Grass fires under vehicles.

Submitted: Thursday, Jun 25, 2009 at 21:47
ThreadID: 70155 Views:3923 Replies:8 FollowUps:7
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Fires under vehicles often cause the total loss of the vehicle. I am rebuilding my Mercedes 4x4 that was totalled in an accident and would like to reduce the fire risk while I have the opportunity. Willem has suggested getting rid of the bash plates. The likely ignition source would be the dump pipe from the turbo that runs red hot sometimes. Has anybody got any ideas on ways to prevent the grass from contacting the exhaust? Thanks, Eric.
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Reply By: Crackles - Thursday, Jun 25, 2009 at 22:36

Thursday, Jun 25, 2009 at 22:36
I've found it doesn't really matter if the grass brushes up against the exhaust, you just have to minimise the places that it can get caught up against the exhaust pipe as it really needs to be in contact with it for a while to ignite. If the grass builds up on top of the bash plate it can be a problem area on some vehicles but don't forget it was put there for a reason & you may be risking damage to the sump etc by removing them all together.
Carry a wire with a hook to clean any grass out, a small water spray bottle & with regular inspection fires shouldn't be a problem.
Cheers Craig.............
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Follow Up By: Member - Mick O (VIC) - Thursday, Jun 25, 2009 at 23:01

Thursday, Jun 25, 2009 at 23:01
Totally agree with Craig's assessment. Leave the bash plate where it is. Regular checking when in grass country and a good fire extinguisher and a water filled spray bottle. Just remember to take your dry powder extinguisher out of the car every few days and give it a shake. A light few taps against the tyre while held upside down is good. This will ensure that the powder which will have settled into a solidly packled mass while travelling over rough roads, is "fluffed" up and loosened so the extinguisher works when you want it to. An ounce of prevention as the old saying goes.

Cheers Mick
''We knew from the experience of well-known travelers that the
trip would doubtless be attended with much hardship.''
Richard Maurice - 1903

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Follow Up By: olcoolone - Friday, Jun 26, 2009 at 10:15

Friday, Jun 26, 2009 at 10:15
Agree 100% with Crackles and Mick O.

When we travel and know we are going to go through long grass we carry a 8Lt. garden sprayer full of water just in case, a garden sprayer is better then a spray bottle as you can get it into more spaces and you have a lot more water at your disposal.

So fires can only be put out with water.

The garden sprayer also acts as our shower.

We are lucky that our vehicle has good ground clearance and not alot of places grass can collect.

Mick O so how was the Holiday?


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Follow Up By: Member - Stephen L (Clare SA) - Friday, Jun 26, 2009 at 13:38

Friday, Jun 26, 2009 at 13:38
Hi Mick
Long time no hear. I hope that you have had a great time. Alan has been keeping us up to date. How much long are you out in the scrub?

Cheers

Stephen
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Reply By: Robin Miller - Friday, Jun 26, 2009 at 07:09

Friday, Jun 26, 2009 at 07:09
Many exhausts like on my patrol come twin walled these days Eric.

Previous to this I used special fibreglass exhaust tape to dramtically lower external temps. (available widely from speed shops)

Robin Miller

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Reply By: Rockape - Friday, Jun 26, 2009 at 08:20

Friday, Jun 26, 2009 at 08:20
Eric,

When I was operating dozers scrub pulling and raking,we used to watch the build up of material above the belly plate like a hawk, cleaning out material daily.

It is a sure way to lose a machine quickly.

Having said that you would never pull the belly plate off for obvious reasons, the reason being damage to the sump and the chance of a stick coming up through the floor and spearing the operator.

You can wrap the dump pipe in fibreglass rope to keep it cool, but remember if the rope becomes saturated with oil it poses a greater threat than having the exhaust open to the air.

You would have to be working the engine hard to create the amount of heat you are talking about, normally you are just poking along slowly through grass with the engine not working. If you clean out the grass ( and that could be quite often) before you start to work the engine I am sure you will have no problems.

Have a good one
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Reply By: Member - Timbo - Friday, Jun 26, 2009 at 12:03

Friday, Jun 26, 2009 at 12:03
You could try installing and exhaust system like this one:

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Even if you have an exhaust/grass fire, it won't be UNDER the car! ;)


AnswerID: 371943

Follow Up By: StormyKnight - Friday, Jun 26, 2009 at 18:37

Friday, Jun 26, 2009 at 18:37
Now thats ingeniuos...if not illegal, but would work very well for whats it designed for (ground clearance excepted)....

Next we will have aftermarket exhausts much like aftermarket snorkels....designed to suit a particular need.
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Reply By: Member - Tony V (NSW) - Friday, Jun 26, 2009 at 12:06

Friday, Jun 26, 2009 at 12:06
I agree with all the above.

Water Spray bottle is a must, once it starts it is hard to put out.

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Its hard to throw water UP under a car

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Too late

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Reply By: D200Dug- Friday, Jun 26, 2009 at 12:33

Friday, Jun 26, 2009 at 12:33
Always have a dry powder extinguisher stored lying down not standing up in a vehicle this prevents most of the problems of the powder packing down while traveling.

Before using a dry powder extinguisher always try to give it a good thump on something solid anyway ( not always remembered when your car is on fire thought !)
AnswerID: 371948

Follow Up By: Member - Timbo - Friday, Jun 26, 2009 at 20:19

Friday, Jun 26, 2009 at 20:19
A dry chemical powder extinguisher is great for oil/fuel/electrical fires but not especially suitable for grass/spinifex fires. This is because they remove the oxygen, once you stop 'spraying', there is still enough heat in the grass/spinifex to reignite the fire - water is best for this type of fire, then remove the remaining grass/spinifex with a long stiff wire.

Remember the fire triangle? Fuel, heat & oxygen.
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Follow Up By: Member - Timbo - Friday, Jun 26, 2009 at 20:20

Friday, Jun 26, 2009 at 20:20
...and switch off the engine to avoid adding more heat!
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Follow Up By: Farko - Sunday, Jun 28, 2009 at 20:06

Sunday, Jun 28, 2009 at 20:06
A clarification. Dry chemical extinguishers do not remove oxygen (one side of the fire triangle) They interupt the chemical chain reaction (stop the sides of the fire triangle interacting). The extinguisher rating is what is crucial for its effectiveness on grass and spinifex. A rating ending in B(E) is suitable for flamable liquid (class B) fires, flammable gas fires and fires involving electricity. If you use these on ordinary combustibles like grass, paper, cars, etc, (class A) the flame will be knocked out but it is likely to re-ignite. Look for a dry chemical extinguisher with an AB(E) rating. (eg. 1A 5B(E) or 2A 20B(E) ) The AB(E) powders leave a covering on the burning material to prevent re-ignition. It will cost a little more but is well worth it. The numbers - the higher they are the more efective they will be. Submit the water bottle and the garden sprayer for testing and they would get an A rating.
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Reply By: kend88 - Friday, Jun 26, 2009 at 19:20

Friday, Jun 26, 2009 at 19:20
I could well be wrong, but I think I remermber hearing years ago that it was usually the extreme heat of the catalyctic converter that causes most grass fires under cars. Don't know how you prevent them.

kenD
bris
AnswerID: 372004

Reply By: Ozhumvee - Saturday, Jun 27, 2009 at 13:13

Saturday, Jun 27, 2009 at 13:13
Ken D it isn't just the exhaust that can ignite spinifex and the like, there is enough friction from halfshafts, tailshafts and anything else spinning to ignite built up spinifex under a vehicle.
Brakes are also an ignition source especially on late model vehicles with traction control which apply the brakes in soft going and when wheelspin is possible, a hot brake disc and caliper will easily ignite grass buildups.
I've experienced the rotating items like tailshafts getting spinifex/grass to smouldering temps in 25 deg ambient temps after only a few k's travel in the northern Simpson a few times on a troop carrier. A petrol with a cat converter only has to collect a few bits of grass before ignition happens. those nice perforated heat shields on cat converters make beaut scythes and allow the grass to build up hard against the cat, right PITA to remove too.
Peter
1996 Oka Motorhome

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