Floor Fire Protection

[planc]

How do you put fire protection on a concrete floor?

The bare slab can be used with just vinyl or tiles with crack mitigation membraned and thin adhesive. But this doesn't protect it from fire.

And what kind of fire can reach the floor? Is it not flame reached up and not down?

Please share your experiences. Thank you.

 

[rowingengineer]

Some more context would be good, normally concrete is designed to have fire ratings.

 

[planc]

A 5 inch slab has fire rating of 3 hours. But even 30 minutes of fire can already damage the slab top portion. Has anyone ever put a 2 inch screed just for fire protection even if the floor is already level?

 

[jayrod12]

Often concrete slabs fire ratings are a function of the concrete cover to the tension steel. At least that's how it is where I practice. So often you need to have your tension steel higher in your slab to achieve a rating higher than 90 minutes (or 2 hours, I don't have my info in front of me).

 

[LuK13]

As I understand it, the point of passive fire protection, such as fire rated assemblies or spray on fire proofing, is to prevent fire spread and to avoid a catastrophic failure so that occupants have time to escape and a fire department has time to respond.

If I fire occurs in an area with a 3hr rated floor I would expect that floor to prevent the fire from spreading to a space below for 3 hours. If it took the fire department 1 hour to respond and extinguish the fire I would not expect the floor to be undamaged, but it would have served its purpose.

Why are you trying to make sure the concrete isn't damaged by a fire for a set amount of time? In a typical building a fire is a rare event that may never occur, and if it does that's why you have insurance. If this is some unique situation where you are intentionally setting fires in a space then we don't have any details on what you are actually trying to do so we can't be of much help.

 

[EdStainless]

We had a floor in a section of the plant that was at risk for liquid spill and fire.
As I recall the slab was extra thick and had significant air entrained in it.
Fortunately it was not a high traffic area, I don't recall what we topped it with for a wear surface.
We accepted that the floor would be sacrificial in a fire, but we needed to protect what was below it.

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P.E. Metallurgy, consulting work welcomed

 

[planc]

Thanks for the responses. What is the fire resistance rating of plain mortar (mixture of cement and sands only)? I kept googling for fire resistance of cement and sand without aggregates and I couldn't find much information. I know aggregates contribute to fire resistance but how about pure cement and sand?

Client building is office use. And for offices, there are a lot of papers and documents and furniture, and fire is a possibility anywhere. Of course it's not purposely setting fire to the floor like nuclear power plants.

The point is If it took the fire department 1 hour to respond and extinguish the fire. If there are mortar or screed, then only the mortar are damaged and not the slabs. So you just replace the mortar and not do any expensive repair of the slabs replacing the rebars for example. How long can a 2 inch thick floor mortar/screed composing of plain cement and sand resist fire and protect the slabs?

 

[LuK13]

Is the building owner or a client asking for this?

Why can't you just use the passive and active fire protection required by code?

IMO this is a waste of time and money for a standard office building. The odds that this matters are slim to none. I doubt you save much money on repairs either, and also doubt it would make economic sense when you compare it to the extra construction costs.

And after all is said and done, lets assume you did manage to cut your slab repair bills by 50%. You still lost the building contents and what about the walls, ceiling, MEP, etc. A fire bad enough to damage a concrete slab is going to be damaging a lot more of the building.

Edit: Just to be clear I'm not saying you can't do this, but I am saying you probably shouldn't. If I were you I would push back on who is asking for this. If they cant be reasoned with I would consider walking away from this job. If I got roped into doing this I would charge a hefty fee for doing something that isn't standard and probably isn't codified. I would also set clear expectations about what I think I could provide and would avoid even implying a guaranteed performance in a fire.

 

[planc]

The client is the building owner.

Anyway.I just need to know some technical now just for future reference even if I deny him.

Attached is the minimum thickness of walls and slabs for fire resistance of concrete of different aggregates.

How about pure cement and sand? I can't find the corresponding thickness and fire resistance. Can someone share the table?

Again this is for technical knowledge and reference (even though I can easily deny him as many of you suggested).

 

[ChorasDen]

How are you quantifying the fire? Every fire is unique, temperatures will vary based upon fuel loads, freely available oxygen, moisture content of air, etc. A 1-hour fire in one room will cause a different amount of damage than the same fire in the room next door.

Fire rated assemblies are intended to provide life safety for those leaving the building, and to a lesser extend, to those working to extinguish the fire. Fire rated assemblies do not provide any assurance of structural performance after a fire. Each and every component should be inspected and verified as adequate after a fire event. You can't simply say scrape the top off and everything is good, unless you are ultra-conservative and use 10x the required topper based upon calculation.

 

[rapt]

Normal fire protection rules are for Separation, Insulation and strength.

The top surface of a slab normally only has a temperature rise of up to about 150C and that is not a problem.

Bottom surface can reach 900 to 1200C.

Thickness of slab is then limited to stop the fire spreading upwards to the next level and to limit the temperature on the top surface.

Cover to the bottom reinforcement is normally limited to a temperature rise in the steel of about 400C to 600C depending on steel type to limit the strength loss in the steel to about 30%, resulting in a capacity under fire of about 70% of ultimate.

I have never heard of anyone trying to protect the top surface of a concrete office slab from fire.