Medical surveillance is a critical component of HAZWOPER, designed to monitor the health of workers exposed to hazardous substances. Under OSHA 29 CFR 1910.120, employees who are regularly exposed to hazardous substances at or above the action level, wear respirators for more than 30 days per year, or respond to hazardous waste emergencies are required to participate in a medical surveillance program. This ensures early detection of work-related health issues and helps maintain long-term worker health.