Complete information about health hazards associated with a wide variety of exotic hardwoods is available from The Wood Database. Additional information about how to best use a dust collection system and personal protective equipment, such as respirators, can also be found through this excellent and comprehensive resource.
Fortunately, I experienced no negative side effects when working with Kingwood.
My Personal Experiences
Unfortunately I was only working with small pen blank sized pieces of Kingwood so my experience is accordingly very limited. However, that said, I had a great time working with the small pieces that I had available to me. The wood was beautiful to look at; it was a dream to turn because it is so hard that it takes a lovely fine cut edge with very sharp tools. I was aware of the high oil content so I was cautious when drilling the bores but I encountered no problems because I conscientiously cleared away the debris regularly. I used Abranet to sand the blanks to avoid problems with gumming up regular paper backed abrasives. To minimize difficulties in gluing the brass inserts I swabbed the bores with acetone prior to gluing. As a finish, I used cyanoacrylate because of its high shine and its durability for desk tools, but for any other application I would have simply buffed the natural oils, or at most added a light coat of wax.
I found Kingwood to be a dream to work with and I only wish that I could afford to buy larger pieces of the material, perhaps a bowl blank, to really experience the true joys and complexities of the material.
As always, I wish all my readers a great experience in whatever their wood working interests happen to be and to those who like working with lathes especially, do a good turn today!