Carbon monoxide (CO) is a dangerous, invisible gas produced by the incomplete burning of fuel, such as natural gas, wood, or propane. Because it is colorless, odorless, and tasteless, it is impossible for people to detect without a specialized device. When inhaled, CO replaces oxygen in the bloodstream, leading to symptoms often mistaken for the flu, like headache and dizziness. High concentrations can cause death within minutes. The time required to air out this contaminant depends entirely on the specific conditions of the environment.
Immediate Safety Steps
The moment a carbon monoxide detector alarm sounds, the first step is to move every person and pet outside into fresh air immediately. Do not stop to investigate the source or gather belongings, as the gas can cause loss of consciousness rapidly. Once everyone is safely away from the building, call local emergency services and inform them of the CO alarm.
If possible to do so quickly and safely from outside the structure, shut off the source of the CO, such as turning off the furnace or generator. Anyone experiencing symptoms like a severe headache, nausea, or confusion must seek medical attention at once. They may require oxygen therapy to clear the gas from their blood. Emergency services will test the air quality with professional equipment and provide official clearance for re-entry.
Variables Determining Airing Time
There is no single, fixed time for airing out a space because the process is governed by several physical variables unique to each incident. The initial concentration of carbon monoxide, measured in parts per million (ppm), is the most significant factor. A high concentration, such as 800 ppm, requires far more time to dissipate than a low-level leak. The volume of the contaminated space is also a major consideration, as a small, enclosed room clears much differently than an entire multi-story home.
The rate at which clean outdoor air replaces the indoor air, known as the Air Exchange Rate (AER), determines the speed of the clearance. A well-sealed, modern building naturally has a low AER, trapping the CO inside, while older or draftier structures exchange air more rapidly. External factors like wind speed can also assist the process by increasing air pressure differences around the building, pushing air through openings.
Techniques for Rapid Ventilation
To speed up the clearing process, implement both passive and active ventilation techniques immediately after evacuating and calling for help. Passive ventilation involves opening all windows and exterior doors throughout the structure to create a strong cross-breeze. This establishes multiple pathways for the contaminated air to escape and fresh air to flow in.
Active ventilation accelerates this exchange by using mechanical force to move the air. Placing box fans in windows and directing them to blow outward creates a negative pressure inside, actively pulling the CO-filled air out of the building. Running exhaust-only systems, such as kitchen and bathroom fans, further supplements this effort. Only use the home’s main HVAC fan system if advised by emergency personnel, as it could inadvertently circulate the CO into uncontaminated areas.
Confirming Safe Re-entry Levels
Re-entry should never be attempted until a professional gives clearance, as the duration of ventilation alone is insufficient confirmation of safety. The only reliable method to confirm safety is to use a calibrated carbon monoxide monitor, not by relying on the absence of symptoms or a set time limit. Professional-grade monitors accurately measure the ambient CO concentration in parts per million.
For safe, long-term occupancy, the CO level must be zero parts per million, or at the maximum safe level determined by the responding emergency team. Fire departments possess the necessary testing equipment and expertise to verify that the gas has fully dissipated. Never rely on the built-in home alarm to indicate safety, as its sensor may have been temporarily overwhelmed or damaged. The final step before anyone returns is to have a certified HVAC professional inspect and repair the source of the CO leak to prevent a recurrence.