5 ms·

Note that a smoke detector should be on the ceiling, and a carbon monoxide alarm at ~1.5m high on a wall. Putting it on the ceiling as well could very well resu

Note that a smoke detector should be on the ceiling, and a carbon monoxide alarm at ~1.5m high on a wall. Putting it on the ceiling as well could very well result in late alarms. (Source: a friend who nearly died from carbon monoxide poisoning)

caw 13y ago
Where are sources of carbon monoxide poisoning? The only two off the top of my head are near the garage and the fireplace. You could augment this system with 2 more plug-in type CO monitors that would put them lower on the wall. For any other room that doesn't have a CO monitor right now this is just a bonus.
- Ygg2 13y ago
  Machines that use gasoline, tobacco, gas/gasoline/wood heaters. GP is right, Carbon Monoxide falls to the bottom, so detecting there is of great essence. Carbon Dioxide floats, so its detectors should be placed up. NOTE: I meant Smoke detectors.
  - deelowe 13y ago
    That's backwards isn't it? CO should be less dense than CO2.
    - deleted 13y ago
      [deleted]
    - JshWright 13y ago
      You are correct. The relevant specific gravities (higher == more dense): Carbon dioxide - CO2 1.5189 Carbon monoxide - CO 0.9667
      - Ygg2 13y ago
        True, however there might be other factors. http://www.newton.dep.anl.gov/askasci/chem03/chem03364.htm http://www.newton.dep.anl.gov/askasci/chem03/chem03364.htm Perhaps the CO is generally produced mixed with other more heavier gasses and is colder, thus less conveyant. I can't find source but I found a pamphlet that mentioned that when in fire you shouldn't try to crawl on the floor for risk of CO poisoning, or something.
        JshWright 13y ago
        CO is a product of combustion, and will therefore be hotter than the ambient air in most cases. The primary reason manufacturers say CO detectors should be a bit lower on the wall is to avoid false positives (well... not really false, just alarms for events you don't really need to worry about). A little CO emission is expected during the normal operation of gas/wood burning appliances. A CO detector at the ceiling might go off when it detects these little 'puffs' of CO. In practice, a CO detector should be averaging the level of a couple minutes, and not worry about short transient peaks (which is what I suspect the nest detector does). If you're in a fire, stay low and get out. Source: I'm a firefighter.
  - metl_lord 13y ago
    There's no such thing as a carbon dioxide detector. It would constantly be going off.
    - VLM 13y ago
      Not really, you can buy CO2 sensors COTS for HVAC guys to prevent "stuffy" rooms. Its industrial grade product and price and you won't be buying them at walmart but the UI is very HVAC-dude oriented. Also if you sell dry ice you're supposed to own a permanently wall mounted one even if you officially keep the stuff outside (depends on local building code and licenses and regs I'm sure) There's a different UI for combustion gas analyzers, most any HVAC guy owns one if he does furnace work. They're about an order of magnitude more expensive and the ratio of CO2/O2 tells you quite a bit about the level of draft (and they usually have a CO sensor too which only comes into play when draft/mixture is tremendously rich)
    - shabble 13y ago
      There certainly are, although they're not typically intended for home usage. But in industrial/commercial setups which use CO2 (beer/drink-cellars, dry-ice handling, pressure pipe-flushing, etc) they're relatively common. Obviously they're always detecting some level, but they're set to trip or alarm when concentration hits some threshold over ambient. http://duomo.co.uk/CO2_Alarms.aspx http://duomo.co.uk/CO2_Alarms.aspx is just one example. Low-O2 detectors are also common, and approach the problem from the other direction. They're more useful for N2 or other inert gases, since you're less concerned with toxicity and more with plain asphyxiation. IIRC they're used in some places to enforce "No riding in the same lift as the liquid-N2 dewar" safety rules.
  - mynameisvlad 13y ago
    Source? Everything I've seen shows that it generally tends to mix with air or rise slightly due to its slightly less dense weight, and all the sources I found say you can either use the ceiling or wall.
- computer 13y ago
  It was a badly ventilated gas heater (in an old house) in my friend's case, in a room nearby the bedroom where she was asleep.
- TeMPOraL 13y ago
  Gas heating of water in bathroom and/or kitchen is a very popular one. We had this discussion a while back here on HN, basically US doesn't have them, but Europe and UK still has a lot.
dlitz 13y ago
That's true for CO2, but CO is actually slightly less dense than air (1.20 kg/m^3 vs 1.23 kg/m^3 according to Wikipedia), and tends to mix with air or rise slightly above it: http://www.ehow.com/way_5545497_proper-elevation-carbon-monoxide-detector.html http://www.ehow.com/way_5545497_proper-elevation-carbon-mono...
- deleted 13y ago
  [deleted]
Osmium 13y ago
Would this be less of an issue if you had a more sensitive detector?
svachalek 13y ago
Read the instructions on your CO or smoke alarm about where to place it. It's true that most CO detectors are designed to be placed on walls, but combo detectors are often built to be placed like smoke detectors, on or near the ceiling. You want to prevent both false negatives and false positives.
warfangle 13y ago
Due to the second law of thermal dynamics, I question the battery status of your friend's CO detector, as CO will fairly quickly equalize throughout the area. Source: http://www.ncbi.nlm.nih.gov/pubmed/21536403 http://www.ncbi.nlm.nih.gov/pubmed/21536403 (This came up in a previous discussion about the Nest smoke detector: https://news.ycombinator.com/item?id=6441343 https://news.ycombinator.com/item?id=6441343 )

caw 13y ago

Where are sources of carbon monoxide poisoning? The only two off the top of my head are near the garage and the fireplace. You could augment this system with 2 more plug-in type CO monitors that would put them lower on the wall. For any other room that doesn't have a CO monitor right now this is just a bonus.

Ygg2 13y ago
Machines that use gasoline, tobacco, gas/gasoline/wood heaters. GP is right, Carbon Monoxide falls to the bottom, so detecting there is of great essence. Carbon Dioxide floats, so its detectors should be placed up. NOTE: I meant Smoke detectors.
- deelowe 13y ago
  That's backwards isn't it? CO should be less dense than CO2.
  - deleted 13y ago
    [deleted]
  - JshWright 13y ago
    You are correct. The relevant specific gravities (higher == more dense): Carbon dioxide - CO2 1.5189 Carbon monoxide - CO 0.9667
    - Ygg2 13y ago
      True, however there might be other factors. http://www.newton.dep.anl.gov/askasci/chem03/chem03364.htm http://www.newton.dep.anl.gov/askasci/chem03/chem03364.htm Perhaps the CO is generally produced mixed with other more heavier gasses and is colder, thus less conveyant. I can't find source but I found a pamphlet that mentioned that when in fire you shouldn't try to crawl on the floor for risk of CO poisoning, or something.
      - JshWright 13y ago
        CO is a product of combustion, and will therefore be hotter than the ambient air in most cases. The primary reason manufacturers say CO detectors should be a bit lower on the wall is to avoid false positives (well... not really false, just alarms for events you don't really need to worry about). A little CO emission is expected during the normal operation of gas/wood burning appliances. A CO detector at the ceiling might go off when it detects these little 'puffs' of CO. In practice, a CO detector should be averaging the level of a couple minutes, and not worry about short transient peaks (which is what I suspect the nest detector does). If you're in a fire, stay low and get out. Source: I'm a firefighter.
- metl_lord 13y ago
  There's no such thing as a carbon dioxide detector. It would constantly be going off.
  - VLM 13y ago
    Not really, you can buy CO2 sensors COTS for HVAC guys to prevent "stuffy" rooms. Its industrial grade product and price and you won't be buying them at walmart but the UI is very HVAC-dude oriented. Also if you sell dry ice you're supposed to own a permanently wall mounted one even if you officially keep the stuff outside (depends on local building code and licenses and regs I'm sure) There's a different UI for combustion gas analyzers, most any HVAC guy owns one if he does furnace work. They're about an order of magnitude more expensive and the ratio of CO2/O2 tells you quite a bit about the level of draft (and they usually have a CO sensor too which only comes into play when draft/mixture is tremendously rich)
  - shabble 13y ago
    There certainly are, although they're not typically intended for home usage. But in industrial/commercial setups which use CO2 (beer/drink-cellars, dry-ice handling, pressure pipe-flushing, etc) they're relatively common. Obviously they're always detecting some level, but they're set to trip or alarm when concentration hits some threshold over ambient. http://duomo.co.uk/CO2_Alarms.aspx http://duomo.co.uk/CO2_Alarms.aspx is just one example. Low-O2 detectors are also common, and approach the problem from the other direction. They're more useful for N2 or other inert gases, since you're less concerned with toxicity and more with plain asphyxiation. IIRC they're used in some places to enforce "No riding in the same lift as the liquid-N2 dewar" safety rules.
- mynameisvlad 13y ago
  Source? Everything I've seen shows that it generally tends to mix with air or rise slightly due to its slightly less dense weight, and all the sources I found say you can either use the ceiling or wall.
computer 13y ago
It was a badly ventilated gas heater (in an old house) in my friend's case, in a room nearby the bedroom where she was asleep.
TeMPOraL 13y ago
Gas heating of water in bathroom and/or kitchen is a very popular one. We had this discussion a while back here on HN, basically US doesn't have them, but Europe and UK still has a lot.

dlitz 13y ago

That's true for CO2, but CO is actually slightly less dense than air (1.20 kg/m^3 vs 1.23 kg/m^3 according to Wikipedia), and tends to mix with air or rise slightly above it: http://www.ehow.com/way_5545497_proper-elevation-carbon-monoxide-detector.html http://www.ehow.com/way_5545497_proper-elevation-carbon-mono...

deleted 13y ago
[deleted]

Osmium 13y ago

Would this be less of an issue if you had a more sensitive detector?

svachalek 13y ago

Read the instructions on your CO or smoke alarm about where to place it. It's true that most CO detectors are designed to be placed on walls, but combo detectors are often built to be placed like smoke detectors, on or near the ceiling. You want to prevent both false negatives and false positives.

warfangle 13y ago

Due to the second law of thermal dynamics, I question the battery status of your friend's CO detector, as CO will fairly quickly equalize throughout the area. Source: http://www.ncbi.nlm.nih.gov/pubmed/21536403 http://www.ncbi.nlm.nih.gov/pubmed/21536403 (This came up in a previous discussion about the Nest smoke detector: https://news.ycombinator.com/item?id=6441343 https://news.ycombinator.com/item?id=6441343 )