Ok, your confusion is my fault. When I switched to wood stove pellets I had concerns about the carbon monoxide, so I asked here on the forums, where nobody has had any respiratory issues with their buns from using wood stove pellets. My litterboxes are open and the amount of pellets that go in them is of course small. The problem arises when people keep wood stove pellets in very large containers in closed, poorly ventilated rooms or compartments. There have been fatalities on ships with cargos of loose pellets, but you can imagine the tons and tons of pellets in question.
The wood types to avoid I think are the types that smell strongly from aromatic oils (terpenes).
I’ve had no problems using wood stove pellets, I’ve been using them for years now, in fact I think they smell way less turpentine-ish than the normal wood shavings that people use for horses and small pets.
Sometimes I give to many facts about stuff, I’m sorry about that =/