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  • OT- Smoke Detector

    Why does a smoke detector go off with no apparent cause (at least to me)? I have one connected in the hall way just passed the kitchen door. It is at lease 12+ years old. It was there when I moved in. It is round and has one small black button on it that does not do anything and is connected to the indoor circut because I have never put a battery in it.
    It goes off two or 3 times a year and always in the middle of the night without any cause that I can notice. And, evey time this happens it goes off 3 or 4 times in a span of an hour. I have to take the cover off and fan it with a magazine or something or just slap it around with the same magazine (today at 3:00 am and me in my death bed with food poisoning)to shut it up. The little black button looking thing can not be pushed in either as I learned many years ago. Thanks for any ideas. DavidH.
    DH

  • #2
    if its 12 years old, and its going off when its not supposed to, i would seriously consider replacing it.

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    • #3
      Two reasons I can think of; low battery and worn out. In my experience smoke detectors in hallways near bathrooms have been notorious for needing replacement every few years (3 to 5 years, IIRC). It must be the humidity.

      Is this one near a bathroom?

      I think dust messes them up and humid dust *may* want to stick to the part that detects. I dunno. Just a guess.

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      • #4
        Humidity definitely does mess them up. It gets pretty humid here, and we don't use A/C, just a big door-slamming window fan.

        They don't last for us, in a few months they start 'ticking", and pretty soon they will go off. As you note, normally they will "false alarm" at 2AM.

        I don't recall seeing any that were conformal coated, maybe they oughtta try that.
        1601

        Keep eye on ball.
        Hashim Khan

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        • #5
          Originally posted by heidad01
          Why does a smoke detector go off with no apparent cause (at least to me)? I have one connected in the hall way just passed the kitchen door. It is at lease 12+ years old. It was there when I moved in. It is round and has one small black button on it that does not do anything and is connected to the indoor circut because I have never put a battery in it.
          It goes off two or 3 times a year and always in the middle of the night without any cause that I can notice. And, evey time this happens it goes off 3 or 4 times in a span of an hour. I have to take the cover off and fan it with a magazine or something or just slap it around with the same magazine (today at 3:00 am and me in my death bed with food poisoning)to shut it up. The little black button looking thing can not be pushed in either as I learned many years ago. Thanks for any ideas. DavidH.

          Dirt and dust will set them off. I have three of them and they are wired into the house circuit. They make a terrible noise when the power goes out and also when it comes back on. I dislike the ones with batteries. Mine are always working. They have test buttons on the side that will cause them to actuate for testing purposes.

          I had a spider make a little web in one once and that set it off. I simply wiped it out and no further problem. Clean them out and you should be OK.

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          • #6
            Replace it. It's past the end of it's life. They are not expensive.

            Charged particles in the atmosphere can set them off. Try standing under one and pulling a wool sweater off over your head. That will set it off. I'm also convinced that they are prone to go off the first time you run your furnace/heat pump in the fall (if you're using forced air heat).

            They should be vacuumed periodically. The black button is a test button. Pressing it should activate the audible alarm. If not, it needs to be replaced.

            I've been called out many many times at night to investigate a smoke detector activation with no evidence of smoke or fire. It happens a lot. Even at my house occasionally.

            I'm a professional firefighter, 35 years, chief officer.

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            • #7
              The garden variety smoke detector isn't a smoke detector. It's an ionized particle detector. Ionized particles are produced by hot fires with flames and by the deterioration of fats when overheated by frying. Inside the detector is a small metal chamber. In that chamber is a tiny amount of radioactive Americium. The radiation from the Americium ionizes the air in the chamber and that makes the air conductive. This causes a small current to flow between two metal parts of the chamber. With clean surrounding air this current is the base value for a "no fire" condition.

              The production of ionized particles in the air by a fire is detected by the increase in current that those particles create since they also help the air conduct as they are ionized and conductive. That sets off the alarm when it goes over a preset threshold.

              Over time the alarm accumulates small quantities of airborne dust particles that adhere to the plates that conduct the small current in the chamber. By itself this doesn't make much different to the detector operation.

              However, if the detector is near the kitchen over time it will collect microscopic particles of ionized fat that will stick to the dust particles in the detector. These fat particles have a particular electrical property that isn't well known. When they cool and solidify they form what is called an "electret". An electret is an electrostatic analog to a permanent magnet and when such a substance "freezes" it also freezes in the static charge it was carrying when it was ionized. Beeswax is such a substance and will hold such an electrostatic charge that you can build an electrostatic motor using beeswax pole pieces that are charged while molten.

              The accumulation of the charged fat particles on the dust in the detection chamber unbalances the detector in favour of sounding a false alarm. This is intentional since a false alarm is preferable to no alarm. If you open the detector and give it a short blast of compressed air toward the chamber it will very likely cure the problem. However, new ones are cheap.
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              • #8
                Do diesel smoke detectors ..the type used in truck emission tests ..have anything radioactive in them ..worth worrying about ...cause I've been driving my car now for a month with one in the passenger footwell..something i picked up from a car boot sale for almost nothing ..

                Do you think i should take the thing out . ..as its about 20 times the size of your average house detector.

                all the best.markj

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                • #9
                  The radiation emitted is strictly alpha particles that are so weak they cannot penetrate a piece of paper. In a smoke detector that tiny lump of radioactive material is sealed in a miniscule gold foil wrapper that permits the alpha particles to escape but prevents the Americium from being chemically reacted by anything.
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                  • #10
                    Americium is also a gamma emitter. It emits far more radiation overall than radium or the older, out-of-fashion industrial radiation source, polonium. Industrial samples of americium in the gram or kilogram range can emit enough ionizing radiation to ionize gasses in air, giving that characteristic blue glow. However, smoke detectors use a fraction of a microgram of an americium oxide as their radiation source. I wouldn't worry about radiation from smoke detectors unless I swallowed the source, and maybe not even then.

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                    • #11
                      The amount of radiation emitted by a smoke detector is so slight that it is essentially unmeasurable. To quantify it the regulatory bodies use a computer simulation that showed a delivery worker who handled 5 million detectors per year would receive a dose of 7 micro-rem (.000007 rem). To give an idea how little that is it takes on average 500 rem to kill a person half the time. You will receive a much larger dose if you fly on a jet aircraft, live in a brick house or have ever had an x-ray.
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                      • #12
                        ok thanks guys ..gamma or alpha ...

                        who is right .. ?

                        Evan are you going to admit youre wrong ...

                        anyway ......its been unloaded today ...

                        all the best.markj

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                        • #13
                          Evan
                          Can you explain that. When my house burn dowm two years ago, theres 4 or 5 of them in the house. ioniser heat sensor and co2. good batt and not old. Not one emit a sound. The firemans explain me they came sarurate. Why?

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                          • #14
                            Americium 241 emits a small amount of gamma radiation in conjunction with the alpha decay. Not all gamma rays are the same. The alpha particles have an energy 5.485 million electron volts. The gamma photons are extremely weak at only a maximum of 59 thousand volts and may be ignored which is why Americium 241 is used in smoke detectors. Contrast that with a strong gamma source such as cobalt 60 which emits copious amounts of gamma at an energy of over a million volts and is used to sterilize food.

                            Can you explain that. When my house burn dowm two years ago, theres 4 or 5 of them in the house. ioniser heat sensor and co2. good batt and not old. Not one emit a sound. The firemans explain me they came sarurate. Why?
                            I am not sure what he meant by that. Smoke detectors are designed to fail safe. That means they are designed to give a false alarm rather than no alarm.
                            Last edited by Evan; 11-03-2009, 09:45 AM.
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                            • #15
                              Thanks all for the wealth of information. DavidH
                              DH

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