This depends on risk: New-starters within 4 weeks of commencement for a baseline of lung function and previous exposure history, after: 6 weeks, 3 months and 6 months for high occupational asthma risks and then every 12 months if no problems are identified. High-risk situations may require more frequent surveillance. These situations include: history of exceeding the Workplace Exposure Limits/high levels of sensitiser exposure (more than 50% of the WEL) with reliance of respiratory protective equipment. employees identified as vulnerable (those on immuno-suppressants; significant reductions in lung functions). Asbestos Medicals are undertaken by an Occupational Physician with specialist training in asbestos work. Silica Medicals may also require chests x-rays and an Occupational Physician appointment depending on exposure history and symptoms.