Does your fire suppression auto-stop work?

[rgano]

Not everybody who has an engine room fire suppression system wants their engine/generator to automatically stop when the fire-suppression agent is released from the bottle. In fact, some systems are installed without the shutdown capacity. I have even seen bottles installed in boats with absolutely no other interface - JUST the bottle. Huh???? I had a system in my trawler which alerted the operator to the bottle discharge, but my current boat came with the capability to shut down the engine and generator, or did it?

Sometime back, something I read here got me to thinking about various alarms on the boat, and I decided I needed to test my fire suppression system's alarm AND shutdown. The method to do this, as stated in the manufacturer's documentation, is to pull apart the two-wire modular plug connecting the bottle to the system with the unit(s) running. My generator shutdown and the system alarmed properly. I was able to press the override button and quickly restart it.

Not so successful with the single main engine. The alarm lighted and sounded ok, but the engine would not stop. After as much research as I could stand over the last month or so, the verdict was that Mainship did not wire the system correctly. The solution ended up being a combination of placing a normally closed relay between the engine stop switch and its wiring running down to the engine (power required to keep the fuel pump solenoid valve open)and running an open-signal wire to it from the unoccupied activation signal terminal of the fire system control box. Now it works a treat as is said down undah.

My concern about this lack of auto-stop feature was that at my normal "hair on fire" cruising at 3000 RPM the engine might suck enough of the released agent out of the engine compartment (and thus more oxygen in) before it conked out or I shut it down leaving the agent concentration diluted to the point of ineffectiveness.

 

[twistedtree]

Good job checking it in the first place. I'll bet there are a LOT of systems that don't work, or where the operator doesn't know about it, nor know how to restart after a discharge.

 

[OldDan1943]

On my AT, the main engine would shut down but not the gen. I had it wired to shut down the generator too. My thinking is, I want the compartment to fill with the suppression gas and leaving the generator running sucking the gas out of the engine room may not suppress leave enough to put the fire out.
Am I wrong in my thinking?

 

[Comodave]

No, with diesels you want them to auto stop because the diesel can probably burn the suppression agent like fuel. Gas engines will die from halon, not sure about the current agents though.

 

[rgano]

I would like to say I was smart enough to test this system when I bought the boat in 2015, but.....

 

[Portage_Bay]

PO of my boat had his halon bottle trip. He said the engines stumbled a bit but did not stop. It wasn't a "real" fire but could have become one. The spray ring at the riser was blocked. The hose after the riser blew out. The heat tripped the bottle. After it melted the loaded vinyl insulation. Charred the wood. Melted some wire insulation. Had he not investigated it would have become a real fire. If it had progressed to fire. If it were a fire caused by electrical problems. If it were a fuel fed fire. The halon would have been diluted beyond effectiveness. Your engine(s) are big air pumps. They will pump the suppressant out and fresh air in very effectively.

He said he grabbed a portable fire extinguisher and went into the engine room. That by the firefighting training I've had was a serious error. Entering a smoke filled confined space solo without protection and no backup.

Auto shut down is important.

 

[twistedtree]

Auto shutdown is not about saving or protecting the engines.


It's about making the fire suppressant work. If you leave the engine(s) running (exhaust fans too), they will evacuate the fire suppressant very quickly, essentially spraying the suppressant outside the boat instead of in the ER where the fire is located. All built-in suppressant systems I'm aware of REQUIRE automatic shutdown. They just don't work otherwise.



Lots of people don't want to relinquish control to an automatic shutdown system, but it's almost certain that you won't be able to assess the situation and shut down fast enough on your own. And if someone else is at the helm, it's pretty much guaranteed to not happen fast enough. So save the manual action for activating the override switch to restart everything after the fire is under control.

 

[Portage_Bay]

Lots of people don't want to relinquish control to an automatic shutdown system, but it's almost certain that you won't be able to assess the situation and shut down fast enough on your own.

Well said. I've evaluated my cruising goals and decided the benefits of auto shut down outweigh the risks. The percentage of miles or hours where auto shut down would be a greater risk than a fire is near zero.

 

[twistedtree]

Well said. I've evaluated my cruising goals and decided the benefits of auto shut down outweigh the risks. The percentage of miles or hours where auto shut down would be a greater risk than a fire is near zero.

And for that near-zero situation, that's why there is an override switch....