A fire starts in your building – an alarm sounds, fire doors activate, and occupants rush outside to safety. But what about your HVAC system?
"In an emergency, air duct systems can transfer smoke, toxic gases, and flame from one area to another, posing a serious hazard to life safety and property," explains Jim Kapparos, national sales manager for System Sensor, a manufacturer of fire alarm systems.
Take the infamous 1980 MGM Grand fire. While the fire was contained to the lower levels of the casino, most of the 85 deaths occurred on the upper floors from smoke inhalation and carbon monoxide poisoning. Faulty dampers accelerated the spread of dangerous fumes to stairwells and emergency passageways.
According to the official investigation report by NFPA, "the distribution of smoke throughout the high-rise tower through the heating, ventilation, and air equipment" was a major factor contributing to the death toll.
To safeguard your ductwork from becoming a pathway for fire, make sure your facility is protected by duct smoke detectors.
How Do They Work?
Duct detectors sample currents in the air handling equipment to determine if smoke or fumes are present. If smoke is detected, the device will close dampers, stop fans and blowers, and trigger an audible and visible signal at the fire control panel, Kapparos explains.
These actions provide early detection, allow facility personnel to investigate the cause, and can protect the air conditioning system itself from fire and smoke damage.
Typically found in large commercial and industrial facilities, duct smoke detectors are a code-mandated device where required by NFPA 72 (90A), NFPA 101, and the International Mechanical Code (IMC), says Kapparos.
Stipulations can also be found in the International Building Code, International Fire Code, and the Life Safety Code 101, adds Bernie Arends, who served as an origin and cause fire investigator for over 30 years and works as a sales associate for Inspection Reports Online.
While local code adoption varies, duct smoke detectors are most common for facilities with 5-ton or more cooling units.
"Duct smoke detectors are needed on HVAC units over 2000 cfm on the return side, and on units over 15,000 cfm on the supply and return sides," says Arends.
Some can also be interconnected to other duct detectors. If one senses smoke, the rest will switch their relays, with the triggered detector reporting to the fire alarm panel so the source can be pinpointed.