Excellent primer on fire in steel framed buildings

[hack89]

Very good explanations of fire science, fire resistance, and fire codes. Chapter 6 has some great explanations and photos of the effect of fire on steel.

http://www.aisc.org/Content/ContentGroups/Documents/ePubs_Innovative_Ideas/FactsForSteelBuildingsFire.pdf

[Jazz2006]

1. Oh, don't confuse the tinhatters with facts, hack... they don't like facts

Facts interfere with their alternate realities.

[Norrin Radd]

2. Not true.

I believe everything I read.

[DoYouEverWonder]

3. Interesting

So far, they can't really explain why 3 building at the WTC failed completely.

BTW: Didn't all three buildings 1, 2 & 7 have sprinkler systems? Why didn't these systems seem to have any effect on 9-11?


7.7 How reliable are automatic sprinkler systems?

While nothing is absolutely failsafe, historic fire performance data indicates that automatic sprinkler systems have proven to be exceptionally effective and reliable when properly designed, installed and maintained, as indicated previously in both Sections 1.5 and
7.6. Sprinklers limit both fire growth and smoke generation. No other approach or combination thereof has demonstrated a comparable effectiveness in reducing loss of life due to fire. 42 / Facts for Steel Buildings—Fire / American Institute of Steel Construction, Inc.

[sabbat hunter]

4. from what i can determine

the WTC were not built with sprinklers originally since they were owned by the PA and as a result excempt from fire code rules.
supposedly they were retrofitted in later on when they were sold by the PA in 1999 but they were not designed with halon sprinklers but a much lighter load (water sprinklers). that the initial fuel explosion probably opened up all the heads and killed the pressure rapidly before any fire could be extinguished.


also here is architectual article on the collapse

http://www.architectureweek.com/2002/0515/news_1-1.html

[mhatrw]

5. Thanks.

In a typical fire, such as in an office, residential or retail occupancy, the maximum temperature of a fully developed fire will likely not exceed 1,500 °F (815 °C), though it could range up to a peak of 2,000 °F (1,093 °C) under more severe conditions. The maximum temperature will typically last for only 10 to 20 minutes during the peak of its burning period within the compartment. Consequently, the average real gas temperature within the fire compartment will not reach its maximum level (see Figure 1.3) over the fire duration for any exposure.

...

For protected structural steel, the temperature increase due to fire results primarily from radiation to the fire protection material and conduction through the protection, with inclusion of the appropriate insulating properties and thickness of the material. Therefore, the temperatures in protected steel will be continually less than those of the fire during the heating phase.

...

The temperature increase in the steel member is governed by the principles of heat transfer. Consequently, it must be recognized that the temperature of the steel member(s) will not usually be the same as the fire temperature in a compartment or in the exterior flame plume. Protected steel will experience a much slower temperature rise during a fire exposure than unprotected steel. Also, fire effects on the steel will be less the greater its distance from the center of the fire, and if more ventilation occurs near the steel in a fuel-controlled condition, wherein the ventilation helps to cool the steel by dissipating heat to the surrounding environment. For an interior exposure, the upper concrete floor slab, and adjacent unexposed elements (walls and floors) of the building, will all provide additional heat sinks to the fire and steel that may limit the steel’s temperature increase relative to what it may have been if the member was in the middle of the fire as an isolated element, or assembly. Also, the time of heating exposure is important, since shorter intervals of high temperatures will be less damaging than longer ones at the same temperatures.

...

Figure 6.1 shows a UL test of a roof assembly in the furnace
after a successful fire test. Steel deck sag and beam
buckling are visible. The effects of actual major fires in two
prominent unsprinklered high-rise steel buildings, One
Meridian Plaza in Philadelphia and First Interstate Bank in
Los Angeles, along with the Cardington test frame in the
U.K. (Bailey, 2001 and Newman, 2000) are shown in Figures
6.2 through 6.4, respectively. In the One Meridian
Plaza and First Interstate Bank incidents, and other cases
that will be further summarized in Section 7, no structural
collapses were experienced during these long uncontrolled
fires, even though the fire damage was extensive.

...

The annual fire occurrences in such high-rise buildings
range from 10,000 to 17,200 per year, with annual civilian
deaths between 23 and 110, civilian injuries between 554 to
950, and direct property damage between $24.9 million to
$150.1 million. To include the fires from other high-rise
property classes and in residences with unreported heights,
an increase of 33 percent is suggested by Hall, thereby
increasing this annual range of actual high-rise fire occurrences
in the U.S. from the range of 10,000 to 17,200 per
year to the range of 13,330 to 22,900 per year.

But not one has ever suffered total collapse before or after 9/11!

As part of a recently completed NIST project to assess
the needs and existing capabilities for full-scale fire resistance
testing, Iwankiw and Beitel (2002) compiled the
results of past multi-story building collapses, either partial
or total, that were directly caused by fires. In this study,
multi-story buildings were defined as those with 4 or more
stories. A total of 22 such cases were identified, with the
September 11, 2001 disasters accounting for 5 of these incidents
(WTC 1, 2, 5, and 7, and the Pentagon). The cases had
occurred not just in the U.S., but also internationally.

...

Fortunately, fires in tall buildings do not often lead to
partial or total collapse, as in these 22 documented cases.
Furthermore, all of the other collapses were not nearly as
catastrophic as those in the September 11, 2001 experience.