HP12: Release of an acute toxic gas
Waste which releases acute toxic gases (Acute Tox. 1, 2 or 3) in contact with water or an acid.
What this usually means in practice
HP12 is about wastes that can release an acutely toxic gas when they contact water or acid. The key risk is what the waste can generate during handling, storage or treatment rather than how it behaves when left undisturbed.
Definition
Exact definition wording taken from WM3 Appendix C / Annex III for this hazardous property.
waste which releases acute toxic gases (Acute Tox. 1, 2 or 3) in contact with water or an acid
What to check when assessing this property
Use the official definition, composition data and waste-process knowledge together. These points are meant to help frame the assessment, not replace WM3.
- Check for EUH029, EUH031 and EUH032 substances and whether the waste can contact acids or water in practice.
- Review WM3 test or calculation methods where fixed concentration limits are not available.
- Consider treatment scenarios, spills and incompatible mixing because those are often what trigger the gas release.
Supporting points
Additional points shown where the official definition or WM3 guidance breaks the hazard into categories or clarifications.
- EUH029, EUH031 and EUH032 are the key supplemental hazard codes for HP12.
- Annex III does not use fixed concentration limits for HP12; classification is by test methods or guidance.
- WM3 provides a stoichiometric calculation method and worked threshold examples for common EUH029, EUH031 and EUH032 substances.
How to use this page
Hazardous properties explain why a waste may be hazardous. They sit alongside EWC classification and they do not replace formal WM3 assessment or site acceptance checks.
1. Start with the waste
Identify the likely EWC entry, the process that produced the waste and whether it is part of a mirror-entry assessment.
2. Check the hazard evidence
Use composition data, SDSs, testing, pH, flash point and process knowledge as relevant to the property in question.
3. Confirm the final outcome
Confirm the conclusion against WM3 and any permit-specific or site-specific acceptance requirements before relying on it.
Wording is based on Annex III of the consolidated Waste Framework Directive opens in a new tab and should be used alongside Waste classification technical guidance (WM3, 3rd edition, 2021) — GOV.UK opens in a new tab.