A Safety Check

[HaroldB]

A recent nearby home fire tragedy prompted me to test our smoke detectors, not the batteries, but the actual functionality of the detectors, since they were more than ten years old. Just as I expected, when I held a smoldering, smoking paper tissue near each one, only one out of three immediately alarmed. I now have three new ones on order and in route to us.

The National Fire Protection Association (NFPA) recommends, in addition to checking the batteries monthly and replacing twice a year, "All smoke alarms should be replaced after 10 years of operation. Ten years is a smoke alarm's useful lifetime and for continued, reliable safety and protection, smoke alarms need to be replaced."

Some other suggestions are:

"Because smoke rises, smoke alarms should be installed on the ceiling or on walls at least 4 to 6 inches below the ceiling.

"Smoke alarms should not be located less than 4 to 6 inches from where the wall and ceiling meet on either surface; this space is dead air that receives little circulation.

"Smoke alarms should not be mounted in front of an air supply, return duct, near ceiling fans, peaks of A-frame ceilings, dusty areas, locations outside the 40 degree Fahrenheit to 100 degree Fahrenheit temperature range, in humid areas or near fluorescent lighting."

So, don't let the new year start without making sure you are protected.

Harold

[TomP]

I just replaced 3 of mine a couple months ago for the same reason. They were also over 10 years old.

[Paul from NWOnt]

For what they cost, if I have to make a special trip to buy batteries, then I just get a new detector. If I have batteries on hand, then I just replace the batteries.

[Kevin A]

Illinois recently passed a law requiring carbon monoxide detectors within 15' of any sleeping areas. The smoke detectors in our home were vintage, so I replaced them with combination smoke/CO2 detectors in both upstairs bedrooms. I'll be adding them to the main living area, too, this weekend. What's nice about these Kidde detectors is that they communicate with each other... if one goes off, they all go off. And they talk the directions, too, so there is more than just an alarm sounding. For about $30 each, I want to be sure we have at least 4 in the house. They also say they must be replaced in 7 years and it appears there may be some sort of disabling function at that time. They start the clock ticking when you add batteries the first time.

In our 16' UHaul, I currently have just a smoke detector, but will look at adding a propane-leaker detector next spring when I take it out of storage.

[MillerK]

The only problem with combination CO/Smoke detectors is that CO sinks and smoke rises. If you place your detector as recommended for proper smoke detection by the time the CO gets to the detector you will, more than likely, already be in big trouble. The reverse is true if you place the detector low for proper smoke detection.

[Pete Dumbleton]

The only problem with combination CO/Smoke detectors is that CO sinks and smoke rises. If you place your detector as recommended for proper smoke detection by the time the CO gets to the detector you will, more than likely, already be in big trouble. The reverse is true if you place the detector low for proper smoke detection.

I strongly disagree with the above. CO is roughly the same density as atmospheric air, so it either stays where it is or rises if warm. Although cold CO2 is denser than air, combustion products are generally warm, so detectors should be placed high, and a combination CO/CO2 detector makes sense to me (and to the people who designed and approved them).

If one were trying to detect CO2 leakage from a bank of fire extinguishers, one would place the detector low, but no so for fire...

OTOH, LP or propane gas has higher density than air and sinks, so LP detectors should be placed low.

One of the Yahoo Scampers recently posted this:

QUOTE
Here is more chemistry than anyone will want to see on a Sunday
morning:

Air (roughly 78% nitrogen, 21% oxygen, and 1% other stuff) has a
molecular mass of ~29 g/mol. Gasses with a higher molecular mass
than air tend to sink and pool at lower levels, gasses with a lower
molecular mass tend to rise (think helium balloon).

Natural gas is ~95% methane (CH4) and has a molecular mass is ~19.5
g/mol; it rises.
Propane (C3H8) has a molecular mass of 44 g/mol; it tends to sink.
Carbon Dioxide (CO2) also has a molecular mass of 44 g/mol and tends
to sink.
Carbon Monoxide (CO) has a molecular mass of 28 g/mol; which is
pretty close to air so it tends not to rise or sink.

The above holds true in quiescent (still) air of a uniform
temperature; if the air is stirred up the concentrations of the
gasses tend to be more uniform. Combustion products such as CO and
CO2 would be warmer than the surrounding air and tend to rise
initially.

Carbon monoxide is produced by incomplete combustion of carbon-based
fuels. Carbon dioxide is produced by normal (complete) combustion of
carbon-based fuels, opening a pop or beer bottle, and when we exhale.

As far as toxicity of carbon monoxide vs. carbon dioxide, the Short
Term Exposure Limit (STEL) for carbon monoxide is 400 parts per
million (ppm), which is a level that can be reached pretty quickly in
a small camper with a defective heater. The STEL for carbon dioxide
is much higher (30,000 ppm), and is probably less of a concern
(unless you are designing a space station or a rebreather for scuba
diving). Normal outdoor concentrations of carbon dioxide are around
300 to 400 ppm.

I think I need a hobby.

Pat
END QUOTE

[MillerK]

That's more research than I have put into it. The Fire Marshall's I have spoken to have told me seperate detectors, high and low mount. I may have been totally wrong as to why.

Just spent the last ten minutes looking around the net. I hate to give bad advice. First alert say's to mount their detector on the ceiling. The City of Stafford fire department say to mount it between knee and chest height. Darned if I know. Both say type of detection element is most important thing to check. I'll look more later, I'm tired.

[Victor Benz]

As an engineer myself, I agree with Pete and follow his reasoning.

However, another factor is to read the installation instructions that come with each unit carefully! Especially with CO detectors and combination CO/smoke detectors. I have seen both high and low mounts recommended by the vendors, and when I investigated, it had to do with the specific detection systems in use. I would always default to the installation instructions on brand-name units.

In cidentally, I have separate smoke and CO detectors. The house CO detector is designed to plug in to a floor level 100v plug. However, the unit in my trailer is designed to be mounted near the ceiling!

Vic

[MillerK]

This is my second attempt at a reply, as on the first attempt I pressed some arcane key combination that sent my computer into a small tizzy. So what was a well thought out reply is now a frustrated quick note. Apologies.

I was wrong, wrong, wrong.. Google carbon monoxide detector placement and then read through the first three or four pages.

Majority say place detector high, if not on ceiling. Seperate detectors are prefered, but for the reason that combination detectors give up detection quality, for both CO and Smoke, due to space limitation, reasonable size, in detector. Majority prefer hard wired, with battery back-up of course, for quality of detector and readout. There were a couple that said place CO detector between knee and shoulder height, fire dept web site and fire marshalls I have spoken too. As to why they would say that when it is different than what manufacturers say, I don't know for sure but I can guess. (Which is what led me into spending a bit of time on this subject in the first place. Incorrect guessing.)

[Pete Dumbleton]

My personal opinion on matters like this is that it really doesn't matter WHO is right, what matters is that in the end we know WHAT is right. This is an informational forum, not a contest...

[HaroldB]

My personal opinion on matters like this is that it really doesn't matter WHO is right, what matters is that in the end we know WHAT is right. This is an informational forum, not a contest...

Safety was the intention of the original post. It matters not which of the many opinions is "right." What matters is whether your "right" detector in the "right" location is functioning.

No apology from here, if this discussion made at least one reader do a detector check, correct a potential problem and have a safe and happy new year.

Harold