Assigning hazard categories
The GHS describes in detail how hazard categories should be assigned for each physical hazard class. A summary of these methods can be found by clicking on the entries below.
- Flammable gases
- Aerosols and chemicals under pressure
- Oxidizing gases
- Gases under pressure
- Flammable liquids
- Water reactive – emits flammable gases
- Oxidizing liquids
- Oxidizing solids
- Organic peroxides
Source: Globally Harmonized System of Classification and Labelling of Chemicals (GHS Rev. 10, 2023)
Back to: Classification of Physical Hazards
Flammable gases [D1-1]
See Chapter 2.2 in the GHS document for guidance and decision logic.
Definitions
A flammable gas is a gas having a flammable range with air at 20 °C and a standard pressure of 101.3 kPa.
A pyrophoric gas is a flammable gas that is liable to ignite spontaneously in air at a temperature of 54 ºC or below.
A chemically unstable gas is a flammable gas that is able to react explosively even in the absence of air or oxygen.
Criteria
Category | Criteria | ||
|---|---|---|---|
1A | Flammable gas | Gases, which at 20 °C and a standard pressure of 101.3 kPa: (a) are ignitable when in a mixture of 13% or less by volume in air; or (b) have a flammable range with air of at least 12 percentage points regardless of the lower flammability limit unless data show they meet the criteria for Category 1B | |
Pyrophoric gas | Flammable gases that ignite spontaneously in air at a temperature of 54 ºC or below | ||
Chemically unstable gas | A | Flammable gases which are chemically unstable at 20°C and a standard pressure of 101.3 kPa | |
B | Flammable gases which are chemically unstable at a temperature greater than 20°C and/or a pressure greater than 101.3 kPa | ||
1B | Flammable gas | Gases which meet the flammability criteria for Category 1A, but which are not pyrophoric, nor chemically unstable, and which have at least either: (a) a lower flammability limit of more than 6% by volume in air; or (b) a fundamental burning velocity of less than 10 cm/s; | |
2 | Flammable gas | Gases, other than those of Category 1A or 1B, which, at 20 °C and a standard pressure of 101.3 kPa, have a flammable range while mixed in air | |
Label elements
Category 1A | Gases categorized as 1A by meeting pyrophoric or unstable gas A/B criteria | Category 1B | Category 2 | |||
|---|---|---|---|---|---|---|
Pyrophoric gas | Chemically unstable gas | |||||
Category A | Category B | |||||
Symbol |
|
|
|
|
| No symbol |
Signal word | Danger | Danger | Danger | Danger | Danger | Warning |
Hazard statement | Extremely flammable gas | Extremely flammable gas. May ignite spontaneously if exposed to air | Extremely flammable gas. May react explosively even in the absence of air | Extremely flammable gas. May react explosively even in the absence of air at elevated pressure and/or temperature | Flammable gas | Flammable gas |
Aerosols and chemicals under pressure [D1-2]
See Chapter 2.3 in the GHS document for classification criteria and decision logic.
Definitions
Aerosols, this means aerosol dispensers, are any non-refillable receptacles made of metal, glass or plastics and containing a gas compressed, liquefied or dissolved under pressure, with or without a liquid, paste or powder, and fitted with a release device allowing the contents to be ejected as solid or liquid particles in suspension in a gas, as a foam, paste or powder or in a liquid state or in a gaseous state.
Criteria
Category | Criteria |
|---|---|
1 | (1) Any aerosol that contains ≥ 85% flammable components (by mass) and has a heat of combustion of ≥ 30 kJ/g; (2) Any aerosol that dispenses a spray that, in the ignition distance test, has an ignition distance of ≥ 75 cm; or (3) Any aerosol that dispenses a foam that, in the foam flammability test, has: (a) a flame height of ≥ 20 cm and a flame duration of ≥ 2 s; or (b) a flame height of ≥ 4 cm and a flame duration of ≥ 7 s.
|
2 | (1) Any aerosol that dispenses a spray that, based on the results of the ignition distance test, does not meet the criteria for Category 1, and which has: (a) a heat of combustion of ≥ 20 kJ/g; (b) a heat of combustion of < 20 kJ/g along with an ignition distance of ≥ 15 cm; or
(c) a heat of combustion of < 20 kJ/g and an ignition distance of < 15 cm along with either, in the enclosed space ignition test: - a time equivalent of ≤ 300 s/m3; or - a deflagration density of ≤ 300 g/m3; or (2) Any aerosol that dispenses a foam that, based on the results of the aerosol foam flammability test, does not meet the criteria for Category 1, and which has a flame height of ≥ 4 cm and a flame duration of ≥ 2 s. |
3 | (1) Any aerosol that contains ≤ 1% flammable components (by mass) and that has a heat of combustion < 20 kJ/g; or (2) Any aerosol that contains > 1% (by mass) flammable components or which has a heat of combustion of ≥ 20 kJ/g but which, based on the results of the ignition distance test, the enclosed space ignition test or the aerosol foam flammability test, does not meet the criteria for Category 1 or Category 2. |
Labels elements
Category 1 | Category 2 | Category 3 | |
|---|---|---|---|
Symbol |
|
| No symbol |
Signal word | Danger | Warning | Warning |
Hazard statement | Extremely flammable aerosol Pressurized container: May burst if heated | Flammable aerosol Pressurized container: May burst if heated | Pressurized container: May burst if heated |
Oxidizing gases [D1-3]
See Chapter 2.4 in the GHS document for classification criteria and decision logic.
Definition
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.
Hazard category
Category | Criteria |
|---|---|
1 | Any gas which may, generally by providing oxygen, cause or contribute to the combustion of other material more than air does. |
Labelling elements
Category 1 | |
|---|---|
Symbol |
|
Signal word | Danger |
Hazard statement | May cause or intensify fire; oxidizer |
Gases under pressure [D1-4]
See Chapter 2.5 in the GHS document for classification criteria and decision logic.
Definition
Gases under pressure are gases which are contained in a receptacle at a pressure of 200 kPa (gauge) or more at 20 °C, or which are liquefied or liquefied and refrigerated.
They comprise compressed gases, liquefied gases, dissolved gases and refrigerated liquefied gases. Gases under pressure are classified, according to their physical state when packaged, in one of four groups in the following table:
Criteria
Group | Criteria |
|---|---|
Compressed gas | A gas which when packaged under pressure is entirely gaseous at -50 °C; including all gases with a critical temperature ≤ -50 °C. |
Liquefied gas | A gas which when packaged under pressure, is partially liquid at temperatures above -50 °C. A distinction is made between: (a) High pressure liquefied gas: a gas with a 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 | A gas which when packaged is made partially liquid because of its low temperature. |
Dissolved gas | A gas which when packaged under pressure is dissolved in a liquid phase solvent. |
Label elements
Compressed gas | Liquefied gas | Refrigerated liquefied gas | Dissolved gas | |
|---|---|---|---|---|
Symbol |
|
|
|
|
Signal word | Warning | Warning | Warning | Warning |
Hazard statement | Contains gas under pressure; may explode if heated | Contains gas under pressure; may explode if heated | Contains refrigerated gas; may cause cryogenic burns or injury | Contains gas under pressure; may explode if heated |
Flammable liquids [D1-5]
See Chapter 2.6 in the GHS document for classification criteria and decision logic.
Definition
A flammable liquid means a liquid having a flash point of not more than 93 °C.
Criteria
Category | Criteria |
|---|---|
1 | Flash point < 23 °C and initial boiling point ≤ 35 °C |
2 | Flash point < 23 °C and initial boiling point > 35 °C |
3 | Flash point ≥ 23 °C and ≤ 60 °C |
4 | Flash point > 60 °C and ≤ 93 °C |
Label elements
Category 1 | Category 2 | Category 3 | Category 4 | |
|---|---|---|---|---|
Symbol |
|
|
| No symbol |
Signal word | Danger | Danger | Warning | Warning |
Hazard statement | Extremely flammable liquid and vapour | Highly flammable liquid and vapour | Flammable liquid and vapour | Combustible liquid |
Substances and mixtures which, in contact with water emit flammable gases [D1-6]
See Chapter 2.12 in the GHS document for classification criteria and decision logic.
Definitions
Substances or mixtures which, in contact with water, emit flammable gases 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.
Criteria
Category | Criteria |
|---|---|
1 | 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. |
2 | 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. |
3 | Any substance or mixture which reacts slowly with water at ambient temperatures such that the maximum rate of evolution of flammable gas is greater than 1 litre per kilogram of substance per hour, and which does not meet the criteria for Categories 1 and 2. |
Label elements
Category 1 | Category 2 | Category 3 | |
|---|---|---|---|
Symbol |
|
|
|
Signal word | Danger | Danger | Warning |
Hazard statement | In contact with water releases flammable gases which may ignite spontaneously | In contact with water releases flammable gases | In contact with water releases flammable gases |
Oxidizing liquids [D1-7]
See Chapter 2.13 in the GHS document for classification criteria and decision logic.
Definitions
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.
Criteria
Category | Criteria |
|---|---|
1 | Any substance or mixture which, in the 1:1 mixture, by mass, of substance (or mixture) and cellulose tested, spontaneously ignites; or the mean pressure rise time of a 1:1 mixture, by mass, of substance and cellulose is less than that of a 1:1 mixture, by mass, of 50% perchloric acid and cellulose; |
2 | Any substance or mixture which, in the 1:1 mixture, by mass, of substance (or mixture) and cellulose tested, exhibits a mean pressure rise time less than or equal to the mean pressure rise time of a 1:1 mixture, by mass, of 40% aqueous sodium chlorate solution and cellulose; and the criteria for Category 1 are not met; |
3 | Any substance or mixture which, in the 1:1 mixture, by mass, of substance (or mixture) and cellulose tested, exhibits a mean pressure rise time less than or equal to the mean pressure rise time of a 1:1 mixture, by mass, of 65% aqueous nitric acid and cellulose; and the criteria for Categories 1 and 2 are not met. |
Label elements
Category 1 | Category 2 | Category 3 | |
|---|---|---|---|
Symbol |
|
|
|
Signal word | Danger | Danger | Warning |
Hazard statement | May cause fire or explosion; strong oxidizer | May intensify fire; oxidizer | May intensify fire; oxidizer |
Oxidizing solids [D1-8]
See Chapter 2.14 in the GHS document for classification criteria and decision logic.
Definition
An oxidizing solid is a solid which, while in itself is not necessarily combustible, may, generally by yielding oxygen, cause, or contribute to, the combustion of other material.
Criteria
Category | Criteria using test O.1 | Criteria using test O.3 |
|---|---|---|
1 | Any substance or mixture which, in the 4:1 or 1:1 sample-to-cellulose ratio (by mass) tested, exhibits a mean burning time less than the mean burning time of a 3:2 mixture, (by mass), of potassium bromate and cellulose. | Any substance or mixture which, in the 4:1 or 1:1 sample-to-cellulose ratio (by mass) tested, exhibits a mean burning rate greater than the mean burning rate of a 3:1 mixture (by mass) of calcium peroxide and cellulose. |
2 | Any substance or mixture which, in the 4:1 or 1:1 sample-to-cellulose ratio (by mass) tested, exhibits a mean burning time equal to or less than the mean burning time of a 2:3 mixture (by mass) of potassium bromate and cellulose and the criteria for Category 1 are not met. | Any substance or mixture which, in the 4:1 or 1:1 sample-to-cellulose ratio (by mass) tested, exhibits a mean burning rate equal to or greater than the mean burning rate of a 1:1 mixture (by mass) of calcium peroxide and cellulose and the criteria for Category 1 are not met. |
3 | Any substance or mixture which, in the 4:1 or 1:1 sample-to-cellulose ratio (by mass) tested, exhibits a mean burning time equal to or less than the mean burning time of a 3:7 mixture (by mass) of potassium bromate and cellulose and the criteria for Categories 1 and 2 are not met. | Any substance or mixture which, in the 4:1 or 1:1 sample-to-cellulose ratio (by mass) tested, exhibits a mean burning rate equal to or greater than the mean burning rate of a 1:2 mixture (by mass) of calcium peroxide and cellulose and the criteria for Categories 1 and 2 are not met. |
Label elements
Category 1 | Category 2 | Category 3 | |
Symbol |
|
|
|
Signal word | Danger | Danger | Warning |
Hazard statement | May cause fire or explosion; strong oxidizer | May intensify fire; oxidizer | May intensify fire; oxidizer |
Organic peroxides [D1-9]
See Chapter 2.15 in the GHS document for classification criteria and decision logic.
Definitions
1. Organic peroxides are liquid or solid organic substances which contain the bivalent -O-O- structure and may be considered derivatives of hydrogen peroxide, where one or both of the hydrogen atoms have been replaced by organic radicals. The term also includes organic peroxide formulations (mixtures). Organic peroxides are thermally unstable substances or mixtures, which may undergo exothermic self-accelerating decomposition. In addition, they may have one or more of the following properties:
- be liable to explosive decomposition;
- burn rapidly;
- be sensitive to impact or friction;
- react dangerously with other substances.
2. An organic peroxide is regarded as possessing explosive properties when in laboratory testing the formulation is liable to detonate, to deflagrate rapidly or to show a violent effect when heated under confinement.
Criteria
See chapter 2.15.2 in the guidance document.
Label elements
Type A | Type B | Type C and D | Type E and F | Type G a | |
|---|---|---|---|---|---|
Symbol |
|
|
|
| There are no label elements allocated to this hazard category. |
Signal word | Danger | Danger | Danger | Warning | |
Hazard statement | Heating may cause an explosion | Heating may cause a fire or explosion | Heating may cause a fire | Heating may cause a fire |
