3 . Specific duties for working with engineered stone
WHS Regulation clause 49 Ensuring exposure standards for substances and mixtures not exceeded
An exposure standard represents the airborne concentration of a particular substance or mixture that must not be exceeded . It does not represent a line between a ‘ safe ’ and ‘ unsafe ’ concentration of an airborne substance or mixture . The exposure standard does not eliminate risk of disease and some people might experience adverse health effects below the exposure standard .
A PCBU at a workplace must ensure that no person at the workplace is exposed to a substance or mixture in an airborne concentration that exceeds the exposure standard for the substance or mixture . The duty to ensure the workplace exposure standard is not exceeded is absolute and not qualified by ‘ so far as is reasonably practicable ’.
This means that a PCBU must ensure that no person at the workplace is exposed to a hazardous chemical , such as crystalline silica , at a concentration above the workplace exposure standard .
The workplace exposure standard for respirable crystalline silica is an eight hour time weighted average ( TWA ) of 0.05 milligrams per cubic metre ( mg / m 3 ).
Adjustment of exposure standards for extended work shifts
A TWA is based on exposure that happens over an eight hour working day followed by 16 hours of no exposure , over a five day working week .
To comply with the WHS Regulation , it may be necessary for the PCBU to adjust the TWA to compensate for greater exposure during longer work shifts and decreased time between shifts . Situations where the TWA may need to be adjusted include where workers have :
− a working day longer than eight hours o for example , a worker ’ s daily hours are 7 am to 5 pm with a one hour lunch break
Monday to Friday − a working week longer than 40 hours o for example , a worker ’ s weekly hours are 8 am to 3 pm Monday and Tuesday and 7 am to 6 pm Wednesday to Thursday with a one hour lunch break , or
− work shift rotations in excess of either eight hours a day or 40 hours a week .
A competent person , such as a certified occupational hygienist , should be engaged to adjust the workplace exposure standard to account for shift variations or longer working weeks .
The workplace exposure standard must not be adjusted upwards , even for shifts less than eight hours .
Managing the risks of respirable crystalline silica from engineered stone in the workplace - Code of Practice 19 of 57