How loud is too loud? I've read somewhere that alarms should be 5dB above ambient, but is there a top end that should be considered?

BS5839 Part 1, 2002 A minimum of 65 dB is required in general areas or 5 dB above any background noise which persists for more than 30 seconds. Where sleeping people are to be woken then 75 dB is required at the bedhead Hope that helps, is all in the BS I've been told ;)

Thank you both...particularly for the reference. My main issue is that I've had number of concerns raised about the sounders being too loud. I think the main problem is that in some places, the alarm is significantly greater than the ambient noise, thus causing peple to jump out of their skins (despite a tannoy announcement beforehand). Guess I'll need to get the alarm engineers in and review sounder locations etc.

AKM - If there was an issue where they could not be heard then fair enough make any necessary changes. But people need to accept a minor inconvenience now and again. I personally would not make or advise changes just because people may not like how loud they are. From experience it can be around £75 per item to make changes to a detection / warning system so this could soon add up. Of course if budget is not an issue then go ahead - keeps the troops happy! For the few seconds it takes for a bell test there should be no risk of hearing damage and in the event of drill / evacuation the expsoure should only be a couple of minutes maximum. You may want to conisider the response team who may have to remain slightly longer but even the sounders would have to be well above 100dB to do damage in such a short period of time. There may be other risk factors ie vulnerable people (keeling over with heart attack) or those conducting hazardous operations (up ladders or 'playing' with nitroglycerine) which could concievably cause problems but if your warning via Tannoy then there should be no real issue.