Personnel exposures to hazardous concentrations of airborne contaminants must be kept within what limits?

The correct answer focuses on "permissible exposure limits" (PEL), which are established regulatory limits on the amount or concentration of a substance in the air to which workers may be exposed. These limits are set to protect the health of employees by minimizing the risk of adverse health effects from workplace exposures to airborne contaminants.

Permissible exposure limits are based on scientific research and are enforced to ensure a safe working environment. They define the maximum allowable concentrations of hazardous substances, ensuring that exposures do not exceed levels that could be harmful to health and safety. Adhering to these limits is crucial in occupational health programs, especially within the context of construction and engineering environments managed by the U.S. Army Corps of Engineers.

Other options, while seemingly related to exposure limits, do not correctly describe the standard language or guidelines used in occupational safety and health. "Unacceptable limits," "excessive limits," and "dangerous limits" lack the specificity and clarity required in regulatory contexts and do not provide a clear framework for establishing safe work practices.