Complex sentence: Some of them, particularly the poor grades of turpentine, have a strong odor, but even the more refined thinners such as odorless mineral spirits can be harmful to the health if used inappropriately.
Split into simpler sentences: Some of them, particularly the poor grades of turpentine, have a strong odor. Both turpentine and odorless mineral spirits can be harmful to the health if used inappropriately.