Timber in Australia is treated to six levels called Hazard (H) Classes. These treatment levels indicate where the treated product may be used.
| Hazard Class | Where the treated wood may be used | What the timber is protected against |
|---|---|---|
| H1 | Inside, under cover, protected from the weather and well ventilated | Insects |
| H1.2** | Inside, under cover, protected from the weather subject to moisture | Insects and decay |
| H2 | Inside, under cover, protected from wetting, no leaching | Insects and termites |
| H2F | Inside, under cover, protected from wetting, no leaching, envelope treated, South of the Tropic | Insects and termites |
| H2S | Inside, under cover, protected from wetting, no leaching, South of the Tropic | Insects and termites |
| H3 | Outside above ground, periodic wetting but where the timber can dry out; some leaching | Insects, termites and moderate decay |
| H3A## | Outside above ground, periodic wetting but where the timber can dry out; some leaching, maintained paint system | Insects, termites and moderate decay |
| H3.1** | Outside above ground, periodic wetting but where the timber can dry out; some leaching, maintained paint system | Insects, termites and moderate decay |
| H3.2** | Outside above ground, periodic wetting but where the timber can dry out; some leaching | Insects, termites and moderate decay |
| H4 | In or on the ground subject to severe wetting and leaching | Insects, termites and severe decay |
| H5 | In or on the ground subject to severe wetting and leaching, with or in fresh water | Insects, termites and very severe decay |
| H6 | In contact with sea water | Marine borers and decay |
** Applies in New Zealand only
## Applies to one preservative system used in Australia
