Can treated wood fencing boards be used indoors for ceiling planks?

https://www.diypassion.com/2016/05/23/the-best-way-to-up-cycle-an-old-fence/

Is Pressure Treated Wood Safe for Indoor Use? - ProWood lumber

www.prowoodlumber.com/en/Blog/2010/.../Is-pressure-treated-wood-safe-for-indoor-us...

I'm thinking that would not be a good idea. Do you know for sure the fence boards were treated? We have used old weathered fence boards for a number of projects, mostly outside. I think the look would be great, but not if they were treated boards.

Much depends o what was used to treat the wood.

If you do, paint on clear matte Varathane to make sure they are sealed.

I would not. Even though treated wood is considered safer than older treated wood they still can off gas. Old treated wood basically were treated with a form of arsenic. New treated wood is treated with a form of copper. It's generally treated for use outside or interior construction where it will be covered and sealed. Mainly where it can come in contact with water or moisture. The chemicals used to treat the wood can react with any clear coat. Even treated decks need some kind of maintenance every four years or so.