Better/Best CO2 Smoke Detectors


Old 06-18-11, 06:22 AM
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Better/Best CO2 Smoke Detectors

Just came across this video.
How much *truth* is in this when looking at a low level CO2 sensor vs. a regular unit.
I have at least 1 BRK Hardwired Sensor in each area where we have gas sources.....and this video makes them look pretty useless ......

YouTube - ‪Carbon Monoxide detector test‬‏
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Old 06-18-11, 07:18 AM
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Based on a bit of quick research, typical CO alarms sound at between 100 and 400ppm, based on how much time the level is measured. Quoted from Wikipedia:

The alarm points on carbon monoxide detectors are not a simple alarm level (as in smoke detectors) but are a concentration-time function. At lower concentrations (eg 100 parts per million) the detector will not sound an alarm for many tens of minutes. At 400 parts per million (PPM), the alarm will sound within a few minutes. This concentration-time function is intended to mimic the uptake of carbon monoxide in the body while also preventing false alarms due to relatively common sources of carbon monoxide such as cigarette smoke.
A major cause of smoke alarms not working in houses is due to false alarms where people take out the batteries "just for a few minutes". I wouldn't want a nuisance beeping of a CO detector doing the same thing.

That said, I'm sure there is benefit in a low-level CO2 detector, as long as you and whoever lives in the house understands the difference between low-level (call the HVAC technician) and high-level (get out of the house and call 911).
Old 06-18-11, 07:22 AM
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Just to nit pick it is CO carbon monoxide not carbon dioxide CO2.

I can't comment with authority but what was lacking to me was how much carbon monoxide is dangerous. You could end up detecting harmless amounts. Like the boy who cried wolf to many false alarms might be worse because they would after a while be ignored.
Old 06-18-11, 08:13 AM
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I'm not the best in this area, but I can try. A common source of CO would be an unvented gas appliance that is not burning properly or even when burning properly it can emit a low level. Other sources can be vented combustion appliances that are being back-drafted by other exhaust appliances. If you have a detector that is picking up a low level of CO, there is a reason/source and you need to identify it and determine if corrective measures are needed.

One of the reasons CO is becoming more of an issue is our new energy efficient building methods which necessarily reduce the typically abundant air leakage we have lived with. However, even a tight home by modern standards will still exchange all of its internal air every 2 to 4 hours. That means the source of CO that registers a low level may actually be a significant source, as once dispersed within the home and then diluted with fresh incoming air it is still able to be detected.

IMO, I would not have a problem with a low level detection device that beeped to remind me there might be a larger problem elsewhere I need to identify. Whatever that source is, it needs to be eliminated or absolutely minimized to within long term acceptable levels and zero is a good level.

Old 06-18-11, 01:22 PM
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In a former life I was a Facilities engineer for a large manufacturing company that shall remain nameless. We had a large compressed air plant and we also used the plant air for breathing purposes. As such it was necessary to monitor the CO in the compressed air because CO can be created by overheated lubricating oil in the compressors themselves.

Our first attempt for monitoring the air was a device that was similar to the "gas monitors" that were once installed in gasoline-powered boats in that it had a platinum temperature detector along with a heater enclosed in a screened module. Since CO is flammable any CO that entered the module would be ignited by the heater and would raise the temperature of the platinum temperature detector and this rise in temperature would activate the alarm. The trouble with this device is that it isn't all that sensitive and it can't be calibrated all that closely.

The next attempt used a wet electrochemical cell that created a measurable (voltage or current, I don't remember which) output when CO was passed through the solution. The original detectors had a range of 0-100 ppm (parts per million) and we wanted an alarm at 10 ppm with automatic compressor shutdown at 20 ppm. This was pretty close monitoring, what we in the instrumentation field call "working in the mud" and maintaining the calibration on these units was pretty difficult. Without going through all the re-engineering I did I'll just say that even with a change to cells that measured 0-50 ppm we had serious problems. These units were so sensitive that I could tell what the traffic was like on the Interstate highway near the plant just by reading the meter on the monitor. The down side was that the monitors would "drift" off of calibration in just a few days and so required re-calibration at a minimum of once a week and sometimes more often.

I finally ended up using a different electrochemical cell that required no routine maintenance and would hold calibration for a month. These were very good units but the cost was close to $1,000 per unit once all the alarms and indicators were included. Since a calibration of the previous units would take the better share of an hour the savings in manpower alone justified the new units and the better monitoring was an added benefit.

For my own home I have a Honeywell model C8600A 1000 alarm. This unit gets good reviews but it is NOT a "low level" alarm. I wouldn't trust any low level alarm UNLESS it was calibrated on a regular basis and that is both onerous and expensive for a homeowner. The "standard" residential CO alarms may not be very sensitive (they're not) but they ARE better than nothing.
Old 06-18-11, 07:56 PM
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This video is nothing more than ad hype. There is no reason for a household CO detector to alarm instantly at 35ppm, because for most people that would not cause any symptoms because they're not in the house 24/7. Even just pulling your car into the garage on a cold day can cause levels as high as 50-75ppm for a short time, which would set their detector off. They make a big deal about how the 'other' units would take 30 days to alarm, but in reality most people wouldn't show any symptoms in those 30 days.

Since CO is colorless, odorless, and tasteless, there is really no way of knowing whether an alarm is false or not without the air being tested. For that reason, the alarms are designed to forgo early warning of low levels (under 100ppm) for 'verified' warning of higher levels. If a CO detector goes off, you KNOW there is a problem. If they alarmed for lower levels, they would become a nuisance, and would be more likely to have their batteries pulled rendering them useless. The danger of this is exasperated by the fact that CO has no outwardly visible signs. You basically just die in your sleep. At least with fire it can be smelled, seen, tasted, and felt. That at least gives you a chance, as slim as it may be, with no smoke alarms.

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