Halon fire suppression systems

Factual Questions
1

Ok, I’ve searched the boards as far back as they will go, I’ve searched the archives, I’ve done a google search, but I can’t seem to find the answer.

How do Halon fire suppression systems work?

I assume that they somehow ‘suffocate’ the fire, but do they force the oxygen out of the room, would it be some kind of powder/mist coming out of the system?
I really do want to know this. It’s a bit of a long story, yeah, but if you can even point me to a site that explains it in terms that I, someone nowhere near involved in fire prevention or suppression, can understand, I’d be eternally grateful.

2

http://www.h3r.com/halon_wk.htm

3

I had some exposure to such systems when reaerching data storage options for an employer in the 1980s. Halon is an inert gas that, just as you describe, suffocates a fire by displacing oxygen. Every place I toured that used it had a halon alarm system to make sure evrybody knew to scram if it was about to be released; when it is released (an invisible gas, I think) people can suffocate as well as any fire.

Here’s some info:

The Halon Recycling Corporation

4

Halon 1211 is being “phased out”.It is a halocarbon and contributes to the depletion of the ozone layer.It is being replaced by a chemical called FM200.

Halon works like any other agent.It is heavier than air.When the gas is released it displaces the oxygen and smothers the fire.

5

This site explains it in general detail. http://www.harc.org/oha2.html

The site’s main concern is how halon affects the ozone layer, but it does describe how halon fights fires.

6

Oh…I forgot…It is a colorless gas released from nozzles in the ceiling.I’ve been in a room when the Halon was released.It is loud and looks like a liquid as it discharges from the nozzles.The discharge is preceded by 30 second time delay where a horn and strobe light warn of “immenent discharge”,allowing people to evacuate or hit the abort button if it is a false alarm.

7

I can’t give you a technical answer, but from what I have learned as a Volunteer Firefighter, halons (or BCF’s (Bromochlorodifluoromethane)) work by interfering with the chemical chain reaction that operates to sustain combustion, as well as replacing the oxygen/air in the area of the fire.

I don’t know exactly how the chemical reaction is stopped, but it has something to do with the slowing or prevention of the production of free radicals from the material that is burning.

Hope this helps!

8

Wytehawk, apparently your recruit school taught you well. Thank your Fire Behavior instructor for me (or Portable Fire Extinguishers, depending on how they set up the program)…they know their stuff (as do you, I’m guessing).

Short Answer
No one is really 100% sure how they work, they just do.

Long Answer
We all know about the fire triangle (if you don’t, check here, I’ve waxed poetic about it before). Add a fourth side to it, the “Uninhibited Chemical Chain Reaction.” As a fire is cooking along nicely, there are millions of little chemical reactions going on just below where the flames are. Take a simple hydrocarbon burning. After it burns, you’ll have CO2 and H2O as byproducts. To get from (lets say) CH4 to CO2 and H2O, there are a bunch of smaller reactions that go on first. At some point, those reactions are going to spurt off some O, H, or OH ions (ie, they have a charge to them). The Halon that is applied to the fire reacts with that O, H, or OH ion faster than the ion would usually react with his neighbor (Thats why the Halogen family elements (F, Cl, Br) are used, they’re the most reactive ones (If I remember my chemistry right)). Thus, the Chemical Chain Reaction gets broken by that Halon-Ion bonding.
Wacky Stuff about Bromine
Its kind of interesting when you look at Bromine’s involvement as an extinguishing agent. The stuff (supposedly) works like this:

  • Fire heats up Halon 1301 (bromotrichloromethane), 1 Bromine atom jumps ship:
    CBrF3 --> CF3 + Br (both ions)
  • Bromine atom reacts with hydrogen ion to make Hydrogen Bromide:
    H + Br --> HBr
  • The HBr then reacts with a hydroxyl or oxygen ion, releasing te Bromine ion to start at the top again:
    OH + HBr --> H2O + Br

Maybe its just me, but thats some neat stuff. I didn’t come up with that one on my own, its from the Fire Protection Handbook, 18th Ed, page 6-283. Should be at your local library (or on the bookshelf of someone like me).

Problems with Halons
The biggest problem (the one that got it taken off the shelf) is that its an ozone depeting gas. The Montreal Protocol caused its production to cease, so the stuff used in aircraft engine fire extinguishers comes from the stuff sucked out of computer room systems.
Another problem, and one that was known about for quite some time, is that the health effects from some of the Halons is nasty. Take Carbon Tetrachloride (Halon 104). Hasn’t been used since the mid 1960’s, and is illegal in most states. Heat up Carbon Tet and it turns into Phosgene gas. Inhale Phosgene and it turns into hydrochloric acid in the lungs, so you drown in your own blood in about 24 hours. For Halon 1211 and 1301 (the ones you usually find), there are no adverse health effects up to 10% agent in air. Still, I wouldn’t want to be in the same room as one of those systems discharging (I’ve seen total flooding CO2 systems discharge, and its quite a sight…the nozzles are 1.5" diameter every 10’ or so, and thats for a gas coming out. Looks like a foggy day in the computer room until the fans push the gas out. Thats some wild stuff).
Whew… ::wipes forehead::

9

<Funny true story:>

A friend of mine works at an ISP/Webhosting company that has a huge server room protected by halon systems. I happened to be getting the dime tour of said room when my friend’s Idiot Coworker, who happened to be playing with a lighter, accidentally lit his copy of Practical C Programming on fire.

I then heard a very loud “WAAAH WAAH WAAH WAAH WAAH” and saw the proverbial strobe light flashing. My friend jumps up on the desk, jumps accross to another desk, leaps off the top of a monitor and slams the abort button on the wall, all the while yelling “FUUUUUUUUUUUUUUUUCK!!!” Imagine Spud Webb going for a dunk in slow motion, except hitting a big button on the wall. Funny stuff. (Though it would have been considerably less funny if the system went off, in which case the fire department has to come and yell at you.)

</Funny true story>

10

Thanks y’all. I really do feel better now, though I was laughing at myself for wanting to know so badly. :slight_smile:

11

An additional problem that KCB615 didn’t mention is that a number of people are violently allergic to it. Another one of the areas these are used in is grain elevators, they can actually suppress a grain dust explosion they work so fast.

12

Another place they are used is in film vaults storing nitrate cellulose prints since any sort of traditional extinguisher or fire containment appartus is completely useless on a nitrate fire.

13

We used CCl[sub]4[/sub] in high school for insect “kill” jars for our insect collections. They had a sawdust layer topped off by a plaster layer with holes. The sawdust was soaked with CCl[sub]4[/sub]. When we caught a bug, we’d stick it in the jar and seal the top. It’d be dead in minutes. (For comparison, a bug in a regular jar can survive for about a day.)

We could only make one jar apiece, but I needed more. When I tried to buy CCl[sub]4[/sub] at a chemical store, they said I needed a permit. Then I lucked out. My sister’s boss ran an old gas station/convenience store just off of I-70 on the way to Utah. Except for food items, he just kept his stock on the shelves until they sold. He happened to have two cans of CCl[sub]4[/sub] on one of his shelves. He sold it to me for whatever price had been marked on the can in the early 1960’s. (This was 1981.)

I never intentionally breathed the stuff, but I could smell it every time I opened my jars to put in an insect. Nasty. And now that I know what it does, I’m glad I didn’t become an entemologist.