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Author Topic: Would cutting off power automatically help in the event of an electrical fire?  (Read 1983 times)
Kevin Warnock
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« on: March 30, 2011, 11:27:33 PM »

I wrote up another of my bus conversion ideas on my blog a few days ago, here:

http://kevinwarnock.com/2011/03/26/why-not-turn-off-electricity-when-smoke-detector-activates-on-a-bus-conversion/

I would like feedback on whether the idea is a good one or not.

I'll summarize it here:

Since some bus fires are electrical fires, I speculate that it might be a good idea to install smoke detectors that have a relay to control external circuits, such as this one:

http://www.totalcomputing.net/System-Sensor-4WTAR-B-4-wire-PE-Smoke-Detector-wThermal-Sounder-Form-C-Relay_p_1196.html&utm_source=googleps&utm_medium=freefeeds&utm_campaign=productfeeds?gdftrk=gdfV21858_a_7c664_a_7c2125_a_7cBK_d_4WTARB

When the smoke detector activates, the relay trips and power is supplied to a set of linear actuators, each one like this:

http://www.surpluscenter.com/item.asp?item=5-1752&catname=

The plunger on the activators would be connected to the power shutoff switches and the master circuit breakers, so everything would be powered down in seconds. These actuators run on 24 VDC and can push or pull 100 pounds, so I think they have the power to turn off the master battery disconnect switches in my RTS battery bay.

I pose a lot of questions about the wisdom of implementing a system like the above on my post, so I won't repeat the entire post here.

I did link to a YouTube video showing a linear actuator in action, for those of you who haven't seen one work.

The components are affordable: the actuators are $39 each and the smoke detectors with relays are $49 each. I could probably find less costly actuators for the circuit breakers, since they don't take 100 pounds to turn off.

I really don't want my RTS to ever burn to the ground, so I am actually considering seriously adding the above safety feature if the consensus is that it would offer worthwhile protective value.

Of course, I would not have the system shut off the vehicle power while the vehicle is running, just when parked.

Thanks,

Kevin Warnock
http://KevinWarnock.com - my blog where I sometimes write about my bus conversion
« Last Edit: March 31, 2011, 12:58:49 AM by Kevin Warnock » Logged
papatony
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« Reply #1 on: March 31, 2011, 04:43:32 AM »

It would help but its not the total answer
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Hobie
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« Reply #2 on: March 31, 2011, 04:44:36 AM »

Interesting idea.   Couple of thoughts.  

1.  Suppose you have an alarm while driving?  I wouldn't want the fuel pump to shut down (  probably mechanical pump, but you get the idea)  until you were able to get stopped off the road.  So maybe a switch or circuit that turns system off when key is on??   

2.  Add an separate small battery led emergency lighting circuit to provide interior illumination to help you see to get out if the alarm activates at night.  

3.  And an interior reset button, again driven by that extra small battery  so in the event you burn your toast Smiley  you can quickly get everything back to normal.  
« Last Edit: March 31, 2011, 04:50:27 AM by Hobie » Logged
WEC4104
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« Reply #3 on: March 31, 2011, 05:19:38 AM »

I'd be concerned about what other bus systems you would be disabling, which could prove essential in a fire situation.  A conventional smoke detector isn't going to tell the difference between an electrical fire and say, a trash fire, cooking fire, etc.

Depending on which electrical circuits get disabled, you could find your house water pump no longer operates and you can't get water to put out a burning small trash can.   Interior lighting is turned off presenting a hazard to exiting passengers, and making it harder to find a small smoldering fire, or maybe even locate your cellphone to call for help.   

If you are on the road driving, your particular bus' electrical system design will determine whether the engine continues to run with the battery disconnected. If it does, and you are safely able to pull onto the shoulder of the road, the minute you kill the engine, your 4 way flashers and all exterior lights are gone (not good at night).     
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« Reply #4 on: March 31, 2011, 05:55:02 AM »

We had a fire in our server room at work back in 2004.  The smoke detectors triggered the automatic fire response.  The first action is all power to the room is cut and the second action is the halon is dispensed.  The fire department was also dispatched although they didn't have to do anything.

In this case, we did have an electrical fire that cutting power put out.  We decided to unplug all of the racks of equipment before turning power back on.  As we reconnected racks one by one smoke started to pour out of one when it was reconnected.  It ended up costing $15,000 to reset the fire supression system plus a few thousand to replace the burned equipment.

The moral of this story is that cutting power can stop some electrical fires.  I don't know that I would go to that extreme in a bus though.
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Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
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« Reply #5 on: March 31, 2011, 07:09:49 AM »

Well folks, after being called a “blathering know-it-all” after my last post, I said that I would refrain from posting.  However, this thread is pretty close to home for me, as I sold alarm systems for RVs at one time.  So I will try posting again and see if the reaction is again negative.

And yes, this will be a bit of a long (blathering?) post.   Roll Eyes Shocked

First lets talk about the smoke detector mentioned.  In an articles in BCM in '04 and '05 I talked about various alarm systems and discussed the two types of smoke detectors available in the public sector.  They are “ionization” and “photoelectric”.  Ionization is most often sold for both home and RV applications, because it is very cost effective.  It is also the type that is quite prone to false alarms – especially when installed close to a cooking area.  The photoelectric is generally less troublesome in terms of false alarms.  Since each type of smoke detector has a process that detects different kinds of fire (flash versus smoldering), it is often recommended that both types be installed for the best protection.

The smoke detector mentioned is photoelectric and that is good.  It says it has some logic that minimizes false alarms from things like dust.  I use photoelectric smoke detectors in our bus.  I got the great idea of putting one in the bays.  That did not work well.  We had a rally in Quartzsite several years ago where we had to drive on “dusty” and I got false alarms.  Kind of embarrassing when you pull into the rally with your security alarm sirens blaring away  Grin Shocked.

So, even though they say that they minimize false alarms, they can't be eliminated.

In both of the above articles, I site studies done in Finland on bus fires.  Indeed, a significant number of fires on these commercial buses were the result of “high current” fires (followed closely by brake/tire and engine fires).  These were overwhelmingly battery cable related fires.  So electrical fires do occur, but my experience is that they are not the major factor in bus conversion/motorhome fires.  The biggest causes are brake/tire, refrigerator, engine and generator fires.  That said, it is always good to think about prevention of any fire.

I think the smoke detector with the relay mentioned above is a good start on an electrical fire detection system.  I am not sure about the use of the relay signal in that device.  First, the relay is rated at 2 amps at 30 volts (AC/DC).  That is a fair size relay, but one linear actuator with a max current of  1.5 amps at 24V would max out the smoke detector relay.  

If I would design the system, I would use the smoke detector relay to trigger several other relays/contactors.  These relays could disconnect both 12/24V circuits as well as 120V circuits.  It would not be a huge deal to design an electrical system with relays/contactors included, or to modify existing systems.

As has been mentioned, disconnecting  certain circuits could result in driving hazards.  This could be dealt with using timer relays (I discuss them in an upcoming relay article in the April issue of BCM).  A timer relay would allow selected circuits to be disconnected at programmable delay periods.

An alternative would be the algorithm used with electronic engines.  Here, the “Stop Engine” function, that occurs because of a major engine problem, can be overridden by the driver for a short period of time to get off the road.

That is enough blathering for now.  
« Last Edit: March 31, 2011, 07:36:32 AM by rv_safetyman » Logged

Jim Shepherd
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« Reply #6 on: March 31, 2011, 01:33:34 PM »

The best way to turn off power is with battery cut-off switches. One switch will work if one of the batteries hasn't shorted out but individual switches are best.

Maybe a combination of one master and individuals is even better.

Of course, if there is a fire, cutting off power won't necessarily stop it but it sure can't do any harm.
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Tim Strommen
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« Reply #7 on: March 31, 2011, 02:16:18 PM »

...When the smoke detector activates, the relay trips and power is supplied to a set of linear actuators...


I would suggest another route...  Instead of requiring more power to be handled, why not use non-electrical means?

If an electrical fire is taking place, it's probably because the safety devices was not correct or correctly functioning: fuse, circuit-breaker, etc...  You should have a Class-T fuse on a large house battery bank, and every positive wire that you have should be fused within 6-8 inches of a wire size change (to protect the down-stream circuit).

Instead of electrical linear actuators, you can get magnetically latched contactors with require ZERO power when not switching, and hold in place.  Contactors are available from 200Amps up to 1800Amps, and just require a short "blip" of power to open or close them (the magnets do the rest).  These same actuators can be pushed open with pneumatic or hydraulic means, so you can put in an electrically isolated "kill switch" that will push air into a small piston and push open the contactor (where the "open" magnet will hold it until reset).  If you are going to do a power disconnect, I'd recommend that you follow NEC guidelines for Hospital circuits with normal-service and emergency power systems (where normal service circuits get cut in an emergency, and critical systems get powered - circuit integrity be-damned...).

This would mean, yes, kill the TV, water heater, and the microwave, but keep power to the brake-lights and headlights and water pumps.  This will require that you sacrifice circuit simplicity to have a second electrical system the runs in emergencies and you need to spare no expense ensuring that those systems NEVER have a problem (you may even want to put a special secondary battery in place for those systems).  Also, if you put anything on the exterior of a bus that says “Kill Switch” or “Emergency Shutdown” – it must do exactly that to EVERYTHING.  You can‘t have a global shutdown that doesn’t turn off some systems, because then you’re over-simplifying and legally liable if someone gets hurt because of it Smiley.

Instead of smoke detectors everywhere you can use heat sensing wires (a piece of wire that acts like a switch).  If you run this in a conduit (low voltage only!!) the wire will connect the two leads together if it get’s hotter than the temperature set point.  With some digital logic you could go so far as to measure down to the inch where a fire is, or you could just shut off everything that is run through that conduit.  Same goes for the storage bays – any power can be shut off in a bay, vents can be closed, fans turned off, and a local fire suppression system can be triggered (if your bays are walled-off).  Then make sure you have a shutdown button on the way out of the bus – because that’s very likely when you’re going to need it.

I am planning on one along each side, and one on the front and rear face of the bus.  Power to this shutdown system is provided by cheap replaceable CO2 cylinders (like the kind you’d use in a BB/Pellet gun).  I’ll be keeping the system charged with CO2 (non-flammable), and when an emergency stop button (30mm button head, over a valve) releases pressure, the spring loaded cylinders will kick up the contactor (another valve will bleed the “Run” piston on the Main engine to stop the engine mechanically.  I’m using the push-to-stop/key-to-reset type button.

This way, even if the CO2 cylinder leaks empty, it fails to a safe condition (a handy security feature is to remove the CO2 cylinder when it’s being stored for a while, which completely “safes” the vehicle…).

-Tim

P.S. I also read in your blog that you want to encase the wires in some kind of fire stop material – DON'T DO THAT!!!  Wires are linear heaters.  If you wrap them in a fire-retardant material, you will likely make a wire heating issue worse!!  The absolute best safety advise that can be given for electrical systems is to size the wire correctly for the environment and load they will be used for – and fuse them properly! -T
« Last Edit: March 31, 2011, 02:42:47 PM by Tim Strommen » Logged

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« Reply #8 on: March 31, 2011, 03:06:29 PM »

The electrical fire I was involved in was not a direct short as far as we could tell so proper circuit protection was not an issue.  We really don't know what happened for sure, but something electrical inside a computer server got hot and started emitting dark oily smoke.  As soon as the power went off the smoke stopped.

Most motorhome and RV fires tend to be related to the RV ammonia fridge.  Either the propane starts a fire or the ammonia catches fire somehow.  I rarely ever hear about electrical fires in RVs although I'm sure they do happen.
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Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
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« Reply #9 on: March 31, 2011, 03:53:54 PM »

  Would cutting off power automatically help in the event of an electrical fire?

  Do dogs chase cats?

  Interesting thread, interesting thoughts.
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« Reply #10 on: March 31, 2011, 10:23:22 PM »

Instead of symptoms, go for the cause?

Put the effort into proper design and maintenance of the coach, disasters take care of themselves?

happy coaching!
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« Reply #11 on: April 01, 2011, 03:03:02 AM »

  I believe electrical fires to be the most common cause of RV fires. Even a standard Bus has two large high capacity batteries, and many are hooked in series to 24 volts, making the potential for burning a rig to the ground due to an electrical short very high.

  Regardless of those beliefs, if you have a short in the DC side, with the amperage available you could light a fire in seconds. In addition, and regardless of cause, any fire has the potential to burn electrical wiring which could lead to a major short circuit, therby adding an electrical fire to a fire that had other causes, and making an otherwise defensible fire indefensible. Cutting power is one of the first things they teach in Fire Fighting. You walk up to a burning house you have no idea what caused it to burn, but you want power off to both protect you, as well as remove a possible fire cause.

  While false alarms would be very troubling, especially if they occured often, cutting power, getting to the side of the road and stopping immediately, should be the goal. While certainly later computer controlled Buses would quit if you cut power, older models with pure mechanical fuel injection will continue to run. In either case, how fast you act could not only save lives, but could save your rig. If your far from home, or using the rig as your home, you obviously dont want to see it destroyed along with all you own.

  There are likely several ways to accomplish something like this, and I hope something affordable and workable comes from the discussion. If all else fails, you can use an axe or bolt cutter to cut your batteries. I could even see a simple pull cable inside the Bus, that could rotate the battery cutoff switch from inside the coach.
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rv_safetyman
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« Reply #12 on: April 01, 2011, 07:57:02 AM »

The statistics that I have, would suggest that electrical fires in RVs is not all that great.  At trade shows I hear all the horror stories and none of them have involved electrical fires.  I also monitor many of the RV yahoo groups and, again, no mention of electrical fires.

As Brian mentioned, refrigerator fires have become a big issue in recent years.  Dometic and Norcold have had recalls on top of recalls and they still seem to have problems.  Reportedly folks have died in these fires.  Huge problem.  Not a good way to prevent it other than stay current with recalls and install a fire suppression system.  It is interesting, many posts on Yahoo suggest that folks are spending big dollars to convert to household type fridges in big dollar new motorhomes.

Buswarrior makes a good point.  Good electrical systems design and implementation will offer very good protection.

On the 120 volt side, you should have an extremely small exposure to fire potential if the system is installed according to acceptable wiring practices.  Lots of debate on what is acceptable, but that is the subject of a huge number of past posts.

The big issue is the DC side of the bus.  There are two systems:  chassis/start and house.  

On the chassis side, most folks do not install auxiliary protection equipment.  The potential for a fire is the greatest in the high current part of that system.  For the most part that is the start and charge cables.  Good routing practice will minimize most of the problem.  For the accessory part of the chassis system, most circuits are protected by either fuses or breakers and again the exposure is minimal.

The big challenge is the house DC system.  First, there is a huge source of stored energy (large battery bank that can supply very high current for long periods of time).  Without question, you must have a fuse at the house battery bank.  Most folks install a 300 amp fuse like the one shown in the photo below.  I installed a similar fuse close to the alternator since that cable to the battery system carries high current.  Obviously the fuse is sized according to the size of the wire/cable.

It is also a good idea to install a house battery shutoff switch.  I installed a Blue Sea 3001 switch on my system (see photo below).

Once the high current circuits are protected, proper wiring practice (including properly sized  fuses/breakers) will protect against almost any chance of fire.

Jim
« Last Edit: April 01, 2011, 08:07:13 AM by rv_safetyman » Logged

Jim Shepherd
Evergreen, CO
’85 Eagle 10/Series 60/Eaton AutoShift 10 speed transmission
Somewhere between a tin tent and a finished product
Bus Project details: http://beltguy.com/Bus_Project/busproject.htm
Blog:  http://rvsafetyman.blogspot.com/
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« Reply #13 on: April 01, 2011, 09:08:55 AM »

  The refrigerator thing. How old of a gas fridge do you have to find to get back to quality? Anyone beside Norcold and Dometic that still remember how to build one?
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rv_safetyman
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« Reply #14 on: April 01, 2011, 12:01:29 PM »

Wow, I was blown away at how far back the fridge recall goes.  I was going to **GUESS** 2002 and I would have been dead wrong.  I was also going to guess that is was only the microprocessor units - again would have been dead wrong.

The official recall site is:

http://www.norcoldrecall.com/

It has recalls back to 1987!!!!

I did not check the Dometic recall, but the following site discusses both:

http://www.rvrefrigeration.com/recalls.asp

This is a huge deal.  Lots of fires. 

If you have an RV type fridge, you should check the serial number.

I don't think there are any other "traditional" (absorption) RV type fridge manufacturers.  There is at least one manufacturer of a unique 12 volt compressor type fridge, but I don't recall the name.  I think Sean has one in his bus.

Going to a household fridge offers a lot of advantages if you can deal with the current draw (inverter/battery bank/charging).

Jim
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Jim Shepherd
Evergreen, CO
’85 Eagle 10/Series 60/Eaton AutoShift 10 speed transmission
Somewhere between a tin tent and a finished product
Bus Project details: http://beltguy.com/Bus_Project/busproject.htm
Blog:  http://rvsafetyman.blogspot.com/
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