The three basic hazard groups within the GHS classification system are:
Each of them is divided into classes and categories – called a building block. In this blog there are briefly presented the 16 physical hazard classes and their categories for classifying chemicals according to the hazards they demonstrate:
Explosives substances and mixtures and articles are divided into 6 divisions based on the type of hazard:
1.1 Mass explosion hazard
1.2 Projection hazard
1.3 Fire hazard and minor blast and /or projection hazard
1.4 No significant hazard in case of ignition/initiation
1.5 Insensitive substances/mixtures with mass explosion hazard
1.6 Extremely insensitive substances/mixtures with no mass explosion hazard.
- Flammable gases
A flammable gas is a gas having a flammable range with air at 20 °C and a standard pressure of 101.3 kPa. It is classified according to its flammability data in:
• Category 1: Extremely flammable gas
• Category 2: Flammable gas
A chemically unstable gas is a flammable gas that is able to react explosively even in the absence of air or oxygen. It is classified according to its chemical instability data in:
- Category A: Flammable gases which are chemically unstable at 20°C and a standard pressure of 101.3 kPa
- Category B: Flammable gases which are chemically unstable at a temperature greater than 20°C and/or a pressure greater than 101.3 kPa
Aerosols are classified in one of the three categories for this Class based on:
– their flammable components (liquid, solid or gases classified as flammable according to the GHS).
– their chemical heat of combustion
– the results of the tests:
- Category 1: Extremely flammable aerosol
- Category 2: Flammable aerosol
- Category 3: Non-flammable aerosol
- Oxidizing gases.
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.
- Gases under pressure
Gases under pressure are gases contained in a receptacle at a pressure of 200 kPa (gauge) or more, or which are liquefied or liquefied and refrigerated.
Compressed gas A gas entirely gaseous at -50 °C; (includes all gases with a critical temperature ≤ -50 °C).
Liquefied gas: Partially liquid at temperatures above -50 °C.
(a) High pressure liquefied gas: critical temperature between –50 °C and +65 °C; and
(b) Low pressure liquefied gas: a gas with a critical temperature above +65 °C.
Refrigerated liquefied gas: Partially liquid because of its low temperature.
Dissolved gas: Dissolved in a liquid phase solvent.
- Flammable liquids
Flammable liquids are liquids having a flash point of not more than 93 °C. They are classified in 4 categories:
Category 1: Extremely flammable liquid and vapour
– Flash point < 23 °C and initial boiling point ≤ 35 °C
Category 2: Highly flammable liquid and vapour
– Flash point < 23 °C and initial boiling point > 35 °C
Category 3: Flammable liquid and vapour
– Flash point ≥ 23 °C and ≤ 60 °C
Category 4: Combustible liquid
– Flash point > 60 °C and ≤ 93 °C
- Flammable solids
Flammable solids are solids which are readily combustible, or may cause or contribute to fire through friction.
Flammable solids are classified in 2 categories for this class based on the results of the burning rate test.
- Self-reactive substances and mixtures.
Self-reactive substances and mixtures are thermally unstable liquid or solid substances or mixtures liable to undergo a strongly exothermic decomposition even without participation of oxygen (air).
There are 7 categories for this class (“types A to G”) according to the results of Test Series A to H described in Part II of the UN Manual of Tests and Criteria:
– Test series A: determine if there is propagation of detonation
– Test series B: determine if there is detonation in the package
– Test series C: determine if there is propagation of deflagration
– Test series D: determine if there is rapid deflagration in the package
– Test series E: determine the effect of heating under confinement
– Test series F: determine the explosive power
– Test series G: determine if there is thermal explosion in the package
– Test series H: determine the self-accelerating decomposition temp.
- Pyrophoric liquids
Pyrophoric liquids are liquids which, even in small quantities, are liable to ignite within five minutes after coming into contact with air. Pyrophoric liquids are classified in only one Category.
- Pyrophoric solids
Pyrophoric solids are solids which, even in small quantities, are liable to ignite within five minutes after coming into contact with air. Pyrophoric solids are classified in only one Category.
- Self-heating substances and mixtures.
A self-heating substance or mixture is a solid or liquid substance or mixture, other than a pyrophoric liquid or solid, which, by reaction with air and without energy supply, is liable to self-heat. They will ignite only when in large amounts (kg) and after long periods of time (hours or days). There are 2 categories for this class based on the ability of the substance or mixture to undergo oxidative self-heating by exposure of it to air at temperatures of 100 °C, 120 °C or 140 °C in a 25 mm or 100 mm wire mesh cube.
- Substances and mixtures which, in contact with water, emit flammable gases
They are solid or liquid substances or mixtures which, by interaction with water, are liable to become spontaneously flammable or to give off flammable gases in dangerous quantities. They are classified in 3 categories:
Any substance or mixture which reacts vigorously with water at ambient temperatures and demonstrates generally a tendency for the gas produced to ignite spontaneously, or which reacts readily with water at ambient temperatures such that the rate of evolution of flammable gas is equal to or greater than 10 litres per kilogram of substance over any one minute.
Any substance or mixture which reacts readily with water at ambient temperatures such that the maximum rate of evolution of flammable gas is equal to or greater than 20 litres per kilogram of substance per hour, and which does not meet the criteria for Category 1.
Any substance or mixture which reacts slowly with water at ambient temperatures such that the maximum rate of evolution of flammable gas is equal to or greater than 1 litre per kilogram of substance per hour, and which does not meet the criteria for Categories 1 and 2.
- Oxidizing liquids
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.
Classification is made in three categories and in accordance with:
a)Whether the mixture substance/cellulose spontaneously ignites; and
b)The comparison of the mean time taken for the pressure to rise from 690 kPa to 2070 kPa (gauge), with those of the reference substances.
- Oxidizing solids
An oxidizing solid is a solid which, while it is not necessarily combustible, may, generally by yielding oxygen, cause, or contribute to, the combustion of other material. They are classified in three categories based on:
(a) Whether the mixture substance/cellulose ignites and burns; and
(b) the comparison of the mean burning time with those of the reference mixtures.
- Organic peroxides
Organic peroxides are liquid or solid organic substances which contain the bivalent -0-0- structure and may be considered derivatives of hydrogen peroxide, where one or both of the hydrogen atoms have been replaced by organic radicals.
There are 7 categories for this class (“types A to G”).
- Corrosive to metals
Substance or a mixture, which by chemical action will materially damage, or even destroy, metals. Substances/mixtures corrosive to metals are classified in a unique category.