NOTICE OF INTENDED CHANGE: For styrene the reduction of TLV to 20 ppm (85 mg m3 and STEL to 40 ppm (170 mg m3) and designation of the carcinogen A4 notation has been proposed. Carcinogen A4: Not classifiable as human carcinogen: Inadequate data on which to classify the substance as a human andlor animal carcinogen.