OSHA standard 1910.136 – Occupational foot protection. is the standard that governs safety footwear in regards construction. Specifically:
General requirements. The employer shall ensure that each affected employee uses protective footwear when working in areas where there is a danger of foot injuries due to falling or rolling objects, or objects piercing the sole, and where such employee’s feet are exposed to electrical hazards.
It gets a bit confusing since the standards have been changed from ANSI Z41-1991 to ASTM F2413-05. You can read about the ASTM requirements here.