Which concentration of carbon dioxide is considered excessive in compressed air for SCBA usage?

In the context of SCBA usage, the concentration of carbon dioxide in the breathing air is crucial for ensuring the safety and performance of the equipment. A concentration of 0.04% (or 400 parts per million) is significant because it represents the threshold at which carbon dioxide levels can begin to impair performance, causing symptoms like headaches and increased respiratory rate.

While lower concentrations of carbon dioxide, such as 0.01%, 0.02%, and even 0.03%, are considered safe or indicative of normal atmospheric levels, a concentration of 0.04% is generally regarded as excessive in the standard for breathable air supplied by SCBAs. Maintaining carbon dioxide levels below this threshold helps ensure that users do not experience the physiological effects associated with elevated CO2, which can lead to impaired cognition, increased heart rate, and decreased mental alertness.

Thus, 0.04% is identified as the point where the air quality may start to become suboptimal for SCBA usage, affirming its classification as excessive in this context.