fire rating of suspended ceiling

[Tim Mitchell]

This is a sort of DIY question since my business is moving to new offices and we are doing some modifications ourselves.

We are building some more offices on a mezzanine floor above some existing offices. The mezzanine floor is wooden joists with chipboard flooring. Beneath the joists is a suspended ceiling with 600x600 tiles.

The BCO wants 30 minute fire protection for this mezzanine floor. This I agree with. Our suspended ceiling contractor says that the existing ceiling tiles provide 30 minutes fire protection, provided that any recessed light fittings are properly hooded. He has given me the manufacturer's specs for the ceiling tiles showing this. The BCO says that it does not provide the protection and we need to plasterboard the underside of the joists to provide the fire protection.

I don't want to antagonise the BCO by arguing that he's wrong, but I don't want to do a lot of extra work if it's already suitable. Advice from the panel please.

[nightjar]

The fire resistance of the panels is not the only factor. In a fire, a strong updraught can develop, which would lift the tiles and allow the fire past them. We did get a suspended ceiling approved some years ago, but the grid had to be steel and we had to fit special clips to hold the tiles down.

Colin Bignell

[Paul C. Dickie]

In article , nightjar writes

Bearing in mind that the heat from the fire could (and would) cause the steel grid to expand and buckle -- possibly to the point where the clips could not hold anything down -- might it not be a wise precaution to paint the joists and the underside of the floor above with a "fire resistant", intumescent paint?

[Tim Mitchell]

In article , Paul C. Dickie writes

Well I am only going on what the ceiling manufacturers say. They say that the ceiling itself, without the tiles being clipped, will give 30 mins fire protection to the floor above.

The alternative is to put a layer of plasterboard above the ceiling tiles but if the ceiling itself is OK, this should not be necessary. The offices above have a fire exit direct to outside and can be evacuated in about 2 minutes, so 30 minutes should be ample.

[nightjar]

The requirement for fire resistance is not based on how long it takes to evacuate the compartment under ideal conditions. It is intended to provide adequate protection for someone trapped inside while the Fire Brigade arrive and make a search. There have been numerous cases where a fire exit has proved to be useless for one reason or another and a surprisingly large number of people either panic or freeze when faced with a real fire. Our mezzanine was deemed to require two hours' fire resistance.

Colin Bignell

[Hugo Nebula]

On Thu, 14 Oct 2004 01:24:33 +0100, a particular chimpanzee named "nightjar" randomly hit the keyboard and produced:

The 'period' of fire resistance is more like a relative measure of the level of protection. A structure or door, etc, which achieves 30 minutes FR in a standard test may last for hours in a real fire, or may collapse or fail in a shorter time. An extreme example: the WTC Twin Towers had a period of two hours, but the South tower collapsed in 56 minutes. The conditions experienced were a lot more severe than those in a standard test.

[Ian Stirling]

And the protection may not have been as specified.