Every industrial facility needs fire protection. International, municipal and state building codes require it.
Alarms detect fires and alert employees when to evacuate. Early detection limits fire spread and reduces property damage. And when integrated with fire suppression systems, they can control or extinguish a blaze.
Though it is common knowledge why facilities need fire alarms, there are many considerations when designing a fire protection system. These include facility hazards, fire system components, fire detection systems, and fire suppression.
Start at the Beginning
Though every facility needs fire alarms, it’s critical to consider different hazards within your facility before designing a fire alarm system. Knowing the hazards helps you design a fire protection system that fully protects your facility.
First, consider the nature and quantities of the combustibles present within the building. Know the ease of combustion and the likely form of combustion for each hazard. Will the hazard produce smoke as it combusts? What about the combustible’s heat release rate or its probability of fire growth and spread? These things affect the fire alarms you select and how they will work in your facility.
Environmental factors also play a role. Temperature and humidity levels, ceiling height, and cleanliness of a building can affect how fire protection systems operate. Work processes also matter, as they can produce sparks that lead to fire. Fire protection systems also can get clogged, operate inefficiently, or produce false alarms in dirty or caustic environments.
What are Fire Detectors?
The fire protection industry defines fire detectors as devices with sensors built in that can detect one or more elements of a fire. These systems fall into the following categories:
- Fire gas detectors
- Flame detectors
- Heat detectors
- Smoke detectors
To pick the right mix of detectors, you need an understanding of how they work and the best applications in which to use them.
Smoke sensors represent the most efficient way to detect a fire. The saying “where there’s smoke, there’s fire” highlights why. Smoke detectors sense fires faster than other detector types.
There are two types of smoke detectors: ionization smoke alarms and photoelectric smoke alarms. Both identify smoke particles in the air. However, it’s important to understand key differences between the two before selecting one technology over the other.
Ionization smoke alarms put a trace amount of radioactive material between two electrically charged plates. This creates a steady flow of ionized air within the smoke alarm. When a fire breaks out nearby, it disturbs the ionized air flow and triggers an alarm.
Ionization smoke detectors work best with flaming fires—fires with aggressive, open flames. But they are less effective with fires that have smoldering flames.
Photoelectric smoke detectors have a light source and a light sensitive sensor. When smoke fills an area, it scatters the light in the photoelectric alarm chamber to trigger an alarm. These detectors work best with slow smoldering fires.
“Photoelectric smoke detectors detect fires earlier than ionization alarms,” says Andrew Guarino, chief executive officer and business strategist at AG Consulting. He explains an ionization detector looks for a flash while a photoelectric detector looks for particles and advises choosing smoke alarms with both technologies built into them.
Dual-sensing photoelectric and ionization smoke alarms work together to achieve the same goal, he says. They work as well with aggressive open flame fires as they do with slow smoldering fires.
Fire Gas Detectors
A fire gas detector detects specific gases at predetermined concentrations. Knowing the gases that may be present in your environment during a fire helps you select the right fire gas detector for the job.
Fires emit a variety of gases depending on the materials burning. The gases can be highly toxic and may deplete oxygen in enclosed areas. The most common gases include ammonia, carbon monoxide, carbon, nitrogen, hydrogen bromide, hydrogen cyanide, hydrogen chloride and sulfur dioxides.
Fire gas detectors use a variety of sensing technologies, including infrared point sensors, ultrasonic sensors, electromechanical gas sensors, and semiconductor sensors, each detecting specific gases.
Infrared gas detectors use an infrared light to detect a combustible gas, while ultrasonic sensors use sound waves rather than light to detect gases. Electromechanical sensors react with a gas of interest to produce an electrical signal proportional to that gas concentration. Semiconductor gas detectors detect total VOC (TVOC) concentrations indoors. Each sensor type works with specific gases, so be sure to match the sensor to the potential gasses present in your facility.
Flame detectors, also known as optical flame detector sensors, detect visible fires within a protected area. These systems contain an electronic circuit with an electromagnetic sensor that detects radiation from defined wavelengths on the electromagnetic spectrum.
UV flame detectors spot UV radiation between 10- and 400-nanometer wavelengths. They measure changes in radiation in the air. When a fire breaks out, a UV sensor detects the resulting increase in radiation and sounds an alarm.
Though UV flame detectors accurately detect a flame upon ignition, other UV sources, including sunlight and lightening, can trigger a false alarm.
Infrared flame detectors also are available. These systems detect heat radiation from open flames within the infrared spectrum (700-1,000,000 nanometers). This technology offers quick response times, can detect a fire within 3-5 seconds, and can spot hydrocarbon or hydrogen flames.
Heat detectors are fire alarm devices that respond when the thermal energy of a fire increases the temperature of a heat sensitive element inside the device. Here, there are two types of alarms to pay attention to: rate of rise and fixed temperature.
A fixed temperature heat detector focuses on the actual heat in the room, rather than the rate of change. When the temperature in the room exceeds a preset number, the detector activates an alarm.
Rate of rise thermal detectors, meanwhile, trigger an alarm when the rate of temperature increase in the surrounding area rises above a certain rate. These detectors measure the rate that air temperature changes during a fire event to deliver a faster alarm response than when detectors just measure the temperature of an area.
Rate of rise detectors work better than fixed temperature detectors, says Guarino. “With a fixed temperature detector, by the time the temperature reaches 180 to 200 degrees, you’ve already got a fire,” he says. These detectors also work better in dirty environments and require minimal maintenance.
Though both rate-of-rise detectors and fixed temperature detectors can detect changes in temperature, they work best for high-heat fires. These systems cannot detect a smoldering fire quickly.
There are detectors available that offer rate of rise and fixed temperature detection in a single unit, adds Guarino.
Though this article only examines fire, heat and gas detection, a total fire protection solution also includes fire suppression. Typically, each system operates independently of each other, but integrating detection and suppression into a single panel simplifies plant operation and maintenance, reduces time wasted on false alarms, and helps operators respond quickly and precisely to potential incidents.
With fire detection and alarm systems, it’s important to choose wisely. These systems help industrial facilities discover fires early in their development while there’s still time for safe evacuations and fire control.