Carbon monoxide (CO) is a dangerous gas, often called the “silent killer” because it is colorless, odorless, and tasteless. This makes its presence undetectable, posing a significant risk in enclosed spaces. A common concern is whether CO is heavier or lighter than air, as understanding its behavior is important for safety.
The Direct Answer: Carbon Monoxide’s Density
Carbon monoxide is very slightly lighter than air. Its molecular weight is approximately 28.01 grams per mole, compared to air’s average of 28.96-28.97 g/mol. This minor difference means CO is roughly 3% less dense than air. However, this slight density difference is largely insignificant in real-world scenarios due to the dynamic nature of gases.
Understanding Gas Behavior and Molecular Weight
The slight difference in molecular weight between carbon monoxide and air does not cause CO to layer significantly. Gases, regardless of minor density differences, tend to mix thoroughly and evenly throughout an enclosed space. This mixing occurs primarily through two processes: diffusion and convection.
Diffusion
Diffusion involves the natural movement of gas molecules from an area of higher concentration to an area of lower concentration, spreading them out over time.
Convection
Convection, driven by air currents, plays a substantial role in distributing gases within a space. Warm air, which is less dense, tends to rise, while cooler air sinks, creating circulating currents. Since carbon monoxide is often produced by combustion sources that generate heat, the CO can initially be carried upward with the warm air. These combined forces of diffusion and convection ensure that carbon monoxide disperses and mixes with the surrounding air rather than settling or collecting in distinct layers.
Practical Safety: Detector Placement and Ventilation
Given that carbon monoxide mixes thoroughly with air due to diffusion and convection, the placement of CO detectors is not restricted to a specific height. Detectors can be effectively placed on a wall, ceiling, or at eye level. The most effective placement is generally outside each sleeping area and on every level of the home, including the basement. It is also recommended to place them near attached garages and at least 15 feet away from fuel-burning appliances to avoid false alarms.
Proper ventilation is a key measure to prevent carbon monoxide buildup. Carbon monoxide is produced whenever carbon-containing fuels, such as gasoline, natural gas, wood, or propane, burn incompletely. Common sources include faulty furnaces, gas stoves, water heaters, fireplaces, and vehicle exhaust in enclosed spaces. Ensuring that appliances are correctly installed, maintained, and vented helps prevent CO from accumulating indoors. Never use appliances intended for outdoor use, such as charcoal grills or portable generators, inside a home or garage, as these can rapidly produce dangerous CO levels.