Domestic Electric smoke alarms were invented in 1965 by Stanley Bennett Peterson and Duane D. Pearsall. Their device, called the “SmokeGard700” was said to be relatively low cost such that it could be installed in most homes, though its use within the domestic environment didn’t start to gain traction until the 1970’s.
Ionisation smoke alarms:
Early smoke alarms relied on ionisation detection – whereby a small amount of radioactive material is placed between 2 electrically charged plates, this ionises the air and allows a flow of current between the 2 plates.
If smoke enters the smoke detector it disrupts the flow of ions between the plates. As the flow of current is reduced the alarm is activated.
Advantages:
Disadvantages:
Optical smoke alarms:
Also known as Photo-electric smoke alarms, these units use a light scatter principle. An infrared pulsating LED directs a beam of light into the detection chamber at a fixed time interval.
If smoke particles enter the chamber these cause the infrared beam to be scattered and this is detected by a photodiode light receptor which activates the alarm.
Optical alarms detect larger particles – such as those emitted from a smouldering fire before it bursts into flames.
Therefore, it’s not recommended to install these in or near to kitchens, as they’re sensitive to cooking vapours and fumes.
The best location for these alarms is living areas with soft furnishings such as bedrooms, lounges etc.
Advantages:
Disadvantages:
Note – Whilst the 2 types mentioned above have different characteristics, ionisation detectors are being phased out by manufacturers such as FireAngel due to environmental concerns with the waste material at the end of life.
Therefore, optical detectors are the preferred choice.
As much as you possibly can – you get what you pay for.
Budget smoke and heat alarms at the lower end of the range won’t be as well designed or constructed of the best components and are more likely to fail prematurely as a result.
Do you want a safety device which may be all that stands between you and escaping a fire in your home to be value engineered?
Thought not.
Heat detectors are just that – they detect heat and are used in locations where smoke alarms can’t be installed such as kitchens, plant rooms and manufacturing environments. They aren’t sensitive to steam, burnt toast, smoke or dust particles.
How can you tell the difference between a smoke and a heat detector?
Domestic smoke alarms tend to be rather flat on the surface, heat detectors tend to have a raised centre and you’ll only tend to find them in the kitchen in a domestic environment (or perhaps if you have a biomass heater or log burner then maybe near these.
