Cigarette smoke and smoke detectors

Factual Questions
1

I’m a smoker, and very occasionally stay in a hotel. I always ask for a smoking room, and even get one from time to time.

There’s always a smoke detector in the room, but for some reason cigarette smoke doesn’t set it off. Why is this?

Similarly, I used to work in a student bar in Glasgow. On some nights, the cigarette smoke was so heavy you could barely see across the room, but the fire alarm was never triggered. Yet all it took to cause a building evacuation was some idiot tearing up a beer mat, putting the bits in an ashtray, and lighting it.

I’m confused. In what way does cigarette smoke differ from “normal” smoke?

2

I gotta say, I wonder about this as well. The smoke detectors in our apartment don’t go off when someone is smoking.

However, if you want your toast a little darker than normal? Instant trigger of the alarm.

3

The sensitivity of ionization-type smoke detectors is in inverse proportion to the size of the smoke particles. Smoldering fires, including cigarettes, tend to produce mostly larger particles, while energetic fires and cooking fumes produce mainly smaller ones which is why detectors largely ignore cigarette smoke, but alarm when your bacon is overcooked. Photoelectric detectors, OTOH, tend to be more sensitive to larger particles and are used wherever smoldering fires may be likely, in kitchens to reduce false triggering and also in aircraft bathrooms to detect cigarette smoke. You can see a set of graphs showing the particle size/sensitivity relationship for various types of smoke detector here, about halfway down the page.

4

I’ve got a detector right over the double-wide entrance to my office, and if my husband stands right under it with a cigarette, it’ll trip the alarm. I’m about 6 feet away from it and smoke all day long and never trip it.

My cooking, on the other hand… :frowning:

5

I am a fire alarm technician with a small fire alarm company in the midwest.
The two more common types of smoke detectors used for private dwellings are Photoelectric and Ionization.

Photoelectric detectors are designed to detect the visible particles of smoke generally produced by smoldering fires. Cigarette smoke while being definitely visible, is not really very dense, having left most of the larger particles in the smoker’s lungs. Ionization detectors are designed to detect the smaller, generally non-visible products of combustion. Friend hekk’s smoke detector that does not detect tobacco smoke but detects the darkness of toast is an Ionization detector.

I would advise against relying on an ionization detector as one’s only defense against fire in the home. You are much better off with a combination style detector with both ionization and photoelectric capabilities.

For a very good demonstration on the different capabilities of each kind of detector, I would encourage you to watch the short film at the Aquarium Test

6

Thanks folks. I’ll check out the links.

Now it begins to make sense. Presumably the aeroplane smoke detectors detect both types of smoke, somehow.