Final answer:
The permissible exposure limit for respirable crystalline silica is set at 50 micrograms per cubic meter of air, averaged over an 8-hour shift to protect workers' health.
Step-by-step explanation:
The standard permissible exposure limit (PEL) for respirable crystalline silica is set at 50 micrograms per cubic meter of air (50 µg/m³), averaged over an 8-hour shift. This limit is enforced by the Occupational Safety and Health Administration (OSHA) to minimize the health risks associated with long-term exposure to silica dust, which can lead to serious conditions such as silicosis, lung cancer, and other respiratory diseases. Employers must implement controls and strategies to limit exposure and protect workers' health under these regulations.