Seek and search times

[messy]

When an AFD system has a time delay feature, I understand that BS5839 recommends 7 mins total seek and search time.

As British standards are advisory benchmarks rather than mandatory requirements, are there any circumstances in which the search time can be extended?

For instance, if the building is predominantly low rise/risk or is fitted with  control measures over and above the norm which would limit the speed of spread of fire, such as sprinklers or pressurised staircases etc.

Any examples of such extensions of time would be useful.

Thanks

[Chris Houston]

7 minutes is quite a long time.  I have always advised my clients that we would only accept 3 minutes, speaking from the perspective of an insurance company.  All clients so far have accepted this.

[kurnal]

I have recently set 5 minutes in a 500,000sq ft warehouse for wardens to verify a pre alarm before it escalates to evacuation. Breaking an MCP goes to immediate evacuation. I think in this case I have been  conservative- sprinklers and HSSD throughout, and a calculated ASET( without sprinklers) of 16 minutes. So my 5 minutes came from 5 minutes to verify, 3 minutes to respond and evacuate ( fire wardens to gee people up) plus 100% safety margin= 16 minutes. In this case the detection and sprinklers were  a bonus- in a building this large it would possibly take at least 5 minutes for a fire  to be detected by the occupiers anyway.

I think that for a conventional building designed around the ADB/ 5588 template, 7 minutes would usually be too long. But if you have calculated an ASET then I cant see any problem in working within the time available, povided there is some safety margin, which needs to take both the management procedures and sods law into acount.

[wee brian]

There are quite a few buildings where the AFD is over provided (in terms of meeting min life safety requirements) in these buildings I see no reason why the period could not be extended.

For instance - an office building where a manual system would be adequate is, instead fitted with a ful blown L1. Given that the detectors are over and above what is necessary then it will be reasonable to extend the investigation time.