OSHA does not mandate air sampling monitoring across the board, but requires it when there is a potential for employees to be exposed to hazardous concentrations of substances to ensure proper selection of controls, work practices, and PPE. Required air monitoring is detailed in specific substance-specific standards, such as those for confined spaces, excavation, and noise exposure, each outlining its own procedures for testing the atmosphere or an employee's personal breathing zone. Employers are responsible for implementing monitoring programs and ensuring the accuracy of results, often involving calibrated instruments, specific sampling methods, and employee notification of findings.