The building fire alarm system goes into general alarm and all the occupants evacuate the building and are standing outside when the fire trucks arrive. After 15 minutes of investigation by the fire fighters it is found that the cause of the alarm was smoke detector in the vicinity of where someone was making popcorn. If you're a building manager or owner, a false alarm can be very costly in lost productivity and revenue.

Because of cost and nuisance, reducing false alarms has been a major focus of the fire alarm industry for many years. Recently, advancements have been made in smoke detectors and sensors by some manufactures to include the detection of carbon monoxide (CO) to reduce the amount of false alarms from a fire alarm system.

Several studies have been performed on the detection of carbon monoxide in a fire event. The conclusion of these studies has been that all actual fire events generate carbon monoxide at toxic levels, but many false alarms do not have CO associated with them. Some manufacturers of fire alarm systems have taken these results and integrated CO detection into smoke sensors not only to comply with new codes being released, but also to improve the rate of false alarms from a detector to make them more reliable.

NFPA 720 is the standard that addresses the installation of CO detectors. Prior to the 2009 edition of this standard NFPA 720 only addressed residential applications of CO detection. The recent release of the 2009 edition has been expanded to address the installation of CO detection in all occupancies. In commercial buildings this means that carbon monoxide detectors must be installed where there is a permanent fuel burning appliance and in dwelling units detectors must be installed outside each sleeping area. The standard also recognizes the use of combination type system detectors that connect to the building fire alarm system. All new buildings will have to comply with the requirements of this standard, and some states have passed legislation requiring existing buildings also be retrofitted with CO detectors before being sold or during upgrades.

To reduce false alarms, a combination detector with CO and smoke detection integrated into one device would alarm only if there is at least 70 parts per million CO and 2.5%/ft smoke obscuration present at the same time. There are many possibilities of false alarms that do not generate CO, including burning popcorn, toast, and butter, steam and dust. With the advantages of combining detection technologies, it might be advantageous to install a combination detector in locations of repeated false alarms if it is determined that the cause of the false alarm is not generating CO, such as a lunch area with a microwave or a hallway outside a shower area that generates a lot of steam.

A combination CO/Smoke device can be used for faster fire detection also. Carbon monoxide is generated at a much higher rate at the beginning stages of a fire than smoke, so if a sensor detects 70 parts per million or more CO it could lower the sensitivity of the smoke sensor to as little as 0.5%/ft obsuration and alarm much faster and more reliably than a standard smoke detector set for 2.5%/ft obscuration. This type of application could mean that there is less damage to a building and the fire is being controlled before getting too big.

Combination devices are probably not a solution for every detector in a facility, but, by doing some research into false alarms that are being experienced in a facility, simply changing out existing smoke or heat detectors and replacing them with a combination type detector that includes CO, a drastic reduction in nuisance alarms from your building fire alarm system may be experienced. Because occupants of a facility are interrupted less to evacuate the building and wait around while the alarm is investigated, the result can be an increase in both productivity and revenue.

Jeff Fulkerson has been with SimplexGrinnell for over 10 years with experience in both field commissioning and design of fire alarm systems. Currently a Field Sales Engineer, he covers a 12 state territory assisting with the design and application of Simplex Fire Alarm equipment. NICET 3 certified.