Substance-Specific Issues

Bromine / Chlorine; classification with respect to oxidizing properties

Substances:

Bromine; CAS No. 7726-95-6
Chlorine; CAS No. 7782-50-5

Issue:

Do bromine and/or chlorine fall within the criteria for Class C - Oxidizing Material set out in section 42 of the [WHMIS] Controlled Products Regulations?

Background:

Although the criteria for oxidizing material in the Controlled Products Regulations, (CPR) were identical to that in the Transportation of Dangerous Goods Regulations, (TDGR), several substances, such as chlorine and bromine have, at various points, been assigned a subsidiary classification of 5.1 in List II of Schedule II to the TDGR, i.e., oxidizing substances, even though they do not meet the TDGR criteria. These TDG classifications resulted from the incorporation of specific recommendations on specific substances as published in various editions of "Recommendations on the Transport of Dangerous Goods, United Nations, New York".

Common substances which can cause or contribute to the combustion of another material by yielding oxygen or another oxidizing substance include chlorates, perchlorates, chromates, dichromates, permanganates as well as some inorganic peroxides. Benzoyl peroxide (a di-substituted peroxide) and mono-alkyl peroxides (mono-substituted) are common organic peroxides that contain the bivalent 0-0 structure and thereby meet the second criterion specified in section 42 of the CPR.

With the exception of the inert gases, relative to the Standard Hydrogen Electrode, all elements could be classified as either "oxidizing" or "reducing" agents. This is not the intent of the criteria specified in the CPR.

Considerations:

Under the new TDGR (subsection 2.23), which come into effect in August 2002, the criteria for inclusion in "Class 5, Oxidizing Substances and Organic Peroxides", is as follows:

Class 5, Oxidizing Substances and Organic Peroxides

2.23 General

Substances are included in Class 5 "if they are oxidizing substances or organic peroxides and meet the criteria for inclusion in one of the divisions of Class 5.

2.24 Divisions

Class 5 has two divisions:

(a) Class 5.1, Oxidizing Substances, which consists of substances that yield oxygen thereby causing or contributing to the combustion of other material, as determined in accordance with section 2.5.2 of Chapter 2.5 of the UN Recommendations; and

(b) Class 5.2, Organic Peroxides, which consists of substances that ....

Under the revised TDGR, bromine will have a primary class of 8 and a subsidiary class of 6.1, while chlorine will have a primary class of 2.3 and a subsidiary class of 8; i.e., neither bromine nor chlorine are included in TDG Class 5.1, "Oxidizing Substances".

The criteria agreed to for the Globally Harmonized System (GHS) is as follows:

"An oxidizing liquid is a liquid which, while in itself not necessarily combustible, may, generally by yielding oxygen, cause, or contribute to, the combustion of other material."

"An oxidizing gas is any gas which may, generally by providing oxygen, cause or contribute to the combustion of other material more than air does."

It is not anticipated that this issue will be revisited; i.e., the GHS criteria for oxidizing substances will not encompass bromine nor chlorine.

Conclusion:

Although bromine and chlorine are relatively strong oxidizing agents in terms of electron-transfer capabilities, i.e., reduction potential (E^o values), as neither yield oxygen nor any other oxidizing substance nor are they organic peroxides which contain the bivalent 0-0 structure, they are not included in WHMIS Class C. The hazard symbol corresponding to WHMIS Class C need not be depicted on the supplier label.

Note: Although the classification criteria specified in sections 34-66 of the CPR may provide a useful guideline for certain MSDS and label information, it is section 12 and Schedule I to the CPR which set out what information must be disclosed on a MSDS and section 19 what information must be disclosed on the label.

References:

Health Canada; Reference Manual for the WHMIS Requirements of the Hazardous Products Act and Controlled Products Regulations; (see section 42 of the CPR).

Globally Harmonized System for the Classification and Labelling of Chemicals (GHS), Draft Integrated Proposal; http://www.ilo.org/public/english/protection/safework/ghs/ghsfinal/index.htm

Transportation of Dangerous Goods Regulations as published in the Canada Gazette Part II, SOR 2001-286, supplement to volume 135, August 15, 2001; (in force as of August 15, 2002).