The workplace exposure standard (WES) for RCS is 0.05mg/m3 averaged over 8 hours, or adjusted for extended work shifts (for example, 12-hour shifts).

You must make sure that no one at the workplace is exposed to levels above the WES.

You must monitor the level of RCS if:

• you're unsure whether it exceeds the WES, or
• you need to determine whether there’s a risk to health from RCS at the workplace.

Monitoring should be done in the worker’s breathing zone for the duration of a worker’s shift to gauge the average amounts that they would be exposed to during normal work activities, including routine breaks.

‘Breathing zone’ means a hemisphere of 300 mm radius extending in front of a person’s face and measured from the midpoint of an imaginary line joining the ears.

Adjustment of 8-hour time weighted average exposure standards.

Where workers have a working day longer than 8 hours or work more than 40 hours a week, the person conducting the business or undertaking must determine whether the time weighted average (TWA) exposure standard needs to be adjusted to compensate for the greater exposure during the longer work shift, and decreased recovery time between shifts.

Safe Work Australia publishes the ' Workplace exposure standards for airborne contaminants (external site)' that contains the revised value for respirable crystalline silica.