Questions · Fire detection
How many sounders are needed and how long do they have to sound for?
As many as it takes for the signal to be heard throughout the building over whatever noise there is. The regulatory reference is that the alarm level should not drop below 65 dB(A), or 5 dB(A) above the ambient noise when that noise goes above 60 dB(A) for more than half a minute, and that in sleeping areas it should reach 75 dB(A) at the head of the bed. With the doors closed, which is how the building is at night.
That means the number of sounders does not come from the floor area: it comes from a measurement. You measure the real background noise of each area and check the level at the bad points, not in the corridor. There is also a ceiling: where people have to stay put, the signal must not reach a level that stops them understanding each other or that hurts.
In noisy places, where there is machinery, or where there may be people with hearing impairments, the audible signal is accompanied by visual devices in line with part 23 of UNE-EN 54. It is not a matter of fitting any old light: they are classified by where they are mounted and by the volume they cover, and they are calculated the same way as the sounders.
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