Siting of detector on pitched roof

[ludo694]

We are looking into installing fire detection in a 8.5m high plant room with pitched roof. However, a unistrut steel frame platform has been installed at 4m with all services installed below this platform. The area above the unistrut platform is now inaccessible and only houses flues from below. Will installation of detectors on underside of the unistrut steel frame platform be deemed to be in conformity with BS standards? Is there an alternative acceptable type of smoke detection installation that could be adopted?

[Chris Houston]

What category of system has been specified?

[ludo694]

None at the moment.

[kurnal]

what is the fire loading in the plant room? What type of fire is likely to occur- if it all air handling plant heating equipment, ducts fans and filters etc or are there any combustible contents or fuels in addition to the plant?

Is the unistrut platform imperforate or would it allow smoke to pass by the 4m platform into  a large reservoir in the upper half of the space?

Have you considered beam detection or aspirating detection systems?

Obviously if point detectors are used only on the underside of the platform unless the detector happens to be immediately over the fire there could be a very considerable delay in operation especially if the lare reservoir above the platform has to fill with smoke first- hence the recommendation in 5839 to mount detectors within 600mm of the ceiling. Aspirating detectors would be much easier for maintenance. Airsense Technology do some small units.

[Chris Houston]

What is the purpose of the fire detection? Life safety, property protection, something else?

[ludo694]

Property protection - the installation is a biomass plant room

[ludo694]

Further, the unistrut platform is perforated and would allow smoke to pass by into the upper half of the space. The problem has occurred due to the method of construction that has rendered the upper half of the space to be in-accessible, especially for maintenance purposes

[kurnal]

Is there no access to the upper side at all even for a one off installation of sniffer pipes or beam equipment?

If not you could think about identifying the areas beneath the platform where fire is likley to occur- motor drives etc and provide a baffle plate / curtains  to form a reservoir above those areas to contain the fire plume and site detectors withint the reservoir, far from perfect but a step in the right direction.

Otherwise can you gain access  by drilling from outside the plant to install beams/ aspiration pipes?

[John Webb]

From experience you will eventually need access into this space. Flues may be damaged, wear out or otherwise need replacing. Is it possible to get a hatch of some sort fitted now that will give you access in the future and also allow you to fit detection immediately?
Are the flues carrying cold or hot gases? If the latter I would be inclined to go for an aspirating system; heat might affect a beam - if indeed the disposition of the flues allows space for beam detection anyway.

[Chris Houston]

If it is a Category P1 system, then you will need detection in the space.  If it is a Category P2 system, then it will depend on the extent of the scope of detection, but any sensible specifier would specify detection in this area.

More importantly (than "will it comply") will the system detect a fire.  The best place to do this would be in the apex.  But perhaps beam detection below the false ceiling would adequatly cover the plant in the roof, but the void above would still be without coverage.

I would guess that the space with the flue from a biomass plant is something that deserves protection too.

The provision of an access hatch seems like a good idea for flue maintenance, in case the roof needs repairs and to solve the problem of fire detection.

[netfire]

It seems that it's hard to work on the fire detection for security purposes. The detector should be attached into a great angle into the roof. The pitched roof should be secured after that installation.

[David Rooney]

Without seeing the construction or knowing what the roof is like, a radical suggestion may be to run aspirating pipework (although it would need to be lagged) on the outside of the roof and mount the controllers at ground level.

Could you drop capillary sampling tubes through the roof construction?