Public Domain Concrete demolition via PXhere

Workers performing concrete chipping at substructure bridge repair sites had the highest level of respirable crystalline silica exposure, a time-weighted average of 527 micrograms per cubic meter of air. That is more than 10 times the PEL of 50 micrograms per cubic meter that OSHA established in its most recent silica regulation (1926.1153).

Source: Another reason to avoid concrete: silica dust | TreeHugger