Fire and oxygen at high altitudes

Factual Questions
1

Help me out here. I was watching the History channel and they stated that La Paz Bolivia is the capital city with the fewest fire disasters. The reason they gave was that at about 12,000 feeet above sea level there is not enough oxygen for fires to get going!?

What? There is enough air for people to live but not enough for a fire?!

This can’t be correct. Maybe they have mostly stone buildings or a great fire dept.

I tried to find some info. on the web but found nothing about the city and the rate of fire disasters. I did find that the Presidential Palace is also called the Burnt Palace because of the fires of the past in that building.

So how much difference do the oxygen levels make to a fire?
Do fires burn quicker or hotter at sea level than at high altitudes?

2

There is enough oxygen to start a fire and breathe, just not enough for them get going. I’ve been there and lighting a smoke can get to be quite a pain sometimes, and a walk to the corner store will leave you panting for breath no matter what shape you are in.

3

You can certainly have a fire at 12,000 feet. Ask a pilot if you can have a fire at 30,000 feet.

But there is less oxygen. A quick look at Google sources reveals mostly talk of hazards in oxygen enhanced environments, but my first pass impression is that the kindling point for solids is higher at the reduced oxygen levels found at higher altitudes. Thus it would be harder for a fire to spread, I suppose. That’s all a WAG.

I should go to bed.

4

I don’t have the figures but when I was at Biosphere 2 the oxygen partial pressure levels dropped to the point that a candle flame couldn’t be susteained. The crew had a very difficult time completing tasks and were fatigued after climbing stairs. A measured amount of oxygen was added - a tanker truck of LOX - and it energized the crew immediately.

5

I live at 11,200. There is certainly enough oxygen for combustion. Another 800 feet really won’t make that much difference. I should know since I heat with wood.

I’m astounded that the history channel could be that misinformed.

6

Here’s a site that says more air is require to run a boiler above 500 feet.

Here’s an article that says that the amount of O[sub]2[/sub] required to support combustion depends on the material being burned.

This is interesting because in one of my computer rooms, the fire protection guys told us that if the Halon is discharged, a human can still continue breathing , but the fire will be extinguished. I just assumed that they were lying and that you would die in there. Maybe they were telling the truth.

7

Not necessarily. Once accimatized to altitude–especially at a relatively low 13,000 feet–a well-conditioned person should not be panting after a walk to the corner store.
Maybe your cig has something to do with it.

8

Nonsense. Halon works by displacing the oxygen. No oxygen means no fire, and suffocation for you if you don’t get out of there pronto.

9

Wait, what is Halon and why is it in your room?

10

I’ve started fires at 16,000 feet in Tibet. Of course, water boils at a lower temperature, and you personally suck serious wind. Everest guys all seem to be able to start fires way the heck up there. Sounds like crapola to me.

11

Halon is an inert gas used for fire suppression, as described by Kamandi. Everywhere I’ve ever visited that had Halon had a very loud alarm that went off 30-60 seconds before the doors shut and the Halon was discharged, so the occupants could scram.

12

Halon is far from “inert”. It oxidizes very quickly, but without much heat and without being set afire. It therefore removes the the O[sub]2[/sub] from the air so that the fire cannot use it.

Any biological life in the room will also be starved of oxygen.

13

You can, it is usually called an engine. However, I don’t know if a fire could be started that high up without using compressed air to sustain it. Old WWII planes could fly that high, but their engines are all equipped with turbochargers to compress the induction air. Jet engines are basically just big air compressors. I know that above a certain alitude it is not possible to restart a jet engine that has a flame-out, but I don’t know how high that is.

14

AWB is right - incorrect info on my part. Because Halon oxidizes rapidly, it rids the environment of combustable and coincidentally breathable oxygen. Thus the safety measures. I believe Halon fire control systems are gradually being retired, actual production of Halon ceased in ~1994.

15

a quick search indicates that THC is not the only group repeating this claim about la paz: http://www.twsseminars.com/howaboutthat.html (13th paragraph)

ironically, though, the U.S. State Dept. – calling the fire/altitude thing “conventional wisdom” in one of its magazines – says the resulting use of gasoline to start fires in la paz may be a fire hazard itself.

http://www.state.gov/www/publications/statemag/statemag_march/feature7.html

16

Halogenated agents do not touch the oxygen in a compartment involved in a fire. Halons extinguish fire by interrupting the actual chemical reaction that fire is. When something burns, it does not just go from chemical + O2 -> chemicaloxide. There are millions of single-molecule reactions going on inside that fire involving free radicals, the super-reactive building blocks of a combustion reaction.

Halogenated hydrocarbons are more reactive than these free radicals are. The halogen thats added to the hydrocarbon molecule (be it Cl, Fl, or Br) attaches itself to the free radicals that the fire is spouting out. When they attach, they stop further reactions, which stops further heat, and the fire stops. Very small quanities of halons are all that is needed to extinguish a fire.

The alarm systems that are found inside rooms protected by halon systems are needed, but not because you’re going to die if you breathe the stuff. There’s a fire, and something is being put onto it that isn’t water. Time for a local alarm to tell you that.

The effects of halon exposure are:
5-7% : Little to no effect
7-10% : Mild CNS effects such as dizziness and tingling in extremities
10+% : Feeling of impending unconciousness after a few minutes, however test subjects in 14% halon for 5 minutes have not lost conciousness.

The reccommended exposure levels are:
7% and below: 15 minutes
7 to 10%: 1 minute
10 to 15%: 30 seconds
above 15%: prevent exposure

The “normal” total flooding halon system should produce somewhere between 5 and 7% agent in the air. Some can go to 9%, depending on what you’re protecting. So being in a “normal” protected room, you’re going to be just fine. Heck, with a high quantity of agent you’ve got some time to get out (of course, exiting as quickly and safely as possible during a fire is of prime importance).

Now, thats the problem with the agent itself. What happens when the halon hits the fire? The problem that follows the agent discharge are the decomposition products from the halon. Hydrogen Flouride is a common one with Halon 1301 systems (those found in computer rooms). HF has a nasty habit of going after calcium in the body. The decomposition products from halons aren’t a big deal in and of themselves, though, as there aren’t a lot of decomposition gasses produced, and the gasses produced from the fire itself would kill you long before the HF or the Halon 1301 did.

All this talk about halogenated agents screwing up the O2 in the air. No one’s brought up CO2 total flooding systems. Those ones feel like they’re sucking the air right out of your lungs. There is a oxygen depletion problem with CO2 systems, and if the alarm goes off, get the heck out of there.

Your fire science lesson for today…

17

getting back to the original topic, I think there’s a misunderstanding here.

The OP quoted a statistic that fires statistically burned less in a city at 12,000’. Then several people stated that they could indeed get fires going at that altitude and higher. I don’t think anyone was claiming that fires couldn’t start there at all, so what’s the point?

18

Speaking of fires at a high altitude, I couldn’t help but notice that most of the posts in this thread were made exactly 1 week before 9-11 happened. If only we knew…

19

You revived the thread for that?
And those towers weren’t at high altitude.

20

Oh, 2001. How naive you were about the ‘History’ Channel.