An 8-hour time-weighted average (TWA) exposure limit is based on exposure that occurs in an 8-hour working day, 5-day working week. Where workers have a working day longer than eight hours, a working week longer than 40 hours or work shift rotations in excess of either 8 hours a day or 40 hours a week, the TWA exposure limit may need to be adjusted to compensate for the greater exposure during the longer work shift and the decreased recovery time between shifts. (Note: Peak limitation or STEL exposure standards must not be adjusted because the adverse effects due to acute over-exposure are already accounted for).
The new AIOH Workplace Exposure Limits (WEL) Shift Adjustment Tool:
The tool was produced by TAC committee members. It provides the same functionality and user experience as the existing AIOH Workplace Exposure Standards (WES) Shift Adjustment Tool (last updated in September 2020) but has been updated to use the new Safe Work Australia (SWA) Workplace exposure limits for airborne contaminants (WEL) list. The tool now also advises the user if a substance is classified as a non-threshold genotoxic carcinogen (NTGC).
The new WEL list commences on 1 December 2026, having the tool freely available to members via the AIOH website as early as possible will facilitate the provision of sound technical advice for the new limits.
Note: The spreadsheet contains macros which may be blocked by certain IT administration systems. The macros can be activated in MS Excel by clicking on the File menu > then click on the Info tab > then Enable content.
The papers which give you the basis for the AIOH WES Shift Adjustment Tool are attached below.
WES Adjustment Tool, Firth & Drolet, AIOH Conference (2013).
Development of a Tool for Adjustment of WES for Contaminants due to Extended Work Shifts, Firth and Drolet, J of Health and Safety, Research and Practice (p7, Sept 2014).
The Workplace Exposure Standards (WES) Shift Adjustment Tool is based on 8 hour shift exposures. However, many workplaces in Australia use a variety of extended work hours and shift rosters. Consequently, the WES value needs to be adjusted and there are a number of ways this can be performed depending on a variety of parameters eg: chronic vs acute health effects.
The AIOH have developed the WES Shift Adjustment Tool which has been based on the well accepted technical information currently available. The WES Tool was last updated in September 2020 with RCS WES.
Download the template tool as a PDF document or Excel Spreadsheet.Basic Thermal Risk Assessment
The Basic Thermal Risk Assessment is a first level qualitative risk assessment tool that does not require specific technical skills in its administration, application or interpretation. It's designed to be used by employers, employees or technicians to provide guidance and also as a training tool to illustrate the many factors that impact heat stress and working in hot environments.
