How long can the BG4 be used to breathe irrespirable air?

The BG4 breathing apparatus is designed to provide breathable air in environments where the air is deemed irrespirable, such as in cases of high carbon dioxide concentration or a lack of oxygen. It functions by supplying a specific volume of air based on its design and purpose.

The correct answer, which states that the BG4 can be used for up to four hours, reflects the operational time that has been determined for optimal performance and safety during rescue operations or similar scenarios. This duration is critical as it allows the rescuer enough time to conduct their tasks while ensuring that they have a reliable supply of breathable air.

In more hazardous environments, maximizing the duration of use is essential for both the effectiveness of the rescue operation and the safety of the individual wearing the apparatus. Other durations such as two, three, or five hours exceed the standard operational guidelines established for the BG4, which could lead to safety concerns if the unit is expected to perform beyond its tested limits. Thus, four hours represents the established safe working limit for the BG4, ensuring it balances usability with effective respiratory protection in emergencies.