Yes Paul thts why I led into my suggestions with "I guess".
As CO diffuses throughout a space and is not confined within the fire plume, unlike smoke, I thought this may help to provide a solution.
CO detectors give a useful response to most fires- all fires generate CO to some extent. A multi sensor head on an analogue system can be set up with a range of states or sensitivity. and can incorporate twin chamber smoke, heat, rate of rise and CO detectors all working in concert. But you need to have a compatible system. Take a look at the Gent SQuad heads for example.
Computer rooms inevitably present a similar problem if simple indirect coolers are used, again siting of detectors and increasing the number of detectors are the usual considerations.
Unless someone does some modelling it is unlikely that any of us can come up with a definitive solution. The effect of the fan will depend on many factors- dimensions of the room, location of a fire, type of fire, distance between detector and fan. It may even turn out not be too much of a problem.
Personally my gut feeling is that if you are not concerned about interfacing the fans to the fire alarm system to shut them down in a fire to reduce fire growth then perhaps they also aint going to be too much of an issue at the detection stage. But then again my gut feelings often get me into hot water, especially where clotted cream and chocolate are concerned.
