Why combine CO and fire detection?
SimplexGrinnell's interest in using carbon monoxide (CO) as a fire sensor was based on some research on how to make fire detection more reliable and less prone to false or nuisance alarms.
Simplex Grinnell's John Haynes explained some of the details. "Photo electric [sensing] relies on smoke particles being present. They're detected optically. With CO, because it's gas, it tends to spread more rapidly throughout a space," he said.
"Smoke on the other hand typically rises with heat and it may take a while before the smoke concentration builds up to the point where it's detectable, whereas the idea of a gas sensor is if you've got a good signature gas for a fire it's going to disperse very rapidly through the air and theoretically would be something you detect more quickly."
The reason to combine CO detection with another technology [photo electric sensing--the primary method used today for fire detection] is that there are other sources of CO that could otherwise cause false alarms.
The product that SimplexGrinnell introduced at ASIS is used for CO detection only. Although it's hooked up to the fire alarm panel, it's not attempting to detect the fire. The product that SimplexGrinnell (and other manufacturers) are exploring potentially could do both, sense gas as well as be useful to detect fire at an early stage.