I used to work on a chemical site that used to make all kind's of tar based product's and one of them was creosote..two of the chemical's that go into creosote are Napthelene and Pitch both are carcinogenic from prolonged exposure.. and burn fook out of your skin which i have experienced several time's..i got burned that bad one time that i had to stay out of the sun for a week and i have seen another lad have to pay a visit to A@E... so my guess is either one of those chemical's..