What is a key characteristic of Air Purifying Respirators?

A key characteristic of Air Purifying Respirators (APRs) is that they utilize a filtering mechanism to purify air being inhaled through a cartridge. This process allows the wearer to effectively remove contaminants present in the air, such as dust, fumes, or vapors, enhancing safety in environments with airborne hazards.

Importantly, APRs are not designed for use in Immediately Dangerous to Life or Health (IDLH) environments, as these situations often present levels of hazards that surpass what the respirator can handle. In IDLH situations, a different type of respiratory protection, such as supplied-air respirators, is necessary because these conditions may require a guaranteed breathable atmosphere that APRs cannot provide.

The other options do not accurately describe the characteristics of APRs: they do not supply oxygen externally, they do not require power to filter air, nor do they come equipped with air conditioning systems. Thus, option B correctly highlights the essential functionality and limitations of Air Purifying Respirators in occupational hygiene contexts.