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Comment by llamaimperative | Hacker News Reader

I did some napkin math on this.

Pacific Palisades and Altadena (at the time I looked) had about 8,200 acres burned (not including the wildlands).

Assume 30% of that is actual structures, then assume only 10% of those structures are on fire at any one time. Assume there are no 60 - 100mph winds blowing embers miles ahead of the fire lighting more fires.

Even then, you'd expect to need ~375,000 gallons per minute to suppress it.

The entire area is pressurized by 3 water tanks that each hold 1 million gallons, so that'd be exhausted and the system depressurized within 10 minutes. It stayed pressurized for longer than that because in practice it's pretty much impossible to produce 375kgpm of flow out of fire hydrants (you'd need several hundred simultaneously).

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Doesn't that depend on when the firefighters started attacking the fire? You don't have to put out the full extend of the fire if you can stop it.

Example: a grease fire starts in my kitchen and burns down my house. I don't need the water required to stop a full bore house fire to put out the grease fire in my kitchen and save my house.

The hydrants ran out of water very quickly, because the reservour feeding them was taken out of commission because there was a tear in its cover. It's been offline since last February. The cover is only needed to prevent evaporation. They could have had water in it, which very well may have been enough to stop the full spread of the fire.

This is gross negligence.

Here's the timeline for the Palisades fire (one of several):

Hour 0 at detection by an automated system: 10 acres

Hour 1: 200 acres

Hour 4: 1260 acres

The first few hours were in the wildlands which are difficult to access, don't have fire hydrants every 500 feet, and aircraft were grounded due to 60 to 100mph winds

No, the fire hydrants did not run out of water because the Santa Ynez reservoir is down for repair. They ran out of water because the system depressurized.

The fundamental issue is extremely dry vegetation and extreme wind. The dry fuel is caused by increasingly violent oscillations between extreme wet seasons (causes lots of growth) and extreme dry seasons (causes dryness).

This is exactly the "hydroclimate whiplash" predicted by climate models: https://newsroom.ucla.edu/releases/california-extreme-climat...

Yes, it is gross negligence, but at a much more massive scale than you're suggesting.

I agree that it is grossly negligent to subsidize the building of a major city in a desert or semi-arid area, and then not invest in sufficient infrastructure to take care of easily forseable issues such as this.

But, come on!

The hydrants, which are fed from smallish tanks, which are fed from the reservoir, did not run out of water because the reservoir was offline?

What magic pixie dust was going to feed those hydrants with the reservoir empty? They could pump water up to those tanks, but we already know that just isn't going to work at any kind of scale. It's barely adequate to meet normal domestic water needs.

I guess we should just throw up our hands and not hold people accountable for basic maintenance of basic systems, or taking systems completely offline to do ancilliary repairs to things like a covering tarp. Or making massive cuts at the state and local level to fire prevention and fighting efforts.

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