its not suggested but it also depends on the varnish.
No. It is illegal to burn anything outside due to air pollution laws.
In MOST cases, yes- if the wood has not been treated with preservative chemicals.
NO. They have been treated with preservatives that will produce possibly poisonous gases.
Depends on what is with treated with. If you mean lumber treated to resist rot and insects, such as wood used on a deck or fence post- NO. The treatment chemicals are toxic- and so is the smoke from burning that wood.
No, it is not safe to burn. It is toxic.
No it is not safe to burn it.
Arsenic treated lumber is not being sold, but other pressure treated wood will be safe to use for your raised beds. Composite lumber and cedar lumber will both be safe and will last a long time for raised beds.
Yes. stainless steel screws are safe with any metal.
Yes, it is safe to burn sassafras and it is commonly burned in many locales.
These may be treated as safe.
It's a waste of time and it will not burn totally.
yes, any fruit wood is safe.