wire? Or maybe even a fuse? Your last claim was that shunts are bad because they act like fuses ...

Which way do you want to go, shunt = fuse = bad or ???
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Old 11-27-2012, 08:36 AM   #13
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Quote:
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The point is a 10A fault can start a fire on a 500A start circuit .

You're going to have to explain that statement.

On many boats the alt output is simply fed to the starter cable , as it existys , is close , and can carry whatever output most alts create bacxk to the batts easily.

Really simple hookups will frequently have a "one wire" alt , where the V reg is turned on and operated by the Alt output.

The alt and regulator can start a heck of a fire being hooked to a starter cable , if fused to 500A , which will not blow.
I am more confused now than after your original post. The ABYC (and common electrical sense) requires overcurrent protection on any conductor except the engine starting circuit. If a boat has unprotected conductors, it is not compliant. More importantly, it is not safe.
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Old 11-27-2012, 08:38 AM   #14
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Some years back I owned a Jeaneau sailboat and it handled the issues being discussed here very nicely and at reasonable cost.

!. Each battery bank had a simple on/off switch on the negative lead and the switch was outside of the battery compartment.

2. There was a fire port on the engine room box behind the companionway. It was a simple hole covered with a plastic plug.

If a fire occurs in the engine compartment, turn all switches off, pull the plug and discharge a fire extinguisher inside.

David
While switching off either the positive or negative battery cable provides the same result, convention is to switch the positive lead.
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Old 11-27-2012, 09:15 AM   #15
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If you run the starting lead(s) all the way from the battery(s) to the external switches and back down that wouldn't do much good would it? If you run a wire from the + battery terminal to a remote switch then back to the starter(s) you create no end of negative (pun intended) potential.

If you break the negative you open all the circuits via a single loop. If that wire grounded it would not create a short circuit and would not cause any great problem.

Running the postive to a remote switch only increases the possibility of problems because you now have an additional unprotected length of wire between the + terminal and the switch.
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Old 11-27-2012, 12:35 PM   #16
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A fuse in an alternator output line is usually considered poor practice as if it does blow while the alt is creating output , the diodes will usually FRY.

No,,, frying the diodes does not start a fire , but not many cruisers carry spares , and the seating tool.

That's cruising sailboat gear , not usually motorboat stuff.

"convention is to switch the positive lead. "

In the USA perhaps , our Beneteau First 32 is set from the factory with the a similar neg. disconnect
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Old 11-27-2012, 05:37 PM   #17
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A fuse in an alternator output line is usually considered poor practice as if it does blow while the alt is creating output , the diodes will usually FRY.
"FRY" is not a technical term in the electrical field.

Regardles, if a fuse blows, it is because of a fault (overload or short circuit). Without the fuse, either the diodes or the wiring will fail anyway with the possibility of a fire. The overcurrent protection should be sized to protect the conductor that it is protecting. If "nuisance" blowing or tripping is a concern, it's easy to just increase the gauge of the wire and the rating of the overcurrent protection.
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Old 11-28-2012, 06:52 AM   #18
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"FRY" is not a technical term in the electrical field.

Perhaps , but it does describe to the non tech folks what happens when most alts are disconnected from their load while in operation.

MUCH UNGOOD
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Old 11-28-2012, 05:16 PM   #19
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It's well known that electronics run on smoke. If the smoke gets out, they quit working.
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Old 08-15-2014, 11:36 AM   #20
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So let's go back to the fire suppression required in the engine room once a fire starts. If you have a automated system to allow halon or one of the newer agents to flow, are you required :
1) to have a manual release outside the compartment.
2) Have a indicator on the helm telling you the system is active.
3) Have a remote shutdown for the engine and blowers ..other then the existing switches ?

I ask because my existing system is not working, it is a custom install with no records or design and one of my two halon tanks has leaked. So I'm in the process of updating it. There is a limit to how much money to spend, so I have be looking at a FIREBOY MA2-1400-227 HFC227 AUTOMATIC 1400CU FT MARINE BOAT FIRE EXTINGUISHER. system.
I was also going to install an audio alarm set at a temperature just below the level of the Extinguisher.

Just wonder what everyone else is doing ? I'm sure all the new boats have all the lights and bells, but I'm not living in that world yet ..LOL

Thanks,

Mark
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