| 📋 Article Summary — WES Values for Common Dusts | |
|---|---|
| Entity | Anitech Group — Occupational Hygiene |
| Article Type | Reference Guide / Regulatory Compliance |
| Target Audience | Occupational hygienists, WHS advisors, safety officers, industrial hygiene students |
| Key Entities | Safe Work Australia, Workplace Exposure Standards for Airborne Contaminants (2020 edition + updates) |
| Regulations & Standards | Safe Work Australia Workplace Exposure Standards for Airborne Contaminants — current edition; model WHS Regulations Part 7.1 hazardous chemicals and substances |
| Key Fact 1 | Australia’s RCS WES (0.05 mg/m³) is among the strictest globally — the EU standard is 0.1 mg/m³ and the US OSHA PEL is still based on outdated formula-derived limits in many states. |
| Key Fact 2 | WES values are ceiling or TWA values for healthy workers performing moderate work — they must be adjusted for extended workshifts (10-hour, 12-hour) using a pharmacokinetic model. |
| Key Fact 3 | The WES document distinguishes between inhalable, respirable and thoracic fractions — using the wrong sampler can make a compliant operation appear non-compliant and vice versa. |
| What This Covers | Comprehensive WES reference table for dust types, fraction definitions, sampler selection guide, work shift correction factors, ALARP principle application |
| What This Does Not Cover | WES values for chemical vapours and gases (separate from dust), biological exposure indices, WES derivation methodology |
| Primary CTA | Contact Anitech for expert interpretation of dust monitoring results against Australian WES values |
| Read Time | 9 min read |
Safe Work Australia publishes and maintains the Workplace Exposure Standards for Airborne Contaminants — the primary reference document for occupational exposure limits in Australian workplaces. Understanding which WES applies to a given dust, what particle size fraction it refers to, and how to correctly interpret monitoring results against it are fundamental skills for anyone conducting workplace dust assessments.
The Three Particle Size Fractions
Not all dust is equal — the health effects depend critically on where particles deposit in the respiratory tract, which is determined by particle size. Three sampling conventions are used:
- Inhalable fraction: All airborne particles that can enter the nose or mouth during breathing — up to approximately 100 µm aerodynamic diameter. Sampled using an inhalable sampler (IOM, 7-hole, button sampler). Relevant for materials depositing anywhere in the respiratory system and for larger particles that deposit in the nose, throat and bronchial airways
- Respirable fraction: Particles small enough to penetrate to the gas-exchange region of the lung (alveoli) — approximately 50% collection efficiency at 4 µm aerodynamic diameter, following the ACGIH respirable convention. Sampled using a cyclone. Relevant for materials causing alveolar disease (silicosis, pneumoconiosis, fibrosis)
- Thoracic fraction: Particles penetrating beyond the larynx — intermediate between inhalable and respirable. Rarely used in routine Australian practice; some coal dust and some rubber dust WES values reference the thoracic fraction
WES Reference Table for Common Dusts
| Dust Type | WES (mg/m³) | Fraction | Sampler Required |
|---|---|---|---|
| Respirable crystalline silica (quartz) | 0.05 | Respirable | Cyclone |
| Coal mine dust (RCMD) | 1.5 | Respirable | Cyclone |
| Hardwood dust (oak, beech, etc.) | 1 | Inhalable | IOM / 7-hole sampler |
| Softwood dust (pine, spruce) | 2 | Inhalable | IOM / 7-hole sampler |
| Wheat flour dust | 1 | Inhalable | IOM / 7-hole sampler |
| Grain dust (all species) | 4 | Inhalable | IOM / 7-hole sampler |
| Total welding fume | 1 | Inhalable | IOM / 7-hole sampler |
| Diesel particulate matter (EC) | 0.1 | Respirable EC | Cyclone + quartz filter |
| Limestone dust (calcium carbonate) | 10 (inhal) / 3 (resp) | Both | IOM or Cyclone |
| Portland cement dust | 10 (inhal) / 3 (resp) | Both | IOM or Cyclone |
| Nuisance dust (PNOC*) | 10 (inhal) / 3 (resp) | Both | IOM or Cyclone |
| Glass wool fibres | 1 f/mL | Fibres (PCM) | MCE filter |
| Refractory ceramic fibres | 1 f/mL | Fibres (PCM) | MCE filter |
*PNOC: Particulates not otherwise classified (formerly PNOR). Applies when no specific WES exists for the material. Does not apply to materials with specific WES values.
Extended Work Shift Adjustments
The standard WES values are derived for an 8-hour workday, 5-day work week (40 hours). Workers on 10-hour or 12-hour shifts receive a higher total daily dose if WES values are applied without adjustment. The Brief and Scala model is commonly used for shift adjustment:
For a 10-hour shift: Adjusted WES = WES × (8/h) × (24-h)/16, where h = shift duration in hours
For a 10-hour shift: Adjustment factor ≈ 0.7 (i.e., 70% of the standard 8-hour WES)
For a 12-hour shift: Adjustment factor ≈ 0.5
This adjustment is mandatory for all hazardous substances on extended roster patterns. Failure to apply shift adjustments to WES comparisons systematically overestimates compliance.
ALARP Below the WES
Compliance with the WES does not mean exposure reduction efforts can stop. The model WHS Act requires exposures to be reduced so far as is reasonably practicable — SFAIRP or ALARP. For materials classified as carcinogens (RCS, hardwood dust, welding fume, DPM), there is no threshold below which carcinogenic risk is zero; every reduction in exposure reduces risk. The WES is the legal minimum — the goal is to achieve the lowest reasonably practicable concentration.