Carbon monoxide levels
What can make it rise fast in a building or area?
Our lives are packed with an endless number of sources and circumstances that can cause carbon monoxide
levels to rise fast.
In a perfect world heating and fuel burning equipment would always work flawlessly and never allow carbon
monoxide levels to rise and vent into a building or vehicle. However, things can and do go wrong in the design and
manufacturing process, and especially with installation and ongoing maintenance.
In order for carbon monoxide levels to stay "safe", exhaust gases (from a furnace, fireplace, gas hot water
heater, etc) must vent outside.
Ideally, the air pressure inside a building should be close to or equal to the air pressure outside a
To vent outside properly, most chimneys* rely on the exhaust gases being hot and staying hot as they rise
naturally up the chimney (called the "stack effect").
To prevent air pressure within a building from becoming "negative" (lower than the exterior air pressure), the
volume of air rising up the chimney must be replaced by an equivalent amount of air coming into the building
through a fresh-air inlet.
Exhaust gases may accidentally be pulled into or spill into a building or confined space under certain
conditions. For example:
- Carbon monoxide levels can rise when a clothes dryer, bathroom fan, kitchen exhaust fan, or built-in vacuum
system is switched on - they all take air out of the building and contribute to creating negative air pressure
within the building.
- Carbon monoxide levels can rise when a home is renovated and a second dryer, bathroom fan, or kitchen
exhaust fan is added.
- Levels of carbon monoxide can rise when a wood burning fireplace is lit. Winds can change air pressure
outside a building.
- CO levels can rise on a cold winter day as exhaust gases cool as they [struggle to] rise up an improperly
or un-insulated chimney or vent.
- The level of carbon monoxide can rise if a fresh air intake into a home or building is partially or fully
- The CO level can rise if a chimney becomes partially blocked (a dead bird, birds nest, insects, small
animal such as a cat or racoon, construction, etc.).
- Carbon monoxide levels can rise when exhaust gases from one apartment or hotel unit are sucked into the
fresh air intake of another unit.
- Carbon monoxide levels can spike when exhaust gases from a vehicle or construction equipment are sucked
into the fresh air intake of a building.
- Carbon monoxide levels can rise if a partially blocked or leaking exhaust system causes some exhaust to
enter a vehicle.
* Some venting systems have electric powered exhaust fans.
** Some devices have carbon monoxide sensors that are designed to automatically shut off the unit if carbon
monoxide levels accidentally rise (because carbon monoxide accidently vented/spilled into the area(the sensor is
sometimes referred to as a carbon monoxide spill switch).
*** The density of carbon monoxide is very similar to, but slightly lighter than air. Unless it is hot, carbon
monoxide will tend to flow in whatever direction the air normally circulates. This can vary a lot depending on
conditions in the building and season.
Also see sources of carbon monoxide.
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