Fire detectors, an indispensable part of security systems, have played a role in saving millions of lives to date. However, many of us do not generally know the working principles of this technology, which is important in detecting possible fires that may occur in our homes and workplaces.
In this article, we will take a short journey to learn the basic working principles of fire detectors.
Types of Fire Detector
So what are the different types of fire detectors and what do they detect?
Fire detectors are generally divided into two types:
Smoke Detectors: They work by measuring the density of particles in the air, which represent the presence of smoke released during a fire.
Heat Detectors: These devices can detect abnormal temperature changes or an increase in heat that exceeds the standard value for a given area.
However, in fire safety, these systems are generally used together under the name of Combined Detectors.
Fire detector representations that work on the principle of heat and smoke detection.
Optical Smoke Detector
The working principle of optical smoke detectors, also known as photoelectric smoke detectors, is based on detecting particles of smoke suspended in the air. The basic structure of these detectors consists of a light source and a photoelectric cell. The light source is usually an LED or laser light, and the photoelectric cell is located on the opposite side of the light.
Under normal conditions, the light travels straight to the photoelectric cell, allowing the detector to function properly. However, if there are smoke particles in the environment, they change the direction of light or block its passage. As a result, less light reaches the photoelectric cell or the light may be completely obstructed. The detector recognizes this change and activates the alarm system.
Generally used for fire safety in homes, businesses and public buildings, optical smoke detectors are generally more effective for detecting slow-growing fires. They are used as an important warning system, especially in situations where smoke is dense or fire is developing slowly. By using these detectors alongside heat detectors, you can create a more comprehensive fire safety system that is capable of detecting fast-spreading fires.
Carrier Edwards SIGA-PD Optical Smoke Detector Internal Wiring: Smoke particles reduce or completely cut off the amount of light reaching the photoelectric cell. The detector detects this change and triggers the alarm system.
Constant Temperature Detector
The constant temperature detector is set with a reference threshold, triggering an alarm when the ambient temperature exceeds this level. For instance, a constant temperature detector can trigger an alarm if the temperature rises above fifty five celcius.
Rate of Rise Heat Detector
Rate of Rise Heat detectors are designed to identify rapid increases in temperature and trigger an alarm accordingly. They prove highly effective in scenarios where fires can escalate quickly, offering crucial time for emergency response. As a result, these detectors are particularly valuable in locations at high risk of fast fire spread.
Combined Detectors
Combined detectors provide a more comprehensive fire safety system by using smoke and heat detection technologies together. The main purpose of these detectors is to detect fire danger more quickly. For example, when using only smoke detectors, it may be difficult to detect temperature changes in the environment before smoke is formed. However, combined detectors constitute a faster warning system by detecting abnormal temperature increases in the environment as well as smoke.
Beam Type Smoke Detectors
Beam smoke detectors, also known as optical beam type smoke detectors, are comprised of a device that can send and receive light from a main unit situated approximately 1 – 1,5 meters from the wall and ceiling. The main unit is equipped with a reflector plate conveniently positioned on the opposite wall. It emits an invisible beam of infrared light which is then reflected back by the reflector plate and transmitted back to the main unit.
The working principle of beam smoke detectors that work with this basic mechanism is quite simple: Under normal conditions where there is no smoke, the beam sent from the light source reaches the receiver directly. However, if there is smoke or other obstructing material in the environment, this beam is cut off or weakened. The receiver detects this interruption and the detector raises an alarm, indicating the danger of fire.
Smoke can easily block the passage of rays, making beam smoke detectors more sensitive than other fire detectors. Their high sensitivity allows them to provide early warning in large areas with high ceilings, such as warehouses, factories, industrial facilities, and shopping malls, thus helping prevent serious damage.
Linear Heat Detectors (LHD)
Linear heat detectors are sensitive devices used to detect temperature changes in the event of a fire. These detectors consist of a thermistor1 , or a thermocouple placed in a cable to detect the fire danger.2 Temperature changes along the cable are detected and alarmed by the linear detector. As the environment's temperature increases during a fire, it causes the temperature on the cable to rise, which is then picked up by the detector to trigger the alarm system.
Linear heat detectors are commonly used in long or wide areas due to their unique capabilities. One of their major advantages is the ability to detect temperature changes at any point along the cable. This allows for quick detection of the fire's origin, providing early warning and valuable time for firefighting efforts.
Linear heat detectors are often used for fire safety in industrial facilities, warehouses, garages and other large areas. Because long cables measured in kilometers can be used, these detectors can cover large areas and effectively detect fire hazards. Therefore, they are used as an important component to ensure fire safety in large areas.
Linear heat detectors can be divided into two groups as fiber optic and wired linear.
Fiber Optic Linear Heat Detector
Fiber optic temperature sensing systems use specially designed fiber optic sensors. These sensors contain a special layer located around the core of the optical fiber. This layer is sensitive to temperature changes, and as the temperature increases, the physical properties of the optical fiber change. Temperature changes affect light reflections or propagation in fiber optic sensors. These changes lead to changes in the light signals carried along fiber optic cables. Fiber optic sensors detect changes in the physical properties of the heat-sensitive layer. These changes may take the form of changes in the length or bending of the fiber.
Detected changes are analyzed by the system. The intensity, speed and other characteristics of temperature changes are examined. When the specified reference temperature threshold is exceeded or an abnormal temperature profile is detected, the system triggers the fire alarm.
Fiber optic detectors are ideal for sensitive fire detection because any minimal bending or extension can be detected by fiber optic detectors. In addition, one of the advantages of this system is that they can be used in harsh environments that traditional detectors cannot reach.
Wired Linear Heat Detector
The working principle of the linear heat detection cable is based on detecting fire or excessive heat situations by detecting thermal changes along the cable.
Linear heat sensing cable usually contains a copper-clad wire because copper is a very good and economical material in terms of electrical conductivity. Electrical signals inside the linear heat sensing cable are transmitted through copper wire. Copper wire allows signals to be transmitted along the cable so data from thermal sensing components can be transmitted to the control panel.
More precisely, the resistance value of the copper cable changes as the temperature increases. Linear cable heat detectors monitor this change and determine whether the temperature increase is a sign of fire. In this way, fire danger is detected at an early stage and necessary precautions are taken.
Linear heat detectors monitor heat change and determine whether an increase in temperature is a sign of fire.
Linear heat detection cable is used as an important component for fire safety in large areas, tunnels, warehouses and other industrial facilities.
Flame Detector
The flame detector operates by sensing the fire hazard through the wavelengths emitted by the surrounding flames. Typically, flame detectors work by detecting specific wavelengths within the visible light, infrared, or ultraviolet spectrum to identify flames.
These detectors are often used in industrial facilities, petrochemical plants, ships and other hazardous areas. They are vital for fire safety, especially in high-risk environments. They are less prone to false alarms. They can quickly detect the speed at which the flame forms.
The use of flame detectors is important in terms of early detection of fire danger, rapid intervention and preventing the spread of fire. In this respect, it is an ideal technology to use in places where fire danger is high, such as petrochemical plants.
What is the Detection Radius of Smoke Detectors? How Far Apart Should Smoke Detectors be Placed in a Corridor Based on its Width?
As stated in the TSE CEN/TS 54-14 standard, the maximum detection radius for the smoke detector is 6,2 meters.
For an open-area square detector array, detectors can be placed a maximum of 8,8 meters from each other and a maximum of 4,4 meters from a wall or large obstacle. In corridors whose width does not exceed 2 meters, only points close to the center line of the corridor are taken into account. In this case, if the smoke detectors are placed 12,4 meters apart and the maximum measurement from the end wall is 6,2 meters, the above requirements will be met.
If the application area has a sloping ceiling, the horizontal distances given above for detectors at or near the top can be increased by one percent, up to a maximum of twenty five percent for each degree of inclination.
What is the Detection Radius of Heat Detectors? How Far Apart Should Heat Detectors be Placed in a Corridor Based on its Width?
As stated in the TSE CEN/TS 54-14 standard, the maximum detection radius for the heat detector is 4,5 meters.
For an open-area square detector array, detectors can be placed a maximum of 6,4 meters from each other and a maximum of 3,2 meters from a wall or large obstacle.
In corridors whose width does not exceed 2 meters, only points close to the center line of the corridor are taken into account. In this case, the above requirements will be met if the heat detectors are spaced and located 9,0 meters apart and the maximum measurement from the end wall is 4,5 meters.
If the application area has a sloping ceiling, the horizontal distances given above for detectors at or near the top can be increased by one percent, up to a maximum of twenty five percent for each degree of inclination.
Is Installation of Fire Detector Mandatory?
In accordance with official regulations, it is mandatory to install automatic fire detection devices in buildings that exceed specific building height or total closed area values.
Where is a Fire Alert System Mandatory?
The two main parameters for this obligation are the height of the building (m) and the total closed area of the building (m2), as stated in the official regulations.
Buildings like residences, office buildings, commercial buildings, and others are required by law to install a fire alarm system if they exceed certain height and area limits.
| Building Height (m) | Total Closed Area of the Building (m2) | |
| Homes | > 51,50 | |
| Buildings for Accommodation Purposes | > 6,50 | > 1000 |
| Educational Facilities | > 21,50 | > 5000 |
| Inpatient Health Facilities | > 6,50 | > 1000 |
| Outpatient Treatment and Other Health Facilities | > 21,50 | > 2000 |
| Office Buildings | > 30,50 | > 5000 |
| Buildings for Commercial Purposes | > 12,50 | > 2000 |
| Buildings for Industrial Purposes | > 21,50 | > 7500 |
| Eating and drinking | > 12,50 | > 2000 |
| Entertainment | > 12,50 | > 2000 |
| Museum and Exhibition Areas | > 6,50 | > 5000 |
| Terminals | > 6,50 | > 5000 |
| Warehouses | > 6,50 | > 5000 |
| High Hazard Places | > 6,50 | > 1000 |
Is Periodic Maintenance of Fire Alarm Detectors a Necessity?
According to the technical specifications of the Turkish Standards Institution (TSE), the maintenance of fire alarm systems should be done on a daily, monthly, quarterly and annual basis.
Do Fire Detectors Work Alone?
Fire detectors are an important component of fire safety systems, but they must be used in conjunction with emergency exit lighting and advanced emergency platforms to ensure complete safety.
A fire alarm alone has limited ability to provide security. Detecting a fire situation is not a sufficient solution on its own. Having the fire detection system in contact with fire extinguishing systems and integrating it with the building management system provides crucial advantages in the successful implementation of emergency management.
For the past twenty-five years, Elekon has been dedicated to safeguarding your life and property by offering advanced emergency solutions from Carrier Edwards and expertly designed emergency lighting solutions from Mackwell.
Furthermore, with our technical service unit providing support twenty four hours a day, seven days a week, we conduct regular maintenance on your fire alarm systems.
To ensure the safety of yourself, your loved ones, and your colleagues, feel free to contact us for a consultation on finding the right system solution.
Conclusion: The Importance of Fire Detectors in Fire Safety
Fire detectors are devices that are vital for fire safety. Understanding how fire detectors work and how they should be used is important to increase your safety. Fire detectors can save lives through early fire detection and rapid response. Having knowledge about the correct fire detector selection, installation and maintenance allows you to implement fire safety measures correctly.
The importance of fire safety systems should never be underestimated. You need to make sure you take the right steps to ensure your safety.
As Elekon, we wish you a healthy and safe future.
- A thermistor is an electrical resistance sensor used to measure temperature changes. Electrical resistance varies depending on the temperature of the sensor. ↩︎
- Thermocouple is a sensor used to measure temperature. It is usually formed by combining two different metal wires. The junction of these wires produces a temperature-dependent voltage. The basic function of the thermocouple is to determine the temperature in the environment by measuring this generated voltage. ↩︎
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