Substance-Specific Issues

Ammonia; classification with respect to acute toxicity

Substance:

Ammonia, (anhydrous), gas; CAS # 7664-41-7; UN1005

Issue:

What is the consequence of anhydrous ammonia no longer being included in Division 4 of TDG Class 2 with respect to the exemption provided in subsection 43(4) of the Controlled Products Regulations (CPR) from inclusion in Division 1 or Division 2 of WHMIS Class D?

Background:

During the development of WHMIS, it had been agreed that a gas which falls in TDG Class 2, Division 4 shall not also be classified as a Very Toxic Material or a Toxic Material in WHMIS as such materials would already be classified as a WHMIS corrosive material ¹. Thus, by virtue of subsection 43(4) of the CPR, Class D of the WHMIS criteria specifically excludes those gases in Division 4 of Class 2 in the Transportation of Dangerous Goods Regulations (TDGR).

With the exception of (i) ammonia, anhydrous, liquefied or anhydrous ammonia or ammonia solutions, relative density (specific gravity) less than 0.880 at 15°C in water, with more than 50% ammonia, UN 1005 and (ii) ammonia solutions, relative density (specific gravity) less than 0.880 at 15°C in water, with more than 35% but not more than 50% ammonia, UN 2073, a subsequent amendment to the TDGR ², moved all of the substances originally included in Division 4 to other Divisions in TDG Class 2. The exemption from inclusion in WHMIS Class D, therefore, continued to apply to liquified ammonia only as this was the only gas remaining in Division 4 of TDG Class 2 after that amendment to the TDGR came into effect on October 1, 1994. However, through administrative policy, it was decided that, in order to respect the original consensus agreement, when the CPR are amended, the applicable subsections, 43(4), will be revised to refer to the substances by name which were included in Division 4 of TDG Class 2 as of October 31, 1988, i.e., when the CPR came into effect.

The "Clear Language"version of the TDGR ³, in effect as of August 15, 2002, no longer includes a Division 4 in Class 2 and also signifies a change in TDG classification for ammonia from 2.4 Corrosive Gas to Class 2.2(8) Non-Toxic/Non Flammable Compressed Gas, Sub Class Corrosive.

As per the policy agreement following the previous TDG amendment, when the CPR are next amended, the applicable subsection, 43(4) and paragraph 65(d), will be revised to refer to the substances by name which were included in Division 4 of TDG Class 2 as of October 31, 1988, when the CPR came into effect; i.e., in addition to ammonia, boron trichloride, chlorine, hydrogen bromide (anhydrous), hydrogen chloride (anhydrous), hydrogen chloride (refrigerated liquid), hydrogen fluoride (anhydrous), hydrogen iodide (anhydrous), nitrosyl chloride and trifluoroacetyl chloride.

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.

Considerations:

An LC₅₀ (mouse) of 2115 ppm, 4-hour exposure, (cited as 4230 ppm, 1-hour exposure) has been reported ⁴. However, the observed "toxicity"has been largely attributed to its corrosivity and ammonia has not been included in TDG Class 2.3, Toxic Gases, which consists of gases that:

(i) are known to be toxic or corrosive to human according to
CGA P-20, ISO Standard 10298 or other documentary
evidence published in technical journals or government publications, or  

(ii) have an LC₅₀ value less than or equal to 5 000 mL/m³.

The gases which were included in TDG 2.4 can have a lethal effect because of the extreme corrosive effect on the tissue of the respiratory tract. Such products will be included in WHMIS Class A -Compressed Gas and, by virtue of paragraph 65(d) of the CPR, these substances are also included in WHMIS Class E, Corrosive Material.

Conclusion:

Labels must continue to display the WHMIS Class E symbol but need not depict the skull and cross bones nor "toxic T" symbol. The exemption from depicting a WHMIS Class D symbol does not preclude the legal obligation to communicate that ammonia is a CORROSIVE GAS and can be fatal if inhaled in addition to disclosing other relevant health and safety information on the label / MSDS.

Note:  The exemption from depicting a WHMIS Class D symbol does not preclude the option of depicting a Class D symbol particularly given that the WHMIS Class E symbol is not normally associated with an adverse health effect through inhalation.

References:

1. Final Report of the WHMIS Steering Committee, April 1985, p.67
   
   
2. SOR/93-525, Canada Gazette Part II, December 15, 1993, p. 4056
   
   
3. SOR/2001-286, Canada Gazette Part II, Supplement to Vol 135, August 15, 2001
   
   
4. Kapeghian, J.C., et al. Acute inhalation toxicity of ammonia in mice. Bulletin of Environmental Contamination Toxicology. Vol. 29, no. 3 (1982). p.371-378