Following the amendment of Appendix 1 of the Quebec Regulation respecting occupational health and safety (RSST, RLRQ, c. S-2.1, r. 13), part of Quebec Occupational Health and Safety Act, which came into effect on March 26, 2020, the TWAEV, STEL and Ceiling values for certain substances are now expressed in ppm. For these substances, the IRSST performed the conversion calculations to express these TWAEV, TWA and Ceiling values in mg/m³, which thus appears in its Sampling Guide for Air Contaminants in the Workplace (Guide d'échantillonnage des contaminants de l'air en milieu de travail ) and the associated Substance Data Sheets. However, it is imperative to refer to the values expressed in the RSST which are legally binding. ×