In a pressurized tunnel or caisson, how does the service life of the SCBA change at 2 atmospheres compared to 1 atmosphere?

The service life of a Self-Contained Breathing Apparatus (SCBA) is primarily influenced by the ambient pressure and the volume of breathable air available in the cylinder. When you increase the pressure, as is the case in a pressurized tunnel or caisson at 2 atmospheres compared to normal atmospheric pressure (1 atmosphere), the amount of air available to the user is effectively reduced.

At 2 atmospheres, the air in the SCBA is compressed, and the user must work against a greater pressure to breathe. This increased difficulty means that the air consumption rate of the user increases, leading to a quicker depletion of the cylinder's air supply. Therefore, in a pressurized environment:

• The air in the SCBA does not last as long because the user consumes it at a faster rate due to the higher pressure condition.

• Specifically, the service life at 2 atmospheres is approximately half of that at 1 atmosphere.

Thus, the correct answer indicates that the SCBA lasts one-half as long under the increased pressure conditions. This concept highlights the importance of understanding how environmental pressures can impact the performance and duration of breathing apparatus equipment in practical scenarios.