OSHA is proposing to amend its existing occupational standard that regulates employee exposure to 1,3-Butadiene (BD), based upon the determination that its current permissible exposure limit (PEL) is inadequate for employee health protection. OSHA proposes to reduce the PEL for BD to an 8-hour time weighted average (TWA) of 2 ppm and a short term exposure limit (STEL) of 10 ppm for 15 minutes.