CLASS 2 ~ Gases

2.1 FLAMMABLE GASES	2.2  NON-FLAMMABLE and  NON-TOXIC GASES
2.3 TOXIC GASES *	OXIDIZING GASES
*US SHIPPERS NOTE:   Five new placards meet HM-181. These may now be used for all domestic and international shipments.   They became mandatory on Oct.1,1994. US-Canada transborder shipments however, must meet Transport Canada TDG Regulations. Call for additional information.

Class 2 - Gases

2.13 General

Substances are included in Class 2, Gases, if they are

(a) compressed gases;

(b) liquefied gases;

(c) gases in solution;

(d) refrigerated liquefied gases;

(e) mixtures of gases;

(f) mixtures of one or more gases with one or more vapours of substances included in other classes;

(g) articles charged with a gas;

(h) tellurium hexafluoride; and

(i) aerosols.

2.14 Divisions

Class 2, Gases, has three divisions:

(a) Class 2.1, Flammable Gases, which consists of gases that, at 20°C and an absolute pressure of 101.3 kPa,

(i) are ignitable when in a mixture of 13 per cent or less by volume with air, or

(ii) have a flammability range with air of at least 12 percentage points determined in accordance with tests or calculations in ISO 10156;

(b) Class 2.2, Non-flammable and Non-toxic Gases, which consists of gases that are transported at an absolute pressure not less than 280 kPa at 20°C, or as refrigerated liquids, and that

(i) are asphyxiants,

(ii) are oxidizing substances, or

Asphyxiants dilute or replace the oxygen normally in the atmosphere. Oxidizing substances cause or contribute to the combustion of other material more than air does, as determined in accordance with ISO 10156.

(iii) are not included in Class 2.1, Flammable Gases, or Class 2.3, Toxic Gases; and

(c) Class 2.3, Toxic Gases, which consists of gases that

(i) are known to be toxic or corrosive to humans according to 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 convention used in these Regulations is to express concentrations of gas or vapour as mL/m³ and to express concentration of dust or mist as mg/L. Note that the dust particles or mist droplets can be concentrated in particles or droplets of 10 microns.

2.15 Packing Groups

There are no packing groups for Class 2, Gases.

2.16 Determination of LC₅₀

LC₅₀ values for a single or pure gas or for a mixture of gases must be determined

(a) by using LC₅₀ values published in technical journals or in government publications;

(b) in accordance with paragraphs 2.2.3(b) and (c) of Chapter 2.2 of the UN Recommendations; or

(c) for a mixture of gases, in accordance with section 2.17.

2.17 Determination of LC₅₀ for a Mixture of Gases

This section provides an acceptable approximation of the LC₅₀, of a mixture of gases. The methods in paragraphs 2.16(a) and (b) are more exact.

To determine the LC₅₀ of a mixture of gases when the LC₅₀ of each of the gases is known, use 5 000 mL/m³ as the toxic limit and, if the mixture contains

(a) only one gas with an LC₅₀ less than or equal to the toxic limit (called Gas A), use the following calculation:

(b) more than one gas with an LC₅₀ less than or equal to the toxic limit (called Gas A, Gas B,…),

(i) determine the contributing number (CN) of each of the gases with an LC₅₀ less than or equal to the toxic limit using

(ii) combine the contributing numbers (CN) of each gas with an LC₅₀ less than or equal to the toxic limit using

(iii) obtain the LC₅₀ of the mixture by dividing 1 by the number T (LC₅₀ of the mixture = 1 /T).