It is probably quite evident that there are a number of fire alarms available, and at vastly varying prices, so it may be very difficult to understand the differences between Optical, Ionisation and Heat alarms. This guide is aimed at taking some of that confusion away.
So what is the difference between the models?
As stated above there are three types of alarm, each with its own uses.
Optical Alarm: This type of smoke alarm usually uses an infrared beam between two points, the alarm being triggered should the beam be disturbed. In much the same way as a criminal might trip an alarm when breaking into a bank vault or museum in the movies, if the beam is broken, the alarm will go off. It detects larger smoke particles best.
Ionisation Alarm: These alarms use 2 small plates (one charged positively, one negatively) and an alpha particle source to create a constant current running across the gap between the plates. When smoke enters the chamber it interferes with this process, interrupting the charge. When the charge drops, the alarm goes off. These alarms are best at detecting smaller smoke particles.
Heat Alarms: A heat alarm will trigger if the room temperature reaches a certain level. They fire alarm system do not detect smoke, and are not to be used as a substitute for a smoke alarm, but should be used in assisting these alarms for greater fire detection.
Why do we need different types of fire alarm?
Different types of alarm exist due to the different types of fire. Believe it or not, fires act in different ways depending on what is burning, and is important to identify the fire as quickly as possible. Different alarms are better at discovering different fires, and choosing the right alarm for the right room could save your life one day.
Fires can be particularly smokey, often caused by the burning of papers or clothing etc, and burn rapidly, producing smaller smoke particles. The Ionisation alarms are better at detecting these fires.
Other fires can be a lot less smokey, often being harder to detect, and are caused by the burning of carpets, sofas or electrical devices. These fires tend to burn less rapidly, producing larger smoke particles. Optical alarms will be better at detecting these fires.
Which fire alarm do I need?
This article is meant as a general guide, and for more detailed safety advice it is highly recommended that you contact your local Fire Service. This being said, the information below should help you decide.
Optical alarm: Living room, dining room, hallway
Ionisation alarm: Bedrooms, walk in wardrobes
Heat alarms: Dusty areas such as garages, unconverted lofts etc where the dust could interfere with the other alarm types.
Alarms are available as either battery operated, or mains operated with battery backup. The mains alarms will continue to work for a time after power is lost to the unit, but only as a backup. If this is the case, mains should be restored to the unit right away, or the battery changed.
Some alarms even come with the option of interconnectivity, meaning if one alarm sounds, then all the alarms sound. This is highly useful in larger properties where one alarm may not be heard by everyone. The idea is to raise the alarm to everybody right away – as soon as a fire starts – and having the alarms linked together will achieve this.
Fires are responsible for a large number of deaths each year, as we all know from the adverts broadcast on television or radio. This is a fact, and can be greatly reduced by just checking your alarm to be sure that it works, and that it is the correct alarm for the location it is placed. Be aware that alarms need replacing after a certain amount of time, and it is worth checking on the unit and to note the replace by date. If you are unsure, check with your local Fire Service.