Could inert gasses be used in sky scrapers? (Halon and it's alternatives)

Factual Questions
1

(I originally titled this “Could Halon be used…” but realized in my research that Halon is an environmental no-no)

I ask because there seem to be a myriad of issues dealing with water-sprinklers in high-rise buildings:[li]pressure (just getting it up 1,400 feet!), []circulation (I’m not sure, but I figure you wouldn’t want it stagnating in the pipes) []ineffectiveness against fuel firesdestruction of property by water damage (and the resulting cascading to unaffected floors.)[/li]
I’m guessing the use of inert gas is fairly expensive, but they would seem to be an ideal fire-retardant/extinguishing material.

Sources and further reading:
Halon Alternatives Research Corporation
Halon: The Search for Alternatives by Joe Ziemba and Steve Waters

2

If you filled up a burning building with inert gasses, wouldn’t all the oxygen-breathing animals (like humans) have a slight problem with breathing?

Granted, the firefighters have respirators, but what about the people on the floors that don’t happen to be on fire? What about the people on the floor that IS on fire, who have followed instructions to “close all connecting doors, stay put, and get low down on the floor, away from the smoke”? It wouldn’t help them much if the room then began to fill with inert gas.

3

Well, most computer rooms have halon or on of it’s alternatives for fire suppression. Problem is, you can’t be in the room when it goes off. Basically, it sucks all the oxygen out(very un-scientfic description). I’ve always been warned about being in the room when the system goes off, and all the buttons that activate the system are outside the room.

4

Fire-suppression gases only worked in a sealed room (like a computer room), and in an un-inhabited room, to boot. In the case of a WTC style fire, the broken windows would have reduced Halon/FM200/etc’s efficiency to near zero. Not to mention the fact that most of the pipes and cannisters would have been destroyed by the collision (something that would have affected a water-based suppression system, too).

There are ways to get around the problems with water that you cited:

–have water storage tanks at higher levels.
–treat the water to prevent build-up of muck. Alternately, periodically flush out the pipes and replace.
–while water wouldn’t automatically put out airplane fuel fires, it would retard or prevent other parts of the building from burning.
–you’re either going to have fire/smoke damage, or water damage. take your pick.

5

Halon and other inerting systems only work in relatively small enclosed spaces. To inert a whole floor (or several floors) of even a small office building would use an enormous amount of gas. And if windows were broken or doors were left open, the inerting gas would leak out and the fire may not be extinguished.

Don’t high-rises have cisterns on the roof to hold the water for the sprinklers? That would eliminate the water pressure problem.

I’d also heard that most sprinkler pipes are empty. They only fill with water when the system is activated. Don’t know if that’s true or not.

Regardless of recent events, most office buildings don’t have a lot of fuel in them, so large fuel fires are not an issue. Foam could be added to the sprinkler water to combat such fires, though.

6

Thank you for the feed-back.

I did think about the human-breathing factor and I know that most places that have Halon/similar systems are closed areas and sometimes have an alarm that goes off prior to the Halon activation, but it still seems a reasonable method of extinguishing fires that would merely ride along on the water traditionally used. At my old place of business, the server room had a pair of O[sub]2[/sub] masks inside, I always figured that they were for anyone unlucky enough to be inside when the Halon went off. Seems to me that you could scatter a number of those around, too.

Foaming agents in the water or agents that would bind to fuels (while maintaining normal extinguishing effects on traditional fires) would be a useful tool, too.

I guess I just don’t know enough about this, which is why I’m spit-balling these ideas to see how they sound. Hope y’all don’t mind.

fixed coding

[Edited by DrMatrix on 09-17-2001 at 01:10 PM]

7

Apart from this past week’s example, normal water-based sprinkler systems work wonderfully in a high-rise building. Here in Massachusetts, they are required in every building over 70 feet tall (no grandfathering, either). In 1986, there was a rip-roaring fire in the Prudential Building in Boston (unsprinklered) that was a cast-iron female dog to put out. Burnt quite a few floors, and smoked out most of the building. Had there been sprinklers, the fire would have been contained to the area of origin. In 1988 the legislation was passed requiring sprinklers in all 70+ foot tall buildings by 1997. Since then, no problems.

The engineering of highrise systems is really rather straightforward. Lower floors (around 12 and lower) are fed from normal street pressures. No big deal there. The rest of the building is divided up into pressure zones of about 12 floor each. Risers (the pipes that go up and down) feed these zones, with “express” risers feeding higher-up zones. Higher zones are allowed to take water from lower zones if you allowed for enough water in the lower zone.

These higher-up zones are where things become a bit more complex, but by no means difficult. In theory, you can pump water all the way to the top of a highrise with one or two pumps at the base of the building.

Rough and tumble sprinkler system calculation

Sprinklers are not designed for every sprinkler head to activate at the same time. You plan for an expected fire, based on the type of occupancy you’re protecting. An aerosol can warehouse would be protected differently than a warehouse storing cement block on metal shelves. The size of this expected area is based on the applicable fire code you’re using for this design (NFPA 13, 1999 ed for me).
Now that you have an expected design area, you can tell how many sprinkler heads are in this area (if the area is 2000 sq ft, and each head protects 100 sq ft, you need to plan for 20 heads to flow). You also need to know how much water is coming from each head. 0.25 gallons per minute per square foot is a decent flow for a normal office building, so we’ll use that.
The next step is to figure out how much water is flowing from each head. Since you don’t know where the fire is going to be, you plan for it to be as far away from the water supply (the riser) as possible. That way, if its closer, you know you’ll have enough water. The heads are laid out on pipes, so you can have multiple heads along one run of pipe. If the head at the end activates, water will flow past closed heads to reach that open one. If the next head opens, there will be a higher pressure there than in the first one, so more water will flow from that head. That rationalle continues all the way down the line. So if that first head is flowing 25 gpm (0.25 gpm/sqft * 100 sqft), the second head may flow 31, the third 46, and so on down the line.
A rough number, since we don’t actually have a bunch of pipe laid out in front of us (and I’m not going to design a system at 11pm), we’ll say we have 460 gallons per minute flowing through our pipes total. Thats at the top of our 110 story building (1,353 ft), since thats the toughest place to get water to. So we have to get 460 gallons per minute up through a pipe to 1,353’.

The simple calculation for getting water through a pipe somewhere is:

EP = NP + FL + EL
EP = Engine pressure (the push you need at the bottom)
NP = Nozzle pressure (what you want at the end)
FL = Friction loss (the resistance of the water to be pushed through a pipe)
EL = Elevation loss (0.433lbs/ft of elevation)

Lets say we have an 8" pipe going all the way to the top of the building (a good size for a very tall building). Nozzle pressure would be (an estimate) 141 psi at the very end of the system (where the farthest head is). Friction loss for 460gpm through 1,353’ of 8" pipe is 3 psi (thats the water resisting going through the pipe). Lastly is the elevation loss. Thats 0.433lbs per foot rise, or 586 psi.

Adding it all up:
EP = 141 + 3 + 586 = 730 psi

Do they make pumps that can do that? Sure. Even better, only pump at 365 psi and put a second pump halfway up the building. Getting water up there, no problem.

The Kicker
The problem arises when you don’t have that “expected fire.” No fire protection engineer in his/her right mind ever expected a 757 to slam into their building. The risers and pumps can’t push enough water up there to battle that fire. 15 floors of fire is beyond the design area by far. Plus, the risers very likely were compromised when the planes came through the building. Can’t put the fire out if there’s no water being delivered. Can you add foam to the water? Sure, but it requires a special type of head, and it doesn’t like to be used with a normal fire/plain water. Could you use a halon/FM200/CO2 system? Not really. That requires storage of the agent nearby where its intended to be used. That means every floor has to have a large bank of agent. Servicing and/or refilling these banks would be a huge undertaking. Plus, once the system discharges, thats it, there is no more agent to put the fire out with. If the fire didn’t go out, you’re not going to contain it (which is what sprinklers are designed to do anyway). Halon has to have a 5% concentration in air to work properly. Thats a lot of agent to put over a 7000 square foot floor.

High rises are a challenge to fire protection, but so far (excluding the very severe fire of last week) sprinklered high rise buildings have fared excellently under some very nasty fires. One Meridian Plaza in Philadelphia in 1991 for example. The fire burned for something like 9 or 10 hours over 8 or 9 floors. It was stopped by 9 sprinkler heads on the 27th(?) floor. What the entire Philly Fire Dept couldn’t do (including the loss of 3 firefighters) was stopped with 9 little metal devices with a water hole in the middle.
Wow…thats a long post…sorry…

8

Heck, I didn’t even answer the OP. My bad…

See above

Not a big deal. There is some settling, but the system is required to be tested at least annually, most insurance companies like to see it done quarterly. The flow tests find any junk in the piping. Also, you’re not drinking the water in the sprinkler system, so stuff in the water isn’t a big deal.

How often does 20,000 lbs of jet fuel appear at the top of a highrise? A system could be designed for it, but no building owner in their right mind would pay for it. Well, they wouldn’t before last week.

I apologise in advance for the following rant.
Every time there’s a fire, big or small, the damn news people complain about “water damage.” There are 3 ways you can “damage” something in a fire. Fire, smoke, and water. If something burns, its gone. Period. You don’t get it back, ever. Smoke, same thing. I have never seen something that was recovered 100% from smoke damage. Clothing is the worst, it falls apart after a few months, even when cleaned “properly.” The last type of “damage” is water. Everyone in the world has gotten their clothes wet. Did they fall apart? Nope. Nearly everything in the world can be dried out. Computer systems, power them down when the water hits it, clean it off with distilled water, dry it, and turn it back on. Presto, it works! Things can be made un-wet, they can’t be made un-burned. Even the Library of Congress is protected with water-based sprinklers. Yale Univeristy retrofitted their libraries with sprinklers after the Los Angeles Library burned down (well, only thier stack room burned, but what else is there in a library?). Water damage is the biggest crock to come across the fire service since the question “why do you have to break all the windows?”
BTW, we break the windows to let the heat out or else we cook inside when we put water on the fire.

Like I said, sorry about that rant.

9

And Jeremy, I’ve been meaning to talk to you about those footprints…:wink:

10

Jeremy, your rants eradicate more ignorance than most people’s scholarly treatises.

Thanks. For everything.

11

Wow! Thank you for all that info, rant or not. Good stuff.

12

To address the question in the OP (and subsequent posts) about Halon (or FM200 now that Halon is banned).

FM200 is a fire-suppresion that is safe for humans. The reason you have to leave to leave the room is because it requires a sealed room, and you can’t go in or out while it is suppressing the fire. It is an extremely dense gas that settles to the ground.

The system that people may be thinking of is CO2, which is deadly. But effective and cheap. Also requires a sealed room to work. FM200 is only used in spaces where water damage is not acceptable - usuallys erver rooms and the like. General office space is sprinklered - and KCB615 has already covered that.

We had a demonstration in my Building Systems class of FM200 - really cool. He just had the vapor drop past a match and it went out.

13

This topic reminds me of Douglas Adam’s Mostly harmless, wherein Ford Prefect find a way to get passed rocket-proof windows: he jimmies them open with a credit card.

Then, of course, he finds out the the windows are destroyed by a rocket fired from inside the building at the distance of a few feet.

Build a more foolproof system, and we’ll build a better fool :smiley: