Fire protection of steels

[saveasteading]

 

  On 08/04/2025 at 19:36, ETC said:

BC said I can just fly over my beam with standard plasterboard because it's within the ceiling void.

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I agree.

 

if there is a fire will it reach the beam?

1. fire in room....ceiling protects it unless there are significant holes in it plus air flow.

2. fire in void.  Protect the steel, OR remove any source of fire (removing the ignition element (lights or fans) OR any flammable material.

 

The easiest way to protect the steel in the case here will be to infill against the webs using appropriate rockwool. the remaining exposed flange base will likely be insignificant in any calculation.....but you don't want to be calculating  for such a minor thing.

 

In reality, no fire will burst through the ceiling lights or from them and get to any temperature to be of concern, as there is no air flow and little fuel in the void.

 

I asked a professor of fire once, how much does it matter if joints in plasterboard fall out in a fire, or other exposed edges.   He said , hardly at all, as the fire won't go through that way in real life.

Plus, in the heat,the plaster changes chemically, and drives water out, especially through the edges.....killing fire at these points.. 

 

 

[Gus Potter]

  On 09/04/2025 at 17:37, saveasteading said:

I asked a professor of fire once, how much does it matter if joints in plasterboard fall out in a fire, or other exposed edges.   He said , hardly at all, as the fire won't go through that way in real life.

Plus, in the heat,the plaster changes chemically, and drives water out, especially through the edges.....killing fire at these points.. 

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Yes I agree. In simplistic terms there is chemically "locked in water" in the plaster board. The heat transfer is slowed as the plasterboard "soaks up the heat" as it is forced to change chemically. But.. often the fixings are the vulnerable point.

 

An easy way of getting your head round this is to go to the BC standards. They talk about fire "resistance" and fire "integrity" The resistance bit is to do with a material transferring heat. The integrity is about making sure that the fixings and the things the fixings go into remain ok.. as if they fail then boards say fail also. The regs combine intergrity with resistance to give you the overall number.

 

In summary though. Say you are completely new to this. I would explain that steel starts to lose its strength when it gets hot.. that can start at temperatures similar to when your oven is at full whack.. say 250C.. this lets the home owner get a feel for what we are talking about in terms of how quickly steel can loose strength when it gets hot.

 

 What we need to do is insulate it so it does not get hot. Then we look at the different ways of doing this.

 

@saveasteading and others have pointed out the different ways we can go about keeping the steel cool.

[saveasteading]

  On 10/04/2025 at 21:30, Gus Potter said:

But.. often the fixings are the vulnerable point.

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The same guy explained that they did a real fire in a test room with 2 x 2 stud and plasterboard screwed in, with no jointing. the stud charred where exposed but no worse. but as this was not the purpose of the test it was not published.

With metal stud I wouldn't be so confident.

  On 10/04/2025 at 21:30, Gus Potter said:

temperatures similar to when your oven is at full whack.. say 250C..

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So our ovens get repeatedly soft, but aren't structural so its ok?

[Nickfromwales]

By the time a steel got to those temps you’d all be long 🪦 or simply stood outside with marshmallows on long sticks anyways, so it’s all quite a lot of nonsense in a domestic 2-storey house with windows tbf.

[Gus Potter]

  On 10/04/2025 at 23:33, saveasteading said:

So our ovens get repeatedly soft, but aren't structural so its ok?

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Good point, as aways. Steel is an elastic material, like all materials. In the UK we don't suffer from particularly low temperatures, but in some cases where we have structural steelwork that is exposed to low temperatures we select a steel grade that is more ductile (less brittle). Going in the other direction when we heat it up it starts loosing "strength" that give designers concern at just over 300 deg C. @saveasteading is correct about the oven There is some softening of the steel at 250 deg but it is for all intents negligeable. . Below is a typical fire curve for steel from the SCI.

 

Simplistically when we design steel for fire we may pick the 550 degree curve. Work out the loads on the building during a fire. When we do this we don't assume the building is fully loaded in the same way as when we are designing for day to day use. Fire is what we call an accidental load case and we reduce the factors of safety and the loads to reflect that this is an accident. If we did not do this then building cost would often be prohibitive.

 

Fire protection is about providing a protective layer of material that insulates the steel in one way or another. Or for example you can use say sprinkler systems that reduce the heat and duration of a fire.

  On 11/04/2025 at 17:24, Nickfromwales said:

By the time a steel got to those temps you’d all be long 🪦 or simply stood outside with marshmallows on long sticks anyways, so it’s all quite a lot of nonsense in a domestic 2-storey house with windows tbf.

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Fire is a terrible thing. What we aim to do is to provide warning of a fire first. Smoke and heat alarms say and this lets people exit the building. We aim to provide them a safe route to do so. Here we may see reference in the regs to escape windows and the like on a single story house, we avoid having a room off a room with no escape window for example. On a three storey house we often want to have a protected stairwell or a sprinkler system with an enhance fire detection system.

 

Once buildings get taller (often 3 habitable floors or more for domestic use) we need to think even  more about people that may be trapped. Here we want to further protect the floors, walls, the structure and so on to provide a safe shelter space until the fire brigade can effect a rescue.

 

During and after the rescue we need to protect the structure so it does not collapse on the fire brigade or set light to any surrounding buildings.. and that is where the other structural aspect of fire design comes into play. Often if your house is well away from other buildings the fire brigade (if sure no one is left inside) will fight the fire from a safe distance.. or if in doubt just let it burn.

 

I take Nick's point.. but at the end of the day it's often the insurer that has to pick up the tab. The more you can limit the extent of the fire damage the less they often need to underwrite and that is reflected in the premium.

[SteamyTea]

It was not the impact of the 737s that brought down the Twin Towers, it was the softening and associated bucking of the steelwork.

As @Gus Potter says, fire is a terrible thing.

 

  On 10/04/2025 at 23:33, saveasteading said:

So our ovens get repeatedly soft

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Is your oven stainless steel?  There is a reason that SpaceX use it for rocket bodies, repeatedly.

 

[Gus Potter]

  On 12/04/2025 at 19:38, SteamyTea said:

It was not the impact of the 737s that brought down the Twin Towers, it was the softening and associated bucking of the steelwork.

As @Gus Potter says, fire is a terrible thing.

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I agree with you. there are a lot of conspiricy theories.. but I'm inclined towards looking at what I know. The fire protection got blasted off the steel.. it got hot, failed, which cuased the building to collapse. The planes impacted on more than one floor. Where the plane hit was at the height where there was a lot of dead load from above. Once that dead load started moving the dynamic effects were multiplied. You only need to lose say 1.0 or 2.0 metres of column fire protection over a number of columns to promote what we call disproportionate collapse. I still find it personally uncomfortable to distill and write about it in this way when so many people lost their lives.

 

  On 12/04/2025 at 19:38, SteamyTea said:

Is your oven stainless steel?  There is a reason that SpaceX use it for rocket bodies, repeatedly.

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No is a hotpoint and looks good!

 

I'm in awe of the Space X Engineering team. Stainless steel is a wonderfull material.. it's ductile, forgiving but comes at a cost. I love what Space X is doing.. they have the best Engineers.. we British used to be like that! For me it's about how the marry up the best young talent with old school testing engineers.

 

 

 

[Post and beam]

My ground floor ceiling, where the 2 steels are located will be packed with Ursa glasswool.  I dont know why it did not occur to me but i checked their website this morning.

It is regarded as fireproof and accepted as a firestop material. Doesn't this give me all that i need to satisy building control? i will certianly making this case to them.

 

 

[saveasteading]

  On 15/04/2025 at 08:39, Post and beam said:

Ursa glasswool. 

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I wasn't aware of this make. Is it readily available and good value?

There are other makes  available as standard so ask around.

 

Yes this principle is a solution and easy.

[Post and beam]

  On 15/04/2025 at 10:38, saveasteading said:

Is it readily available and good value?

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Provided by Potton with the kit frame in great quantity. Since found it online and yes it seems to be widely available.

I have it in 200mm, 150mm 100mm and cavity Bats  dependant on the location it is needed.

[saveasteading]

  On 15/04/2025 at 08:39, Post and beam said:

to satisfy building control

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Tell them your proposal first. Steel protection isn't generally their expertise, and they like to see a detail straight from the brochure.