I was a tech writer for about 20 years. Did museum exhibits, plumbing and zoning codes, landmarks preservation law, hazmat regs, and National Register nominations.
In all those disciplines, you have to write as if you are explaining to someone outside the field, and also be clear not to leave loopholes or ambiguities that could possibly be exploited (Plumbing code, Zoning an Preservation law.) Hazmat regs need to be written so a fourth grader can understand them.
What is your dissertation on?