Black walnut is some freaky wood. I moved up to the North Carolina mountains from Georgia. Never heard of the black walnut.
I made a big garden, roto tilled the area, brought in peat moss and cow manure, built a 3 foot fence all around, planted all the potatoes, expensive blueberry bushes, etc.
Everything died. It turned out, the nearby black walnut tree had killed the garden.
Some freaky sap comes off of the black walnut and it kills potatoes. Also the roots of black walnut are toxic.
So I had a grudge against that tree. I was going to build an addition onto my log cabin, I whacked that black walnut tree to make the summerbeam.
And I sawed it down with my chain saw, so that it was 18 inches high, and 8 inches thick, and 17 feet long. What beautiful wood!
Of course we had to sand it down. I got my helper to work on it, he had on a respirator etc, but after 30 minutes he was feeling sick. Now, all the sawing I did with the chain saw, hours of it, I was producing wet, chainsaw sawdust it didn't bother me. But sanding the beam with the disc grinder produces very fine dry sawdust powder, like flour. This made Adam sick, he felt like he was coming down with the flu. So I sent Adam home. With the respirator you are breathing in little, if any, of that sawdust. Perhaps it gets in through your skin.
But, I wanted the thing sanded so I sanded it myself. I was on it for about 5 hours, disc grinder and belt sander. It made me feel a little sick but it wasn't too bad. It affected my helper worse than it did me.
So I am sorry for your doggie but that black walnut is some freaky wood.
summerbeam