IRSST - Institut de recherche Robert-Sauvé en santé et en sécurité du travail

Mixie: Mixtures of substances in the workplace: computer-based tool for evaluating the chemical risk (Calculation of the Rm)

Exposure to mixtures of chemical substances in the workplace raises many questions. ROHS recommendations (1), other regulatory agencies (2, 3, 4) or organisations, such as INRS and ACGIH® (5, 6), prescribe or indicate to take into account the combined potential impact of substances with similar effects on the same body organs or systems rather than that of either individual compound in the mixture. In this case, their contribution to the overall toxicity should be considered additive... unless it is established otherwise. The last portion of this statement implies that any possible interactions (infra and supra additive) between of substances in a mixture should also be examined.
The miXie computer tool integrates the results of a research project on toxicological interactions initially made in the early 2000s by researchers at the University of Montreal in collaboration with IRSST scientists.


  • This utility is a decision support at the disposal of occupational health professionals. It informs them about the additivity or interaction potential between chemical substances in a mixture found in the workplace. It cannot replace the informed judgement of an occupational health professional.
    Adolf Vyskocil et Daniel Drolet

IMPORTANT: Application of the Regulation Respecting Occupational Health and Safety (ROHS) in Quebec

Contrary to the utility for the adjustment of PEVs of the ROHS in relation to unusual work schedules, the use of this utility is not mandatory for applying the ROHS.

Part 3 of Schedule 1 of the ROHS mentions that ... «Where two or more substances… are present at the work location and where they have similar effects on the same organs of the human body, the effects of these substances are considered to be additive, unless it is established otherwise.» Thus, the sum of the fractions of the mixture, called "Rm" shall be calculated from the individual exposures concentrations of substances and their TWAEV (Time-Weighted Average Exposure Value) or AAEV (Adjusted Average Exposure Value).

This provision applies only for TWAEV and AAEV and not for short-term exposure values (STEV) or ceiling values (CV).


  1. Regulation Respecting Occupational Safety and Health. S-2.1, r.13.  Éditeur officiel du Québec (update to December 2014). Web link
  2. Regulations (Standards - 29 CFR) - Table of Contents
  3. EH40/2005 Workplace exposure limits, HSE,
  4. Guidance on the Interpretation of Workplace Exposure Standards for Airborne Contaminants. Safe Work Australia,
  5. Bruno Courtois and Stéphane Gadou, Valeurs limites d'exposition professionnelle aux agents chimiques en France, ED 984, Aide-mémoire technique, INRS, July 2012,
  6. American Conference of Governmental Industrial Hygienists (ACGIH®). 2014 TLVs® and BEIs®. ACGIH®, Cincinnati, Ohio, 254 p.

Additional Information

  • Daniel Drolet
  • François Lemay
Research Project: 0099-0730, 0099-8930
Publication no.: UT-001
Version: v. 2014
Language: French, english
Online since: January 01, 2005
Format: Application / Website