Are cardboard ashes safe for chickens to dust bathe in?

[Sire12]

I'm burning some wood to get ashes for them to dust in I also have alot of cardboard I could burn too but is it safe to add it in with the wood ashes?

 

[EggSighted4Life]

Well, here in California it's illegal to burn cardboard...

I don't know WHY it wouldn't be safe...