Should the placement of carbon monoxide (CO) detectors be influenced by CO's weight relative to air?

J Emerg Med. 2012 Apr;42(4):478-82. doi: 10.1016/j.jemermed.2011.03.015. Epub 2011 May 4.


Background: Numerous states and localities have recently passed legislation mandating the installation and use of residential carbon monoxide (CO) detectors/alarms. Interestingly, there seems to be confusion about the optimal placement, if any, of CO alarms inside the home.

Objectives: It was the goal of this study to demonstrate the behavior of CO in air and to help provide a data-based recommendation for CO alarm placement.

Methods: CO was calculated to be slightly lighter than air. An 8-foot-tall airtight Plexiglas chamber was constructed and CO monitors placed within at the top, middle, and bottom. CO test gas (15 L, 3000 parts per million) was infused at each of the three heights in different trials and CO levels measured over time.

Results: Contrary to a significant amount of public opinion, CO did not layer on the floor, float at the middle of the chamber, or rise to the top. In each case, the levels of CO equalized throughout the test chamber. It took longer to equalize when CO was infused at the top of the chamber than the bottom, but levels always became identical with time.

Conclusions: As would have been predicted by the Second Law of Thermodynamics, CO infused anywhere within the chamber diffused until it was of equal concentration throughout. Mixing would be even faster in the home environment, with drafts due to motion or temperature. It would be reasonable to place a residential CO alarm at any height within the room.

MeSH terms

  • Air Movements*
  • Carbon Monoxide / analysis*
  • Carbon Monoxide Poisoning / prevention & control*
  • Protective Devices*
  • Temperature


  • Carbon Monoxide