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Amarie
02-27-2009, 06:38 AM
I have been researching forest fires but an editor wants to make sure I have my facts as accurate as possible, and so I'd like any input anyone has on a couple of issues. I know it is extremely hard to predict how fast a fire will travel, because so many factore influence it, but here's the setup: The fire in the story is in a state forest in Maryland, after a very dry summer. Is there any rough estimate as to how fast the fire will travel per hour? Also, how far ahead of a fire does the smoke spread out? Can people still breathe if the fire is within a few hundred feet of them? (not firefighters with equipment, ordinary people) Any help would be greatly appreciated.

Hesperides
02-27-2009, 07:49 AM
I have been researching forest fires but an editor wants to make sure I have my facts as accurate as possible, and so I'd like any input anyone has on a couple of issues. I know it is extremely hard to predict how fast a fire will travel, because so many factore influence it, but here's the setup: The fire in the story is in a state forest in Maryland, after a very dry summer. Is there any rough estimate as to how fast the fire will travel per hour? Also, how far ahead of a fire does the smoke spread out? Can people still breathe if the fire is within a few hundred feet of them? (not firefighters with equipment, ordinary people) Any help would be greatly appreciated.

I studied controlled burns here in TN...

Not sure about the rate per hour. I think it would depend on what was being burnt and the wind.
And your smoke questions also depend on wind. I have been toe-to-toe with a forest fire (controlled, not wild) and could still breathe. I mean, when you start it, you're at arm's length with a flame thrower... But if the wind was blowing in your direction, that would certainly hinder your breathing.
I'm not a fire-fighter, though!

Tsu Dho Nimh
02-27-2009, 10:21 PM
I have been researching forest fires but an editor wants to make sure I have my facts as accurate as possible, and so I'd like any input anyone has on a couple of issues. I know it is extremely hard to predict how fast a fire will travel, because so many factore influence it, but here's the setup: The fire in the story is in a state forest in Maryland, after a very dry summer.

I spent one job hanging out with wildfire fighters while I rewrote the manuals for their trucks. It's complex.

How fast does the plot NEED it to move? Tell me that and I'll tell you if it's possible, and if so, what the conditions need to be.

1 - It depends on terrain - Fires have a harder time going downhill, which is why you cut the defensive barriers along the tops of ridges, not in canyons.

2 - It depends on the wind, and the size of the fire. A small fire is at the mercy of external wind and a stiff breeze can stall it or even stop it until it burns out. A big fire, like Arizona's Rodeo-Chediski fire, creates it's own weather - the heat coming out of the fire can cause inflow at the bottom which makes it burn hotter. Those can wobble any which way.


Is there any rough estimate as to how fast the fire will travel per hour?

Mostly wind-dependent. Somewhere between 1/2 mile an hour for a creeping fire in pine needles or grass on a windless day to 60+ mph if it's a crown fire with a strong wind behind it. You can't outrun most of them, and some can catch a speeding brush truck as it runs cross-country.

Wind can carry burning debris a mile or more ahead of the fire, starting small fires in advance of the main one.


Also, how far ahead of a fire does the smoke spread out?

Strongly depends on the wind ... but we could smell California's fires here in Phoenix, and the Rodeo-Chediski fire could be smelled all the way to the Rio Grande ... 300+ miles. Typically a large plume rises hundreds or thousands of feet in the air, then spreads out downwind. Lesser quantities stick close to ground level and trickle down canyons and you can smell smoke spread for miles.

[/quote]Can people still breathe if the fire is within a few hundred feet of them? (not firefighters with equipment, ordinary people) [/quote]

You can still breathe ... the quality of the smoke may be poor.

Depends strongly on the wind and the intensity of the fire. I've seen crews without respirators working right at the flanks of a fire to prevent it spreading, and unless the wind is wrong or it's a monster of a fire, you can work fairly close to the front as you build firelines and remove fuel.

Amarie
02-28-2009, 02:02 AM
Thanks both!

Tsu Doh Nimh (pseudonym?)-
Here's more details:

First, there isn't any wind, except what the fire creates. It starts out as a campfire that gets out of control. The fire travels first downhill and then uphill. I need the characters to have about three hours in which they become aware of the fire, smell it, and eventually see it, as they are trying to get away. The forest where the fire starts is hardwood, and eventually the fire will reach a cleared area (dry grass) of about 20 foot wide. The fire needs to cross this area to reach the forest beyond that. I have the fire starting about a mile away in my current story. Do I need to put it further back?
Thanks in advance!

jclarkdawe
02-28-2009, 04:35 AM
Tsu is right that there are a bunch of factors to consider here.

The first, and the worst one for your story, is the state this is located in. Maryland has about 600 brush fires per year. Average size? About six to eight acres. See http://dnr.maryland.gov/forests/wfm.asp. Needless to say, most brush fires are very small. A large brush fire in Maryland might have a hundred acres, which is less than a sixth of a square mile.

Out west and in Florida they measure large fires in square miles. A big brush fire in the Northeast just isn't.

The Northeast doesn't have crown fires very frequently. Because of population density and fire towers, brush fires just don't get a chance to get going. Crown fires require some heat before they get going. These are the big fires out west. California and Florida have brush-type fires.

The Northeast have low level brush fires where most of the fuel is pine needles and leaves on the forest floor. Most living trees and brush in the Northeast have a high water content and don't tend to burn. We also have grass fires, which do burn a bit hotter as the fuel load is higher in height.

Frequently in brush fires you can literally walk right over the fire. However, let's give you the formula for a big, Northeast fire.

First off, you start off with a Red Flag day. This is a day with extremely low humidity and high winds (25 mph+). The forest consists of a lot of dead and fallen trees, approximately ten years old. Terrain is uphill.

Fire will spread faster than you can walk, as long as the wind blows. Flame height might hit 5 to 10 feet. As soon as the wind stops blowing, flames would come down to the 3 - 5 foot range. And as soon as it tops the ridge, it will die back down.

Main difficulty fighting it will be getting personal and equipment to the scene. Normally it would be contained within about a quarter of a mile of when the fire department arrives. If the terrain is really bad, it might take until the next day.

Worst brush fire I went to wasn't contained until the next day. Burned about 800 acres. The terrain was so bad that the deer had different size legs so that they could stand level. It took another two days after it was contained to put the whole thing out. For people who've been on fire lines out west, it was very boring.

Now looking at your specific facts:


First, there isn't any wind, except what the fire creates. Then it isn't going to move very fast, maybe as slow as a 100 feet per hour. It starts out as a campfire that gets out of control. The fire travels first downhill and then uphill. Without wind, it won't go downhill very well. Literally a beer and urinating could have a significant impact. I need the characters to have about three hours in which they become aware of the fire, smell it, and eventually see it, as they are trying to get away. They won't have to try very hard. This isn't moving fast. Unlikely it will burn for three hours without a fire tower spotting it. Once it reaches about 100' diameter, the smoke plume will be noticeable. The forest where the fire starts is hardwood Where the only thing that will burn are probably the leaves on the ground., and eventually the fire will reach a cleared area (dry grass) of about 20 foot wide. The fire needs to cross this area to reach the forest beyond that. Not a problem. I have the fire starting about a mile away in my current story. It will get there eventually, but by the time it does, it will be a fifth alarm fire. But with no wind, this isn't going to expand very fast. To travel a mile would probably require all day. Do I need to put it further back?
Thanks in advance!I'm sorry but I think your editor is right that you have a problem. I'd contact the Maryland Department of Natural Resources for more information and ideas on how to make your story work.

Best of luck,

Jim Clark-Dawe
Former volunteer firefighter/EMT

Tsu Dho Nimh
02-28-2009, 11:58 PM
First, there isn't any wind, except what the fire creates. It starts out as a campfire that gets out of control.

Without wind to blow embers or burning bits, someone stupidly making the fire in the middle of a patch of dry grass leaves, or someone stupidly tossing some gasoline on it, that fire will not go very far or grow very big.


The fire travels first downhill and then uphill.

Without a stiff wind blowing them downhill, fires will crawl uphill ... rather slowly. With enough wind, you can throw burning bits across a small ravine, but their natural movement is side-hill and uphill.


I need the characters to have about three hours in which they become aware of the fire, smell it, and eventually see it, as they are trying to get away.

Around here, the first thing they would see, and quite quickly, is a forest service slurry plane dropping a load of red goopy stuff on the fire if it's in an area where letting it burn is not an option.


The forest where the fire starts is hardwood, and eventually the fire will reach a cleared area (dry grass) of about 20 foot wide. The fire needs to cross this area to reach the forest beyond that. I have the fire starting about a mile away in my current story. Do I need to put it further back?

A mile in 3 hours is a fast-moving fire, in the absence of wind.

For this to work, they need to be uphill of the fire, and quite close to it, or have it be a windy day. Having it start much nearer to the edge of the grassy area and explode across it with a light breeze shoving it is plausible.

But it's going to be small enough to dodge easily. The trick is you don't try to outrun it. You move at right angles to the oncoming flame front until you are to one side of it, and then head towards the rear to get to a safe burned out zone. (standard Montana kid training, how to dodge grass and forest fires).

Amarie
03-01-2009, 12:44 AM
thanks to all of you! Now I know what I need to do to make this work.
It's fantastic to hear from experienced people.

JrFFKacy
03-02-2009, 05:37 AM
Tsu is right that there are a bunch of factors to consider here.

The first, and the worst one for your story, is the state this is located in. Maryland has about 600 brush fires per year. Average size? About six to eight acres. See http://dnr.maryland.gov/forests/wfm.asp. Needless to say, most brush fires are very small. A large brush fire in Maryland might have a hundred acres, which is less than a sixth of a square mile.

Out west and in Florida they measure large fires in square miles. A big brush fire in the Northeast just isn't.

The Northeast doesn't have crown fires very frequently. Because of population density and fire towers, brush fires just don't get a chance to get going. Crown fires require some heat before they get going. These are the big fires out west. California and Florida have brush-type fires.

The Northeast have low level brush fires where most of the fuel is pine needles and leaves on the forest floor. Most living trees and brush in the Northeast have a high water content and don't tend to burn. We also have grass fires, which do burn a bit hotter as the fuel load is higher in height.

Frequently in brush fires you can literally walk right over the fire. However, let's give you the formula for a big, Northeast fire.

First off, you start off with a Red Flag day. This is a day with extremely low humidity and high winds (25 mph+). The forest consists of a lot of dead and fallen trees, approximately ten years old. Terrain is uphill.

Fire will spread faster than you can walk, as long as the wind blows. Flame height might hit 5 to 10 feet. As soon as the wind stops blowing, flames would come down to the 3 - 5 foot range. And as soon as it tops the ridge, it will die back down.

Main difficulty fighting it will be getting personal and equipment to the scene. Normally it would be contained within about a quarter of a mile of when the fire department arrives. If the terrain is really bad, it might take until the next day.

Worst brush fire I went to wasn't contained until the next day. Burned about 800 acres. The terrain was so bad that the deer had different size legs so that they could stand level. It took another two days after it was contained to put the whole thing out. For people who've been on fire lines out west, it was very boring.

Now looking at your specific facts:

I'm sorry but I think your editor is right that you have a problem. I'd contact the Maryland Department of Natural Resources for more information and ideas on how to make your story work.

Best of luck,

Jim Clark-Dawe
Former volunteer firefighter/EMT

Jim Clark-Dawe: nice to 'meet' you, so to speak. I've read stuff you've written about barn fires on other sites and learned a lot.

Melia: I'm a Junior Volunteer Firefighter, but I've only been on for six months and forest fire season was mostly over when I joined up, so I haven't responded to a brush fire yet. As far as fires go though, I've done four structure fires and every one was completely different. None really had a lot of smoke, and we could get pretty close before we had to put on a Self Contained Breathing Apparatus (SCBA). At one fire, I was close enough to the house I could've reached out and touched it and couldn't smell smoke at all because the fire was mostly in the upstairs.

From what I've learned from talking to experienced guys, we don't tend to wear a lot of protective gear at a brush fire, it's just too danged heavy. Usually coveralls, workboots and helmet are all that's going to happen. Brush fires require walking, walking, walking, usually carrying our firefighting equipment.

If you need info about firefighting, try looking up www.firehall.com (http://www.firehall.com) (or google 'Firehall' in case that address is wrong). It's a fantastic Canadian website devoted to firefighting. The forum has lots of good info (and a section on Wildland firefighting).

JrFF