A medical surveillance program is part of a control program that aims to monitor, assess, and reduce workers exposure to hazardous substances in the workplace. In Ontario, The Designated Substances Regulation, under the Occupational Health and Safety Act (OHSA) addresses the employer’s obligations and requirements with regard to designated substances in the workplace.

A guide to designated substances in the workplace provides employers details on the above mentioned regulation and its applications. The substances that are prescribed as designated substances in the regulation include: acrylonitrile, arsenic, asbestos, benzene, coke oven emissions, ethylene oxide, isocyanates, lead, mercury, silica and vinyl chloride. The law requires that employers to “take all necessary measures and procedures by means of engineering controls, work practices, hygiene facilities and practices to ensure that a worker’s airborne exposure to a designated substance does not exceed the Occupational Exposure Limit…”. Every workplace where the regulation applies as set out in the regulation is required to undergo an assessment to determine if a control program is needed. Medical surveillance is only a part of the control program with the aim to monitor workers’ health in relation to occupational exposures. In 2020, the code for medical surveillance was updated to include detailed components that must be included in a medical surveillance program.

In general, a medical surveillance program for designated substances should include a medical history, a physical examination and clinical tests as required by the examining physician. The examinations should be conducted at pre-placement, at periodic intervals, when acute exposure occurs, and when a worker leaves their placement. The control program is responsible for identifying which jobs require medical surveillance. It is the examining physician’s responsibility to determine if the worker has an occupational illness due to exposure to the designated substance, whether the worker is fit, fit with limitations, or unfit to continue working with exposure to the substance. The physician also has responsibility to report to the Ministry of Labour should a worker be deemed fit with limitations, or unfit to continue working in exposure to a designated substance. Of note, worker participation in the medical surveillance program is strictly voluntary under the act.

Inorganic lead, a designated substance, is a heavy metal that be found in various industrial processes and settings. The Code for Medical Surveillance details the components of an inorganic lead medical surveillance program. The code dictates that medical examinations should include initial medical, and occupational history, frequency and duration of exposure, and enquiry for signs and symptoms consistent with exposure to inorganic lead including the gastrointestinal, nervous, musculoskeletal, hematologic and renal systems with corresponding physical examinations of these systems.

A blood lead level is the clinical test of choice under the code. The frequency of blood lead level assessment is dependent on the worker’s length of employment, and their last blood lead level. The code further describes blood lead level limits where the workplaces need to review their existing control program, and limits where workers need to be removed from the workplace.

Clinical tests with clearly defined action levels are not included in the code for all designated substances. For instance, for isocyanates, a respiratory and skin sensitizer, the code indicates that “an assessment of a worker’s fitness to continue working in exposure to isocyanates is based on the results of the medical examination in conjunction with results of the clinical tests”.

The interpretation of medical surveillance examination can be further complicated by a worker’s pre-existing medical condition. Therefore, each case requires an individualized assessment with carefully considered recommendations to the workplace and the worker.