When most people think of fire alarms - loud, piercing noise and strobing lights usually come to mind. No one really enjoys experiencing a fire alarm, but most people understand their importance and immediately begin to evacuate the building. Fire alarm systems save lives. Their reliability depends on having a detection system with the right kind of fire detectors.
Fire detectors are devices with sensors built into them that are capable of detecting one or more of the products or phenomena resulting from a fire. They are a key component of a fire protection system, which consists of several subsystems including at minimum the fire detection devices, the notification and/or suppression activation, and a controller that receives the signals from the detection devices to initiate the appropriate actions. While all of these components are equally important for the system to function properly, it’s easy to see how dependent the system is on having the right initiating devices for the detection system – the wrong detection devices or improperly functioning detectors can cost lives.
Most fire detection systems fall into three major categories based on the type of sensors they use:
- Smoke detectors
- Flame detectors
- Fire gas detectors
Many of the devices on the market today combine two or more of these sensor technologies to achieve a better balance between fire detection and the risk of false alarms. To choose the best fire detection system for your business, it is therefore important to understand the basic technology used in each type of sensor.
This post describes how each type of sensor works and some of the most important factors to consider when choosing fire detectors for your fire protection system.
Smoke Detectors
There are two primary types of sensor technology used to detect smoke – optical (also called photoelectric) technology and ionization, which is a physical process.
Optical (photoelectric) technology uses a light source, and a system for collimating the light from that light source (turning it into a single beam of light), and a photoelectric sensor to convert light into an electrical current. When smoke begins to enter the dark optical chamber of the device, it crosses the beam of light. The particles in the smoke disrupt the beam, “scattering” the light. The scattered light is then picked up by the photoelectric sensor, which increases its voltage to trigger the alarm.
Optical (photoelectric) smoke detectors are good for sensing smoldering fires that create a lot of smoke with little to no visible flames. However, they are vulnerable to dust and dirt, which can build up in the unit and trigger false alarms.
Ionization detectors work by holding a small amount of radioactive material (Americium-241) on two electrically charged plates with space between them. The radiation emitted by the radioactive material creates a small current (ionizes) between the two plates, ionizing the air. Smoke entering the chamber will absorb the alpha particles, which interrupts the current and reduces the ionization to initiate the alarm.
Ionization smoke alarms are sensitive enough to detect very small particles that are typical of smoke resulting from fast, flaming fires. However, they are slow to respond to smoldering fires and like their optical counterparts, can initiate false alarms when dust, dirt and other particles build up inside them.
Flame Detectors
Open flames and fire emit heat radiation, the transfer of energy in the form of electromagnetic waves. Flame detectors contain an electronic circuit with an electromagnetic radiation receiver (the sensor), which can detect radiation from one or more defined wavelengths on the electromagnetic spectrum. Their sensors are designed to detect increases in heat radiation above a threshold value for either ultraviolet (UV) radiation or infrared (IR) radiation. Both UV and IR have different wavelengths. Therefore, flame detectors are distinguished based on the type of radiation they are designed to detect.
UV flame detectors are designed to detect the UV radiation, which occurs at wavelengths between 10 and 400 nanometers on the electromagnetic spectrum. They work by measuring changes in the levels of radiation in the atmosphere. When a fire occurs, the UV sensor detects the increase in radiation and initiates the alarm. UV detectors are capable of accurately distinguishing the type of flame at the moment of ignition, within mere milliseconds. Given the sensitivity of UV detectors, they can also be triggered by other UV sources, including sunlight and lightning. Most UV detectors are equipped with a 2-3 second delay to minimize false alarms.
Infrared flame detectors are designed to detect the heat radiation emitted by open flames within the infrared spectrum (700 - 1,000,000 nanometers). Spectral patterns are analyzed with a small thermal imaging camera within the device to render the infrared radiation to visible light. Although not quite as fast as their UV counterparts, IR detectors also offer very fast response times with most capable of detecting in 3-5 seconds.
Fire Gas Detectors
Fires can emit a wide variety of gases depending on the materials that are burning, most of which are highly toxic and/or quickly deplete the oxygen within an enclosed space. These gases can include carbon monoxide, carbon, nitrogen, sulfur dioxides, hydrogen chloride, ammonia, hydrogen bromide, hydrogen cyanide, ammonia, and others.
Fire gas detectors are designed to detect certain gases at predefined concentrations. Therefore, devices must be selected based on the specific type(s) of gases that might occur given the types of combustibles present.
Gas detectors may use any number of technologies including infrared point sensors, ultrasonic sensors, electrochemical gas sensors, and semiconductor sensors. However, because they are made for specific gases, your selection should first be based on the type of gas they detect. Then you can evaluate the technology to determine the best one for your setting.
Factors to Consider When Choosing Fire Detectors for Your Business
As you can probably see, no single method of fire detection is universally applicable. They all have their strengths and weaknesses. And, given the wide variety in the types of fires that can occur and the many different applications and environments in which they are needed, every application is going to be unique.
Understanding your fire risk is essential to choosing the right devices. The list below provides several factors you should consider before making any selection.
Combustibles
- Nature and quantities of combustible materials present:
- Their ease of ignition
- Likely form of combustion
- Their propensity for smoke production
- Heat release rate
- Probable rate of fire growth and spread
Environmental Factors
- Temperature and humidity
- Cleanliness
- The extent of any pollutants present
- The type(s) of work processes that occur in the area
- The height and geometry of the protected area
- Other active and passive fire protection measures present
Once you have a clear understanding of your fire risk, you will be better able to identify at least generally, which types of detection devices you need – smoke detectors, flame detectors, fire gas detectors, or some combination of these.
For any device you are considering, always evaluate the performance criteria to ensure it will meet your unique needs, including the speed at which the device can detect a fire and any interferences or other vulnerabilities that can lead to unintentional alarms.
Koorsen Can Help
With so many types of sensor technologies now available, choosing the right devices for your business can be a daunting task. Whether you are retrofitting an existing fire protection system or installing a new one, all of your detection devices should integrate seamlessly with your fire alarm and automated fire suppression systems where needed.
At Koorsen, we service and inspect and install all brands of fire alarm systems from a range of high-quality manufacturers. Our certified technicians stay on top of evolving sensor technologies and can help you determine the types of detectors most appropriate for your business as well as the brands of equipment that will be compatible with your current fire protection system. Contact us today to get the expert advice you need!