Home Reviews A Short Guide on the Working of Photoelectric Smoke Alarm

A Short Guide on the Working of Photoelectric Smoke Alarm

by Naveen Agarwal

Smoke detectors in houses are meant to warn the residents of a possible fire as quickly as they can. Every property in Australia is required by law to have a few smoke alarms so that the fire and safety departments can reach the place and neutralise the threat as quickly as possible. Smoke alarms have different functionality based on their working, like the photoelectric smoke alarms that can detect smouldering fire. This short guide will help better understand the technology that keeps every house safe.

Smoke alarms are essential to have for a secure household. Research published in 2019 has revealed that house fires kill more Australians than all the natural hazards combined.

Common Causes That Lead to House Fires

  • Being absent-minded during activities, such as falling asleep or not being careful while holding a cigarette or keeping equipment on, can cause fires. Most people don’t realise that it takes only a spark to create a fire, and this tiny spark can come from a seemingly insignificant source.
  • Misuse of heating equipment or devices by young children or adults is another cause. Children can be careless around specific equipment and are often unaware of their activities. This can lead to carelessness and equipment or devices getting misused.
  • Deliberate use of materials to burn down a house where there are no indications of the accidental or natural formation of fires, or in simple terms, ‘arson’, is another not so uncommon cause.

Common Equipment That Causes House Fires:

  • Devices that produce heat, like heating systems, water heaters, chimneys and other open fireplaces: These objects tend to reach high temperatures that can start a fire.
  • Fireplaces can also throw out hot coal or burning particulates that can let carpets or curtains catch fire.
  • Ovens, stoves or other types of equipment for cooking and heating that are left unattended
  • Electrical failures of appliances, wiring, bulbs and circuits can create short-circuiting that leads to electrical fires. These fires are very difficult to put down and often require strenuous effort.

How Do Photoelectric Smoke Alarms Work?

As the name indicates, photoelectric smoke alarms use light to detect the presence of fire in a home. The smoke alarm has a casing that can sense light of a specific wavelength. Inside the chamber, an LED light shoots a straight ray of light across the chamber constantly. When smoke enters the chamber as fire starts, the light ray scatters due to its refractive nature and changes direction. The LED is deflected from the straight line and hits a photosensor that is present in another compartment. When the light beam hits the sensor, a circuit gets activated, and the alarm starts sounding.

The sensing chamber houses the light-emitting diode and sensor that capture incoming light. The scattered light rays due to the smoke particles present are responsible for triggering this sensor and setting off the alarm.

How Photoelectric Smoke Alarms Compare to Other Types of Smoke Alarms

Ionisation smoke alarms are the most commonly used in households, followed by dual sensor smoke alarms. Although ionisation alarms detect rapidly growing fires, photoelectric are effective against slower fires that are smouldering in nature. As a result, they are very quick at sensing smouldering fires compared to the ionisation alarms.

When using smoke alarms, it is always recommended to have as many as possible to cover every area or room. A proper layout for the alarms must be maintained for full effectiveness so that a fire spread can be contained as soon as possible.

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