Laser, Paper, Vacuum

Yes, exactly, you can disrupt a fire by removing one or more of the oxygen, fuel, or heat, just like I said.


Okay - consider Halon based fire extinguishers. It doesn’t really remove oxygen, Fuel or heat. It’s added in a very small quantity for it to do that. Without bringing in too much chemistry, halon stops the free radicals in a flame from propagating by binding them. Free radicals are responsible for initiating new fuel to fire.

This is widely considered disrupting the chemical reaction.

Or disrupting the reaction.

Halon systems are handy for putting out fires in situations where you’d rather not asphyxiate any occupants who happen to be in the room; you can deploy it in concentrations high enough to kill a fire, but not so high as to displace life-sustaining oxygen. Contrast this with CO2 fire suppression systems, which will kill people who don’t leave the room promptly.

We did that too, it was our very first lab experiment of the semester. So for the whole rest of the year our test tubes were dirty and gross because you can’t effectively clean out all the crap from that experiment.

This is pyrolysis however wanted to point out that what comes out of the hose depends on the temperature and the rate of heating.

At lower temperatures (like a burner) you get the liquids (tar, phenols, benzene …) but at higher temps you get CH4, CO, CO2…

I did not know that. I’ve seen signs in computer and server rooms that have warned about halon gas fire suppression systems and their asphyxiation hazards.

Always assumed that it would be a good idea to GTFO if they went off. Still probably a good idea, but maybe not quite as urgent as I thought.

I think one issue is that halon is a carcinogen. It doesn’t get used much anymore. The data centers I worked at in CA all used something else that I cant quite remember.

I believe another part of the hazard in server rooms is that the halon may be deployed very rapidly, so the concentration may be temporarily greater in some areas than others, and may displace oxygen in those areas.

Production of halon was banned in the US in 1994 as part of the Montreal Protocol because of halon’s significant ozone depletion and global warming effects (it looks similar to many of the now-banned CFC refrigerants). There’s no one-size-fits-all replacement but there seem to be several better options to choose from now.

Could they just use nitrogen?

Still an asphyxiation hazard, but not as environmentally unfriendly. Also, not a carcinogen, though obviously you may have far more immediate concerns if you are in a room filled with it.

Not practically.

Nitrogen is plenty reactive enough if you have a reasonable amount of energy to hand. Just hand-wavily, if you’re dealing with relatively low energy fires, I guess you could, but you’d just be a lot better off with boxes of baking soda mounted in the ceiling, with strings tied to 'em so you could yank 'em down.

I think nitrogen can only be stored in usable quantities in liquid form, and that requires it to remain chilled to −346 °F. The temperature is maintained for transport and storage by venting small quantities of it continuously to atmosphere. That won’t work for a fire suppression system since it would need constant refilling. Plus the liquid to vapor expansion ratio is something like 1:700 and malfunctioning bleed valves have caused some pretty spectacular explosions.

Many years ago I attended a short course on fire prevention and part of that was a series of demonstrations of different fire extinguishers and where and why they are used.

One of these involved a tray of petrol. It was set alight and then different extinguishers were used with predictable results. Halon was astonishing. One short squirt from a small canister and the flame just stopped. No flicker, no hesitation, it went out like it had been switched off, leaving a tray full of unburned petrol.

The whole and entire “magic” of Halon was it is in effect an “anti-catalyst” to the chemical reaction that is fire. In the presence of Halon, the fire can’t burn even with plenty of fuel, heat, and oxidizer.

So you don’t need the great volume of it that would be necessary to defeat the traditional fire triangle by cooling enough to disrupt the heat leg. Nor the great volume that would be necessary to displace / dilute enough oxygen to disrupt the oxidizer leg. heck, it even works decently well on self-oxidizing fires as long as they’re not too energetic. Nor enough to blanket the fuel source to remove it from the site of reaction disrupting the fuel leg.

Any chemical which doesn’t have that “anti-catalyst” feature is not going to be a drop-in replacement. And if not drop-in, you’ll need to resize the whole system from supply to spray nozzle and everything in between. And all the consequential personnel & equipment safety stuff too.

Yes. There are others available now that interrupt the chemical chain reaction without acting as a bulk asphyxiant, and with a much less detrimental effect on climate change (e.g. 3M Novec).

I’m not aware of any fire suppression systems that do. Where I work, we have some rooms that use FM200 or Novec, but there is one room that uses CO2, which works pretty much like nitrogen does. No exotic-material fires expected in that room, just motor fuels. Occupants of that room receive an audible warning for something like 10-15 seconds before the CO2 dispenses, which is their warning to evacuate RIGHT NOW, because the CO2 can lay you out after one or two breaths after which you will probably die (because nobody is allowed to come in and rescue you until the fire department shows up with their self-contained air supplies).

FM200! That’s the one I was trying to remember. Ok. I can die now.