Ken,
have to disagree on point 1....
Why? Although they are old and dry the dust, if heated by cutting and or drilling, will release volatile components from the creasote. So fine sawdust from any impregnated timber should be treated with caution, as should mdf dust.
There is unproven evidence that mdf dust is as nasty as long fibre asbestos. We will know for sure in 25 years or so.
