Derek Engel, Scott Davis
GexCon US, 8433 Rugby Ave. Suite 100, Bethesda, MD 20814
Presented at International Symposium on Fire Investigation, 2012
The current NFPA 720 code requirement for carbon monoxide (CO) detectors in residential structures requires placement outside of each separate sleeping area and on each floor of the residence. There is however no further guidance to specific placement of the detector (high, low, near or within furnace closets, etc.), as well as no acknowledgement to different housing and HAVC styles (forced hot air, hot water, etc.). As the concentration of CO approaches several hundred parts per million, the time for detector alarm can be as little as a few minutes, much smaller than the characteristic mixing time of the residence. The general basis for detector placement requirements assumes that once the flue gases cool CO is generally neutrally buoyant in air, and becomes well mixed and distributed evenly throughout the residence. Previous investigations have concluded that the CO is well mixed for residences with forced hot air heating systems and the CO in hot flue gases stratifies due to buoyancy for systems without an air-handling device to cause mixing.
Using the CFD software FLACS, a study was performed to evaluate how CO would disperse and migrate in various residential structures and various HVAC designs. The goal would be to evaluate the migration of CO originating from hot flue gases, which are improperly vented into structures, and assess the validity of the well-mixed assumption as well as study the general dispersion patterns. In addition, the study will provide further guidance as to optimal places for detector placement to allow early detection, while minimizing nuisance alarms.