TDG Training for Safe Hazardous Materials Handling

Dangerous Goods Transportation Hazard Classes

 

Part 2 of the Transportation of Dangerous Goods Regulations defines the different hazard classes and the classification criteria for each. Here is a brief summary of each class.

 

Class 1: Explosives

A substance is considered an explosive under TDG if it falls into one of the following two definitions:

• It is a substance that, through chemical reaction, generates gases at a pressure, temperature and speed sufficient to cause damage to the surrounding area
• It is a substance that has been designed to produce an explosive or pyrotechnic result. These substances have been designed to produce heat, light, smoke, gas or sound, by means of a self-sustaining exothermic chemical reaction, without detonation.

Examples of explosives include dynamite, fireworks and smoke signals.

 

Class 2: Gases

 

The gases class includes gases, their mixtures, objects charged with a gas and aerosols. There are 3 divisions in Class 2:

 

Class 2.1: Flammable gases

These are products that are gaseous at room temperature and pressure and are flammable. A gas is considered flammable if it meets one of the following two conditions:

• Its lower flammability limit is 13% or less
• The difference between its upper flammability limit and its lower flammability limit is at least 12 percentage points

Common examples of flammable gases are propane and natural gas.

 

Class 2.2: Non-flammable, non-toxic gases

 

Non-flammable, non-toxic

These are products that are transported under pressure, at least 280 kPa at 20°C, or that are refrigerated liquids. In both cases, products must not fall into class 2.1 or class 2.3 to be classified as a class 2.2 product.

 

Common examples of non-flammable, non-toxic gases are nitrogen and argon.

 

Oxidizing gas

Class 2.2 may also use another pictogram, if the gas being transported is an oxidizing gas. In this case, the yellow label with the oxidizing symbol must be used instead of the green label of class 2.2.

 

Oxygen is a typical example of an oxidizing gas.

 

Class 2.3: Toxic Gases

Class 2.3 includes gases that meet one of the following two definitions:

 

• The gas is known to be toxic or corrosive to humans
• The gas has an LC50 of less than or equal to 5000 mL/m3

The LC50 is the 50% lethal concentration, i.e. the concentration of the product in the air which, when breathed over a period of 4 hours, causes the death of 50% of the group of animals studied.

 

Ammonia and carbon monoxide are examples of this class of gases.

 

Class 3: Flammable Liquids

Flammable liquids are substances that are liquids at room temperature and have a flash point of 60°C or below. Also included in this class are liquids that have a flash point above 60°C but are transported at a temperature equal to or above their flash point. The flash point is the lowest temperature at which a substance generates enough vapors to form a mixture with air that can ignite. When a product is at a temperature equal to or above its flash point, a single spark or shock can be enough to cause ignition. Examples of flammable liquids include rubbing alcohol and gasoline.

 

Class 4: Flammable Solids, Substances Liable to Spontaneous Combustion, and Water-Reactive Substances

 

Like Class 2, Class 4 contains 3 divisions. Each of them has its own classification criteria.

 

Class 4.1: Flammable Solids

Class 4.1 includes substances that ignite easily, as well as those that are likely to cause a fire by friction. Examples include matches.

 

This class also includes desensitized explosives, if they no longer fulfill the requirements to be classified as explosives, and self-reactive substances.

 

Division 4.2: Substances Liable to Spontaneous Combustion

This class includes pyrophoric substances, i.e. substances that ignite spontaneously on contact with air in 5 minutes or less. Also included are self-heating substances that, in large quantities, ignite spontaneously on contact with air over a long period of time.

 

Examples that fall into this division include activated charcoal and powdered magnesium.

 

Division 4.3: Substances that, in contact with water, emit flammable gases (water-reactive substances)

Substances that are included in this class react with water to form flammable gases.

 

The most common examples are sodium and lithium, both in their metallic state.

 

Class 5: Oxidizing substances and organic peroxides

 

This class includes 2 divisions: class 5.1, oxidizing substances, and class 5.2, organic peroxides.

 

Division 5.1: Oxidizing substances

Oxidizing substances are solid or liquid substances that release oxygen. They are therefore substances that can cause a fire, when brought into contact with combustible materials, or aggravate a fire.

 

Among oxidizing substances, we can think of hydrogen peroxide and chlorine tablets for swimming pools.

 

Class 5.2: Organic Peroxides

Organic peroxides are carbon-based substances that have a peroxide function, or "R-O-O-R'", within their chemical structure. These substances can have several properties that make them very hazardous, such as:

 

• Being susceptible to self-accelerating exothermic decomposition
• Being susceptible to explosive decomposition
• Burning rapidly
• Being sensitive to shock or friction
• Reacting hazardously with other materials
• Causing serious eye damage.

Examples of common organic peroxides are difficult to find, as these substances are generally extremely specialized products. An example would be lauroyl peroxide, which can be used as a bleaching agent.

 

Class 6: Toxic and Infectious Substances

 

Class 6 substances are products that are likely to cause serious harm to the health of humans or animals exposed to them. It includes two divisions: class 6.1, which are toxic materials, and class 6.2, which are infectious materials.

 

Class 6.1: Toxic substances

Class 6.1 includes toxic materials, i.e. materials that can cause death, serious injury, or harm human health if absorbed into the body. There are 3 distinct absorption routes in this class: ingestion, skin absorption, and inhalation. Inhalation is itself separated into different inhalation modes: inhalation of vapors is distinct from inhalation of dust and mists. Note that inhalation of gases is not considered in class 6.1, since toxic gases are defined in class 2.3.

 

For materials that are toxic by ingestion and skin contact, the classification criterion used is the LD50. The LD50, or 50% lethal dose, is the dose that, in a test on a group of animals, causes the death of half of the group. The lower the LD50, the more toxic the product is.

 

To be classified in class 6.1 due to its toxicity by ingestion, a product must have an oral LD50 of 300 mg/kg or less. To be classified in class 6.1 due to its toxicity by skin contact, it must have a skin LD50 less than or equal to 1000 mg/kg.

 

A product can be classified 6.1 for its toxicity by inhalation of dusts or mists if its LC50 for this mode of inhalation is less than or equal to 4 mg/L.

 

For the inhalation of vapors, the situation is more complex, because there are two criteria:

 

• The product must have a LC50 for inhalation of vapors of at most 5000 ppmV
• The product must have a concentration of vapors at saturation in air, at room temperature and pressure, of at least 20% of its LC50.

Examples of substances classified in 6.1 are sodium cyanide, mercury salts and several arsenic compounds.

 

Class 6.2: Infectious substances

This class contains substances that are likely to infect humans or animals. Among the different substances included in this hazard class, we find:

 

• Microorganisms, such as viruses, bacteria or fungi
• Prions
• Toxins
• Biomedical waste

Class 7: Radioactive materials

This product class includes materials that are defined in the regulations on the packaging and transport of nuclear substances.

 

Class 8: Corrosives

This hazard class includes substances that can destroy human skin and substances that can attack metals. This can include acidic substances, basic substances, as well as pH-neutral substances that also have corrosive properties.

It is very important to mention that corrosives are the only class in the TDGR within which products are not always compatible. Since this class includes acids and bases, special attention must be paid to this class to avoid incompatibilities during transport and storage.
To be classified as a corrosive material due to its action on human skin, a product must cause the destruction of intact skin tissue over its entire thickness, within an observation period of 14 days, after an application lasting no more than 4 hours.
To be classified as a corrosive material due to its action on metals, a product must exhibit a corrosion rate on steel or aluminum of at least 6.25 mm per year when tested at 55°C. Corrosive materials include hydrochloric acid, sodium hydroxide, and mercury.

Class 9: Miscellaneous products, materials or organisms

Products that fall into Class 9 are products that do not fall into any other class but may still present a hazard during transport.
Some products are directly mentioned in the regulation as being part of Class 9, such as First Aid Kits.
The regulation also states that materials are classified in Class 9 if they are:

• Lithium batteries or cells that meet certain conditions
• Marine pollutants
• Liquids transported at 100°C or more
• Solids transported at 240°C or more, without tar or binder