| 📋 Article Summary — Personal Dust Sampling Methodology | |
|---|---|
| Entity | Anitech Group — Occupational Hygiene |
| Article Type | How-To Guide / Methodology Reference |
| Target Audience | Occupational hygienists, WHS advisors, safety professionals conducting workplace monitoring |
| Key Entities | Safe Work Australia, NATA, AIOH, AS 2985:2009 (workplace air sampling), AS/NZS 3580 series |
| Regulations & Standards | AS 2985:2009 Workplace atmospheres — method for sampling and gravimetric determination of respirable dust; MDHS101 analytical method; AIOH Occupational Hygiene Guide |
| Key Fact 1 | Pump flow rate calibration error of just ±10% propagates directly into a ±10% error in calculated exposure concentration — highlighting the criticality of calibration. |
| Key Fact 2 | Statistical analysis using AIHA IHSTAT or lognormal modelling requires a minimum of 6 samples per SEG to make reliable exceedance probability estimates. |
| Key Fact 3 | The 95th percentile exposure — not the mean — is the statistically appropriate WES comparison point, as it captures the most exposed workers in the SEG. |
| What This Covers | Full-shift sampling protocol, pump types and maintenance, sampler selection (inhalable vs respirable), filter selection, field QC procedures, data analysis and reporting |
| What This Does Not Cover | Specific NATA accreditation requirements for laboratories, area (static) sampling methods for source characterisation |
| Primary CTA | Contact Anitech for expert occupational hygiene dust sampling surveys |
| Read Time | 10 min read |
Personal air sampling for dust is a core occupational hygiene technique used to assess worker exposure to airborne particulate against a Workplace Exposure Standard (WES). When conducted correctly, it produces legally defensible data for compliance assessment, risk management decisions and worker health protection. When conducted poorly — inadequate pump calibration, wrong sampler type, unrepresentative sample selection — it produces meaningless or misleading data that provides false assurance while workers continue to be overexposed.
This guide provides a practical, step-by-step methodology for conducting valid personal dust sampling in Australian workplaces, aligned with AS 2985:2009 and AIOH best practice guidelines.
Step 1: Define the Purpose and Design the Survey
Before any equipment is deployed, the survey purpose must be clearly defined. Is this a baseline survey to establish current exposure levels? A compliance check against the WES? An evaluation of new controls? A post-incident investigation? Each purpose requires different decisions about sample numbers, timing and statistical analysis.
The Similar Exposure Group (SEG) approach is the framework for survey design. Workers are grouped by task type, duration, proximity to sources, and environmental conditions. The goal is that every worker in an SEG has an approximately similar probability distribution of exposure. SEGs should be defined before sampling, not post-hoc to explain results.
Step 2: Select the Correct Sampling Equipment
Sampler Type
The most fundamental equipment decision is the particle size fraction to be sampled:
- Inhalable fraction: Use an IOM sampler (SKC), 7-hole inhalable sampler, or button sampler at 2 L/min. Required for: total dust WES, wood dust, flour dust, grain dust, nuisance dust, inhalable metal WES
- Respirable fraction: Use a BGI GS-3 or Casella Dorr-Oliver cyclone at 2.2 L/min. Required for: respirable crystalline silica, respirable coal mine dust, respirable limestone/calcium carbonate, some metal dust WES values
- Thoracic fraction: Rarely required in routine Australian practice; specific WES values apply (e.g., some coal dust entries)
Filter Type
Filter selection depends on the analytical method:
- PVC membrane (5 µm pore, 25 mm): Standard for gravimetric dust analysis, total welding fume, most inhalable metals
- Quartz-fibre filter: Required for elemental carbon (DPM) analysis and organic carbon methods
- Mixed cellulose ester (MCE) filter: For asbestos fibre counting (PCM) and some metal analyses
- PTFE filter: For demanding gravimetric applications requiring low filter mass variability; also for some acid mist analyses
- NaOH/Na₂CO₃ impregnated PVC: Specifically for Cr(VI) sampling
Pump Selection
Personal air sampling pumps must maintain a constant, accurate flow rate throughout the sampling period. Key specifications:
- Flow rate range appropriate for sampler type (typically 1–4 L/min)
- Flow constancy: ≤±5% variation against back-pressure equivalent to loaded filter
- Battery life sufficient for a full-shift sample (8+ hours)
- ATEX/intrinsically safe certification if used in flammable atmosphere
- Audible alarm for flow rate out-of-tolerance conditions
Suitable pumps include SKC AirChek TOUCH, Casella Apex2, Gillian BDX-II. All pumps must be within NATA calibration certification.
Step 3: Calibrate Pumps
Flow rate calibration is performed immediately before and after each sampling period using a primary standard calibrator — either an electronic bubble meter (e.g., DryCal) or piston calibrator. The calibration procedure:
- Attach the actual loaded sampler assembly (cyclone + filter cassette or IOM sampler) to the pump — calibration must include the same back-pressure as sampling
- Connect the calibration device upstream of the sampler
- Take three readings at the target flow rate. Record mean ± SD
- Adjust pump if outside ±5% of target
- Record pump ID, calibrator ID, date, time, operator, and calibration readings on the field data sheet
- Repeat post-sampling — if post-sampling flow differs by >10% from pre-sampling, the sample is suspect and must be flagged
Step 4: Fit Samplers to Workers
Personal samplers must be positioned in the breathing zone — within 30 cm of the nose and mouth, typically on the lapel or collar. Orientation of the IOM sampler face (downward 45° recommended) matters for collection efficiency. The pump body is clipped to the belt or pocket. Tubing must be routed to avoid kinking or restriction.
Workers must be informed of the purpose of sampling, instructed not to touch or relocate the sampler during the work period, and asked to perform their normal duties as if the sampler were not present. Any deviation from normal work — unusual tasks, longer breaks, equipment failure — must be recorded on the field data sheet for interpretation.
Step 5: Document Field Information
A comprehensive field data sheet records: worker name, job title and SEG, task description, sampling start and end times, pump ID and flow rates, sampler type and filter ID, site conditions (temperature, humidity, ventilation status), any abnormal events, and the hygienist’s observations. This documentation is as important as the analytical result — without it, results cannot be correctly interpreted.
Step 6: Handle and Submit Filters Correctly
Filters must be carefully removed from samplers in a clean environment, capped immediately to prevent contamination and moisture uptake, and stored in a cool, dry location. At least 10% of samples (minimum one per batch) must be field blanks — loaded cassettes or IOM samplers transported to site and back without airflow. Filters are submitted to a NATA-accredited occupational hygiene laboratory with chain-of-custody documentation.
Step 7: Calculate Exposure and Interpret Results
The 8-hour TWA concentration is calculated as:
C (mg/m³) = Filter mass collected (mg) ÷ Volume sampled (m³)
Volume sampled = Average flow rate (L/min) × Duration (min) ÷ 1000
Individual results are compared to the WES. For multiple samples across an SEG, lognormal distribution analysis using AIHA IHSTAT (or equivalent) estimates the geometric mean (GM), geometric standard deviation (GSD), and upper confidence bound on the 95th percentile (UCB95). The UCB95 compared to the WES determines whether the SEG can be classified as acceptably controlled.