U.S. Department of Labor Occupational Safety and Health Administration

What are the record keeping requirements for asbestos exposures?
You must keep accurate records of the following:

• All measurements taken to monitor employee exposure to asbestos—30 years;
  
• Medical records, including physician’s written opinions—duration of the employee’s employment plus 30 years; and
  
• Training records—1 year beyond the last date of employment.