What is the maximum acceptable level of carbon monoxide (CO) in flue gas?

The maximum acceptable level of carbon monoxide (CO) in flue gas is considered to be 400 parts per million (ppm). This threshold is crucial for ensuring safety and preventing harmful health effects associated with carbon monoxide exposure. Continuous exposure to CO at levels above this limit can result in symptoms of poisoning, including headaches, dizziness, confusion, and even life-threatening conditions.

The 400 ppm level is aligned with safety standards and guidelines from various health and safety organizations, which aim to minimize the risk of carbon monoxide exposure to occupants in homes and buildings. Ensuring that flue gas emissions remain below this level is vital for the effective operation of gas appliances and for maintaining indoor air quality.

Other options, such as lower levels, would not adequately reflect the standard used to assess carbon monoxide safety in flue gases. Therefore, 400 ppm is recognized as the critical threshold for ensuring safety and contributing to effective ventilation in environments where gas appliances are used.