Rainwalker is rightly cautious about commercially available lumbers. But it is not true that all wood from the lumber yard is poison.

Contractors do not always use treated timbers. That’s a matter of economics. Creosoted or pressure treated timbers are more expensive than plain, kiln dried, untreated beams and scantlings. They only spend the extra bucks where the end purpose requires it, or the architect’s specs demand it. Where the job doesn’t need treated wood, they use regular, untreated lumber. I’m not saying you don’t need to be cautious, using wood from a construction site. But not all of it is automatically poisonous.

Creosote treated timbers look dark, as though they’d been painted with thinned down hot tar. If it looks funny that way, leave it alone. I haven’t knowingly dealt with PCP treated wood, so I can’t advise you about that one. In both cases you’re dealing with big timbers. I’ve seldom seen even 4 X 4s treated with creosote. 6 X 6s and up, or telephone poles, are more likely to be treated with the stuff.

You can spot pressure treated lumber by its physical appearance. Be it CCA or ACQ, the surface will look as though someone had stapled it all over. There aren’t any staples, just dimples in the surface of the wood, running parallel to the length of the timber. Pressure treated wood comes smaller than creosoted wood. Any size of 2 X can be pressure treated. (The nominal size of building lumber is larger than the actual size. A 2 X 4 isn’t 2” X 4”, it is 1 ½” by 3 ½”.) Occasionally 1 X stock will be pressure treated. Pressure treated lumber may not be obvious, if for some reason it has been milled down on site. The carpenters may have needed something smaller than a 4 X 4, and so they trimmed the edges off of a standard stick. That would eliminate the staple marks. But it’s rare for builders to have to fiddle with timbers that way. It costs man-hours = money.

The other building materials you should be caution about burning or cutting or sanding are plywood and especially particle board. Most plywood isn’t made with poisonous additives, but some is. Especially marine grade plywood. On the other hand, it is rare for particle board to be safe. Usually it is glued together with arsenic and worse.