The BC requirements for respirators are contained in Part 8 of the OHS Regs., specifically (note that fit testing rules are in Sec. 8.40). There’s too much to summarize everything but I’ll be happy to help if you have Qs on any particular aspect:
RESPIRATORS
8.32 When respirator required
8.33 Selection
8.34 Maximum use concentration
Table 8-1: Respirator protection factors
8.35 IDLH or oxygen deficient atmosphere
8.36 Emergency escape respirators
8.37 Respirable air quality
8.38 Corrective eyewear
8.39 Face seal
8.40 Fit tests
8.41 User seal check
8.42 Medical assessment
8.43 Optional use
8.44 Records
8.45 Maintenance and inspections

As for the CSA Standard, if you don’t have access to the actual standard, you can refer to the WorkSafeBC Guidelines on Part 8 which explains the relevant parts of the CSA that apply to a particular rule that you need to know to comply. https://www.worksafebc.com/en/law-policy/occupational-health-safety/searchable-ohs-regulation/ohs-guidelines/guidelines-part-08#SectionNumber:G8.33-1

Hope that helps. Glenn