ADR tank special provision TU21
Substance must be protected by nitrogen, water and nitrogen, or a water layer of at least 12 cm, with filling limits of 96 % or 98 % at 60 °C.
The cargo must be kept under one of three protective agents set out in a table. With nitrogen alone, the substance (including any water) may fill at most 96 % at 60 °C. With water and nitrogen, or with water alone as a layer at least 12 cm deep, the limit is 98 % at 60 °C. Where water is present it must carry enough anti-freeze to prevent freezing at low ambient temperatures, the anti-freeze being non-corrosive and non-reactive with the substance. When nitrogen is used, the space left in the tank is filled with it so that pressure never drops below atmospheric after cooling, and the tank is closed gas-tight.
| Value | Applies when |
|---|---|
| 60 °C | temperature at which the degree of filling is assessed |
| 96 % | maximum degree of filling with nitrogen as the protective agent |
| 98 % | maximum degree of filling with water and nitrogen, or with water |
| 12 cm | minimum depth of the water layer when water is the protective agent |
Note. The protective-agent table on page 225 is printed in scrambled columns, with some cells as an unreadable character; the anti-freeze requirement is read as applying to the two rows that contain water.
Carried by 3 Table A entries
Source: ADR 2025 (ECE/TRANS/352), Volume II, section 4.3.5, TU21, page 225.
Paraphrase in FreightUtils' own words, not the official text. Not yet reviewed.
ADR 2027 amendments (accepted, applying from 1 January 2027) are not yet reflected on this page.