by kbrownie »
Thu Aug 13, 2009 11:37 pm
The requirements within BS7671:2008 (know as the regulation)
Ask for provisions to be taken to reduce the risk of fire and the spread of it.
the spread of fire/smoke, involves the materials the building are constructed of, and passages where fire/smoke can spread should be sealed.
ie when cables pass through walls.
As far as the hoods are concerned, again it's a risk that needs to be evaluated and no hard set rule.
Preventions the key, there's a 30 minute rule concerning the prevention of fire/smoke spreading.
With down lights you have two factors the heat dissipated above the ceiling by the light and the hole made to install the light.
The heat dissipated within the ceiling void should be kept at a safe level or restricted. In the event of thermal insulation being in the ceiling void it must be kept at least 150mm from the light fitting as this will add to thermal effects.
The cut-out hole for the fitting also opens an area where fire/smoke can spread from below, up through the hole and above. Even with the light fitting installed, a barrier has been broken.
So it wise for both cases dissipation and fire/smoke spread from below to fit at least 30 minute fire rated hoods.
Also the hood will protect and keep clean the fitting from dust and muck within in the ceiling void.
Hope info helpful
KB