We’re often asked when to use smoke detectors and when to use heat detectors. Both types of detectors can detect a fire, but these products are actually designed to serve different needs:
Heat detectors are intended to minimize property damage by reacting to the change in temperature caused by a fire.
Smoke detectors are intended to protect people and property by generating an alarm earlier in the development of a fire. People need time to react, and every second is critical during an actual fire event.
When it comes to protecting people, it is critical to warn building occupants before smoke accumulates. Some types of fires “smolder,” or burn very slowly without flames. Burning slowly causes incomplete combustion, which in turn generates more smoke, carbon monoxide, and other poisonous gases. Smoldering fires also generate very little heat, making them difficult to detect with heat detectors. When people are harmed during a fire, the culprit is almost always smoke and poisonous gases like CO: not the heat or flames.
If smoke detectors are the ideal solution for protecting lives, why do we still see heat detectors being installed instead of smoke detectors?
When property protection is the primary objective, heat detectors can be a reliable and virtually trouble-free solution. In some cases, heat detectors are chosen because of their low cost and greater immunity to contaminants and environmental extremes. In other cases, the heat detectors are used to trigger fire sprinklers or other types of fire suppression systems.
Today’s multi-criteria spot detectors and aspirating smoke detectors are designed to tolerate higher levels of airborne contaminants and broader temperature ranges. Although these solutions are generally more costly than heat detectors, they respond much earlier. In addition to giving building occupants more time to react, advanced smoke detectors often allow first responders to address the fire hazard before serious property damage occurs. Our application guides can help you determine if either multi-criteria spot detectors or aspirating smoke detectors are the right solution for your application.
When smoke detection is not practical, choosing a faster-acting heat detector can provide a quicker response time. Standard, fixed-temperature heat detectors respond as expected in a majority of fires, but they suffer from thermal lag when fires build quickly. “Thermal lag” occurs when rapid temperature increases cause the heat detector to alarm at a temperature higher than its set point. Adding rate-of-rise capability can speed up reaction times to fast-building fires, but they can also lead to false alarms if the installation environment naturally sees rapid changes to the ambient temperature. Rate-of-rise compensated fixed-temperature detectors can help to prevent both thermal lag and false alarms due to rapid temperature changes. These detectors respond like a standard, fixed-temperature heat detector with slowly developing fires. When fires build quickly, the rate-of-rise compensation prevents thermal lag, allowing these detectors to respond when their set point is reached.
For more information including detector spacing requirements, dealing with various ceiling types, or special applications, refer to the National Fire Alarm and Signaling Code (NFPA 72) and your locally applicable codes and standards.