Under what condition would the CO2 system be acceptable to the EPA regarding passenger cabin concentrations?

The correct answer regarding acceptable CO2 concentrations in a passenger cabin, according to EPA guidelines, is based on the understanding of how carbon dioxide (CO2) affects human health and comfort. The EPA has established safety thresholds for various gases, including CO2, to ensure passenger safety and comfort during travel.

A concentration of carbon dioxide above 3% for 15 minutes is considered a limit beyond which adverse health effects could occur. Keeping levels at or below this threshold helps prevent issues such as headaches, dizziness, or other symptoms that might arise from excessive CO2 exposure. This concentration level is significant because it denotes a point where the air quality could start to negatively impact occupants.

The other options reflect levels that exceed this threshold, indicating that they are not acceptable according to the EPA guidelines for air quality and human safety in enclosed spaces, such as vehicle cabins. Keeping CO2 levels within the acceptable range ensures a safe and comfortable environment for passengers.