BTW, the NIST report concluded that even if the sprinklers had been fully functional, they did not have the capacity to contain massive simultaneous fires on multiple floors in the towers.
Yeah, I was a little unclear there. The jet fuel ignited and spread fire faster than would have been possible by any conventional accident scenario, so it was the most important factor in how the fire got to that point. The idea I was trying to get across is that if you were to deactivate the sprinkler system in most skyscraper office buildings (and firefighters and civilians weren't fighting the fire), a fire started with a match in a wastebasket could eventually (probably around 30-60 minutes, if open stairwells connect adjacent floors as they did on some WTC tower floors) reach the same condition. The exceptions would be (generally older) buildings designed for fire control by compartmentation -- and even then, since comparmentation was replaced by active suppression (sprinklers) in most building codes due to being less effective, it's only a matter of time.
I've been curious about the exact meaning of NIST's FAQ statement about the sprinklers (that is, the 1,500 square feet limit per floor on its designed capacity) since I first read it. As far as I know, if one assumes that each individual sprinkler head is working as it's designed to, the ability of sprinkers to contain a fire shouldn't, in theory and within practical limits, depend on the area or volume of the fire per se. Therefore, I've interpreted this limit as reflecting limits on the rates of water flow through the relevant supply pipes. In other words, activating too many sprinker heads would have the an effect analogous to opening too many fire hydrants in a city, the reduction of water supply pressure below what's needed for any individual sprinker head to be effective.
Now that I've had occasion to focus on that question, I find that information in the full NIST report confirms my suppositions:
NIST calculations showed that the installed automatic sprinkler system was capable of delivering the minimum requred water flow for control of office fires up to 4500 ft^2. [NIST NCSTAR1 pp. 12-13; emphasis mine]
Even had this [damage to sprinkler water supply pipes] not happened, the system was designed to supply water to about 8 sprinkler heads at one time, enough to control the flames from as much as 1,500 ft^2 of burning material. The water supply was likely sufficient to control fires up to triple that size. [ibid. p. 24]
Figure 5-2, page 63, is a schematic of the sprinkler and standpipe plumbing for WTC1.
Respectfully,
Myriad
, you blokes have completely melted him!
