Bombing forest fires sounds ridiculous, but is grounded in physics | Hacker News Reader

Bombing forest fires sounds ridiculous, but is grounded in physics

popularmechanics.com

81 pointsraleighm78 comments

Using explosions to put out fires isn't an entirely novel idea: it's actually used in oil-well firefighting[1]. That said, I have some serious concerns about the applicability of this technique to wildland firefighting.

In the interest of full-disclosure, I am a former firefighter, but I was mainly focused on structural firefighting. We did respond to wildland / brush fires, but only got involved in direct suppression activities on the smaller fires. Larger wildfires we just provided protection for exposed structures and let the Forestry Service handle the primary suppression efforts. Anyway...

One of the main dangers of wildland fires involves something called the "wildland / urban interface"[2]. This is where homes and urban construction border on and/or intermingle with wildland areas. When you hear about "Wildfire X destroyed N homes" this is usually referring to events that happen in the WUI. I don't think it's hard to see how dropping bombs in this area could be problematic - even using the specially tuned bombs referred to in the article.

Also, a wildland fire isn't like an oil-well fire in that you don't have all the fire concentrated in one small, well-defined area, where you can quickly "snuff" it out. In a wildland fire - especially in the driest, most dangerous conditions - it seems likely to me that the same shockwave that snuffs out flames in a certain area, might well spread embers that actually spread the fire to an even larger area.

Maybe there's something to this, but overall I'm somewhat skeptical.

[1]: https://en.wikipedia.org/wiki/Oil_well_fire

[2]: https://en.wikipedia.org/wiki/Wildland%E2%80%93urban_interfa...

What an excellent comment. This is probably a naive question would it help on the leading edge of the fire? Maybe there is not such a thing. Large fires might not have a leading edge.

thanks!

I mean, I can imagine some scenarios where this might be useful, but I see a LOT of open questions that I'm not sure anybody has the answers to yet. OTOH, I'm not a specialist in wildland firefighting specifically, and it's entirely possible there is research out there related to this topic that I'm just not familiar with. Which is, I suppose, a long winded way of saying "I'm not sure". :-

Very much this.

Most effective bushfire combat involves fuel denial, rather than directly putting out flames. And one of the most effective forms of fuel denial is setting backfires.

Fires spread generally via embers.

Bombing bushfires does nothing against fuel, and will likely increase ember spread.

And the prospects for ground crews encountering UXB might be problematic.

I believe the thinking is that a giant crater doesn't burn, and a thermobaric bomb consumes all of the oxygen in a wide area for a short while.

But that isn't going to help with embers that are pushed ahead of the leading edge of the fire by the shockwave. And burning embers stay hot and can spread fire over surprisingly long distances. If you've ever seen news footage where a wildfire "jumped" an 8 or 12 lane wide highway, you can bet that it was ember spread that was responsible.

I'm not going to say that this idea has no merit; and I think it may be worth further investigation. But at the moment I have some major concerns about it.

I assume the idea is to drop the bomb in front of the fire so the shockwave pushes the embers backwards?

I mean, yeah, probably. But it might not be that simple. Which is why I say I'm skeptical, but don't claim to be sure this wouldn't work well.

Consider that air currents tend to be chaotic systems in general, mix in a shockwave from a bomb, and ask "can we really predict where the embers are going to go?" Especially as they rise and encounter different air currents that are moving around helter-skelter. Remember, large fires can release so much heat energy that they create their own hyper-localized weather.

Anyway, again, just to be clear: I'm skeptical, but I don't want to sound completely dismissive. I do think this merits further study. I just see a lot of potential ways this could fail to work out.

Also, it isn't just an out of the box solution. At the beginning of the 20th century the United States army tried this as a "solution" to the San Francisco earthquake and ended up blowing up the city and setting new fires on their own.

In 1666, it worked quite well for London.

What about the Sonic boom idea?

Not to mention the risk of accidentally bombing firefighters on the ground.

Also, one important thing that is missing in the article, the fire in question in Sweden, was (partially) on a large training range for the Army that had been in uses since the 60's, which made it easy to go ahead and test dropping a bomb on the fire.

> Using explosions to put out fires isn't an entirely novel idea: it's actually used in oil-well firefighting

Probably the most powerful explosive used in such firefighting was an atomic bomb, which was used by the Soviet Union in 1966 to put out a large oilwell fire in Uzbekistan.

photos and the video...

https://www.mirror.co.uk/news/world-news/soviet-union-detona...

The word “probably” seems highly unnecessary.

I agree, this article just seems to strain credibility. Forest fires aren't candles. You can't just "blow out" a solidly burning piece of tree.

And after the explosion, you still have a lot of fuel hanging around—it's just going to start burning again moments later... long before any fire crew can traverse the safe distance from a FREAKING BOMB DROPPED FROM A PLANE.

(The key reason bombs work for oil fires is because the fuel gushing out of the well isn't hot. Blowing it up denies it oxygen for enough time to deny it heat. Plus any hot oil gets flung a good distance from the well head.)

probably a dumb idea, but perhaps automated tracking and targetting embers from a mobile platformm?

either speed up their combustion in flight (CO2 laser? releasing oxygen?), or stop their combustion (small targetted water jets?)

> severe droughts, meaning more dry fuel, as well as more intense heat waves”. The conditions set the stage for more, larger fires throughout the year. The trend will threaten people, property, and natural spaces

It’s funny that we often phrase forest fires as some ecological disaster, when in reality they are a normal and healthy part of a forest. I fact, some seeds won’t even germinate until they’ve been roasted by a forest fire [1].

It’s only now that we live all around and inside them that it’s become our problem.

1. https://www.britannica.com/list/5-amazing-adaptations-of-pyr...

Agreed. Like the lodge pole pine that covers much of northwestern Wyoming and has serotinous cones that rely on heat to release their seeds.

Well, it’s both. Native Americans used to intentionally burn as a method of maintaining a healthy oak Savanah. Today, we don’t do that anymore and, like you said, we’re building in fire prone areas — but climate change is also creating longer fire seasons, and more droughts. It’s a deadly combination.

Totally agree about Nature needs the odd wildfire. On the point of the bombing maybe the Vacuum bombs aka Thermobaric bombs could be a solution. https://en.wikipedia.org/wiki/Thermobaric_weapon They burn more intensely so could the advancing edge be bombed so what is on fire burns out more quickly so that t can not advance? Although many will be familiar with the Fire triangle, if you can burnt an area at an accelerated rate, the fire can put itself out. As the vacuum bombs are essentially just fuel that suck/use the oxygen in the environment, they could steal the oxygen from the fire. These are also slow exploding bombs as a result but it would be interesting to see how they work on the advancing face of a wildfire. Hard part would be getting the right sized explosion, the Military cant control the size of an explosion that well, but Reaper drones could be used effectively with their laser targeting.

But are the severe droughts "normal and healthy"? California has over 100 million newly-dead trees in the last few years, which is unprecedented.

https://www.livescience.com/57124-california-drought-killed-...

Climate is never static. All weather is, "normal."

Unless we are about to put 300 ppm of carbon into the ground, Californian forests will either have to deal with the new normal, or die out.

Severe droughts are historic to California (and therefore "normal", though perhaps not "healthy"). https://www.nytimes.com/2015/04/14/science/californias-histo...

Also, these are to a large extent not “natural forests”; these forests can be huge areas of human planted forest with vast areas being covered by trees all the same age and size. This could mean it burns faster and recovers slower than a natural forest.

Also in natural land there are natural borders such as wetlands to limit spread, and if those wetlands have been ditched to increase forest area then the reach of the fires will grow.

But you are absolutely right this is a human problem not a forest problem. Humans live in these areas, and live off these forests. Not seldom the people whose homes are threatened by the fires are also landowners whose livelyhood is the forest itself. That the ecosystem grows back cyclically is no comfort, they expect their homes and livelyhood to be protected.

Since 1910, 95% of fires are caused by man: http://www.marinij.com/article/NO/20180812/NEWS/180819940

More unnatural issues: https://www.vox.com/energy-and-environment/2017/10/12/164582...

I think it is a realistic firefighting tool but overall I think we just need to get more realistic about how we live with wildfires, especially in ecosystems that are specifically adapted to have wildfires. For all homes built next to a fire line/brush area make sure they have systems implemented to prevent them from burning. For urban areas you can just have exterior sprinklers. If the area is a subdivision then have a good margin of brush-free clearing. Have a water suppression system built in place to pump water directly on the burning zones. Then you simply let the fire burn itself out until it reaches the fire suppression system knowing that system will stop the fire from destroying homes.

For homes that are directly in the forest areas (rural) then we just need to build those homes with fireproof materials and have some sort of basic fire suppression system. Maybe a fire-proof/heat resistant tarp over the structure? Perhaps a novel solution would be to simply build UNDERGROUND homes in these areas instead. No need to worry about fire at that point. I am watching the news and see a lot of these structures and just wonder what the people were thinking when they built it. Really...a log cabin in a forest that is known to have forest fires somewhat regularly?

Building homes underground is an order of magnitude more costly. And people like windows. And you'd have to build them pretty deep and have some really good entryway insulation before you can stop caring about a wildfire raging overhead. Those things get hot.

The problem with bombing a forest fire is that not all bombs that are dropped explode. So, instead of a fire that will eventually stop being a fire, you've got a fire and an unexploded bomb.

What is the failure rate of modern ordinance?

An interesting question in the field of public administration...

"The quality required of fuze designs is usually specified by two values: functional re-liability, which ranges typically from 0.95 to 0.99 for complex missile fuzes, and to 0.999 for projectile and bomb contact fuzes; and safety reliability, for which a failure rate not greater than 1 in 106 must be proved prior to release of items for service usage."

https://fas.org/man/dod-101/navy/docs/fun/part14.htm

The reason cluster munitions were banned is that the form factor and econonics lead to less reliable detonation, not because we can't build a reliable fuze, given a larger space and weight budget.

The convention on cluster munitions wasn't signed by the world's 5 largest armies, so the ban is of limited extent. (Or do you mean another agreement?)

1 in 106 is a strange ratio. It seems that this article was reformatted, particularly because of all the random hyphens. Is it possible that the original said "1 in 10⁶"? I would be a little concerned if I was in the military dealing with bombs that had around a 1 in 100 chance of exploding (or even arming) unexpectedly.

I'm hoping that's the failure rate for detonation and not unintentional detonations.

Yeah 1 in 106 seems like an unbelievably high allowable failure rate.

I think "functional reliability" of > 0.95 means that a failure of 1 in 20 to detonate could be acceptable, whereas "safety reliability" of > whatever refers to the chance of improper arming of a weapon. False negative vs. false positive, if you will.

While both could be catastrophic under some circumstances, it seems reasonable that you would expect "safety reliability" to be much higher because it's tested more often. Near the end of the document it talks about how safety reliability should be very high.

I'd strongly suspect it was OCR'd 10^6 into 106.

Specifically as they talk about using multiple systems in series to increase safety reliability, where every system must function correctly in order for the weapon to be armed.

It's a funny question with that spelling :-) it's "ordnance".

Thanks! Too late to edit...

What the article doesn't seem to mention is that the fire that was bombed in Sweden was on a military training ground. Undetonated ammunition was the very reason why bombs were used, as conventional methods were considered too dangerous.

I guess the resulting solutions are just ... more bombs followed by more bombs.

The idea is that in a few hundred years, the ground will be all unexploded bombs. Then you don't have to worry about forest fires anymore.

To be fair it is easier to deal with undetonated explosives when the area isn't on fire. Granted removing all ordinance from an area is an expensive and painstaking process to do safely - hence why they prefer to just slap on an 'off limits' cordon and sign around the old areas instead of remediating and reusing it.

"...an aircraft will generate a sonic boom along the length of its flight path at a rate of one mile per thousand feet."

Can someone explain what is being measured as one mile per thousand feet?

One mile wide per thousand feet in altitude?

Doesnt matter. Sonic booms have virtually no real power. All the tales of them breaking windows and starting avalanches are pure myth. (See the anti-concorde media campaign.) Forest fires release atomic bomb-levers of energy. A slight puff from a tiny f-15 is a butterfly compared to the winds generated by the fire itself.

Here’s the Brazilian Supreme Court windows breaking from a sonic boom.

https://youtu.be/43Kl7c2yU3g

Yes. One or two breakings here and there when all the conditions are perfect. Look at the mythbusters tests with the usaf. They came to nothing. Ive sat under many an f18 doing a mach1+ flyby (rcaf). Car stereos create more power, and worldwide probably break more glass.

Upon looking at that video again, I have to wonder if the building design and construction didn't play into that as well, with the very overhang taking energy reflected off the ground and directing it back down towards the windows.

>A slight puff from a tiny f-15 is a butterfly compared to the winds generated by the fire itself.

May be all that's required [0].

[0] https://en.wikipedia.org/wiki/Butterfly_effect

You keep using that word. I do not think it means what you think it means.

I remember sonic booms in the 1960's in the midwest. They weren't worthy of note.

This is what Boots and Coots did so well during the Kuwaiti Fires that were started during Desert Storm.

A great documentary on the Kuwaiti fires shows this technique, along with others, being used. [1]

[1] https://www.youtube.com/watch?v=L77BSBKvMJk

We should at least try this while the fires are going even though it's expensive. There's no wildlife in the middle of a fire other than rodents under ground. Just bomb the area that's burning wider than the blast radius.

As I replied to another comment, there's a lot more to object to than just wildlife. Natural and cultural/archaeological resources can be destroyed by explosions while fire may not destroy or damage them. (Think rock formations, rock shelters/caves, rock art sites, and the like.)

How did they justify it in Sweden then?

Just because another country does something stupid doesn't make it a good idea. Also, as noted in another comment, the one time this was done in Sweden, it was a fire on a military base.

In the U.S., cultural resource protection is one of the considerations in wildlands firefighting, and a significant number of wildfires in the U.S. west occur within designated Wilderness areas where minimum impact suppression efforts are required by law. This means, e.g., you can't run a bulldozer through to cut a fireline in Wilderness, and in some cases can't even drop slurry because it might cause permanent staining on rock outcrops, damaging a natural resource. Dropping weapons-grade bombs is going to be a non-starter, as it should be.

Weird. Because there are all sorts of bulldozing at work right now in the California wildfires: https://www.ocregister.com/2016/07/13/these-bulldozers-are-f...

Bulldozers are used in fireline construction, but not in designated Wilderness areas. Wilderness restrictions were one example of why this is a bad idea, but they are not the only reason.

The fire was in a military weapons area, there were unexploded ordinance there making normal fire fighting difficult .... on the other hand it was likely easy to get permission to drop another bomb there

This reminded me of the technique of combating a forest fire with another from the opposite direction. Read about it as a kid in Physics for Entertainment by Yakov Perlelman.

We did it a few weeks ago in Sweden, burned 800 hectare (2000 acres) to slow down the progress of the largest wildfire this year.

Source in Swedish: https://www.svt.se/nyheter/lokalt/dalarna/800-hektar-skog-sk...

To add unbounded credence to this idea, it's basically what Macgyver did using nitroglycerin to put out a wellhead fire in the 1985 episode "Hellfire"

I feel a lot of people will object this because of wildlife. But even excluding that, how can you be sure there are no persons there?

There's a lot more to object to than just wildlife. Natural and cultural/archaeological resources can be destroyed by explosions while fire may not destroy or damage them. (Think rock formations, rock shelters/caves, rock art sites, and the like.)

Because it is in the middle of a wildfire that has raged for weeks, in an area that was off limits for people even before the fire started.

It's grounded in MacGyver!

its seems totaly legit to use hydrogen bombs for fighting against wildfires.

This came up a couple of days ago. I'll just leave this link to what I had to say then.

https://news.ycombinator.com/item?id=17726721

We've merged that thread into this one and rolled back the clock on your comment. Thanks for pointing it out.

.. except that "fire-dependent forests" are undergrad level knowledge in Forestry Science.. e.g.

United States Department of Agriculture Forest Service Pacific Northwest Research Station General Technical Report PNW-GTR-727 July 2007

So are there plans in place to use fire proactively to do controlled burns on overgrown / older forests?

Planned forest fires are pretty common

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