Powered air filtering respirators must be worn when asbestos fiber concentration is over what level?

Powered air filtering respirators (PAFRs) are necessary in environments where asbestos fiber concentrations exceed certain thresholds to ensure the safety and health of workers. The correct choice involves understanding the established permissible exposure limit (PEL) for asbestos, which is set by organizations such as OSHA (Occupational Safety and Health Administration).

When asbestos fiber concentrations reach or exceed 10 times the permissible limit, traditional respirators may not provide adequate protection, which is why powered air filtering respirators become necessary. These respirators enhance airflow and provide a higher level of filtration, effectively protecting workers from inhaling hazardous asbestos fibers.

Using a powered air filtering respirator in environments with asbestos fiber concentrations above this specific level ensures compliance with safety regulations and significantly reduces the risk of asbestos-related illnesses. The remaining choices correspond to levels that do not align with the established guidelines for when PAFRs are required, as they would either overestimate or underestimate the protective measures needed for effective safety.