Smoke alarm

The Definitive Smoke Alarms Guide

The idea of waking up to a burning home is frightening enough to convince most people to install smoke alarms. Residential dwellings with working fire alarms are half as likely to have a fatality in home fires. This reason alone explains why we need them.

With new technology and a variety of smoke alarms on the market, installing these alarms isn’t so simple anymore. We’re going to break down everything you need to know about smoke detectors and alarms so you can keep your family safe. On top of that, you won’t be needing to apologise to your neighbours for another smoky cooking mishap ruining their quiet evening in.

Why Do We Need Smoke Alarms?

Smoke alarms are one of the best ways to identify the warning signs of a house fire. Homes without working alarms are 80% more likely to lose part or all of their home than those with a working alarm. These homes are also 50-80% more likely to have a fatality from a house fire as well! Ensuring your home has smoke alarms installed and that they’re working will prevent these deaths.

The Building Code of Australia requires that all homes built and renovated since 1997 have mains-powered smoke alarms with battery back-up installed. Beyond this, each state has its own requirements:

  • ACT: All homes built or renovated since 1997 must have at least one mains-powered alarm; photoelectric preferred.
  • NSW: At least one alarm per level/apartment; mains-powered and interconnected recommended.
  • NT: At least one photoelectric alarm that is mains-powered or has a 10-year battery.
  • QLD: Interconnected photoelectric alarms that are mains-powered or have a 10 year battery (as of 2017); current alarms that are less than 10 years old need to be replaced when they expire.
  • SA: At least one alarm per home that is mains-powered or has a 10-year battery; new homes and extensions require interconnected alarms.
  • TAS: At least one per home; mains-powered or 10-year battery operated.
  • VIC: At least one alarm per home; photoelectric recommended.
  • WA: At least one alarm that is mains-powered; 10 year battery powered only allowed when mains-power is not possible.

How Do Smoke Alarms Work?

Smoke alarms come in several different types and they all work differently. There are two main types of alarms found in Australia – ionisation and photoelectric – and many states are moving more towards one than the other.

Types of Smoke Alarms

Ionisation Detectors

Ionisation smoke alarms typically give quick responses to flaming fires. These alarms use two ionisation chambers and an electric circuit to detect fires.

These alarms contain a small amount of radioactive material. This ionises, or charges, the surrounding air around it. This ionised air is positively and negatively charged and flows between two charged plates, also positive and negatively charged. This creates a current. The first chamber is open to the air, while the second is enclosed and acts as a control reference. Both chambers have the same current.

When smoke is present in the first ionisation chamber of the alarm, the ionised air attaches to some smoke particles. This disrupts the flow between the charged plates. This means there is a discrepancy in the current between the two ionisation chambers, and triggers the alarm.

Photoelectric Detectors

Photoelectric, or optical smoke detectors, are better for detecting fires with a long period of smouldering.

This type of alarm uses light and a photoelectric sensor to detect smoke. If smoke enters the chamber and crosses the path of light, the smoke particles scatter the light.

One alarm type directs light at a sensor, and the scattering of light by smoke reduces the amount of light that reaches this sensor. This will trigger the alarm. Alternatively, the light is not directed at a sensor, and the scattering caused by smoke will cause light to reach a sensor that will trigger an alarm.

Dual Sensor Detectors

Dual sensor smoke detectors combine both the ionisation and photoelectric methods of smoke detection. This means you’ll get both the benefits and negative features of both types.

Heat Detectors

Rather than detecting the presence of smoke to alert you to a fire, heat detectors use temperature.

When there is a fire, the heat rises to the alarm fixed to your ceiling. A heat detector contains a thermistor which detects temperature changes and triggers an alarm when it goes above a set temperature. A lightproof chamber encloses the thermistor to prevent light affecting the temperature reading.

What Type of Smoke Detector is Best?

Most fire authorities recommend photoelectric smoke alarms. They have the quickest response time to smouldering fires and are also adequate for flame fires. Despite ionisation alarms being better for flame fires, they are not adequate for detecting smouldering fires. Regulations across most states recommend photoelectric alarms as well. Photoelectric alarms require regular cleaning to work properly, however.

If you want to double down on your fire detection, consider dual sensor alarms for your home. Kitchens should not have dual sensor or ionisation alarms installed. They are prone to nuisance alarms caused by smoky cooking.

Heat detectors are not recommended for use by themselves but could be useful for rooms prone to smoke. These rooms include the kitchen and garage, for example.

Where Should I Place Smoke Alarms?

Each Australian state has different smoke alarm requirements, but the placement is generally the same. At a minimum, alarms should be placed in the hallway or corridor connected to bedrooms. For levels that don’t have bedrooms, at least one fire alarm should be placed in the most likely path of travel to evacuate the building.

Smoke and steam are common in kitchens and bathrooms and so you should not have smoke alarms in these rooms. Steam can also set off a smoke alarm. Otherwise, nuisance alarms might be a common occurrence.

The centre of your ceiling is the best position for your smoke alarm. For cathedral ceilings, an alarm can be positioned 500 – 1500 mm from the apex. Alternatively, you can install the alarm on your wall 300 – 500 mm below the ceiling.

How Often Do I Need to Change My Smoke Alarm?

Here at Metropolitan Electrical Contractors, we recommend you test your smoke alarm every month to ensure it still works. Most alarms have a test button for this very purpose. Every 6 months you should clean it with your vacuum cleaner to ensure no dust or build-up affects its sensitivity.

If you use a battery-operated alarm, the batteries should be replaced annually. Finally, your alarm should be completely replaced every 10 years. Like most things, your smoke alarm will deteriorate with age. An old alarm is less sensitive to what triggers it. This sensitivity could mean the difference between escaping a fire or not.

What is the Difference Between a Smoke Detector and a Smoke Alarm?

Our everyday language uses smoke alarm and smoke detector interchangeably. They are actually different devices though.

An alarm is a standalone system that detects smoke and sounds the alarm all in one unit. A smoke detector has units that detect smoke across a home, but a single alarm system that interconnects them all. Many Australian states now recommend you have your alarms interconnected.

Smoke detector installation requires a licensed electrician. Contact Metropolitan Electrical Contractors to learn more about what smoke detector will suit your home.

Published: 30 Jun, 2020

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