Smoke / CO2 Detector Discussion

I've actually brought this discussion up with my brother who is a fulltime firefighter.
I put the question to him which smoke detector is better (the ionization or photocell type). He recommended the ionization type since the photocell type are prone to false alarms due to humidity, dust or insects. This explains why they are the cheapest.
I understand that one smoke detector per floor should be sufficient, preferably outside of the bedrooms in a central area.
A CO2 detector should be installed on the floor where the central heating system is located but not too close to it.
Here's an odd fact; I thought it would be best to install detectors that are powered from 120VAC however most common fires occur when the power is out (i.e.: from candles). If you do choose detectors that are powered from 120VAC be sure to choose one with a battery backup. Kind of defeats the purpose of the 120VAC feature doesn't?
I'm curious though, what is the expected life of a smoke or CO2 detector?, perhaps seven years?
I'm interested to hear your thoughts.
later guys...
Handi
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subject to your climate and the air conditions of your dwelling rooms and ordinance requirements, there are also heat detectors. humidity and laundry room dust bother our smoke detectors. most smoke detectors are disconnected due to falsing from stove top frying, so we teach everyone to microwave bacon with a paper towel or two above and below the slices around one minute per slice. if the laundry room falses we blow the smoke detector clear with a leaf blower. during construction cover the detector heads with a plastic bag to keep out dust while you maintain protection because the fire will burn thru it. for safety we install smoke detectors and separate CO detectors in all sleeping rooms as well as the usual places specified in installation instruction booklets. cost of these life saving alarms is wonderfully low. some alarms now talk as well: http://www.google.com/search?hl=en&lr=&rls=GGLG%2CGGLG%3A2005-48%2CGGLG%3Aen&q=%22talking+smoke+detector%22
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buffalobill wrote:

http://www.google.com/search?hl=en&lr=&rls=GGLG%2CGGLG%3A2005-48%2CGGLG%3Aen&q=%22talking+smoke+detector%22
The talking alarms are very useful for small children. Research has shown that children between the ages of 1 & 4 years may sleep through the alarm from a standard single station smoke detector. The recorded voice models are affective in waking children who respond well to the primary care providers voice at a lower volume then they do to an alarm horn at a higher volume.
--
Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous
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"INSTRUCTIONS ON SMOKE DETECTOR REQUIREMENTS Smoke detector requirements are found in the CABO Residential Building Code Book. These smoke detector requirements were adopted by the State of Indiana as the rules to govern by the Authority Having Jurisdiction. The smoke detectors are required to be installed in a permanent manner. The smoke detectors are required to be 120 volt powered, and with battery back up. These smoke detectors are required to be installed within each bedroom, in the vicinity of each bedroom area , and at least one on each floor including a basement. These smoke detectors must be 120 volt powered with a red or yellow conductor that ties all smoke detectors together on a third wire so that if one smoke detector sounds off then they all must sound off. When it comes to the smoke detector rule, the term existing does not apply. This smoke detector rule applies to all dwellings." as quoted from a very helpful site at: http://www.selfhelpandmore.com/homewiringusa/2002/maindwelling/newdwel/newdwelshow.htm#15
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buffalobill wrote:

http://www.selfhelpandmore.com/homewiringusa/2002/maindwelling/newdwel/newdwelshow.htm#15
Sounds like the smoke detector industry wrote the code!
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Handi wrote:

I seriously doubt a firefighter would get them mixed up that way. It's photocell detectors that are more expensive, at least in the U.S., since they're much less common. But they are not more prone to false triggering, and if anything they're less so because they're sensitive only to dust and smoke particles, unless the house is in a fog bank, while ionization detectors are affected by all sorts of combustion products, including very fine invisible ones, and even by static electricity generated by air currents (one reason they sound when their detection chambers are vacuumed). Ionization detectors are commonly $5-10 and sometimes as little as $2. If you absolutely must have only one type of detector, get the ioniaztion type since it can detect both smoldering and flaming fires, while photocell detectors are good only for smokey fires and may never sound if a fire gives off flames but little smoke. However you really should have both types of detectors since ionization detectors can take twice as long to react to smoldering fires. There are combination ionization/photocell models, about $20-30, but you may find that 2 individual units are cheaper.

The problem with that reasoning is that occupants may not hear the alarms behind their bedroom doors, especially if the sound is high-pitched, which it almost always is now, and fires do start inside bedrooms. Even the most-sensitive detectors aren't triggered until the smoke is fairly heavy and easily smelled, and ionization detectors are so cheap there's no reason to avoid installing them in almost every room. Follow the installation instructions exactly since some locations, such as the peaks of cathedral ceilings, are inherently bad for detectors since there's no air flow there.

CO2 detectors are used in commercial buildings, to measure the amount of outside ventilation, but for a home it makes much, much more sense to have a CO detector because thousands times as many people die from excessive CO than from CO2.

The 120VAC backs up the battery, just as the battery backs up the 120VAC. It's probably better for average people to install battery-only detectors since bad 120VAC wiring can itself cause fire, and there have been cases where homes have burned down due to faulty smoke detector wiring.

Please quit writing "CO2." It's CO, a much, much more toxic gas that should be your concern.
Manufacturers and fire departments recommend smoke detectors be replaced every 10 years, and that's reasonable, considering that detector elements become coated with dust and oils and electrolytic capacitors break down. Some detectors come with permanent lithium batteries and instructions to replace the detector every 10 years. For detectors with replacable batteries, be sure to change the batteries every 2 years if they're alkaline, every 5-7 years if lithium. Some detectors now include conventional carbon-zinc or carbon-chloride batteries, and they should be replaced after just 1 year with an alkaline. If your detector comes with a replacable lithium battery, don't switch it to alkaline because the circuitry that warns of low battery level is calibrated differently for each type.

You should be more interested in the facts.
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Handi wrote:

I would like to point out that the two different detectors are sensitive to different kinds of fire indicators. Your best protection is s combination of both. Ionization type is sensitive to a smoldering fire not making smoke while the photocell is more sensitive to a flaming fiire.

That should be CO detector for home use and should in the bedroom areas. I have one on each floor. .

--
Joseph Meehan

Dia duit
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Joseph Meehan wrote:

Joseph You reversed the two types of detector in your reply. It is the Photoelectric type that responds best to the larger particles given off by smoldering fires. An ionization detector will respond somewhat more quickly to free flaming fires.
--
Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous
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Handi wrote:

IIRC the applicable US national standard calls for replacement or sensitivity testing every ten years. Since the equipment and skills necessary to perform the testing are expensive it is generally less expensive to replace the detector.
--
Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous
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Thanks for your input and the facts surounding smoke detectors. Boy, did I get my facts wrong, thanks for the corrections.
After reading the responses I chose to buy a Garrison smoke & carbon monoxide alarm and placed it outside the basement bedrooms. This model operates off of 120 or batteries and cost about sixty dollars Cdn.
The instructions on the package were very informative and actually answered every concern I had including the choice between ionization and photoelectric. The instructions recommend using both types since they detect fire at different stages.
Handi
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