Heat Detector

 

How a Heat Detectors Works

Every day, in the United States, 1,500 houses burn. Often, these fires are preventable, common house fires that were noticed too late. Fires only take a couple of minutes before they become uncontrollable, with flames reaching over 1,000 degrees Fahrenheit. House fires are dangerous, killing 6,500 and injuring 280,000 people every year.
The good news about fires is that, if they are caught before the flames escalate, the fire is easy to handle and easy to put out. Heat detectors and fire detectors save thousands of lives every year. Here’s how a heat detector can save your home.

What Is a Heat Detector?

A heat detector is a device that can sense heat in a room. Its purpose is to alert homeowners and business owners that there is a fire before the fire becomes irreversible. The device responds to convected thermal energy radiated from a fire. There are two main types of heat detectors on the market: rate-of-rise heat detectors and fixed temperature detectors.

Rate-of-Rise Heat Detector

 

Rate-of-rise heat detectors sense the heat in the room. The detectors register 70 degrees as a baseline; when the heat in the room rises rapidly above 70 degrees, the alarm is activated. This type of sensor is triggered by the “rate of change” rather than the temperature itself. Usually, the alarm is triggered when the rate of change is a 15 degree increase in less than a minute. When a house fire starts, the temperature in the room will rise rapidly—in some cases, the temperature will rise 30 degrees in 45 seconds.

Fixed Temperature Detector

 

The fixed temperature detector focuses on the actual heat in the room, rather than the rate of change. When the temperature in the room surpasses a preset number, the alarm is activated. Typically, the preset temperature that triggers the alarm is around 135 degrees. High temperatures are a good indicator of fire (unless you have your heater set to 135 degrees).
Both the rate-of-rise detectors and the fixed temperature detectors are great for sensing fires. However, heat detectors have drawbacks. Although they are great at heat detection, they won’t be able to detect a smoldering fire quickly. They are best for detecting high-heat fires.

Types of Fires for Heat Detection

Low-Energy Fire

There are two main types of fire: low-energy fires and high-heat fires. A low-energy fire smolders; it consumes fuel slowly and gives off a lot of smoke. However, this type of fire emits very little heat. Because this fire gives off more smoke than heat, thermal detection may fall short and take too long to detect this fire. By the time the heat sensor is activated, the fire will have caused severe damage to the home.

High-Heat Fire

The second type of fire is a high-heat fire. A high-heat fire consumes fuel quickly. As the fire eats, the flames grow higher and higher. These types of fires can be caused by an explosion or combustion. These fires feed off of easy-to-burn material such as paper, hay, or dry wood. This fire will trigger a heat detector fairly quickly. Heat Detectors are optimal for sensing this type of fire.

Heat Detectors vs Smoke Detectors: What's The Difference?

In a nutshell, here’s the difference between heat detectors and smoke detectors:

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.

Areas of application of the heat detectors

Areas of application are especially rooms where a smoke alarm is not suitable due to frequent smoke, dust or steam development. In this way, frequent false alarms caused by disturbance variables can be avoided.

These include production plants, logistics centres, workshops or kitchens. However, the maximum permissible room height for the heat maximum and heat differential detectors (6 m to 7.5 m) must be observed.

Important: Heat detectors are not a complete alternative for smoke detectors, but only a supplement. They are also primarily suitable for property protection, as they react more slowly than smoke detectors. Our experts will be happy to advise you on the best fire detectors for your building.

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