HP12: Release of an acute toxic gas
Waste that gives off a toxic gas in contact with water or an acid.
What HP12 means
HP12 covers waste that gives off a toxic gas when it meets water or an acid.
How WM3 decides a waste is HP12
There are no concentration limits and no cut-off. A waste holding a substance with one of these statements is tested, worked out by calculation, or assumed to be HP12:
| Hazard statement | Meaning |
|---|---|
| EUH029 | Contact with water releases a toxic gas |
| EUH031 | Contact with acids releases a toxic gas |
| EUH032 | Contact with acids releases a very toxic gas |
WM3's calculation finds the amount of a substance that would release one litre of gas per kilogram of waste. Its worked levels include 0.2% for cyanide salts (not complex cyanides), 0.4% for sodium sulphide and 0.6% for calcium hypochlorite (WM3 pages C43 to C44).
What it changes when the waste moves
A waste needs only one hazardous property to be hazardous waste. In England and Wales it then moves on a hazardous waste consignment note in place of a waste transfer note, and the note goes with the load to the site that receives it.
On Digital Waste Tracking, the site that receives a hazardous load records its HP codes alongside the EWC code (the six-digit code from the List of Wastes that says what a waste is).
Sources
- WM3: Waste classification technical guidance (v1.2.GB): Appendix C12, pages C41 to C44
- Annex III to the Waste Framework Directive (HP1 to HP15)
- GOV.UK: Hazardous waste consignment notes
- The Digital Waste Tracking (England) Regulations 2026: the paragraphs on hazardous properties and POPs, 15 and 16
This page explains the rules. Check the waste itself against WM3 before it moves.
Get the next guide by email
We write a plain-English guide whenever the Digital Waste Tracking rules move, and these reference pages get updated with them. Leave your email and the next one comes to you.
Start on the free plan
CarrierNote is on the GOV.UK software provider list, connected to DEFRA's Digital Waste Tracking service. Receiving sites are in scope from October 2026 and carriers from October 2027, and you can be recording to DEFRA's standard from your first load, whenever you start.