Guidance document on actuation times of smoke and heat detectors

[Tadees]

Hi Guys,

Is there any research which shows the actuation times of the different types of detectors on the market and a comparison with the evacuation times of the average person that is sleeping, awake, of average mobility etc?  If so, where can I read about this?

[Mike Buckley]

Smoke and heat detectors do not normally have actuation times, they operate on the physical circumstances. A heat detector will have a set temperature at which it will activate, smoke detectors have a similar system.

Hence if you look at a heat detector for example, it will take much longer to detect a small slow growing fire which is producing much heat than it would a blow torch directly on it.

[Fishy]

PD 7974 series has guidance - e.g. PD 7474-4 - Detection of fire and activation of fire protection systems (Sub-system 4).

[Phoenix]

As Fishy states PD7974-4 does give some answers but they cannot be relied upon.  They are too simplistic.  Think of all the uncontrollable variables that can affect the flow of gases through a room, leaky windows, open windows, radiators being turned up or down or off, AC units with multiple settings, doors open or shut, windy day or still day, temperature of the smoke, item on fire, etc.  These all make any attempt at modelling the process meaningless.

[Fishy]

As Fishy states PD7974-4 does give some answers but they cannot be relied upon.  They are too simplistic.  Think of all the uncontrollable variables that can affect the flow of gases through a room, leaky windows, open windows, radiators being turned up or down or off, AC units with multiple settings, doors open or shut, windy day or still day, temperature of the smoke, item on fire, etc.  These all make any attempt at modelling the process meaningless.

I'd agree - though I've never used this particular PD it does appear to be a somewhat 'academic'  document & to me it raises more questions than it answers!  I don't like PF 7974-7 (probabilistic risk assessment) either, for much the same reason.

[Phoenix]

And if you want a really good laugh, have a read through PD7974-5.

[Phoenix]

Tadees, to return to your original question, you might get some indicative times for detectors from manufacturers but I don't know.  As for evacuation times PD7974-6 does give some reasonable guidance but for sleeping people it indicates huge response times of 30 or 60 minutes, something like that.  These figures may be true and that is likely to undermine any analysis you are doing comparing ASET and RSET where sleeping people are involved.  In a hotel it is possible to counter these huge response times by involving staff in rousing people but in flats this cannot be done.