Respirable crystalline silica
The fraction of silica dust small enough to reach deep lung tissue. Federal rules set a permissible exposure limit of 50 micrograms per cubic meter as an 8-hour average.
What does respirable crystalline silica mean?
An action level of 25 micrograms per cubic meter triggers exposure assessment and medical surveillance obligations for employers. Construction employers may comply either by fully implementing the specified controls listed in the regulation's task table or by measuring exposures and controlling them below the limit. There is no exemption for small crews, residential work, or outdoor tasks.
In practice
Any contractor whose crew cuts, cores, grinds, or chips concrete needs a written exposure control plan and a competent person, regardless of company size.