Yes. Under the Occupational Health and Safety Regulation if you have 20 or more employees you must have a safety committee. There is no difference noted between full and part time workers and the Prevention Policy does not provide any further clarification. Looking at the WorkSafeBC guidelines they indicate that cyclic workers are to be considered when counting the number of employees at a given location.
Under the Canada Labour Code Part II section 135.1, if there are twenty or more employees in the workplace then a workplace health and safety committee must be established. There is no differentiation between full and part time in the code and regular part time employees could be counted in the number of employees regularly on the work site.