6 ms·
Now, if you're annoyed by the false positive rate on your actual smoke alarms, go replace the one nearest your kitchen with a photoelectric type, not the standa
by Syonyk 4y ago
Now, if you're annoyed by the false positive rate on your actual smoke alarms, go replace the one nearest your kitchen with a photoelectric type, not the standard ionization type that's cheaper, the default style installed, and ought to be illegal in homes (IMO).
There's been quite a bit of research done, generally easy to find if you look, that talks about the difference and tests them, but the short summary:
- Ionization type sensors detect the products of fast flaming combustion and "things cooking in the kitchen." Your oven, if a bit dirty, will reliably trip an ionization type. They are quick on the draw for this. The downside is that they're very, very poor at detecting the sort of slow, smoking, smoldering combustion that is associated with house fires that kill people in the middle of the night.
- The photoelectric type is very good at detecting smoke in the air - but it isn't nearly as prone to false triggers on ovens, a burner burning some spills off, etc.
They've been A/B tested in a wide variety of conditions, and in some cases, the ionization type is a bit quicker. In other cases, the ionization type is slower, by time ranges north of half an hour - I've seen some test reports where there was a 45 minute gap, while the photoelectric type was going off, before the ionization type fired!
In general, "rapid fires during the day" are somewhat destructive to property, but rarely kill people. If your kitchen catches on fire while you're cooking, it may burn the house down, but generally people are able to get out.
The fires that kill people are "slow starting fires during the night" - the sort that smolder for potentially hours, often slowly filling the house with toxic smoke, before actually bursting into open flames. On this sort of fire, the photoelectric type will fire long, long before the ionization type - in some cases, they get around to alarming quite literally "after the occupants are dead from the smoke."
Using smoke alarms as a way to talk about monitoring systems is nice, but in terms of actual smoke detectors, get at least a few photoelectric sorts in the main areas of your home.
Do not get the "combined sensor" sort, since these tend to be and-gated and the worst of both worlds.
Edited to add some resources:
A presentation on the matter from a while back by one of the experts in this field: https://wahigroup.com/Resources/Documents/Ion%20vs%20Photo%20Smoke%20Alarms%20WAHI%20Conference%20Slides%20031415.pdf https://wahigroup.com/Resources/Documents/Ion%20vs%20Photo%2...
Another paper: https://www.semanticscholar.org/paper/Detection-of-Smoke-%3A-Full-Scale-Tests-with-Flaming-Einar/b1227142af0ff8d38df5e2ed69371866442c6859 https://www.semanticscholar.org/paper/Detection-of-Smoke-%3A...
> Full-scale fire tests are carried out to study the effectiveness of the various types of smoke detectors to provide an early warning of a fire. Both optical smoke detectors and ionization smoke detectors have been used. Alarm times are related to human tenability limits for toxic effects, visibility loss and heat stress. During smouldering fires it is only the optical detectors that provide satisfactory safety. With flaming fires the ionization detectors react before the optical ones. If a fire were started by a glowing cigarette, optical detectors are generally recommended. If not, the response time with these two types of detectors are so close that it is only in extreme cases that this difference between optical and ionization detectors would be critical in saving lives.
- bluGill 4y agoThe law requires you have both types of good reason. Either alone will detect less than half of all house fires. Dual sensors are not and gated. While nobody will admit what algorithm they use, they detect most fires unlike the single sensor type.
- Syonyk 4y agoWhere does the law require both types? I'm not aware of any housing codes specifically requiring photoelectric types, and any house I've looked at, including mine, came with purely ionization types. Though it's been a few years, and it may have changed recently - this is less of a niche concern lately. As for dual sensors and gating... do you actually trust your life to "nobody will admit what algorithm they use"? My house has all the smoke detectors wired together (they're on an AC circuit, with battery backup, with a signal line running between them all), so I have some photoelectric and some ionization, depending on where in the house they are.
- riceart 4y agoLol “the law” .. what law? Maybe in some dumb ass jurisdiction - but you’re a bit full of yourself if you think where you happen to live is “the law”.
- bluGill 4y agoUs fire code, though inspectors often don't check.
- Syonyk 4y agoAs far as I can tell, it's state by state, so... you want to cite some sources?
- riceart 4y agoOh that I happen to know something about - you’re making stuff up. I’ve got NFPA 72 right here if you want to point out where this alleged requirement for “multi-sensor” detector exists. In fact there are specific requirements to use only single sensor type alarms - such as near cooking equipment. You can go the the NFPA website though where the publicly facing website notes they are “recommended”. They are not and have never been required.