Took forever to get there and read it, but here is the OSHA webpage link:
http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=FEDERAL_REGISTER&p_id=13309 In short, OSHA requires protective clothing (PPE) only when the worker may be exposed to some hazard. Shorts on construction projects are not automatically forbidden by OSHA, just as short sleeves are not automatically banned.
This quote is interesting:
V. "Protective clothing and equipment"
Employees should be provided with and be required to wear appropriate protective clothing wherever there is significant potential for skin contact with liquid EtO or EtO-containing solutions. Protective clothing shall include impermeable coveralls or similar full-body work clothing, gloves, and head coverings, as appropriate to protect areas of the body which may come in contact with liquid EtO or EtO-containing solutions.
Employers should ascertain that the protective garments are impermeable to EtO. Permeable clothing, including items made of rubber, and leather shoes should not be allowed to become contaminated with liquid EtO. If permeable clothing does become contaminated, it should be immediately removed, while the employer is under an emergency deluge shower. If leather footwear or other leather garments become wet from EtO they should be discarded and not be worn again, because leather absorbs EtO and holds it against the skin.
Any protective clothing that has been damaged or is otherwise found to be defective should be repaired or replaced. Clean protective clothing should be provided to the employee as necessary to assure employee protection. Whenever impermeable clothing becomes wet with liquid EtO, it should be washed down with water before being removed by the employee. Employees are also required to wear splash-proof safety goggles where there is any possibility of EtO contacting the eyes.
This was typical of the many hazards OSHA identified. What interested me was the fact that OSHA required the employer to provide and maintain any protective gear required. So, if your contractor requires long pants for safety reasons, then he can buy them and launder them for you. But, if he calls it a dress code, then you are on your own. He can't use OSHA as the reason.