'They are essential': How smoke detectors are evolving
59 minutes ago Share Save Chris Baraniuk Technology Reporter Share Save
McConnell Family The McConnell family home was left partially destroyed by fire
The school run was over and laundry was in the tumble dryer. Mum and step-mum of four Liz McConnell was about to sit down to work at her Dover home last September. But that's when the sound of a fire alarm cut through her morning. She walked towards it and eventually found smoke billowing out of the tumble dryer. Touching the machine, she realised it was hot and, looking closer, she saw that part of it was on fire. "At that point I called the fire brigade," she remembers. They advised her to leave the property immediately. McConnell says the fire developed "very, very quickly". While Kent Fire & Rescue Service battled the blaze for hours, the McConnell family home was left partially destroyed. "Had I not have heard [the smoke alarm], I would have just been in there," says McConnell. "They are essential, absolutely essential."
Smoke alarms have been around for many decades. The technology has barely changed in recent years – but is modern life slowly outpacing the capabilities of these life-saving devices Detecting e-bike battery fires, for example, is particularly difficult, since these can unfold suddenly. Some researchers are working on new ways of sensing smoke and fire, perhaps even more quickly than before. But, take note: any certified, working smoke alarm is better than nothing. "People are about 10 times more likely to die in a fire if there isn't a working smoke alarm in the property," says Suzanna Amberski, head of customer and building safety at Kent Fire & Rescue Service. Her organisation alone found roughly 6,500 expired smoke alarms in Kent properties between 2022 and 2024. At a national level, a survey by insurer Direct Line published in December suggested that nearly four million UK adults might be living in a home without any smoke alarm at all. In the US, an estimated 16% of households do not have a functioning smoke alarm.
Raman Chaggar Lithium-ion fires develop at an "incredible" pace says Raman Chaggar
There are two main types of smoke alarm tech, says Raman Chagger, principal consultant at BRE, the Building Research Establishment. Ionisation-based systems use a tiny amount of radioactive material to charge, or ionise, particles in the air which flow between two small plates. Should smoke interrupt that flow of charged particles, the alarm goes off. Optical-based smoke alarms use light instead. They are slightly better at detecting the large smoke particles created by slow, smouldering fires. When such particles enter a chamber in the device, they scatter light from a small light source, which is then picked up by a photoelectric sensor. Heat sensors, often installed in kitchens to avoid false alarms if you simply happen to burn the toast, generally sound when temperatures climb above roughly 50C. The tests used in standards for evaluating smoke alarms were developed back in the 1980s. However, despite changes in building materials since then, smoke alarms remain reliable, says Chagger: "They still respond to all the main fires we get today." And Chagger has personal experience of tumble dryer fires. Some years ago, a fire alarm went off in his own home – in a room where his tumble dryer was operating. "I couldn't believe my ears," he recalls but, on close inspection, he realised a thin layer of smoke was hovering beneath the ceiling above the machine. Chagger was able to deal with the fire safely and says he recommends putting a smoke alarm in the same room as a tumble dryer.
But e-bikes containing lithium-ion batteries are a newer challenge. "When a battery fails, it doesn't necessarily ignite, it will often produce some off-gases," says Stephen Welch, senior lecturer at the University of Edinburgh's Fire Research Centre. "Those off-gases are toxic and flammable. If they accumulate, you can have an explosion risk." In experiments, Chagger has documented how lithium-ion battery fires develop. "It's just incredible," he says. "Nothing's happening, then: outgassing and boom-boom-boom – all these explosions."
PA Media Detecting fires caused by lithium-ion batteries is challenging
Some smoke alarms have been designed to be ultra-sensitive. Aspirating devices, for example, constantly suck in air in order to detect even small quantities of smoke in a room. They are often used in commercial settings, including server rooms packed with expensive computer tech. "A lot of stately homes will have that system," says Niki Johnson, fire systems technical adviser for the UK Fire Association, a trade body, and owner of fire detection firm Derventio Fire and Security. "You could be looking at £3-4,000 just to do a corridor." Such installations require substantial pipework, he explains.
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