Guide to chemical hazard classification: Part 1, substances

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You must check local legislation to be confident of correct classification and labelling, and prevent costly delays, fines or product withdrawal

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Contents: Legislation: CLP and the GHS; How to classify substances; Classification inventories; EU classification lists harmonised classificationsREACH Registration dossiersClassification and labelling inventory; Classification for the purposes of the SDS; References

You must classify chemical substances and mixtures before they are placed on the market. This guide tells you how the classification processes work. Substance classification is usually achieved through testing, although structure–activity relationships may also help. There are also inventories of hazard classification, that simplify substance classification.

A later post will cover mixture classification.

Legislation: CLP and the GHS

Chemical classification is a shorthand description of the hazards of a product, and the cornerstone of chemical hazard communication in the supply chain, as expressed in safety data sheets and on labels.

A compendium of chemical hazards, some not covered by the CLP, is given here. We also have a useful glossary of technical terms used in this article.

The Classification, Labelling and Packaging (CLP) Regulation [1] specifies the criteria for the classification of hazardous properties of chemical products in the EU.

The CLP Regulation is based on the United Nation’s (UN) Globally Harmonized System of Classification and Labelling of Chemicals (GHS) [2]. Versions of the GHS are implemented in all industrialized nations, and provides an ‘off-the-peg’ chemical control policy for developing countries.

the GHS ensures a much greater harmonization of classification and labelling between trade areas, allowing consistent use of pictograms and warnings, with a consequent reduction in trade barriers

One might assume that all countries would fully adopt the GHS, so eliminating differences in chemical classification throughout the world. However, there are important reasons why this ideal situation is not realised.

The GHS criteria are recommendations, and do not act directly in any country. Each country, or trade area (eg the EU), may bring in the GHS as they see fit. Thus, the EU Commission, in 2008, adopted those parts (‘building blocks’) of the GHS that most closely resembled the existing classification system at that time (the Dangerous Substance Directive [3] and the Dangerous Products Directive [4]).

The GHS contains some deliberate variations in criteria for classification, such as the threshold concentration in mixtures causing classification of the product. A striking example is the case of a product containing an ingredient with a classification as Reproductive Toxicity, Category 2, where the threshold concentration causing the product to be classified is either 0.1 or 3%; both options are given in the GHS.

Furthermore, the GHS is not static. New versions of the GHS are published biennially, in odd-numbered years, to incorporate the latest changes agreed at international level. The EU CLP Regulation, and equivalent legislation in other trade areas, lag behind the current version of the GHS. The CLP Regulation is based on the GHS Revision 7. The US Hazcom Standard 2012 [5] is based on GHS Revision 3.

Consequently, you must check local legislation to be confident of correct classification and labelling, and prevent costly delays, fines or product withdrawal. Do not assume GHS implementation in a country means that classification and labelling are predictable.

Nevertheless, the GHS ensures a much greater harmonization of classification and labelling between trade areas, allowing consistent use of pictograms and warnings, with a consequent reduction in trade barriers, and an increase in safety.

Also, the UN GHS and EU CLP classification criteria are similar to the UN Model Regulations criteria for classification for transport of dangerous goods [6], so that there is more harmonization between supply classification and transport classification.

Brexit has complicated the picture. Great Britain has separate legislation to the EU and Northern Ireland (which retains the EU system). The GB legislation [7] is currently very closely aligned with the EU, as all EU legislation was transposed into UK legislation up to 31 December 2020. The UK government has pledged to take account of changes in EU legislation, but new transpositions into UK law will be delayed, and divergence over time looks likely.

How to classify substances

Classification is the categorization of chemical hazard (see our Compendium of chemical hazards) into easily identifiable, standard descriptions, such as flammable, toxic, irritating, or hazardous to the aquatic environment.

The details of the criteria and definitions, and references to test methods, are given Annex I of the CLP Regulation as follows:

  • Part 2: Physical hazards
  • Part 3: Health hazards
  • Part 4: Environmental hazards
  • Part 5: Supplemental EU hazards

The process is presented in Scheme 1. The GHS and CLP Regulation break chemical hazard into a number of Hazard Classes; 29 in total. Not all chemicals hazards are covered, for example dust explosivity and ecological hazards to the terrestrial environment, so that a substance that is ‘not classified’ may still pose a risk.

For each Hazard Class, with its Category subdivisions, there is a definition, which is linked with the test method to give a set of criteria, as illustrated in Scheme 1.

Image describes the process for the hazard classification of chemical substances.
Scheme 1: Process for substance classification

When a substance is tested according to the prescribed test method, the data from the test are compared with the criteria for the respective Hazard Class and Categories. If the criteria are fulfilled, then the substance is classified in that Hazard Class.

To ensure complete classification, the substance should be subject to the test methods for all Hazard Classes, or the result of the test should be predictable without the need for testing.

Ideally, the specific test method has been used so that the results are easily compared with the classification criteria. When other methods have been used to determine results, the assessor must use expert judgement to determine if the method is suitable and the results reliable

Usually, some test data is missing, or not generated from the specified test method. Then, other data and some judgement is required to complete classification. Calculation or structure–activity relationships can be used but even more care is required to assess the validity of conclusions.

The classification comprises the hazard classes, their subdivisions (usually called Categories, but also called Types or Divisions), and the associated hazard statements.

In the EU CLP, but not the GHS, a short, coded description of the classes and categories may be used. This is useful for the regulatory professional, but can be confusing for others. Thus a classification of: ‘Flammable Liquid, Category 2, Highly flammable liquid and vapour’ and ‘Acute Toxicity: Oral, Category 4, Harmful if swallowed‘ can be shortened to: ‘Flam Liq 2, H225; Acute Tox 4, H302.’

The labelling is sometimes confused with the classification. The labelling is what appears on the packaging. It uses the hazard statements from the classification, but with additional elements of the pictogram (symbol), signal word, and precautionary statements.

Detailed information on labelling is given in our Guide to labelling of chemical products.

There are cases where the classification does not lead to the expected labelling, eg when the product as presented cannot exert a particular hazard.

Classification inventories

If you compare classification inventories, it is clear that national authorities interpret the classification criteria differently, even though they are based on the same text from the GHS.

To simplify the classification process, some countries have produced lists of hazard classifications for substances, based on a review of the available data. The EU resources are best, because they are based on a recent compilation of available information and new testing under REACH. These resources are described in detail below.

The UK is playing catch up with the EU. They transposed EU harmonised classifications, valid on 31 December 2020, into UK law. Recent EU classifications are being considered. But the UK do not have access to the background REACH data available to the EU authorities.

If you compare classification inventories, it is clear that national authorities interpret the classification criteria differently, even though they are based on the same text from the GHS. National authorities arrive at different classifications for the same substances, based on the same data.

The Japanese NITE–CHRIP database is not mandatory, but influential in Japan and Asia. The database gives consistently more severe classifications compared to EU. A UN project found that none of the 89 substances common to the EU and NITE–CHRIP lists had identical classifications.

Korea, China, and Malaysia have mandatory classification inventories. If selling into a country with a mandatory classification inventory, then you should check your chemical product conforms to the listing.

Taiwan, Australia, and New Zealand have advisory databases.

Most countries implementing the GHS, including the US and Canada, do not have a classification database.

Where the classification database is not mandatory, or one does not exist, then it is a choice of the supplier which substance classifications they regard as most reliable.

It is disappointing that the UN has not produced a classification inventory of its own. One has been under discussion for years [8]. Given the different national approaches to classification, and the current diversity of classifications for the same substance, I think it would now be too difficult to reach a consensus for an international classification inventory.

EU Classification Lists

The EU lists go some distance to achieving classification Utopia, where all substances have an agreed classification, based on sound data.

There are three main sources of substance hazard classification in the EU:

  • Harmonized classifications agreed at EU level and published as part of the CLP Regulation.
  • REACH Registration dossiers, that contains classifications that have been agreed by manufacturers.
  • The Classification and Labelling Inventory (CLI), that contains the above classifications, and also the classifications for substances that do not require REACH Registration, perhaps due to low tonnage. The CLI notifications are made by industry to ECHA as described in the CLP Regulation, Title V, Chapter 2.

Harmonised classifications

Harmonised classifications are listed in the CLP Regulation, Annex VI, Table 3. There are about 4300 harmonised classifications.

The supplier is obliged to use harmonised classification for a particular substance, unless there is very good reason not to, eg because there is information that the hazard is greater than the harmonized classification. In this case the authorities should be informed of this fact (see below).

Two Hazard Classes, ‘acute toxicity’, and ‘specific target organ toxicity repeated exposure (STOT RE)’ often have minimum harmonised classifications reported in the harmonised classsification list. These should made more severe if supported by the test data. The minimum classifications originate in the best-guess translation of the classifications from the pre-CLP Regulations which had significant differences in criteria.

The harmonised classifications are also incomplete. Any Hazard Classes not specified in the harmonised classification need to be classified according to available data, eg from the REACH registration dossier, literature, structure–activity relationships, as outlined above.

New harmonised classifications are usually only made where the substance shows potential for carcinogenicity, mutagenicity, reproductive toxicity (CMR) or sensitisation. These are usually supported by certain EU Member States (MS), although industry can also make applications to ECHA.

In GB, the EU ‘harmonised classifications’ up to 31 December 2020 have been transposed into UK legislation, and renamed ‘mandatory classifications’. It looks likely there will be delay and divergence in converting newer EU harmonised classifications into UK legislation.

In summary, the CLP Regulation provides a list of mandatory substance classifications. If industry supplies a substance on the list, then that classification should be used in the Hazard Classes and Categories stated. The classifier is responsible for collating information and classification in other Hazard Classes.

REACH Registration dossiers

REACH Registration dossiers are publicly available for ca. 23 400 substances on the ECHA ‘Search for chemicals’. These dossiers contain a compilation of available data on substances, including test data summaries, to fulfil the data requirements given in the REACH Regulation.

The data requirements are specified in REACH Annexes VII to X, with more comprehensive data required at higher manufacture or import tonnage, as given below:

  • Annex VII: 1 to 10
  • Annex VIII: 10 to 100
  • Annex IX: 100 to 1000
  • Annex X: > 1000 tonnes/year.

The dossier also contains the hazard classification, that has been agreed by all the joint registrants of the substance.

The database is valuable for giving the classification information, but also because the assessor can check test information to assess the quality and reliability of the classification.

Following Brexit, GB (ie UK excluding Northern Ireland) chemical companies are required to make GB REACH Registrations, in order to recreating the EU database. The GB REACH transitional arrangements means that GB REACH database will be 9 years behind, thus impairing GB chemical policy.

Classification and labelling inventory

A final list, and the least reliable, is the classification and labelling inventory (CLI) (Title V, Chapter 2 of the CLP Regulation).

The CLI contains both the harmonised classifications, and those in the REACH registration dossiers. But it also contains most other substances placed on the market that are classified as hazardous, specifically:

  • Neat substances classified as hazardous under CLP, regardless of the tonnage.
  • Substances classified as hazardous under CLP, and present in a mixture in sufficient amounts to make the mixture hazardous, regardless of tonnage.

Therefore companies manufacturing or importing such substances are obliged to notify ECHA for inclusion into the CLI. The notifier must assess the substance in all of the hazard classes. The notification has to be made within a month of the first placing on the market.

The CLI classifications can be useful, but are often wildly varied for the same substance. An assessor might pick the one with the most notifiers, if no further information is available. For CLI classifications with no harmonised classification or registration dossier, there is rarely further data on which to base the choice.

The CLP requires that where the CLI has different classifications for the same substance then the notifiers should make every effort to come to an agreed classification, which should be informed to ECHA (Article 41). In this way, the classification and labelling inventory should develop into a large, robust source of reliable classifications. Unfortunately, this process has been slow or non-existent.

Classification for the purposes of the SDS

Ideally, substance classification is made using test data on all hazard classes using valid test methods.

In reality, the classifier of a substance usually relies on an inventory listing. Experience teaches whether to rely solely on this, or whether a check with available test data is warranted.

Occasionally, you may be faced with classifying a substance that will require expert judgement and intuition – natural products, UVCB substances, new chemical entities.

Article 5 of the CLP Regulation requires suppliers of substances to identify information for classification, whether this is from testing, scientific literature, databases, or from structure–activity relationships.
The information should be evaluated for its suitability for classification, and if adequate, the supplier should use it for classification ‘without undue delay’.

Only if you purchase and market the substance without altering its composition may you forego this checking procedure.

Testing is not mandated for the purposes of SDS preparation. However, there is a general duty to provide products whose hazards are understood, so that it can be handled safely. If the substance is suspected of being hazardous, perhaps from structure–activity relationships, then I would recommend testing for that hazard.

SDS compilers should specify how the classification was made which can be included in the SDS. In particular, if the substance is not classified in a particular Hazard Class, the compiler should state the reasons:

  • Sufficient substance data available, but not classified: based on available data, the classification criteria are not met. The CLI phrase for this is: data conclusive but not sufficient for classification.
  • If sufficient data is not available, then the reasons should be clearly stated, eg not classified due to lack of data, hazard not applicable to the substance (eg flammable solid for liquid substance), or other cases where testing is not feasible or the results are inconclusive.


[back to Legislation: CLP and the GHS] [back to Classification inventories]

[1] Regulation (EC) No 1272/2008 of the European Parliament and of the Council of 16 December 2008 on classification, labelling and packaging of substances and mixtures (as amended).

[2] Globally Harmonized System of Classification and Labelling (GHS); Eighth Revised Edition; United Nations; 2019.

[3] Directive 67/548/EEC on the approximation of the laws, regulations and administrative provisions relating to the classification, packaging and labelling of dangerous substances (as amended); (classification criteria are given in Annex VI).

[4] Directive 1999/45/EC Concerning the Approximation of the Laws, Regulations and Administrative Provision of the Member States Relating to the Classification, Packaging and Labelling of Dangerous Preparations (as amended).

[5] Hazard Communication Standard; 29 CFR 1910.1200; Occupational Safety and Health Administration; 2012 (HCS 2012).

[6] Recommendations on the Transport of Dangerous Goods – Model Regulations; United Nations; Twenty-First Revised Edition; 2019.

[7] The Chemicals (Health and Safety) and Genetically Modified Organisms (Contained Use) (Amendment etc.) (EU Exit) Regulations 2019; UK Statutory Instrument 2019 No. 720.

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