Цахиурын тоосыг агаараас яаж зайлуулах вэ? Do pavers have silica? Recognizing that very small, respirable silica particles are hazardous, OSHA regulation 29 CFR 1926.55(a) requires construction employers to keep worker exposures at or below a Permissible Exposure Level (PEL) of 50 µg/m 3 .