If you primarily manage or supervise work at a site, you are a supervisor. This is also applicable even if you take part in practical work as well.
As a supervisor, you are obliged to assist in ensuring that working conditions are entirely correct in terms of health and safety. You are also obliged to attempt to prevent hazards which may occur in the event of errors or shortcomings.
You must immediately notify your employer of any working environment problems if it is not possible to resolve them immediately.