Re: disposing of old redwood deck
Crosote is created by burning green wood, a 25 year old deck doesn't fit that description.
The only reason NOT to burn it is if it's been treated with any preservatives over the years. There can be some nastiness from those coatings that wouldn't be good to breath. Other than that, have at it.
Other means of disposal would be to meter it into your garbage can. Be forewarned, some municipalities get cranky about "construction" debris in your can, so only put what will fit with the lid closed. Or, you could haul it yourself to a building materials recycler where fees are usually about half of what a landfill would charge.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!