UKC

I've just had our 60-70 year old roof re-slated, as a result I have a yard full of 60-70 year old battens. I *think* they are covered in some sort of preservative, so a) am I OK to dispose of them by burning, (we're quite far away from any other houses), or b) could I use them for kindling for our log burner?

I'd avoid doing that.  Some of the preservatives used at that time are highly toxic and now banned.

A neighbour gave me some old battens, I constructed a log store.

Very nice, but they're a bit too old and rotten for that!

If they are preservative treated, and you plan to burn them (not that I am recommending this), it would be safest to burn them in a hot fire to give the greatest chance of the preservatives being broken down. Using them as kindling would be more likely to release any potential toxins.

If you have a steel flue or steel flexi liner is best to not burn  as the preservatives can cause corrosion ...

The legal way to dispose of timber now is to get a skip driven to you, then driven away, then driven somewhere else to shred and either reuse or landfill so the rogue chemicals will ultimately get back into the environment...

I'd have a bonfire 🔥

Hmm ... Good old t'interweb! Every possible answer you could wish for! Taking them down the tip is not a pain free option, how environmentally catastrophic is incinerating them in my garden incinerator likely to be?

That's good to know, thanks. I have always burned the odd bit of treated wood (not creosoted!) in my burner if (a) the treatment had almost weathered/worn away and (b) it was mixed in with proper firewood, but I'll think twice now.I

Are any treatments worse than others for this? Indoor gloss paint vs outdoor garden stains/paints?

https://www.gov.uk/government/publications/storing-and-treating-hazardous-w...

I think you're overthinking it. Unless it's a truly industrial quantity just burn them. 

Likely to be considered hazardous according to this: https://woodrecyclers.org/wp-content/uploads/WRA-Waste-Wood-Assessment-Guid...

Ask the folk at your local tip which of their waste streams goes for incinderation and use that, or at least dispose of the ash rather than spread it in your garden, following burning outside as already suggested. 

I was, formerly, a waste management professional in a niche area. Although none of this constitutes advice, I would consider the following points:

The UK environmental regulators can barely afford to pursue the industrial operators that fund them - prosecution is unlikely unless you *really* upset a third party,

The guidance and regulatory positions linked above are targeted at permitted operators. Again, you'd really have to upset a third party.

If your burner at home has a good air flow and is designed to achieve complete combustion (basically any non-range stove that could reasonably be called modern), then:

A) Metal based preservative compounds will mostly decompose and you'll have mass segregation of the metals into your retained ash. Don't dispose into the garden and the personal, public, and environmental risks are likely to be below negligible.

B) Modern stoves, if running good and hot, will allow near complete reaction of older organic preservatives and in most cases product compounds would be less environmentally detrimental than undiluted leachate the original preservative.

C) To be practically and legally 'hazardous', my understanding is that you would need a veeeery high concentration of older-school preservatives. To be acceptable, an industrial facility would optimise either through: running even hotter, burning smaller quantities among more benign waste (blending - depending on regulatory engage), or cleaning the off-gas (not viable).

If I decided, regardless of legal position, to get rid of this at home then my most risk-averse method would be:

- Run my stove good and hot on clean fuel,

- Add small loads of the recovered wood only (maybe when trying to get things really toasty),

- Make sure I have good air flow (a good draft would also negate any need to increase ventilation in the home,

- As a belt-and -braces safeguard, put any ash into the domestic waste - don't use in compost etc., and

- If I was being reeeeeeeeeally careful, do this on windy days to increase the dilution factor

If you ever use (non-smokeless) house coal or get rid of plastic at low-airflow you probably, per gram, cause more damage than this does.

Unless you're burning something that seeps preservatives (railway sleepers, some agricultural timbers) the regulator-accepted optimised process would likely be very similar. 

I know there have been some downbeat stories about impacts of domestic burners but a hot, well oxygenated stove with some recombination and a good draw is actually pretty decent. A lot of those articles can be summarised as 'using stoves inappropriately achieves inappropriate outcomes'.

Thanks all for the comprehensive range of answers, I' m now a lot more comfortable about what I propose to do. And I won't be spreading any ash on the garden!