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Post by JayUtah on Oct 26, 2005 15:11:31 GMT -4
Just to clarify, I'm talking about WTC 7. Comments that Leslie Robertson may or may not have made with respect to WTC 1 and 2 are not relevant to the comments made by other engineers regarding WTC 7.
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Post by nomuse on Oct 26, 2005 15:52:08 GMT -4
Been reading a bit about methods of bringing water to fires in tall buildings. Fascinating stuff.
The consensus seems to be the best situation for firefighters and occupants is a functional sprinkler system. The notes to an abstract I found by an architecture prof at University of Hong Kong lists typical engine at 100 meters, portable pump at 80 meters, (okay, 360 l/min at 8 bar for a 36-kilo pump carried by a single firefighter). Obviously, the closer undamaged building water is to the fire, the better. But that backs up the guess that firefighters could get water to the upper floors but it would be limited by the pumping capacity they could carry on their own backs and the volume of hoses they could wrestle up the stairs.
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Oct 26, 2005 16:31:56 GMT -4
And there's no shortage of hydrants in downtown Manhattan they could have used. I believe the City of New York specifies a Metropolitan Fire Hydrant, which has a maximum working pressure of 250 PSI. The water mains probably have an actual working pressure much lower than this. Nonetheless, if we assume the highest possible pressure and no head loss, then the maximum height the water could reach is 577 feet, and at this height the flow rate is zero. In other words, a fire hydrant is useless for fighting a fire at 900+ feet without a fire pump to boost the pressure.
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Post by JayUtah on Oct 26, 2005 17:02:13 GMT -4
This is why most tall-structure firefighting techniques presume large stores of water that have been previously pumped to holding tanks above where the fires are likely to occur. Sure, you can use boost pumps if you want, but that presumes power to the pumps -- another system that has to be up and running in a fire in order for you to fight it. Gravity-fed fire suppression water is fail-safe because you always have gravity. The only problem is what happens when a massive mechanical injury severs the water pipes and allows all the cached water to run out. This happened in both WTC towers and in WTC 7. New codes require life-safety equipment to be shielded from mechanical injury, including fire suppression water trunks.
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Post by sts60 on Oct 26, 2005 17:04:03 GMT -4
The consensus seems to be the best situation for firefighters and occupants is a functional sprinkler system.
nomuse is right that the best defense is a functional sprinkler system, which will contain or at least slow down typical fires which start in a single room and tend to spread. But these were not typical fires, and the sprinkler system would have been ineffective even if it hadn't been torn to shreds.
But that backs up the guess that firefighters could get water to the upper floors but it would be limited by the pumping capacity they could carry on their own backs and the volume of hoses they could wrestle up the stairs.
IIRC, some firefighters - carrying hand tools only, wearing PPE (personal protective ensemble) but no SCBA (breathing apparatus) reached the 75th floor.
Now, I've climbed a 60-story building, in one of those races where they send people up every 45 seconds or so, in roughly 23 minutes. That was in shorts, T-shirt, and sneakers.
Let's compare that to FFs dealing with a high-rise fire. You are wearing turnout gear and SCBA, which together weigh something like 50-65 lbs. Where I volunteer, you're typically carrying one or more of the following forcible entry tools (up to 25 lbs of hand tools), a pressurized water extinguisher (about 25 lbs), a "rabbit tool" (hand-operated hydraulic tool, about 30 lbs), or of course a standpipe pack (about 150 feet of 1-3/4" hose, nozzle, and gated valve, about 65 lbs).
Did I mention that turnout gear is very good at holding in all the heat your body generates climbing stairs saddled with as much as 130 extra pounds?
I don't know what FDNY brings up stairs, but whatever they did that day, it really was up stairs - few of the elevators were working - and they had to contend with thousands of panicky civilians trying to get down the stairs, not to mention noise, poor radio communications, and smoke and rubble at places.
It is simply impossible under those conditions to mount an effective fire attack 60, 70, or 80 stories very quickly. You could not even start to put water on the fire from a handline within half an hour. And that's even if the building's fire suppression system wasn't compromised - if you had working fire pumps and an intact standpipe system.
If the fire pumps were not working, then you simply could not pump water up from the ground. For example, a typical pumper can deliver about 600 GPM of water at 250 psi net pump pressure. Even if you had another pumper feeding it at the typical maximum inlet pressure of 100 psi, for a total discharge of 350 psi, you lose about 5 psi per floor, and thus you have no pressure at the 70th floor. And that's without taking into account friction loss through the standpipe system and hose lines. And if the standpipe system is damaged, you might not get any water up there at all anyway.
Not to mention that a few hundred GPM would have been exactly as effective as spitting on those fires anyway.
(edit to add) Of course, the above applies to bringing water up from below. Jay's remarks about the water tanks above the fire are good ones.)
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Post by sts60 on Oct 27, 2005 15:17:55 GMT -4
I've spent a little time looking at some of the reports on the fire protection system. The gist is that while there may have been 5000 gallons above and 10,000 gallons below, the ability of the standpipe system to deliver the water was compromised, the ability of the fire pumps to pump water up was compromised, and the firefighters didn't have the time to mount an attack anyway.
If the buildings hadn't collapsed and the system hadn't been compromised, they could have eventually controlled the fires. But that just wasn't the case.
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Post by sts60 on Oct 27, 2005 15:41:03 GMT -4
I realize I misinterpreted turbonium's remark Because they would have extinguished those fires easily if they had gone into the building. He was referring to WTC7 in particular.
My comments stand, though; in this case, though, the factors have more to do with damaged water mains, the loss of an enormous number of firefighters and apparatus, and the presence of fires on multiple noncontiguous floors - some of them apparently diesel-fed by internal fuel supplies. In this case, the building's standpipe system was probably in better shape, but there were no large internal tanks and the water main system was compromised during the WTC 1 and 2 collapse. Not to mention that FDNY had just suffered the loss of hundreds of firefighters and dozens of pieces of apparatus.
The idea that firefighters could have gone in and "easily" suppressed the WTC 7 fires (let alone the WTC 1 or 2 fires) is not just grossly wrong - disconnected from reality - but frankly insulting to the memory of the firefighters killed that day.
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