Related Rule
Australia
Practice Relating to Rule 75. Riot Control Agents
Australia’s Commanders’ Guide (1994) repeats the prohibition of the 1993 Chemical Weapons Convention, specifying that the use of riot control agents “by [Australian Defence Force] members in peacetime requires approval at the highest level of command. Where such approval is given, strict rules of engagement are likely to prescribe the specific situations in which they may be employed.” 
Australia, Law of Armed Conflict, Commanders’ Guide, Australian Defence Force Publication, Operations Series, ADFP 37 Supplement 1 – Interim Edition, 7 March 1994, § 312.
Australia’s Defence Force Manual (1994) states:
Riot control agents, including tear gas and other gases which have debilitating but non-permanent effects as a means of warfare, is prohibited in armed conflict under the 1993 Chemical Weapons Convention. This does not mean riot control agents cannot be used in times of conflict (e.g. against rioting prisoners of war). Legal advice should be sought on the occasions when their use is considered. 
Australia, Manual on Law of Armed Conflict, Australian Defence Force Publication, Operations Series, ADFP 37 – Interim Edition, 1994, § 413.
Australia’s LOAC Manual (2006) states in its chapter on “Weapons”:
The use of riot control agents, including tear gas and other gases which have debilitating but non-permanent effects as a means of warfare is prohibited under the CWC [1993 Chemical Weapons Convention]. This does not mean riot control agents cannot be used in times of conflict to maintain order, for example, in a prisoner of war camp, or to contain a riot by the civilian population. Legal advice should be sought on the occasions when their use is considered. 
Australia, The Manual of the Law of Armed Conflict, Australian Defence Doctrine Publication 06.4, Australian Defence Headquarters, 11 May 2006, § 4.19.
The LOAC Manual (2006) replaces both the Defence Force Manual (1994) and the Commanders’ Guide (1994).
Australia’s Chemical Weapons (Prohibition) Act (1994) provides: “A person must not intentionally or recklessly: … use riot control agents as a method of warfare. Penalty: imprisonment for life.” It adds, however, that use for “law enforcement including domestic riot control purposes” is not prohibited. 
Australia, Chemical Weapons (Prohibition) Act, 1994, p. 13, Section 12(f) and p. 95, Section 9(d).
In 1969, during a debate in the UN General Assembly on the question of chemical and bacteriological (biological) weapons, Australia stated:
The draft resolution [on chemical and bacteriological (biological) weapons under discussion] would declare as contrary to the [1925 Geneva Gas Protocol] “any chemical agent of warfare” with “direct toxic effects on man, animals and plants”. It is the view of the Australian Government that the use of non-lethal substances such as riot control agents … and defoliants does not contravene the Geneva Protocol nor customary international law. 
Australia, Statement before the First Committee of the UN General Assembly, UN Doc. A/C.1/PV.1716, 9 December 1969, § 180.
In response to a question without notice in the Australian Senate on 5 October 1989 relating to tear gas agents, the Minister for Community Services and Health stated:
It is now generally accepted internationally, however, that riot control agents are not chemical weapons. The Australian Government’s view is that widespread availability and use of these agents and their relative lack of toxicity and persistence makes it impossible to include these agents within the scope of a convention which is to attract widespread adherence and is to be effectively verifiable. 
Australia, Senate, Minister for Community Services and Health, Question Without Notice: Chemical Agents, Hansard, 5 October 1989.
The Report on the Practice of Australia refers to a document of 1971 entitled “Protection of the Civil Population Against the Effects of Certain Weapons”, which states:
In answer to a question in the House of Representatives, the Australian Minister for External Affairs … stated that the use of non-lethal tear gases, C.N., C.S., and C.N.D.M., as used in South Vietnam “would not be contrary to any international convention, nor would it contravene the [1925 Geneva Gas Protocol]” …
Neither lethal nor non-lethal gases are employed at present in any part of [the Australian Military Forces], including [the Pacific Islands Regime]. No soldiers are trained in use of weapons involving the use of either such type of gas. In [Papua New Guinea] the civil constabulary are trained in the use of and have available non-lethal gas weapons. 
Australia, Protection of the Civil Population Against the Effects of Certain Weapons (unknown author), Doc. AA-A1838/267, File No. AA-889/702/7/2 Pt 1, May 1971, Report on the Practice of Australia, 1998, Chapter 3.5.
In this connection, the report states:
As a state party to the [Chemical Weapons Convention], Australia is obligated not to use riot control agents as a weapon of war. The [Chemical Weapons Convention] does, however, explicitly allow the use of such agents for riots and quelling civil disturbances. 
Report on the Practice of Australia, 1998, Chapter 3.5.