On behalf of the Norwegian Directorate for Civil Protection and Norwegian Building Authority, SP Fire Research has conducted the study "Mapping of gas concentrations, effect of dead-air space and effect of alternative detection technology in smouldering fires". 

The objectives of this study were:

• to investigate if smoke detectors with CO sensing can alert residents at an earlier stage than photoelectric smoke detectors, consequently increasing chances of egress and survival for a sleeping person.
• to measure concentrations of toxic gases in a room where a smouldering fire occurs and investigate if tenability limits are exceeded when an photoelectric smoke detector is activated.
• to investigate if smoke detectors placed within dead-air space are activated at a later stage than smoke detectors placed according to the recommendations.

Main conclusions:

• Combination detectors with a CO sensor are activated significantly earlier than photoelectric smoke detectors. This may increase the chances of survival in a smouldering fire.
• Tenability limits for CO can be exceeded at the time an photoelectric detectors is activated. This may be lethal.
• The results show insignificant differences in times to activation for combination detectors placed on walls and on ceiling. This shows uniform spread of CO in the room. Thus CO sensors may be placed at locations more accessible to persons who cannot reach detectors placed on the ceiling.
• The results with regards to differences in time to detection for photoelectric smoke detectors placed inside and outside of a dead-air space, respectively, were inconclusive.