Reichstag Fire: 102 minutes that changed America

[dennis]

You won't find that out by studying the twin towers as they didn't collapse straight down. The tops tilted a good few degrees before they fell onto the lower floors causing the whole lot to drop down within a smallish area.

Once there was enough weight to collapse the undamaged floors the whole thing was contained inside the tube formed by the outer frame as the floor trusses pulled the sides in. Thus it is very likely that the bottom of the building will collapse straight down the tube. If you look at the videos you can see each floor drop onto the lower ones and the sides pull in.

It won't make any difference to you of course as you have already decided what happened and will ignore the truth.

What gets me is how many people in a burning building continued to work. The first rule in the UK is to get out of a burning building and this cut the death toll amongst the British companies in the trade centre as they just left the building. Its also the reason why British skyscrapers are not as high, you have to be able to exit a burning building by law. There is no way the trade centre towers could have been built in the UK as they were inherently unsafe in a fire.

[The Natural Philosopher]

yes, for a time.

Ultimately all fire protection of steel is about the insulating of the structure, and the energy used to sublimate the coating..but eventually, a fire hotter than the melting point of steel, will destroy the steel. You can buy time, but not prevent failure.

Regulations say about 45 minutes, and the WTC lasted 52 I think. A bit longer on the second tower.

And a lot longer on WTC7 which didn't get smashed into and jet fuel sprayed about, its just caught fire in sympathy ;-)

All three collapsed more or less in the same way. As you might expect. And as many at the site, at the time, predicted. Leading to the infamous 'BBC reports collapse 30 minutes before it happened' story.

[The Natural Philosopher]

For a few extra precious minutes ONLY.

[The Natural Philosopher]

I thought the walls were in fact glass by and large? it was the steel frame that was load bearing. Once that went, the lot went.

[dennis]

That is clearly untrue.

The weight is supported on the ends of the floor trusses. Therefore the load is on the inner core and the walls. As there is more floor area alongside the walls a greater load will be near the outside. The walls must, therefore, support more weight than the core.

[Col]

Incorrect. Such paint systems are rated as giving up to 2hrs protection.

Col

[Col]

A hydrocarbon fire will not reach the melting point of steel, which is around1500C. Burning jet fuel will reach about 1100C. That said, getting close to the melting point isn't really all that important. At 550C, steel has half the strength it has at room temperature and this temperature is taken as the 'time to failure' for determining the fire rating for intumescent coatings.

Col

[Brian Morrison]

Class 37 or 40 I thought, and yes, I've seen it.

They said that the critical flask valve was protected by how the flask was positioned. Of course, that couldn't happen in a real accident could it? It was an expensive demonstration of the fact that such a flask can survive a massive impact. Equally you could create a similar demonstration where the flask fails.

I read a report about how some fairly radioactive thing that had been in a UK power station (I think) was driven around in a similar flask, but somehow there was an open aperture through which X and gamma rays were passing at a level that would have badly injured or killed anyone in the beam for more than a second or two. By pure luck, the beam was passing down into the road surface and no one was injured.

So far, we've been lucky.

[Brian Morrison]

Presumably not available in the early 1970s when WTC was built?

[Steve Terry]

The twin towers were probably the most top loaded towers in the world with hundreds of tons of air conditioners, aerial towers, and water tanks, etc. Then every floor under the roof loaded with furnishings, office equipment and tons of paper

It's a miracle they didn't fall down under the best of conditions

Steve Terry

[Col]

No, were're talking late 80s when these materials really took off.

Col

[Col]

Water tanks? Why didn't they just blow 'em to put out the fire like they did in 'The Towering Inferno'? Sheesh....

Col

[The Natural Philosopher]

Total bollocks.

The trade centers were build in accordance with very similar laws. The central areas were escape routes, had more than one means of use, and were fireproofed. The were not however built like bunkers to withstand a direcdt hit from an aircraft.

The planes sliced right through the middle. It wasn't JUST a fire. It was a fire that started across 2-3 floors simultaenously. And included the escape routes. The top was cut off from the bottom.

I would guess that 99% of people above the impact died, and 99% below made it out.

[The Natural Philosopher]

whilst you are reasonably correct that the outside structure was pretty load bearing, your reasoning is totally false.

It would be completely possible to build a tower with floors cantilevered out from a central column, and having no walls at all.

I.e. the walls do not HAVE to be load bearing, it just happens in this case they were, or at least the steel columns were. The walls were not, being mainly glazing IIRC.

[Yeti]

I've skipped over most of this thread - because I don't have time right now. I'll catch up later.

If found this - and it's too funny NOT to post.

[The Natural Philosopher]

gosh, 120 minutes!

whereas standard techniques are good for 60-100 minutes. Big deal.

The people wont survive 5 minutes in a fire like that.

[The Natural Philosopher]

Odd that, since a bessemer converter is wholly carbon fuelled, and is used to melt steel.

And in fact all steel is traditionally made using carbon fuels.

Yeah sure, that's why they use special alloys in the exhaust of jet engines.reheat gets up to a lot more than you might think. The temperature is a function of the air blast I suppose, and a tall building with a nice service area chimney can create quite a blast..

I suppose an oxy acetylene welder isn't a hyrdocarbon fuel fire either..sure melts steel tho.

Exactly.

[Brian Morrison]

And a lot of extra oxygen, blown through the charge.

In a jet engine you're worried about loss of strength, maintaining clearances and service life, it *really* isn't a good idea to allow the fast spinny bits to lose strength and collide with the stationary bits.

Come on TNP, you're surely fishing here....

[The Natural Philosopher]

So you didn't!

[The Natural Philosopher]

Not that much.

I've seen pictures of fire damaged steel frame buildings without protection - typically warehouse or barn fires with flammable material inside, and they may not have melted, but they sure buckle.

a quick google reveals.

Now imagine a few thousand tons on top..