CO Monitors, PLEASE READ!

[firefighterjake]

Personal and professional experiences . . .

CO detectors save lives . . . regardless of which make or model you get.

Most -- if not all -- of the CO incidents I've seen here are in places that simply had no CO detectors . . . and a good many of those could have been prevented with some commonsense (i.e. not having a generator running inside a home).

Personally, I think one of the most important features in a CO detector is having a battery back-up . . . since a good many of the CO calls I've seen occur in times of power outages when the generators are fired up and ye olde space heaters are dusted off and fired up for the first time in many eons.

 

[colebrookman]

Personal and professional experiences . . .

CO detectors save lives . . . regardless of which make or model you get.

Most -- if not all -- of the CO incidents I've seen here are in places that simply had no CO detectors . . . and a good many of those could have been prevented with some commonsense (i.e. not having a generator running inside a home).

Personally, I think one of the most important features in a CO detector is having a battery back-up . . . since a good many of the CO calls I've seen occur in times of power outages when the generators are fired up and ye olde space heaters are dusted off and fired up for the first time in many eons.

Great point, the next town over lost an older resident when the home lost power and he ran a generator in the garage. The garage door was open so the CO just migrated into the home. Be safe.
Ed

 

[Vic99]

When I the fire dept for a recommendation, they told me to buy any CO detector with a digital readout.

Got a Kiddie Night Hawk at the box store for about $40. Plug in with a battery back up. Will display number and alarm at 30 ppm, otherwise reads "0". Built-in timer from when you plug it in to automatically fail after 7 years so that you replace it. All those features were pretty standard in the models that I compared.

 

[RnG17]

Remember too, Co is lighter than air, I know the NSI's recommend installation at eye level. Thats the only thing I never cared about with the Nighthawks.

 

[henkmeuzelaar]

Remember too, Co is lighter than air, I know the NSI's recommend installation at eye level. Thats the only thing I never cared about with the Nighthawks.

CO is only marginally lighter than air. 6 gallons of CO (at standard pressure and temperature) weigh ~ 27.6 grams, whereas the equivalent volume of air (with 80% N2 and 20% O2) weighs ~ 28.4 grams. If oxygen levels are reduced (such as in combustion exhaust gases) the difference will become even smaller. The relative weight of nitrogen gas alone is only 0.07 % lower than that of carbon monoxide.

Moreover, in air containing significant quantities of H2O (water) and CO2 (carbon dioxide), both very "sticky" molecules that tend to form small clusters, particularly at low temperatures, the whole calculation becomes way more complex.

In short, among the various good reasons to mount CO detectors in certain places rather than others, the slightly buoyant nature of CO should be near the bottom of the list in importance, IMHO.

Henk

 

[RnG17]

Henk you lost me at 6 gallons, haha. But I read it twice, and great info! I like the science stuff that goes with it, cool stuff man!

 

[greythorn3]

http://www.reuters.com/article/2011/03/10/us-fire-children-idUSTRE72901320110310

horriblle story today

 

[lumbajac]

I have a new home with hardwired smoke detectors per code. CO detection is not yet code here so I went the cheap route 2 years ago when finishing up the home as money was tight at the end of the project and have, I think, 9 smoke detectors in my system at $11 each.

I want to start upgrading to hardwired CO/smoke combination detectors. Can I replace a couple at a time as money becomes available and still have the system function properly as one cohesive unit? I believe so as any unit that is set off will just set off the whole system, regardless of what kind or brand of detector is in the circuit - right?

Any thoughts would be appreciated. Thanks.

 

[andrewdee]

When I the fire dept for a recommendation, they told me to buy any CO detector with a digital readout.

Got a Kiddie Night Hawk at the box store for about $40. Plug in with a battery back up. Will display number and alarm at 30 ppm, otherwise reads "0". Built-in timer from when you plug it in to automatically fail after 7 years so that you replace it. All those features were pretty standard in the models that I compared.

Hey vic99 I got a couple of the same ones.Reads 0 for readings under 30 ppm is there any way to get it over 30 ppm to get a test reading to make sure it is working?

 

[henkmeuzelaar]

Henk you lost me at 6 gallons, haha. But I read it twice, and great info! I like the science stuff that goes with it, cool stuff man!

Thanks for the kind words.
"
I imagine you're not the only one who may have thought "6 gallons to be an odd measure. The reason I used it is that the common volumetric standard for quickly calculating the weight of a gas is 22.4 liters. Since I did not want to be responsible for even more brain cramps by throwing in liters and 22.4 liters happens to be 5.9 gallons, I went to 6 gallons (and adjusted the weights accordingly).

Just think of it as ~1 jerry-can full of carbon monoxide.

Henk

 

[Battenkiller]

CO is only marginally lighter than air. 6 gallons of CO (at standard pressure and temperature) weigh ~ 27.6 grams, whereas the equivalent volume of air (with 80% N2 and 20% O2) weighs ~ 28.4 grams. If oxygen levels are reduced (such as in combustion exhaust gases) the difference will become even smaller. The relative weight of nitrogen gas alone is only 0.07 % lower than that of carbon monoxide.

While this is quite true of CO itself, the CO-rich exhaust gases are usually a lot warmer than regular room air and will rise because of the buoyant nature of the entire gas mix.


There are two potential CO hazards that I have identified with the use of my stove. One is to leave the bypass damper closed while the front doors are open. The other (and even worse) thing is to leave the top load door open while working on the stove with the doors open. Neither one would be a likely event when the stove is at operating temperatures, but both have happened to me in the AM by being careless during startup.

During the daytime I usually open the top load door to check on the condition of the coal bed (no window), pull the coals together with a poker if needed, then drop the appropriately sized splits in from the top and close the door. In the morning, however, I have sometimes opened the top load door out of habit, even though I will be getting down on my knees to work on the stove with the doors open to take care of ashes and start a new fire. On a few occasions I have forgotten to close the top door again before getting down on my knees to attend to the morning fire, and once kneeling down and working on the inside of the stove in the dim morning light, it is not immediately obvious that it is open. The CO-rich gases given off by the hot coals from the night before then rise directly through the open top door since the draft is not yet strong enough to pull them past the top opening and up the flue.


I have had CO spikes show up on my detector within minutes of forgetting to open the bypass before working on the stove with the doors open. The detector is actually in the bathroom at the top of the basement stairs, a good 25' away and 10' higher than the stove top. That's why I placed it there in the first place, because I knew that the warm CO-laden air would be funneled into the bathroom directly opposite the basement door.

Moreover, in air containing significant quantities of H2O (water) and CO2 (carbon dioxide), both very "sticky" molecules that tend to form small clusters, particularly at low temperatures, the whole calculation becomes way more complex.

Not sure what CO2 has to do with this discussion, but regarding the "sticky" nature of CO2 and H2O molecules, high concentrations of either CO2 or H2O are unlikely during the most dangerous part of the burn... the late coal bed stage. For starters, little combustion air is being pulled into the stove because of the weak draft at the end of the burn, leading to an abundance of CO in the box rather than CO2. And essentially no H2O is being formed at all during the late coaling stage since nearly all of the hydrogen in the wood has been consumed during the early stages of the burn.

 

[jimbom]

I have a new home with hardwired smoke detectors per code. CO detection is not yet code here so I went the cheap route 2 years ago when finishing up the home as money was tight at the end of the project and have, I think, 9 smoke detectors in my system at $11 each.

I want to start upgrading to hardwired CO/smoke combination detectors. Can I replace a couple at a time as money becomes available and still have the system function properly as one cohesive unit? I believe so as any unit that is set off will just set off the whole system, regardless of what kind or brand of detector is in the circuit - right?

Any thoughts would be appreciated. Thanks.

I had the same situation, when one of my hardwired smoke detectors failed. Replacements of the same model were not available. The supply house where I had purchased the original detectors sent me home with two different replacements to try. One worked. So my system has different models wired together and works just fine. Perhaps you could experiment by replacing one at a time.

 

[jimbom]

I have had CO spikes show up on my detector within minutes of forgetting to open the bypass before working on the stove with the doors open. The detector is actually in the bathroom at the top of the basement stairs, a good 25' away and 10' higher than the stove top. That's why I placed it there in the first place, because I knew that the warm CO-laden air would be funneled into the bathroom directly opposite the basement door.

I read hearth.com for many reasons, but this kind of smart thinking/experience is at the top of the list. Thanks for sharing. I always learn something here. Before reading this post, I ignored the temperature of the CO gas in my thinking. Of course I should know that the temperature would make a difference, but I just was not thinking. Thanks again for sharing.

 

[velvetfoot]

You might also want to think among mixing in both photo electrics and ionization smoke alarms. One type is better than the other in certain situations.

 

[henkmeuzelaar]

There are two potential CO hazards that I have identified with the use of my stove. One is to leave the bypass damper closed while the front doors are open. The other (and even worse) thing is to leave the top load door open while working on the stove with the doors open.

On a few occasions I have forgotten to close the top door again before getting down on my knees to attend to the morning fire, and once kneeling down and working on the inside of the stove in the dim morning light, it is not immediately obvious that it is open. The CO-rich gases given off by the hot coals from the night before then rise directly through the open top door since the draft is not yet strong enough to pull them past the top opening and up the flue.

I have had CO spikes show up on my detector within minutes of forgetting to open the bypass before working on the stove with the doors open. The detector is actually in the bathroom at the top of the basement stairs, a good 25' away and 10' higher than the stove top. That's why I placed it there in the first place, because I knew that the warm CO-laden air would be funneled into the bathroom directly opposite the basement door.

Great practical information!! It would be very useful to have some statistics regarding the relative frequency of woodstove-originating CO alarms/poisoning events caused by: (1) stove doors left open accidentally; (2) poorly closing doors or leaky manifold and flue connections; (3) air flow blockages (at various points in stove and flue); (4) fireboxes overfilled with smoldering and smoking wood, particularly wet wood splits; (5) cats failing to take off on severely dampened burns; (6) downdraft siphoning among twin flues; and (7) improperly placed/spaced chimneys plus intake vents.

Of course, most of these 7 scenarios (there might be lots more) tend to be somewhat interrelated. For instance, a blocked or overfilled stove will make it more likely that a cat fails to take off and none of these two situations is necessarily going to release any CO into the room unless there is some type of stove/flue leak or backdrafting air intake.

Perhaps Firefighter Jake might have access to some case statistics?

CO is only marginally lighter than air. 6 gallons of CO (at standard pressure and temperature) weigh ~ 27.6 grams, whereas the equivalent volume of air (with 80% N2 and 20% O2) weighs ~ 28.4 grams. If oxygen levels are reduced (such as in combustion exhaust gases) the difference will become even smaller. The relative weight of nitrogen gas alone is only 0.07 % lower than that of carbon monoxide.

While this is quite true of CO itself, the CO-rich exhaust gases are usually a lot warmer than regular room air and will rise because of the buoyant nature of the entire gas mix.

I only submitted these values to correct the assumption that CO was significantly lighter than air and I do agree that spontaneous or forced convection currents in the room will play the biggest role in deciding where any escaping CO actually goes. One could indeed envisage a situation where an open, backdrafting stove door could set up its own major flow of warm air.

Most of the time, however, the (spontaneous or forced) convective flow patterns already emanating from the hot stove are likely to be stronger than the spontaneous hot air flow from the door (after the initial "whoosh" upon opening the door). If so, the temperature and direction of any combustion gases evolving from the door opening are likely to be mixed-in, equilibrated and redirected by the major stove flows. Moreover, I would expect that many of the possible CO emission scenarios, particularly the more insidious flue leaks, are unlikely to produce a readily noticeable flow or heat disturbance until all of a sudden the CO alarm goes off.

Moreover, in air containing significant quantities of H2O (water) and CO2 (carbon dioxide), both very "sticky" molecules that tend to form small clusters, particularly at low temperatures, the whole calculation becomes way more complex.

Not sure what CO2 has to do with this discussion, but regarding the "sticky" nature of CO2 and H2O molecules, high concentrations of either CO2 or H2O are unlikely during the most dangerous part of the burn... the late coal bed stage. For starters, little combustion air is being pulled into the stove because of the weak draft at the end of the burn, leading to an abundance of CO in the box rather than CO2. And essentially no H2O is being formed at all during the late coaling stage since nearly all of the hydrogen in the wood has been consumed during the early stages of the burn.

I better should have left CO2 out of the discussion. However, the point I was trying to make, in nontechnical terms, was that relative gas density values can change significantly under real-life conditions (i.e. when we are no longer dealing with an ideal gas). Water vapor is of course notorious but associated combustion products such as CO2 can get in on the act (e.g. by dissolving into water clusters and forming carbonic acid).

Agree about the high CO formation rate during the late coaling stage as well as the near-absence of H2O and CO2. However, if we plot the relative concentrations of CO, H2O and CO2 as a function of burn time, logic predicts that we will see dangerous levels of CO long before the CO2 and H2O levels have gone down very far. So, I think it is wrong, and potentially dangerous, to focus only on the very late coaling stage.

Henk

 

[firefighterjake]

Just a dumb firefighter so I can't add a whole lot to this debate except to say that a whole bunch of folks a lot smarter than me who eat, live and breathe carbon monoxide (well not literally) and carbon monoxide detectors sit on a committee with the NFPA -- these consist of firefighters, CO manufacturers and just about anybody and everybody who cares deeply about CO and CO poisioning . . . and the thing is they don't seem to have many issues with the placement of the CO detectors in relation to height in the room since they say while CO will be found at the upper limits of a room while warmed, once it cools down it quickly percolates out through the entire strata of the room . . . meaning that it doesn't matter so much as to whether the CO detector is on the ceiling or a foot or so off the floor . . .

As to the most likely source . . . haven't run across any concrete studies . . . but I have seen stuff from the NFPA that indicates the most prevalent CO sources are from generators and heating appliances -- often gas-based being used indoors. Personally, I've seen and read of a few cracked heat exchangers in oil or gas furnaces, generators being used inside, too small of a tank being used on a gas oven, etc. . . but never once have I run across a CO issue due to the woodstove . . . not saying that it could not happen . . . just figure it is pretty rare and low on the Firefighter Jake Fire Safety Risk-o-Meter . . .

 

[Milton Findley]

When I the fire dept for a recommendation, they told me to buy any CO detector with a digital readout.

Got a Kiddie Night Hawk at the box store for about $40. Plug in with a battery back up. Will display number and alarm at 30 ppm, otherwise reads "0". Built-in timer from when you plug it in to automatically fail after 7 years so that you replace it. All those features were pretty standard in the models that I compared.

Hey vic99 I got a couple of the same ones.Reads 0 for readings under 30 ppm is there any way to get it over 30 ppm to get a test reading to make sure it is working?

Holding it over a bucket full of hot coals will not work. I tried that for my digital 0 reading Kidde. Still read 0. Putting it in the flue pipe might work, or better still, the exhaust pipe of the car might set it off. Going to be hard to do with a wood stove.

 

[henkmeuzelaar]

When I the fire dept for a recommendation, they told me to buy any CO detector with a digital readout.

Got a Kiddie Night Hawk at the box store for about $40. Plug in with a battery back up. Will display number and alarm at 30 ppm, otherwise reads "0". Built-in timer from when you plug it in to automatically fail after 7 years so that you replace it. All those features were pretty standard in the models that I compared.

Hey vic99 I got a couple of the same ones.Reads 0 for readings under 30 ppm is there any way to get it over 30 ppm to get a test reading to make sure it is working?

Holding it over a bucket full of hot coals will not work. I tried that for my digital 0 reading Kidde. Still read 0. Putting it in the flue pipe might work, or better still, the exhaust pipe of the car might set it off. Going to be hard to do with a wood stove.

Try spraying/misting a small amount of water on the glowing coals.

This should generate plenty of CO (according to the laws of chemistry).

Haven't tried it myself, though

Henk

 

[Milton Findley]

Try it. Let us know what you find.

My guess is that it will not work all that well if at all, but if you do it with a dozen charcoal briquet's you will get a much different reading. Temperature and burning stages are one of the keys to the chemistry.

That is what I like about all of the measuring equipment I have purchased over the last several months. I get to experiment and see if there is truth in these forums. Like the poor guy who was told to tear out his stone hearth because it was not quite up to specs, as one example. I have the same stove, and the floor under it never got over 130 degrees, and a 3 inch square of newsprint that I put under there is still under there, and still looks like it did the day I put it under there. I had the same idea with the CO detector and the ash bucket. 0 reading. I was also told that I could not use a prefabricated fireplace to run my flue through. I can, and it is up to code in all respects. There is an amazing amount of crap that shows up that the amazing amount of good information provided in the main informational articles debunks.

 

[henkmeuzelaar]

As to the most likely source . . . haven't run across any concrete studies . . . but I have seen stuff from the NFPA that indicates the most prevalent CO sources are from generators and heating appliances -- often gas-based being used indoors. Personally, I've seen and read of a few cracked heat exchangers in oil or gas furnaces, generators being used inside, too small of a tank being used on a gas oven, etc. . . but never once have I run across a CO issue due to the woodstove . . . not saying that it could not happen . . . just figure it is pretty rare and low on the Firefighter Jake Fire Safety Risk-o-Meter . . .

Thanks for the valuable input, Jake!

Now that I know that statistical information about wood stove involvement in CO exposure is not already on everyone's table, I Googled a bit and found the following interesting tables in a 2001 article in the Journal of Emergency Medicine. The authors of this article used news-feed clips to collect 3,571 cases of CO exposure, with a total of 289 human fatalities.

Exposures involving faulty heating systems appear to constitute the majority of all causes. Unsurprisingly, about 60% of all exposures occurred at home although school/day care exposures also constituted a surprising 28% (without fatalities, fortunately). About 25 % of the survivors credited CO detectors with saving their lives.

Wood-burning fireplaces and stoves were not specifically singled out but 318 cases of "blocked chimney" exposures (with 21 fatalities) suggest to me that they must play a fairly important role in the overall picture.

The demographic distribution is also interesting, with the highest fatality rates in New Orleans, Detroit, Atlanta and Dallas. To my surprise, 2 big California cities (Los Angeles and ,to a lesser extent, San Jose), were not very far behind.

At any rate, everyone can study these tables and draw their own conclusions.

Henk

 

[Battenkiller]

Agree about the high CO formation rate during the late coaling stage as well as the near-absence of H2O and CO2. However, if we plot the relative concentrations of CO, H2O and CO2 as a function of burn time, logic predicts that we will see dangerous levels of CO long before the CO2 and H2O levels have gone down very far. So, I think it is wrong, and potentially dangerous, to focus only on the very late coaling stage.

Yes, CO is formed all throughout the burn cycle, but it will usually signal it's presence at other times by filling the room with the accompanying smoke. It's only my opinion, but I feel that the late coaling stage is the most dangerous because the smoke has largely disappeared and the flue temps are low enough that spillage is possible. CO is odorless, so without smoke to alert you, you really need a CO detector to give the warning that may save your life. Plus, folks seem a bit cavalier at the end of the burn. Many here have reported burning down coals with the door open. The very low flue temps at this time can drastically increase the chance of a flue reversal, which would spill out CO gas without your awareness of its presence.

BTW, Henk, I really like your well thought out responses. ;-)

 

[firefighterjake]

As to the most likely source . . . haven't run across any concrete studies . . . but I have seen stuff from the NFPA that indicates the most prevalent CO sources are from generators and heating appliances -- often gas-based being used indoors. Personally, I've seen and read of a few cracked heat exchangers in oil or gas furnaces, generators being used inside, too small of a tank being used on a gas oven, etc. . . but never once have I run across a CO issue due to the woodstove . . . not saying that it could not happen . . . just figure it is pretty rare and low on the Firefighter Jake Fire Safety Risk-o-Meter . . .

Thanks for the valuable input, Jake!

Now that I know that statistical information about wood stove involvement in CO exposure is not already on everyone's table, I Googled a bit and found the following interesting tables in a 2001 article in the Journal of Emergency Medicine. The authors of this article used news-feed clips to collect 3,571 cases of CO exposure, with a total of 289 human fatalities.

Exposures involving faulty heating systems appear to constitute the majority of all causes. Unsurprisingly, about 60% of all exposures occurred at home although school/day care exposures also constituted a surprising 28% (without fatalities, fortunately). About 25 % of the survivors credited CO detectors with saving their lives.

Wood-burning fireplaces and stoves were not specifically singled out but 318 cases of "blocked chimney" exposures (with 21 fatalities) suggest to me that they must play a fairly important role in the overall picture.

The demographic distribution is also interesting, with the highest fatality rates in New Orleans, Detroit, Atlanta and Dallas. To my surprise, 2 big California cities (Los Angeles and ,to a lesser extent, San Jose), were not very far behind.

At any rate, everyone can study these tables and draw their own conclusions.

Henk

Good stuff . . . but the issue on the blocked chimney . . . doesn't necessarily have to be creosote from a wood burning appliance . . . could be due to animals nesting or blocking the chimney, chimney degradation or even in the case of my old oil boiler -- even though I cleaned it twice a year it would gunk up with enough oil soot to block the chimney . . . I finally gave up on the old system after losing heat one too many times and growing tired of shop vaccing the messy soot from the oil boiler every few months . . . and replaced it with a new oil boiler which has been very reliable.

 

[henkmeuzelaar]

Good points, Jake

Let's hope someone can find CO exposure statistics that are more directly related to wood burning than these.

Since it only took me a couple of minutes to find these tables, I have a hunch that something better is likely to be out there.

Henk

 

[colebrookman]

Agree about the high CO formation rate during the late coaling stage as well as the near-absence of H2O and CO2. However, if we plot the relative concentrations of CO, H2O and CO2 as a function of burn time, logic predicts that we will see dangerous levels of CO long before the CO2 and H2O levels have gone down very far. So, I think it is wrong, and potentially dangerous, to focus only on the very late coaling stage.

Yes, CO is formed all throughout the burn cycle, but it will usually signal it's presence at other times by filling the room with the accompanying smoke. It's only my opinion, but I feel that the late coaling stage is the most dangerous because the smoke has largely disappeared and the flue temps are low enough that spillage is possible. CO is odorless, so without smoke to alert you, you really need a CO detector to give the warning that may save your life. Plus, folks seem a bit cavalier at the end of the burn. Many here have reported burning down coals with the door open. The very low flue temps at this time can drastically increase the chance of a flue reversal, which would spill out CO gas without your awareness of its presence.

BTW, Henk, I really like your well thought out responses. ;-)

Excellent points from both of you! I know for firefighters after the flames die down and they start to overhall, the smoldering remains are very dangerous. Most depts. will keep their firefighters breathing from their SCBAs pacs until their gas meters indicate that it's safe to remove them. Be safe.
Ed

 

[JotulOwner]

I keep several (many) CO detectors around so I have a better idea if they are working correctly. Unlike smoke, you can't smell CO.