[Introduction] [Physical forms in the CLP Regulation] [Metals and polymers in bulk forms] [Bioavailability] [Foreseeable use] [Solutions] [Large forms] [Nanomaterials] [Fibres] [References]

The classifier is obligated to collect hazard data that relates to the ‘forms or physical states in which the substance or mixture is placed on the market’.

This post informs you of how physical forms of a chemical product can alter its hazard. Fine powders and fibres can increase the hazard compared to standard forms. Large forms or encapsulated product can reduce the hazard, and associated warnings on the label. When classifying products, the physical form should be taken into account.

If you wish to find out more about our services on product safety assessment, hazard classification, or labelling see our services page or contact us. For help with the jargon, check our glossary.

Introduction

Not only may the physical form determine the Hazard Classification, but if the physical form leads to an unacceptable risk, some uses may become restricted.

This blog post looks at how changes in physical form can change the hazard profile of chemicals, and particularly how changes affect the hazard classification.

Sometimes the physical changes are deliberate and welcome, such as when a dusty powder is formulated into granular form in order to reduce inhalation exposure or dust explosion potential.

Sometimes a particular physical form, such as a nanomaterial, may raise the potential for harm, for example due to increased physical reactivity or exposure. Not only may the physical form determine the Hazard Classification, but if the physical form leads to an unacceptable risk, as determined in the REACH Chemical Safety Assessment, some uses may become restricted or designated a ‘use advised against’. The Hazard Classification and ‘uses advised against are communicated in the supply chain in the Safety Data Sheet (SDS).

Physical Forms in the Classification, Labelling and Packaging Regulation

Only in this way can the supplier ensure that the product is not over-classified, leading to unnecessary labelling and costs, or under-classified, leading to legal challenge.

The CLP Regulation [1] gives the rules for the hazard classification of substances and mixtures. The classifier is obligated to collect available hazard data, from testing, literature, structure–activity relationships, and human experience that relates to the ‘forms or physical states in which the substance or mixture is placed on the market and in which it can reasonably be expected to be used’.

We often regard the hazards of a chemical – flammability, toxicity, etc – as being an intrinsic property, and therefore that the classification is fixed. However, it is clear that the physical state (solid, liquid, gas) or form (powder, solution, aerosol) in which the chemical is marketed can strongly affect its hazard.

For example, carbon dioxide may be supplied in solid form (dry ice), or in pressurized cylinders, or used as a propellant in aerosols. The hazard and Hazard Classification for each form is different: cold burns (not recognised as a Hazard Class in the CLP Regulation); may explode if heated (gas under pressure); pressurized container may burst if heated (non-flammable aerosol).

Red phosphorus (flammable solid, no hazard classification for health effects) and white phosphorus (pyrophoric solid, fatal if swallowed or inhaled) have different chemical bonding (allotropes) and present very different hazards to the user.

It is therefore important to evaluate how the available data on the product, on which the Hazard Classification and labelling is based, applies to the specific physical state and form which is placed on the market. Only in this way can the supplier ensure that the product is not over-classified, leading to unnecessary labelling and costs, or under-classified, leading to legal challenge.

Metals and polymers in bulk form

The CLP Regulation contains derogations from labelling of products on the basis of physical form for metals in massive form, alloys, and mixtures containing polymers or elastomers (see CLP Regulation, Article 23). Such materials, although they may be classified as hazardous, do not need to be labelled if they are supplied in bulk forms such as ingots or large pellets.

In these cases, the potential for harm is reduced in the following ways:

• The product cannot be inhaled
• The product cannot be swallowed, or even if swallowed the components do not transfer to the animal (ie no adsorption)
• Components do not transfer from the product to the skin when the product is handled
• Components do not transfer from the bulk material to the aquatic environment

In bulk forms, any hazardous ingredients are encapsulated, and do not migrate to the surface, reducing their potential to cause harm.

These bulk forms may be classified as hazardous, and therefore require an SDS, but are exempt from hazard labelling.

A polymeric substance with a higher molecular weight (number-average molecular weight, Mn > 1000 Da) and low water-solubility (< 10 mg/L) is associated with lower biological absorption and health concerns and may be designated ‘polymers of low concern’ [2].

In Article 12, the CLP Regulation gives a more general derogation for when hazardous ingredients are not bioavailable (see below).

Bioavailability

‘Bioavailability’ or ‘biological availability’ means the extent to which a substance is released from a product and absorbed by an organism. If the substance is not released from the product, or not absorbed, then there is no possibility of an adverse effect.

These factors depend on the state and form in which the product is marketed. The derogation above for bulk metals and polymers is likely based on consideration of bioavailability.

If the assessor can show that the substance or mixture is not released from a product or not absorbed by the organism, then the product requires neither classification or labelling.

Bioavailability considerations are only relevant with respect to classification for health and/or environmental Hazard Classes.

It is possible that a substance is bioavailable by one route but not another (eg absorbed following inhalation but not absorbed through the skin). In such cases the lack of bioavailability may be apply for the specific route.

The burden of proof to use this derogation is high: conclusive scientific experimental data is required that the substance or mixture is not biologically available (CLP Regulation, Article 12), and expert judgment may be required.

Bioavailability is not commonly evaluated in chemical hazard assessment, so if the classifier wishes to use the derogation, then specialised testing may be required, eg:

• Leaching tests to show a lack of release of a harmful substance from a product
• Solubility testing (perhaps in simulated biological fluids) to show substance cannot be absorbed
• Toxicokinetic testing to show all substance is excreted from the organism without absorption or transformation (especially to more soluble forms).

For example, when considering the hazard classification of a fragranced candle, the author considers a ‘common sense’ approach – that the candle can forego hazard classification and labelling because the hazardous fragrance ingredients are encapsulated in a non-hazardous wax – cannot be legally justified without further evidence.

All decisions on not applying a classification due to non-bioavailability should be documented in case the decision is challenged by customers or the authorities.

Foreseeable use

The hazard classification should be based on data not only on the ‘forms or physical states in which the substance and mixture can reasonably be expected to be used,’ but also ‘reasonably foreseeable conditions of misuse’ and ‘reasonably foreseeable accidental exposure’. The scenarios exclude criminal or deliberately harmful actions [3].

Therefore, a granulated product may become powdery during transport, storage, and use, and the classifier has to take this into account.  

Or a consumer may load a liquid paint stripper into a spray gun. In this case the assessor has to decide whether this is reasonably foreseeable, bearing in mind any instructions and warnings on the product.

Solutions

If there are no circumstances in which the hazard of the mixture would be manifested, then classification for that hazard need not apply

Some physico-chemical Hazard Classifications are specific to a physical state. For example:

• Flammable solid
• Flammable gas
• Oxidising solid
• Pyrophoric solid

How do we classify a product that contains such solids or gases dissolved in a liquid? The only answer is to test the solution according to the relevant methods for the corresponding liquid.

Classification for health Hazard Classes involving inhalation exposure also requires expert consideration, because the classification criteria differ for gases, vapours, mists and solids (dusts). What happens to the hazard classification if we change the physical form of a product, eg from a powder to a liquid solution?

If an ingredient with a health Hazard Classification is present in a mixture above the generic concentration limit for the adverse effect, we would normally also classify the mixture for that effect (see previous post on mixture classification).

For example, how do we classify a solution comprising a solid classified for Acute Toxicity (inhalation, dust) in a non-hazardous solvent? Because the product is liquid, then dust inhalation is not likely. However, the liquid could be inhaled as a mist or spray, and the solvent may evaporate leaving the powder. The assessor should consider the uses, and determine whether a breathable form of the product is reasonably foreseeable.

If there are no circumstances in which the hazard of the mixture would be manifested, then classification for that hazard need not apply, using the derogation given in the CLP Regulation, Article 6.

All decisions on not applying a classification due to physical form should be documented in case the decision is challenged by customers or the authorities.

Large forms: tablets, pellets, blocks

Labelling derogations for metals, alloys, and polymers in bulk forms, as discussed above.

Hazard Classification is based on available information, often derived from testing according to specific methods. The CLP Regulation, Article 8, states that new hazard testing for chemical products should be on the form and physical state as it is placed on the market.

For powders, particle size distribution (granulometry) is crucial for several physico-chemical Hazard Classes, particularly explosive properties, flammability, self-reactivity, pyrophoric properties, self-heating substances, solid organic peroxides, oxidizing solids, and substances which, in contact with water, emit flammable gases. It is the finer particles within a sample that give the most concern, due to the increased surface area available for reaction with air or water.

Also, finer dusts may present a dust explosion hazard. They are more likely to become airborne and form higher density dust clouds. They also ignite more easily and react more violently than coarser ones. Dust explosion is not part of the hazard classification system in the EU or UK, but it is in the USA.

It is often not appropriate to test larger forms such as tablets, pellets, blocks. For example, the testing for flammability of solids requires that the sample is in powder, paste, or granular form [4].

For health hazards, it is not practical or desirable to test each form for each hazard due to animal welfare concerns. Usually testing is conducted on the form giving the highest risk, which is likely to be the smallest particle size for solids. The prescribed test for toxicity following dust inhalation recommends small particle sizes to ensure exposure of all parts of the respiratory tract to the substance.

Physical forms do not play a large part in general ecotoxicity for classification, because only soluble forms are considered. However, very fine particulates can confound ecotoxicity testing as they are difficult to separate from solutions and can cause physical harms to aquatic organisms.

Products in large forms can be tested by grinding to a powder, increasing the likelihood of a positive result.

The classifier has to use expert judgement to determine:

• Whether smaller forms (eg powders), eg from abrasion or crumbling of the larger forms, can be foreseen during the lifecycle of the product,
• Whether sufficient information is available on the particle-size distribution (granulometry) to make a judgement on the hazards of the product
• Whether testing of the product as it is marketed, or on a ground sample, is desirable or appropriate for product stewardship and legal liability purposes
• Whether to classify the product based on the results of tests on smaller forms (eg powder) as a reasonable worst case, or to override a classification on the basis of the actual form as placed on the market.

The classifier uses a weight-of-evidence approach making a judgement on the Hazard Classification based on all available information, including physical forms and foreseeable uses (CLP Regulation, Article 9).

Thus, the classifier can override a test result showing positive for a Hazard Classification if he or she can demonstrate that the physical form of a product does not produce the hazard. The supplier company bears the responsibility and should ensure the evidence is strong enough to support the decision.

Usually, the product is classified on the basis of the tests on smaller forms, ie powder, unless such forms cannot be foreseen during the lifecycle of the product.

Nanomaterials

At the other end of the granulometry spectrum are nanomaterials.

These have very small particle sizes and can show enhanced physico-chemical hazards, eg flammability, due to their increased surface area and reactivity. They also have a greater potential to cause harm to health, by crossing biological membranes and being breathed deeper into the lungs.

General considerations regarding the enhanced hazard of smaller particle-sizes are given above in the discussion above on large forms.

Nanomaterials generally have a size of 1 to 100 nm in at least one dimension (see definition). Some other forms are additionally included: fullerenes, graphene flakes and carbon nanotubes.

Specific REACH [5] obligations apply for registration of nanoform products, including characterisation (ie size and shape) and assessment for any additional hazards compared to non-nanoforms.

Specialised physico-chemical and toxicological methods may be required for some tests [6] used to assess the hazards of the nanomaterial.

The classifier has to take into account available information to assess the Hazard Classification of a substance. If the substance is marketed in the EU or UK at > 1 tonne/year, even if some of this is the non-nanoform, then REACH registration is required, and the data for the substance including its nanoforms should be available.

The nanoform characterisation and hazards are included in the product safety data sheet (SDS). Details of the content of SDSs is given on our Resources page.

A downstream user (DU) who creates nanomaterials from a standard substance should tell their supplier, so that the use can be included in the substance Chemical Safety Assessment (CSA). If the DU wishes to keep this use proprietary, then the DU should create their own CSA for the nanomaterial. For product stewardship and legal liability purposes the DU may wish to conduct safety testing on a new nanomaterial if there is doubt about the hazards.

Fibres

Some substances take the form of fibres, which can have enhanced health hazards due to their physical form, ie the shape and size.

Fibres may produce irritation by piercing or lodging in biological membranes. Insoluble, persistent fibres may cause serious adverse effects if inhaled.

For regulatory purposes, fibres are defined as being > 5 µm long, having a ratio of length to width of > 3:1, and a diameter < 3 µm. The diameter of a fibre is important because thin fibres suspend more easily in air and are deposited deeper in the respiratory system. Generally, glass wool, rock wool, slag wool, and refractory ceramic fibres have smaller diameters than filament glass fibres.

Durable fibres in the lung can lead to long-term inflammation, pulmonary fibrosis, or lung cancers. High doses and long exposures are usually required for these conditions to develop. Fibres with lengths greater than 15 µm are more likely to lead to lung injury than shorter fibres.

The CLP Regulation contains harmonized classifications for several fibres, such as asbestos (Carc 1A, STOT RE 1), mineral wool (Carc 2), and silicon carbide fibres (Carc 1B).

The assessor tasked with hazard classification should take into account the fibrous nature of a product, especially if a new manufacturing process gives a more fibre-like form. Measurement of fibre morphology can determine if the product falls into an existing fibre classification (eg machine-made mineral fibres, MMMFs) [7].

If a product is found to be fibrous, then new testing might be required to assess whether the fibrous form is more hazardous, and support REACH registration. The water-solubility, or solubility in interstitial fluid, and metabolic studies are relevant for the persistence of fibres in the lung, and for assessing the increased potential hazard due to fibre inhalation. A new determination of safe limits for inhalation may be required [8].

The safety assessor may wish to commission such testing for product stewardship and legal liability purposes.

References

[Back to Physical form in the CLP Regulation] [back to Foreseeable use] [back to Large forms] [back to Nanomaterials] [back to Fibres]

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

[2] Data Analysis of the Identification of Correlations Between Polymer Characteristics and Potential for Health or Ecotoxicological Concern; OECD Joint Meeting of the Chemicals Committee and the Working Party on Chemicals, Pesticides and Biotechnology; ENV/JM/MONO(2009)1; 27 January 2009.

[3] Guidance on the Application of the CLP Criteria; Guidance to Regulation (EC) No 1272/2008 on classification, labelling and packaging (CLP) of substances and mixtures; ECHA; Version 5.0, July 2017.

[4] Recommendations on the Transport of Dangerous Goods; Manual of Tests and Criteria; United Nations; Eighth Revised Edition; 2023.

[5] Regulation (EC) No 1907/2006 of the European Parliament and of the Council of 18 December 2006 concerning the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) (as amended).

[6] Guidance on Information Requirements and Chemical Safety Assessment; Chapter R.7a: Endpoint specific guidance; Version 6.0; ECHA; July 2017.

[7] A.22. Length weighted geometric mean diameter of fibres; Regulation (EC) No 440/2008 laying down test methods pursuant to Regulation (EC) No 1907/2006 (REACH) (as amended); 12 May 1981.

[8] Machine-made fibres; Airborne number concentration and classification by phase contrast light microscopy; Health and Safety Executive; MDHS59/2; June 2014.