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Fire Alarms: How do They Work, and Why are There So Many Types?

Fire Alarms: How do They Work, and Why are There So Many Types?

  2012-09-24         sparksdirect         Safety » Fire Safety

A common misconception a lot of people hold is that there is just "one kind of fire alarm", the kind that is stuck on the ceiling in the kitchen and makes a horrible noise when you burn the toast.

But that isn't true; there are actually several different kinds of fire detectors, each with its own sensors, each with its own function.

The three most common fire detectors found in domestic properties are the optical and ionisation type smoke detectors and the heat detector. Today, we'll try to explain how each of them works and where they work best.

Ionisation Smoke Detectors

Ionisation-type smoke detectors are the most inexpensive type of detector and probably the most common.

The sensors release a tiny amount of radiation (around 1/5000th of a gram) to ionise the air inside the sensor.

If there is a fire, ions in the smoke will attach themselves to the ions in the sensor and trigger the alarm.

These types of sensor are usually quick to respond before the smoke gets too thick, which make them great for use in the bedroom or living room, where they can safely ignore the dust and cigarette smoke.

Note: if there is a risk of fire due to cigarettes, an optical sensor might be best.
However, because of their general sensitivity to the non-visible byproducts of the fire, ionisation smoke detectors are not suited for use in the kitchen.

The grill alone can trigger a false alarm when all you wanted was a delicious cheese toastie.

Optical Smoke Detectors

An optical smoke detector aims a thin beam of light at a specific point in the sensor.

All around that point is photosensitive material which is not usually exposed to that light.

However, when smoke gets into the sensor, the light is scattered onto the photosensitive material, and the alarm is triggered.

These detectors are sensitive to slow-burning, smouldering fires such as when a piece of furniture ignites or when faulty electrical wiring overheats.

On the other hand, a little bit of steam can cause a false alarm.

So don't install these next to the bathroom; a hot shower could trigger the alarm exactly when you don't want it.

Heat Detectors

Generally speaking, a heat detector works in one of two ways: the heat sensor sounds the alarm when the temperature reaches a certain level, or the sensor measures how quickly the temperature is rising - too fast and the alarm is triggered.

The Aico heat detectors offered at Sparks Electrical are calibrated to trigger an alarm when the local temperature reaches 58°C.

They are best installed in the kitchen or the garage, but because they can be relatively slow to respond to a fire they should only be used as part of an interconnected fire alarm system that includes smoke detectors.

We have a number of these smoke and heat detectors online and in our showroom, as well as a top-of-the-range multi-sensor device that combines optical and heat detection technology for installation almost anywhere in the house.

There is no "one-size-fits-all fire alarm" that will be effective everywhere in your home: each type of sensor is suited to a specific use.

If you're in need of a little more advice on fire alarm systems, particularly for corporate and industrial purposes where the regulations are different, feel free to come down to our showroom.

We'll be happy to help you choose the right alarms for your purposes!