Some hazards and their controls will be specifically outlined in legislation. In all cases, the employer has a duty of due diligence and is responsible for 'taking all reasonable precautions, under the particular circumstances, to prevent injuries or accidents in the workplace.
In situations where there is no clear way to control a hazard, or if legislation does not impose a limit or guideline, you should seek guidance from occupational health professionals, such as an occupational hygienist or safety professional, about what the standard practice or best practice is when working in that situation.