Fire Rated FeaturesFire-rated letterplates are fitted with an intumescent liner around the telescopic sleeve section of the letterplate. In the event of a fire the intumescent liner expands to seal the letterbox aperture and retains the fire integrity of the door.
Product TestingThe door grame was tested opening into the furnace which is considered to be the most onerous direction, however the opinion of the Chiltern laboratory was that doors could be applied to open in either direction. The door was measured at 1978mm high x 835mm wide x 53.5mm thick and was fitted with a latch which was disengaged. The intumescent letterplate was fitted 1410mm from the leaf head and 295mm from the closing edge of the door.
When tested in accordance with BS476: Part 20/22: 1987 and part 31.1: 1983, the requirements of the standard were satisfied for the following periods:
Integrity failure recorded to the intumescent letterbox assembly was 43 minutes and 45 seconds on the termination of this test
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