I had to watch a training film last week called Fire In the City (I think it was from The Learning Channel). Two of the blaizes featured involved highrises with loss of life (one was the MGM in Vegas, and the Other was a highrise in Philadelphia in the early 1990’s). Basically, the film concluded that it was difficult or impossible to stop fires that started over around 200feet (or the highest that ladders can reach). They even covered several innovations being researched in Japan such as lateral access from adjacent buildings and even a fire helocopter.
Here’s one possible “failsafe” idea that should stop most fires in their tracks that could be integrated into building designs. How about having huge water storage tanks on the roof of the buildings (think of an Olympic size pool that is twenty feet deep). These would be connected to an intricate network of “plumbing” that could dump water into virtually every room in the building if “the plug” were manually or electronically pulled. Furthermore, the “level” at which water would start pouring could be specified (thus if the fire was on the 15th floor, you could start flooding at the 17th floor, but spare above that level) with gravity doing most of the work. Obviously, this would cause a great deal of damage so it would be reserved for so called “infernos” or those that were quickly heading in that direction. I think that something like this might even have spared the WTC towers from collasping (although maybe not).
The difference between this idea and sprinklers is the difference between a swimming pool and a lake.
This would be in addition to no in place of sprinklers.
Don’t many highrise buildings already support swimming pools on top?
Actually, what gave me the idea was an article that I read in Popular Science about “fail safe” fission reactors several years ago. One idea involved building the reactor underneath a pond which could be released onto of the reactor in a meltdown situation.
Well we would really need someone knowledgable in structural engineering and architecture to carry the discussion much further. However, consider the following:
Currently there really are not any good options in fighting high rise fires. So even an idea which is difficult and expensive might be worth considering (providing it would be effective in most scenarios).
I’m not sure how much water we would need. I think that as little as ten to twenty tons or even less might do the trick since we don’t need to flood every floor (just those on fire and those at risk of flashover ignition). In addition, a few inches of water on the affected floors would probably be sufficient.
How much weight can the average, modern highrise stand anyway? Those swimming pools that you see on the top of buildings cannot be light (how many tons is your average highrise pool)?
Perhaps the “pools” could be shared between several or even many buildings that were somewhat close together with elevated “tubes” connecting them. We might even consider constructing one super strong high rise near the center of a city (and higher than the surrounding buildings) which would serve as the “hub” for the water distribution. Of course it would still function as commercial space in its own right (but would be built to substanially higher and therefore more expensive standards to stand the additional weight). In this way the smaller buildings would not have to bare the load of the water (and after all one “pool” would be sufficient in almost all cases since these fires are extremely rare).
One Meridian Plaza, in which three PFD firefighters perished was a combination of numerous factors. Without getting into overwhelming detail, the point of origin was on a floor being renovated, so smoke detector coverage was not adherent to code, there was a significant delay in retransmission of the alarm to PFD allowing fire to spread, the pressure reducing valves installed on the standpipe system were incorrectly set and precluded development of adequate fire streams, the electrical system of the building and backup generator failed owing to improper protection, absence of fire dampers in ventilation shafts permitted smoke and fire spread both vertically and horizontally. Although listed as fire resistive construction, once windows on the facade failed, there was exterior fire extension. Despite all of that, when fire finally reached a sprinklered floor, the sprinklers extinguished the blaze.
The MGM Grand was an unsprinklered occupancy. Fire marshals insisted on sprinklers, but MGM balked at the additional cost, and a County building official sided with the resort. 85 people died in that incident, and computer modeling has indicated that the fire which began with electrical equipment would have been controlled by a sprinkler system.
Sprinkler systems only fail to control/extinguish fires when they are ill-maintained, water supplies fail, intentionally compromised, or the occupancy is modified/changes in a way that renders them ineffective. Example would be an occupancy sprinklered for warehouse operations which is then used as a boat repair and storage facility. The head spacing for warehousing would not be effective for the higher hazard occupancy with greater volume of flammables with higher burn intensity.
There is one exception, and that is when a massive volume of fire fuses a large number of heads and water pressure cannot be maintained, or where an explosion damages the water distribution system, shutting down sprinkler flow. Examples would be the World Trade Center twin towers, and the K-Mart distribution center in Falls Township, PA.
So would a “gravity” dependent system such as the one described above have likely been effective in the case of the WTC? All in all it sounds like you are saying that a good sprinkler system is almost always the way to go. If that is the case maybe there’s not a problem with stopping high rise fires after all.
But it still would not stop the chain reaction. Instead, the water would boil over, turn to steam and possibly spread radioactivity over a large area. Then there is the contamination of the groundwater, yadda, yadda.
I have my MS in structural engineering but I’m not practicing. That being said…
Is this really true? Building codes for high-rise structures certainly include fire resistance, sprinklers, etc. Floors can be sealed off and pressurized so that fire and gasses have a harder time spreading. If you have a raging inferno a few hundred feet up it’s hard to get to (though there are specialized high-rise ladders and water pumps that can reach astonishing heights) but there are standpipes all the way to the top so the FD can plug their hoses in onsite.
I found one cite that says that the MINIMUM flow rate of sprinklers must dump 0.05 gallons per minute per square foot. I’ve seen those things go off and it’s a frickin’ downpour. At that minimum rate it’d only take ten minutes to have an inch of water on the floor which is probably faster than the local FD can get there anyhow. And remember that you don’t have to turn the whole floor into an aquarium, you just have to douse the area that’s on fire.
No hard and fast rule, there’s an awful lot that goes into those calculations but “A Whole Lot”. The problem isn’t really that a big tank of water is going to break all the columns but that you’ll overload a specific area and your 20 ton tank comes through the ceiling. Live and dead loads for floors are generally measured in tens of psf with safety factors tacked on, so let’s say up to 200 pounds per square foot for an area with high dead loads, high live loads and high safety factors. Consider that a tank of water 3 feet deep exerts about 200psf right there and you can start to see the design concern. Water is really heavy stuff. I’d also be a little concerned about sloshing at the top of a building (where the swaying is greatest from wind and earthquake loads). 20 tons of water that starts moving might not stop easily.
Dunno that that’d work - you’d have to get cooperation from all the property owners and those buildings would have to be pretty darn close to make it feasible.
Not trying to be a wet blanket (my first project in college was to design an escape system for highrise buildings in the event of a fire!), I just think that strong firecodes will help more. Keeping the amount of fuel to a minimum (fire resistant furniture and so on), proper smoke alarms and sprinkler systems, fire resistant building materils (concrete, or steel with right coatings) will all make a huge difference. If you’re talking about an extreme event such as 9-11 then all bets are off. You design the building so that as many people as possible will get out alive but you assume that the building will probably be a massive loss afterwards.
I seem to recall reading that at Chernyobl when the emergency crews sprayed water that some spots were so intensely hot that H2O dissociated and became H2 and O2 with predictable results.
Not that I know squat about nuclear reactors, but I think that the idea is to have the pond water kick in long before the reactor “melts”. It’s my understanding that the real danger of a reactor going critical is some sort of interruption in the water cooling process. By having a water supply that only requires gravity to be activated (as a fail safe) the idea is that you reduce the chances that such a interruption can occur.
The problem is that you probably need pressurized water to cool the reactor. Ordinary water would just flash to steam. In some reactor designs, steam bubbles result in an increase in reactor power (positive void coefficient). Steam is also a poor conductor of heat. You want the fuel rod assemblies to be immersed in water, not steam.
I was watching a documentary the other day about some old filmstock that was discovered. Old nitrate film is very flammable and apparently, the National Film Archive stores it in a network of small, insulated, climate-controlled bunkers. Each bunker has a glass roof above which is a large water tank, the idea being that if a fire occurs in one bunker and it cannot be extinguished conventionally, the heat will break the glass ceiling and fill the bunker entirely with water, preventing the fire spreading to adjacent bunkers.
The physical impact of the plane destroyed or severely impaired the fixed protection systems.
WTC was a ‘protected steel’ construction class, but engineers hadn’t imagined impact forces and blast wave physically removing the sprayed protection. The comments you may have heard regarding the building being built to withstand impact of an airplane were true from a physical standpoint, and both towers remained standing after being impacted upon. The massive volume of Jet-A was not part of the calculation.
The effect of fire on ordinary unprotected steel construction is straightforward regarding structural failure. Although I wanted to have optomistic thoughts on the morning of 9/11, the little voice inside said it’s not a matter of ‘if’, it’s a matter of ‘when’.
Some of the other problems with the gravity concept in addition to static loading of the structure are:
Provision for freeze protection in heating climates
Another structure to be maintained
HVAC lives there, antennae, signage all adorn building tops. It’s really a crowded spot to think about putting something else.
Excepting the conditions expressed in my previous post, I don’t recall a high-rise fire of any consequence in a fully sprinklered occupancy.