Everything You Need to Know on Fire Detectors

It could be so easy to see, choose and install a fire detection system or even just a fire detector. But detectors are as different as the scenarios that they need to protect. For example, if you have high ceilings, smoke must first get to that point where the detector is mounted – it costs valuable detection time. So, let’s start with explaining which detector is suitable for which scenario.

What Different Kinds of Fire Detectors Are There?

• Smoke detectors: Optical, Ionization, Dual Sensor Detector, Aspirating Smoke Detector
• Heat detectors: Thermal and thermovelocimetric detector:
• Flame detectors: IR detector (Infrared), UV detector (Ultraviolet)
• Linear infrared detectors/thermal imaging
• Video fire detectors
• Gas detectors

There are smoke detectors, heat detectors, flame detectors, linear infrared detectors/thermal imaging, video fire detectors, and gas detectors. These subcategories of detectors cover the most regularly used detectors. As one can tell only by their names, the way they detect fires functions differently. Some detect the difference in smoke particles, others use temperature or deviation in infrared light.

Smoke Detectors: What Is the Difference Between an Optical, an Ionization and a Dual Sensor Detector?

The most classical detectors are smoke detectors. They are widely used and are easiest to install. Oftentimes, many will call them “point type smoke detectors” or “point detectors” which refers to the most standard ceiling-mounted detectors.
Smoke detectors detect smoke particles in the air. As soon as the quality of air changes, they give out an alarm. That being said in an easy way, there are four kinds of smoke detectors:

1. Optical smoke detector or photoelectric detector: These kinds of detectors contain a light beam to detect smoke particles in the air (photoelectric technology). When the light is intermitted by floating particles, it triggers the alarm. They are very sensitive to smoke from a slow, smoldering fire, as they detect rather medium and large smoke particles. Therefore, it takes a bit for them to get triggered.

2. Ionization detector: The function of this detector is a bit harder to imagine. It produces ionized air. That means they create an electrical charge and a current to flow inside the detector. When smoke particles get inside, they detect a deviation in electrical charge and the alarm sounds. These kinds of detectors are very sensitive and easily triggered by changes in air (pressure, temperature, etc.) Hence, they are sensitive to fast, flaming fires and analyse smaller and medium size particles.

3. Dual sensor detector: This detector uses both ionization and photoelectric technologies in one alarm. This is why it is best for earliest possible warnings, regardless of the type of fire.
It is a tough choice to decide what kind of fire detectors are useful for each individual scenario. Sebastian Wehr, Product Manager for Fire Detectors at Bosch Building Technologies says: “One trend in the industry is certainly to use multi-sensor technology to further improve detection capabilities. We recommend the multi-sensor approach for demanding environments. Two or more sensors combined in one device can increase the false-alarm stability and, at the same time, make a system more robust.”

The Avenar detector 4000 series from Bosch is a flexible series of nine detectors for both manual and automatic addressing systems. They are available in single, dual and multi-sensor versions for specific applications and are equipped with intelligent signal processing based on more than 4,000 fire patterns to deliver highly reliable detection performance.
As you can see now, many providers today combine different functions of detectors already, because it makes the system more secure.

Another fire detection system, the Zettler Profile, a brand by Johnson Controls, comes with associated 3oTec detectors and offers very stable technology with rapid response time and less frequent nuisance disruptions, e.g. by false alarms. Flexibility and scalability of the panel and the parameterization of the addressable detectors allow quick adaptation to all customer needs.

Optical smoke detectors using the light-scattering principle are a very good compromise between cost and efficiency. Using a detector which combines smoke detection with heat detection and even CO detection reduces false alarms significantly.

4. Aspiration smoke detector (ASD): This detector per se is the same as the others. It also uses either optical or ionic detection. The difference is: It leads the air to the detector through suction pumping and through pipes. Therefore, it can cover larger areas and volumes of air, as well as areas with higher ceilings. Siemens explains it like this: Their ASDs continually sample air from the monitored room using a connected pipe system with aspirating holes distributed along the length of the pipes. The air is drawn through these holes and into a detection chamber by an aspirator fan. It is then analyzed optically for the presence of smoke, using red and blue light (see Figure below).

A current example of the aspiration smoke detector comes from Siemens. In 2023 they have launched their new ASD+ that has two independent detection chambers in only one device and enables monitoring of rooms up to 6,700 m². According to Siemens, it is the largest area of coverage of any product currently on the market.

ASD+ is used in data centers, warehouses, road and rail tunnels, cable channels and other applications requiring very early detection, and where point detectors are hard to reach for service and maintenance. The ASD+ operates across a broad temperature range of - 20 to + 60 degrees Celsius, effectively functioning in both clean and harsh environmental conditions. Its versatility and robustness make it an ideal choice for diverse industries and demanding environments.