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Fire Extinguisher Systems
If you haven't yet read the overview of the fire triangle and various classes of fires, as well as the various fire extinguisher styles available I highly recommend you read that first on my Fire Safety Page. That will make it easier to understand the Cold Fire system.
After seeing plenty of pictures of burning RVs It's become apparent that once an RV begins to burn, it's very hard to stop it. There is so much fuel in an RV (wood, carpeting, glues, drapes, propane, diesel fuel, etc) that it doesn't take much to get a major conflagration started. RVs come with equipped with the bare minimum legal requirement, which is usually a small 5 lb dry chemical extinguisher near the entry door. However, small dry chemical units aren't overly effective on class A fires. On my 2004 Allegro Bus I replaced my 5 lb dry chemical extinguisher with a larger 10 lb unit that had much better coverage than the small OEM model. I also added a second extinguisher in the bedroom in case a fire broke out during the night and I couldn't get to the front fire extinguisher.
But dry chemical has it's limitations. You need to whack the base of the extinguisher every 6 months to prevent the dry chemical from packing up inside the cylinder. Once deployed the dry chemical leaves a huge mess and the powder is corrosive to any electrical components so you can plan on replacing any electrical component that gets a whiff of the dust. So, I did some research and when my 2007 Bus arrived I replaced the two dry chemical units with designer foam units. This gave me much better protection for the RVs interior.
But, most of the major fires, where the RV burns to the ground, appear to have a few things in common. First of all, they are generally rear engined diesel pushers. Secondly, the fires seem to start in the engine compartment. Now, this makes sense. Remember the fire triangle? In addition to oxygen, you need fuel and enough heat to raise the fuel to it's flash point. Today's DPs have plenty of fuel. There's lots of wood, rubber, electrical wire insulation, and diesel fuel present in that area. The turbochargers and exhaust systems on these engines can get extremely hot, providing the necessary heat to provide ignition. It's just a matter of putting it all together. There is so much wiring in today's RVs that it's easy enough to have an electrical short. This wiring is not run through steel conduit like a commercial building. Instead it's usually run through plastic wire loom. If this wiring short circuits or comes into contact with a hot part of the engine a fire can begin. There's also the occasional fuel leak to contend with. A cracked injection line or leaky diaphragm can squirt fuel. If it falls on the ground that's well and good but if it lands on a hot exhaust pipe or the turbocharger you're going to get a fire.
With these thoughts in mind I began my research into finding an adequate fire extinguishing system for the engine compartment of my 2007 Allegro Bus. The following paragraphs describe my thoughts as well as my procedure for installing a system.
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Mark Quasius - "Cruzer"
There's a wide variety of agents used in fire extinguishers. Automatic systems narrow that down a bit so it became easier to choose. Here are a few of the basic types that are available, their advantages, and their disadvantages.
Halon - Halon gas was popular in the 1980s and was used in computer rooms and other places. Halon is great for extinguishing fires because it displaces the oxygen in the room, effectively smothering the fire. It's harmless to electrical components so damage and cleanup are pretty well eliminated. The drawback is that any occupants in the room need to evacuate immediately or else they too will suffocate. Halon has basically been legislated out of the market so it's no longer an issue and I did not consider it.
FM-200 - FM-200, is a great replacement for Halon. It's safe for people and is actually used as a propellant in asthma inhalers. These system are very popular in marine engine rooms and data processing centers where minimal collateral damage is required. The problem I found with the RV's engine compartment is that it's not a sealed room. FM-200, like other gasses, function by starving the fire from the oxygen in the surrounding air. Once the gas is purged or drifts away, the potential exists for re-ignition. In a fairly open engine compartment, like an RV, the odds of putting the fire out, only to have it re-ignite a minute later were too high. I needed something that would laying an insulating blanket, like foam, to keep the fire from flaring up again.
Cold Fire - Cold Fire operates in two areas of the fire triangle. First of all, it is dispensed so that it leave a foam covering over the fuel to prevent re-ignition. This foam separates the oxygen from the fuel. Secondly, it is very cold so it removes heat from the fire, lowering the temperature of the fuel below the ignition point. It's also environmentally friendly with minimal collateral damage. I decided that this would be the system that I would use.
Automatic fire suppression systems work on a fail safe basis. When they get hot enough, something melts and triggers the valve to dispense the high pressure suppressants from the cylinder. That part's fine but if a small fire were to begin, then get extinguished, you might not even know it when you're driving down the road and the fire was 40' behind you.
A typical example would be a small fuel leak. The diesel fuel might flare up once it gets to something hot enough to ignite it, such as the muffler or turbocharger. The heat would trigger the extinguisher by melting the sprinkler head plug and dumping the entire contents of the extinguisher onto the fire. Once the fire was out, the cylinder would be empty but the fuel leak would continue. After a while the foam suppressant would be gone and the fire could re-ignite while you are still driving along. By the time you notice the fire it might be too late.
Alarms work off a pressure switch on the extinguisher tank. Once the tank pressure drops, the switch opens the loop circuit to the warning and display unit. An Alert lamp will light up and an audible alarm will sound. Now you know that you have to pull over to the side of the road immediately, shut down the engine, grab a hand held extinguisher, and go check it out. At the bare minimum the automatic system basically fights a holding action until you can deal with it permanently and evacuate the RV if necessary. These systems work on a normally closed loop so that if a fire melts the wiring the alarm will sound by default.
Fire Extinguisher Types
There were three basic designs of automatic extinguishers. The first is a simple tank with sprinkler valve. This RV specific valve is designed to open at 280 degrees. The tank can be mounted either horizontally or vertically, but you need to specify this up front. An optional pressure sensor will trigger the alarm once the pressure leaves the cylinder. The second system uses a poly tube that can be run around the engine compartment. This tube serves as both the detection method and the dispensing method. When a fire heats up any portion of the tube, that portion ruptures and triggers the valve to dispense the suppressant out the ruptured tubing at that same spot. The advantage is that the tube can cover a large area yet still deliver a pin point blast to the source of the fire. This is great for a large engine bay on a huge earthmover. The disadvantage is that the tubing ruptures at 175 degrees, which can easily be obtained inside the engine bay of a diesel pusher with having any fire. The third version uses that same poly sensing tube but has a pair of distribution ports on the cylinder valve. You then run two lines to specific places. When the poly tube ruptures, the suppressant is distributed through the ruptured tube but also is dispensed by these other two nozzles. This method also trips at 175 degrees so I decided to go with the simpler sprinkler head system
The Cold Fire RV systems were available in 4 sizes - 1, 2, 3, or 4 liter cylinders. The price wasn't that much different so I opted to go with the largest one that would fit. In my case, that was the 4 liter bottle.
I began by mounting the cylinder in the engine bay. I chose the horizontal 4 liter cylinder which fit well alongside the engine. I removed both of the floor panels to expose the engine and take a look at where I could best locate the system.
I decided that with the turbo on the driver's side it'd be best to locate the extinguisher system on the passenger's side of the engine. This was also the side where the engine's fuel system is located and the muffler is underneath so it was a logical choice.
The extinguisher comes with a mounting bracket that is used to clamp the cylinder in place.
I removed the mounting bracket, which made it much easier to handle and drilled the holes a bit larger to accommodate 1/4" bolts rather than smaller screws, which could pull out.
I drilled the 4 holes and bolted the unit to the underside of the engine bay. I oriented the tank so that the valve was centered over the side of the engine. The sprinkler head has a 10' radius so the suppressant will easily blanket the entire engine bay.
This location also made it easy to see the pressure gauge from the rear of the coach when the engine bay doors were open. I then extended the wires on the pressure sensor to the front of the coach and ran them up to the dash area. I utilized a weatherproof quick disconnect fitting to allow easy removal of the tank for servicing.
Normally these wires would go to the monitoring gauge, which would also require 12 volt power and ground. I liked the Cold Fire suppression method but they didn't have a decent monitoring system. Instead I chose a remote monitor from Sea-Fire, the makers of the FM-200 system. Either system uses a pressure switch to open a normally closed circuit so it really doesn't matter who's monitoring system you use. I was going to build my own system with parts from Radio Shack but the 2" round display that Sea-Fire had available looked very good and was a perfect fit for my dash so I decided to go that way. I actually got a deal on a closeout from West Marine where they were selling a more advanced engine shutdown system which featured the monitor as well as a 8 circuit relay box that cost me less than just the monitor alone. The shutdown system might be fine if you need to shutdown a FM-200 protected engine room in a boat to prevent the blowers, engines, and generator sets from venting the FM-200 out but it wouldn't be very handy for getting an RV pulled over to a safe location on the side of the road. But, I liked the display better because it gave me a green "Charged" LED as well as the piezo warning alarm and red "Discharged" LED. I just left the engine shutdown terminals unconnected and used it strictly as an alarm.
After connecting the wires from the sensor to the module I also connected a ground and a switched 12 volt power lead that was hot whenever the ignition key was on. I then mounted the monitoring gauge in the dash, drilling a 2" diameter hole. I chose to place it at the top left of the dash because I had a SmarTire tire pressure monitoring gauge of the same size on the exact opposite side and that gave a neat, symmetrical look to the dash.
The Sea-Fire monitoring gauge has a loud piezo warning alarm that will sound whenever the pressure drops in the cylinder. A red LED will illuminate to show that the system has discharged. Under normal operation, with the ignition key on, the green "charged" LED will be illuminated to indicate that the system is ready to go. Because this monitor is designed to function with the relay box that shuts down the engine and various sub-systems in a marine application, there is also a bypass switch that will silence the alarms and allow the engine to run. This isn't desirable in an RV application so it merely silences the alarms in my situation.
Hopefully, I'll never have the chance or need to test this system. But, should an engine fire begin, I feel confident that I'll have sufficient warning and time to deal with it. Hopefully the Cold Fire will put the fire out and it'll stay out. If not, it will at least fight a holding action that will allow me to get pulled over and deal with it with my hand-held foam extinguishers. In a worst case scenario it'll give me more time to evacuate the RV safely. The system isn't that hard to install and the potential savings can be huge. Following is a listing of website links that'll help you learn more about these systems:
This article written 8/25/07