Each year, the American Conference of Governmental Industrial Hygienists (“ACGIH”) publishes a list of substances for which they have set new or revised Threshold Limit Values (“TLVs”). A TLV is an exposure limit that is the suggested maximum allowed airborne concentration for a particular substance where nearly all workers are believed to experience no adverse health effects over a working lifetime. TLVs may be an 8-hour time weighted average, short-term exposure limit or ceiling limit.

Prior to the adoption of the new or revised ACGIH TLVs that are published each year as BC occupational exposure limits (“OELs”), WorkSafeBC reviews and stakeholders are consulted on potential implementation issues. WorkSafeBC’s Board of Directors (“BOD”) then decides which of the new or revised ACGIH TLVs are to be adopted as BC OELs. The existing OELs for these substances continue to be in effect until the BOD makes the decision to adopt the ACGIH TLVs as BC OELs.

In order to retain the existing BC OELs, the substances are added to the Table of Occupational Exposure Limits for Excluded Substances in Prevention Policy R5.48-1. Once the BOD approves the adoption of the ACGIH TLVs as BC OELs, the substances are removed from the Table of Occupational Exposure Limits for Excluded Substances, and the ACGIH TLVs then apply.

The ACGIH has published the 2013 new or revised TLVs. The following substances, for which there are new or revised ACGIH TLVs, have been added to the Table of Occupational Exposure Limits for Excluded Substances in Prevention Policy R5.48-1 on May 1, 2013. The current BC OELs are maintained until such time as the BOD makes a decision on the adoption of the ACGIH TLVs.

• Aliphatic hydrocarbon gases, Alkanes [C₁ — C₄]
• Clopidol
• Diethylene glycol monobutyl ether
• N,N-Diethylhydroxylamine
• Ethyl tert-butyl ether
• Manganese, elemental and inorganic compounds, as Mn
• Methyl isoamyl ketone
• Tributyl phosphate

The other substances for which the ACGIH has revised the TLVs are already listed in the Table of Occupational Exposure Limits for Excluded Substances and the current BC OELs are also maintained. These substances are as follows:

• n-Butane
• 2,4-D (2,4-Dichlorophenoxyacetic acid and its esters)
• Glycerin mist
• 1-Methoxy-2-propanol