Unfortunately no timber is classed as 'non-combustible' when tested to Australian Standard 1530 Part 1: Combustibility test for materials. The test involves placing specimens in a furnace at approximately 750°C, at which temperature they must produce only a limited amount of heat and flame. However, blackbutt is one of the seven species classed as 'bushfire-resistant' in accordance with AS 3959:2018 if that is any help.

Debarking is the first operation in a sawmill, before logs are cut up for sawn timber, or peeled for veneer production. Preservative treatments are applied at a later stage, after removal of the bark, so it is unlikely that bark chips from a sawmill would contain any chemicals that would leach out into the soil. However, if the bark chips were in place for a long time they might have taken nitrogen from the soil as they started to break down. This could affect the future growth of some plants.

Thermally modified timber is not currently included in any Australian Standards, and has not been tested by Australian research bodies as far as we are aware. It has been tested by Scion Forest Products in New Zealand (comparable to our CSIRO) and the results of exposure tests conducted by Scion can be found on this website https://www.tunnicliffes.co.nz/thermowood-.html. Note that the test program only included material treated at 230 degrees C.