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Comment by mooneater | Hacker News Reader

"I noticed some white smoke at the south end of town and within 15 to 20 minutes, the whole town was engulfed in flame." -- town mayor

That is terrifying speed.

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Strong winds fan flames in a hurry, but for a typical forest fire, the problem isn't actually the flame front - it's the firebrands (burning pieces of wood tossed ahead of the fire by the wind). They get lofted by the rising hot air, catch a breeze, and extend typically half a mile or more in front of the actual flame front. So you end up with a ton of spot fires that, if not addressed, do things like "light the whole town on fire." Buildings burning create a ton more of these, and you're screwed.

If you look at the aftermath, you're almost certain to see buildings mostly burned from the top down, with intact landscaping around them - that's a strong sign that the spread was firebrand based.

Unfortunately, if you've not built for it ahead of time (and sometimes even if you have), there's literally nothing you can do when the fire hits in high winds.

I mostly deal with grass fires locally, and even those can get going in a hurry with a strong wind. Of course, the only days they ever seem to burn is in a strong wind...

Here's a terrifying example from fort McMurray where it's raining embers: https://youtu.be/7E_OLgC4nV0

Yeah, that's a great example. You can see some spot fires starting in a few places in the video along the side of the road.

If you know what you're doing, have backup power, and some water storage, someone staying behind to deal with the spot fires before they grow can have a large impact on the survivability of a house or neighborhood. If you're somewhere prone to wildfires and you have a pool (and are the sort to stay behind...), a good propane powered pump and enough hose to run good lines around the house will have a huge impact - and even if you don't have that, a few thousand gallons of water storage isn't that expensive (compared to a house). If you've got a properly set up wildfire rated house without much debris around it, a good Class A rated roof, and some water, you can do a lot.

Of course, you can always roll a 1, and certain houses (shake roof) will simply go up like a candle in an ember storm like this, but in that situation, I'm not sure a car stuck in traffic is the better option.

Houses can handle an awful lot of radiant heat, and they'll survive perfectly fine a radiant heat flux far beyond what a human can tolerate. You just can't let direct flame impinge on them for very long before it spreads.

Yup. The only defense against firebrands is to build such that your house won't catch fire in a rain of firebrands.

Locally, a combination of stucco and concrete tile roofs can make a house basically immune to fire rain--but concrete tile roofs are not an option in most places.

You don't actually need non-flammable roofing - just a roof rated for the fire type.

Check Class A roof tests. A lot of asphalt shingles, properly installed, actually are Class A fire rated - which is a 12x12 2kg grid.

https://www.builddirect.com/learning-center/building-materia...

Interior corners on the roof or house tend to cause problems, though. Debris builds up and ignites, and just impinges on the siding until you light something behind it.

You can also have firebrands entering through attic vents and bypassing the roof - there are vent types that are resistant to this, but tend to cost a good bit more.

Why we don't do this in urban wildland interfaces... no idea.

Or keep the roof wet. As long as your water supply exists, roof sprinklers work. They're popular in Australia with people living in bushfire prone areas. https://build.com.au/roof-sprinklers

(It also helps that bush properties have large water tanks attached to them)

A firefront moves a lot faster through grass than through forest fuels given the same moisture content. Totally different strategies required to fight them.

They don’t throw embers like a crowning bushfire, though.

Out of curiosity I plugged Lytton’s weather readings into the Mccarthur tables we use to calculate forest fire danger in Australia.

I’m using guesstimates for humidity and wind speed based on the spotty data available from the local government website. Also just totally fudging the fuel load number.

I’m reading spotting distances between 1.5 and 2km.

Overall FFDI of 41 so a bad day but not extreme by our standards. Would have been a lot worse with lower humidity.

Parts of the province were down to 11% humidity. Lytton is renown for being extremely dry.

This is what happens when you spend a century putting out every single fire you can and allow decades of match ready fuel to accumulate around residential property. The problem ironically is that the people who would benefit the most from prescribed burns that would save their town from this are often the most vocal opponents out of air quality concerns during the course of the controlled burn.

There's that, too. It's the forest version of technical debt. You can build it up for a while, but if it doesn't burn, when it does, get out of the way...

The huge crown fires of the last decade aren't how forests are supposed to burn. A "standard" forest fire is a lower intensity event, burning along the debris on the floor, taking out a few trees (usually older/weaker/dead ones), but it doesn't come through as a wall of several hundred foot flames, incinerating everything in its path.

That's a fairly new feature for forest fires, and it's going to take a long time to get rid of all the built up debris.

We need to just catch up and actually fund these controlled burns. It doesn't help that lands might be managed by different forms of government depending on where it is, and they all have different policies and funding levels to this sort of thing. When you look at Mexico its an entirely different story than even nearby southern california. Fires in Mexico in wildlands have historically not been fought, so there is much less fuel, and they don't get so unnaturally large and catastrophic like they do in the US and Canada.

You may be surprised to learn that places that have had a fire can get them again, only a few years later. It doesn't take a lot of fuel to create a fast moving fire. Grasses and weeds can grow quickly after a forest fire.

Certainly managed control burns are a good thing, but having lots of control burns doesn't solve the problem on its own.

The underlying problem is building permanent housing in areas that historically burn perennially. Outside of that, it's management that is needed to ensure fires are manageable enough where property can be protected. A grass and weed fire burns out much faster and is much less intense than one where there are dead trees and logs and a significant amount of larger dead accumulated brush that need much more time to burn to ash, and produce a lot more heat. The grass and native chapparel fires hardly seem to last a few days when they happen in southern california in areas that have recently burned. Whenever you see a long winded fire roasting away, like the one that threatened Mt. Wilson Observatory last year, you will inevitably also read something like "The last time this forest burned was in a fire that was fought 60 years ago."

Sure, you can have grasses build up, but a couple years of grass growth isn't going to lead to crown fires destroying the entire forest. It'll rip along the ground, kill the weak trees, clear the ground, etc.

Grass fires also don't tend to toss much in the way of firebrands - it's direct flame spread along the ground, and that's a lot easier to block/protect a property from than the flying ember variety of ignition sources. I keep a 15-20' bare dirt firebreak around our property because the hill burns every few years. A grass fire isn't going to cross that, even in the wind. If it does, it's in a few spots that are easy to keep up with - it's not a large flame front.

I do keep the discs on the tractor now, though, all summer unless I'm actively using something else. Much as I hate "start, pin the governor wide open, roll" style startups on the tractor, I'll do it if there's a fire and I can go get ahead of the fire line or extinguish chunks of it.

We also keep a pickup around the hill with a couple hundred gallons of water and a fire pump in the back, for similar reasons. Local fire service is good, but it's better to be able to deter and redirect things on your own - and against burning grass, you can easily do that.

> doesn't solve the problem on its own.

Nothing will completely solve the problem, but controlled burns do considerably cut down on the total area burned.[1]

1: https://www.researchgate.net/publication/237866254_Effective...

Firestorms will be the new normal as temperatures accellerate.

https://www.co2levels.org

Many people don't understand how quickly fire spreads when it is so dry out. A single ember or piece of hot ash in the wind can create a huge fire in less than a minute. We are in drought conditions already this year, and we had to move our fire pit because the usual location is so unsafe.

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