![]() ![]() ![]() We’ve also removed these alarms from our results. Since we reported that the ionisation smoke alarms we tested were much slower at responding to smouldering fires, ionisation models have been removed from sale in New Zealand. Our Product test manager Paul Smith sat down with RNZ's Simon Morton to discuss our findings on smoke alarms. Our test found that photoelectric alarms were good at detecting both flaming and smouldering fires. Smoke from a flaming waste paper bin or cooking oil fire is different from that produced by the cooler smouldering of upholstery foam, bedding or the plastic bits of electrical equipment. Fire and Emergency New Zealand also recommends photoelectric alarms, and the Residential Tenancy Act requires landlords to replace expired smoke alarms with long-life battery photoelectric smoke alarms. But, hey, you should be changing it every six months anyway.We recommend you choose photoelectric alarms. So your battery life span may not be as good. The photoelectric ones probably are more power intensive. It’s similar to the Americium-241 smoke detectors in some ways. And again, you can get false positives because organic compounds often absorb infrared light really well. If it is tuned correctly, you can interpret that change in current as the presence of smoke. But when smoke goes in, it will make the light scatter a different way, or block the light in a certain way, and that will change the amount of current that’s flowing. The light can be shining and you get current. Engineers figured out how to tune a light source in a way that is sensitive to smoke. When light hits something, it generates electric current – it’s very much like a mini solar cell. It’s what Albert Einstein got the Nobel Prize for. Is there a better smoke detector?Ī newer kind of smoke detector is based on the photoelectric effect. Smoke particles block the ions, stopping or reducing the flow of current, which sets off the alarm. So, that lowered current is what your sensor interprets as, hey, there’s smoke here. If smoke is coming into the area where this breaking apart is happening, it will block the charged particles from moving, reducing the current. Alpha particles from the radiation source strike air molecules, which causes them to eject ions, creating a current. This movement of charged particles is what we call electrical current. And those two oppositely charged ones will be attracted to the negative and positive battery terminals in the smoke detector’s battery. When that happens, some broken pieces will be positively charged, and others will be negatively charged. These little bullets come out of the source and hit air molecules to break them apart. It emits alpha particles, which you can think of as little bullets. Inside your smoke detector, there’s a small Americium-241 radiation source that’s a byproduct of nuclear fuel. The Camille and Henry Dreyfus Foundation, CC BY-NC-ND ![]()
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