Hazard classification

UK and EU chemical regulation is designed to protect workers and the public from the harmful effects of chemicals.

Chemical substances undergo hazard classification, based on a comprehensive search for information on their hazardous properties. This is a requirement of the CLP Regulation [1]. Suppliers use the hazard classification to produce product labelling and safety data sheets (SDSs) to communicate the hazards of the product to users.

See our guides to hazard classification of substances, SDS content, and labelling.

Nitrous oxide, aka dinitrogen oxide (N₂O) or laughing gas, has been in the news as a recreational drug. There are proposals to ban its sale to the public due to littering and antisocial behaviour. Reports rarely focus on the harm to health of nitrous oxide.

A proposal [2] adopted by the EU Risk Assessment Committee includes a controversial new harmonised classification of nitrous oxide as Toxic to Reproduction, Category 1B (may damage the unborn child), which indicates its inclusion in the Candidate List of Substances of Very High Concern (SVHC) for eventual restriction on sale or withdrawal from the market.

The harmonised classification, if passed by the European Commission, will be mandatory throughout the EU.

Some consider this an over-classification, because nitrous oxide has been used safety for decades as an anaesthetic, and is deliberately administered in high concentration as a medicine, particularly during childbirth.

An important part of the controversy is that the classification for reproductive or developmental toxicity sometimes relies on high doses in animals that are not relevant for humans during normal use.

Check out our handy glossary of definitions and abbreviations of technical terms used in this article.

Harmonised classification for nitrous oxide

The EU Risk Assessment Committee (RAC) has recently adopted a proposal for the harmonised classification of nitrous oxide as:

• Toxic to reproduction, Category 1B, H360Df (may damage the unborn child. Suspected of damaging fertility);
• Specific target organ toxicity (repeated exposure), Category 1, H372 (causes damage to nervous system through prolonged or repeated exposure);
• Specific target organ toxicity (single exposure), Category 3; H336 (may cause drowsiness or dizziness);
• Ozone 1; H420 (harms public health and the environment by destroying ozone in the upper atmosphere).

The proposal is controversial for the following reasons:

• Nitrous oxide has a long-standing use as an anaesthetic. In particular it is used in ‘gas and air’ (Entenox) pain relief for mothers in labour. Containers of the gas may require the warning ‘may damage the unborn child. Suspected of damaging fertility’. The current UK NHS advice is that ‘there are no harmful side effects for you or the baby’ [3];
• The reproductive effects have been seen in laboratory animals at very high doses (up to 60% nitrous oxide), and the so the relevance for workers or consumers not engaged in deliberate misuse is doubtful;
• Some stakeholders see the classification as a reaction to misuse as a recreational drug;
• There may be unintentional consequences for the legitimate use of nitrous oxide, such as manufacture of whipped cream.

The UK has promised to take into account any EU harmonised classifications in its own list of mandatory classification and labelling (GB MCL) list, but could decide to ignore this proposal.

References

[Back to Hazard Classification] [Back to Harmonised Classification]

[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] Minutes of the 64th Meeting of the Committee for Risk Assessment (RAC-64); ECHA; RAC/M/64/2023; 16 March 2023.

[3] Pain relief in labour; https://www.nhs.uk/; 12 April 2023.