Can I fit a letter plate or eye viewer to my fire-rated door?
Fitting a letter plate or eye viewer will breach a fire rated doorset and has the potential to allow a direct passage for hot gases and flames. It is therefore important that:
- There is test/assessment data for the fire rated doorset to tolerate the ironmongery.
- The ironmongery being fitted has been previously tested in a doorset of comparable construction.
- The maximum height at which the letter plate can be fitted is adhered to (see below).
The test conditions of BS476: Part 22: 1987, are such that the neutral pressure axis is at 1000mm from the threshold of the door (500mm in BSEN 1634 – 1 2000); below the axis the pressure is negative and above the axis the pressure is positive. This means that above the neutral pressure axis hot gases will be forced against the doorset and without supporting test data, a letter plate fitted at this location may compromise the integrity of the doorset. The tested height of a letter plate relative to the neutral pressure axis is therefore an important constraint in limiting its location.
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