Wood
A lot of people offer scrap wood, or even furniture, for burning. This isn't illegal, but the person receiving the wood should take some care.
See this article on pallets and reuse, and this firewood warning.
CCA (chromated copper arsenate)
A particular concern is that some treated timber contains CCA (chromated copper arsenate) and shouldn't be burnt as firewood. CCA is a wood preservative used for timber treatment from the mid-1930s until it stopped in 2006. As the name suggests, it's a mixture of chromium, copper and arsenic, giving the timber a greenish tint. It's highly effective as a preservative, often used as a substitute for creosote, protecting against fungal decay and wood-eating insects and providing good weather resistance. But when burnt, toxic arsenic is released into the air, and the ash from burnt CCA-treated timber can contain up to 10% (by weight) arsenic, chromium and copper. Swallowing just a few grams of this ash can be harmful, with symptoms including nausea, vomiting, diarrhoea, and pins and needles in the skin. The general advice is never to burn CCA-treated timber as firewood, in fireplaces, barbecues, wood stoves or any wood fire.
Wood designed for indoor use, or first used outdoors before 1933 or after 2006, is likely to be safe to burn. CCA was mainly used in fences, sheds and decking. Its use was initially restricted voluntarily to external applications, then later restricted by law, and it's no longer available at all.
A general safety document on what can be burnt on a domestic open fire: https://uk-air.defra.gov.uk/assets/documents/reports/cat09/1901291307_Ready_to_Burn_Web.pdf
MB (methyl bromide)
Some pallets have been treated with this highly toxic pesticide, which is sometimes needed in regions with pests that can't be eliminated by heat treatment. Never use MB-stamped pallets for a craft project, and never burn them on a fire. Methyl bromide treatment was made illegal in the UK in 2010 and is being phased out worldwide, but pallets last a long time, so some MB-stamped ones are still in circulation. Always check pallet stamps carefully - if you can't tell what a stamp means, don't use the pallet.
For safety, it's probably best to assume that any pressure-treated wood may contain chemicals that are harmful to health and the environment once burnt.
CHEP pallets
The blue pallets you might see offered, or get requests for, are legally owned by the CHEP company and should be returned directly to them, either through the company they were obtained from or to CHEP directly. These shouldn't be allowed on Freegle. A member can arrange a free collection by phone or email on 0800 515 320 or collect@chep.com, or via www.chep.com.
2021: government announcement
The government announced restrictions on fuel for woodburners: "To help improve the air we breathe and ensure householders choose cleaner fuels, sales of coal and wet wood - the two most polluting fuels - will be phased out between 2021 and 2023."
If freshly cut logs are offered as firewood, it's worth passing on the above information.
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