According to OSHA's preface to the regulation:
The items excepted from payment by this rule are: Non-specialty safety-toe protective footwear (including steel-toe shoes or steel-toe boots) and non-specialty prescription safety eyewear, that is allowed by the employer to be worn off the job-site; Shoes or boots with built-in metatarsal protection that the employee has requested to use instead of the employer-provided detachable metatarsal guards; Logging boots required by 1910.266(d)(1)(v); Everyday work clothing; or ordinary clothing, skin creams, or other items used solely for protection from the weather.
For a long, detailed discussion and the regulation itself, please see here.