A car running in a closed garage can produce lethal levels of carbon monoxide (CO) in as little as two minutes, with the entire space becoming dangerous well before the car's fuel runs out. The primary risk isn't the car stalling but the rapid accumulation of this odorless, colorless gas, which can cause unconsciousness and death in under ten minutes. This is a critical safety issue, not a theoretical exercise.
The danger stems from the car's internal combustion engine. As it burns fuel, it emits carbon monoxide, which quickly displaces breathable oxygen in the confined space. A standard two-car garage has limited air volume, and even a modern, efficient vehicle can fill it with toxic levels of CO alarmingly fast. The vehicle's size or fuel tank capacity is irrelevant; the human body succumbs to poisoning long before the engine does.
The following data illustrates how quickly CO can reach dangerous concentrations in an enclosed space, based on a typical mid-size sedan:
| Vehicle Condition | Approximate Time to Reach Dangerous CO Levels (≥200 PPM) | Potential Human Impact |
|---|
| Idling with a properly functioning exhaust system | 2-5 minutes | Headache, dizziness, nausea within 15-20 minutes. |
| Idling with a small exhaust leak | 1-3 minutes | Loss of consciousness and risk of death in under 10 minutes. |
| Revving the engine (e.g., trying to charge a battery) | Under 2 minutes | Rapid onset of symptoms; high risk of fatality. |
| Modern Electric Vehicle (EV) in "Ready" mode | No CO emissions from tailpipe. | No CO poisoning risk, but battery drain is the only concern. |
Your best protection is to never start a car's engine inside a closed garage. If you need to warm up the car, always pull it completely outside first. Ensure your home has working carbon monoxide detectors installed, particularly in areas adjacent to the garage. If you ever suspect CO poisoning, get fresh air immediately and seek medical attention.
