How to Conduct a DPM Exposure Assessment: A Step-by-Step Guide for Safety Managers

Diesel particulate matter (DPM) poses a significant health risk to workers in industries ranging from mining and construction to transport and logistics. In December 2026, Australia’s Workplace Exposure Limit (WEL) for DPM will drop to 0.01 mg/m³, making accurate exposure assessment more critical than ever before.

But conducting a proper DPM exposure assessment isn’t just about taking a few air samples. It requires a structured, methodical approach that begins long before any sampling equipment is deployed and continues well after results arrive from the laboratory.

This guide walks safety managers through the eight essential steps of conducting a DPM exposure assessment that will stand up to regulatory scrutiny and genuinely protect your workforce.

Step 1: Preliminary Assessment — Identifying DPM Sources and Risk Level

Before you buy a single piece of sampling equipment, you need to understand what you’re looking for.

A preliminary assessment is a detailed audit of your workplace to identify:

• Diesel equipment in use: Which machines, vehicles, or generators produce DPM? Are they in continuous operation or used intermittently?
• Worker exposure patterns: Which roles bring workers into proximity with DPM? How much time do they spend near sources?
• Environmental conditions: What’s the ventilation like? Are there enclosed spaces, open-air sites, or semi-enclosed areas?
• Existing controls: What dust suppression, extraction, or isolation measures are already in place?

This step typically involves:
– Walking the site with the relevant workers and supervisors
– Documenting equipment specifications and operating hours
– Photographing problem areas and noting ventilation sources
– Reviewing maintenance records to assess equipment condition (poorly maintained engines produce higher emissions)
– Identifying seasonal variations (e.g., higher usage in certain months)

The output is a risk map that identifies which roles face the highest potential exposure and therefore need priority sampling.

Why this matters: A thorough preliminary assessment prevents you from wasting resources sampling low-risk roles while missing high-risk ones. It also ensures your sampling strategy is defensible—you can explain why you chose to monitor specific workers.

Step 2: Sampling Strategy — Who to Monitor and for How Long

Once you’ve identified risk zones, you need to decide which workers to sample and when.

The AIHA (American Industrial Hygiene Association) strategy recommends a minimum of three samples per exposure group to establish statistical reliability. An “exposure group” consists of workers performing similar tasks under similar conditions.

Key considerations:

• Worker selection: Choose workers performing typical tasks during typical conditions. Avoid sampling during unusually busy or quiet shifts.
• Sampling duration: Personal sampling must capture a representative exposure period. For an 8-hour shift worker, this typically means an 8-hour sample during a regular work day. For shift workers or those doing DPM-generating tasks only part of the day, sample during the period when they’re actually exposed.
• Frequency: At minimum, conduct initial baseline samples. After that, the frequency depends on your risk profile and regulatory expectations. High-risk sites may need quarterly or semi-annual resampling; lower-risk sites may only need re-assessment when operations change.
• Timing: Avoid sampling during maintenance days, shutdowns, or other atypical periods unless those are regular operational scenarios you need to understand.

Practical tip: Coordinate with supervisors and workers. Let them know what to expect and why you’re doing it. Workers are more likely to allow sampling if they understand it’s for their safety, not as a monitoring mechanism for performance.

Step 3: Equipment Setup — Pumps, Filters, and Cyclone Assemblies

Personal DPM sampling requires specific equipment configured correctly. Using the wrong components or incorrect flow rates will invalidate your results.

Essential components:

1. Personal sampling pump: Battery-operated, field-calibrated. Flow rate must be set to 2 L/min for respirable DPM.
2. Cyclone assembly: A size-selective inlet that removes larger particles and collects only the respirable fraction (particles less than approximately 4 µm). This is critical because the WEL is specifically for respirable DPM.
3. 37 mm quartz fibre filter: The filter media onto which DPM particles are deposited. Quartz fibre is required for NIOSH Method 5040 analysis (thermal-optical analysis depends on the filter medium).
4. Filter support cassette: Holds the filter in place within the cyclone.
5. Connecting tubing: Connects the pump to the cyclone assembly. Must be relatively short (ideally less than 2 meters) to minimize particle loss.

Calibration is non-negotiable:
– Every sampling pump must be calibrated before the sampling shift begins and immediately after the shift concludes.
– Calibration verifies that the pump is running at the correct flow rate (2 L/min). Temperature and atmospheric pressure changes during the shift can affect flow rate, so pre- and post-calibration captures any drift.
– Use a soap bubble flow meter or electronic flow calibrator. Record the actual flow rates; these will be needed for laboratory calculations.
– If pre- and post-calibration flow rates differ by more than ±5%, the sample becomes unreliable and may need to be discarded.

What to check before deploying:
– Pump batteries are fully charged
– All tubing connections are tight (no leaks)
– The cyclone assembly is clean (residue from a previous sample contaminates results)
– The filter cassette is properly seated in the cyclone
– There are no visible cracks or damage to any component

Step 4: Conducting the Sample — What Happens During the Shift

This is the phase where your worker becomes a mobile air sampler for the duration of their shift.

During the sampling period:

1. Attach the pump to the worker: The pump is typically clipped to the belt or placed in a small backpack. The cyclone assembly and filter cassette are positioned in the worker’s “breathing zone”—ideally at shoulder height or close to the mouth and nose, typically within 15–30 cm of the face.

2. Document start time and conditions: Record the exact time sampling begins, the worker’s name/ID, their assigned task, ambient temperature, and atmospheric pressure. This information goes on the filter cassette label and in your sampling logbook.

3. Inform the worker: Make sure they understand that they’re wearing the sampler and that it needs to stay in the breathing zone. Remind them not to cover the inlet or lay it down. Some workers become self-conscious; normalizing the presence of the pump beforehand helps.

4. Monitor battery and equipment: If possible, periodically check that the pump is still running (visual indicator light, audible tone, or periodic checks). If the pump stops mid-shift, the sample is compromised.

5. Document any incidents or anomalies: Was the worker exposed to unusually high diesel fumes? Did equipment malfunction during the shift? Were there any unusual conditions? These notes provide context for interpreting results.

6. Record end time: When the shift ends or the representative exposure period is complete, record the exact time and note any relevant final observations (equipment condition, worker complaints, visible emissions).

Critical point: The integrity of personal sampling depends entirely on the sample remaining undisturbed and in the breathing zone throughout the collection period. Any interruption, relocation, or covering of the inlet invalidates the data.

Step 5: Chain of Custody — Getting Samples to the NATA Lab Correctly

Once the sample is collected, it becomes legal evidence of workplace exposure. From this point forward, every step must be documented.

Proper chain of custody procedures:

1. Seal the sample: Immediately after collection, the filter cassette must be sealed. Most cassettes have a protective cover or can be wrapped securely. Label it clearly with:
2. Worker name/ID
3. Date and time of collection (start and end)
4. Pump model and serial number
5. Pre- and post-calibration flow rates
6. Worker’s job title/task performed

7. Any anomalies or notes

8. Segregate samples: Place sealed samples in a protective container (typically a padded box or seal bag). Protect them from:

9. Moisture (no damp environments)
10. Extreme heat or cold
11. Contamination from other airborne dust

12. Physical damage (crushing or bending)

13. Complete the submission form: Your NATA-accredited laboratory will provide a sample submission form. Complete it fully with:

14. All worker and sampling details
15. Pre- and post-calibration flow rates (the lab needs these to calculate actual air volume sampled)
16. Analysis requested (NIOSH 5040 for elemental carbon determination)

17. Any special notes or concerns

18. Document transport: Record who transported the samples, the date, time, and method of transport (courier, hand delivery, post). If using a courier, keep the tracking number.

19. Lab receipt: The laboratory should provide a receipt confirming receipt of samples. Keep this documentation. If results are ever questioned, you can prove the samples reached the lab in the expected condition.

Why this matters: If your results are ever challenged—whether during a regulatory investigation or a worker’s compensation dispute—the chain of custody proves that the sample wasn’t contaminated, lost, mislabeled, or altered between collection and analysis.

Step 6: NIOSH Method 5040 Laboratory Analysis

Once the NATA lab receives your samples, they’ll conduct thermal-optical analysis using NIOSH Method 5040 to determine elemental carbon (EC) content.

Here’s what happens behind the scenes (you don’t need to run this yourself, but understanding the process helps you interpret results):

The analytical process:

1. Sample preparation: The lab removes the filter from the cassette in a controlled environment.

2. Thermal-optical analysis: The filter is placed in an analytical instrument that heats it in stages. Initially, it heats in an inert atmosphere (no oxygen), which drives off organic carbon (OC). Then it heats in an oxygen atmosphere, which combusts elemental carbon (EC). A laser measures light transmission changes, allowing the instrument to distinguish EC from OC.

3. Calibration and quality control: The instrument is calibrated daily using known standards. The lab runs quality control (QC) samples alongside your worker samples to ensure accuracy.

4. Calculation: The lab calculates the mass of EC on the filter (in micrograms) and divides it by the volume of air sampled (in cubic meters) to express results as mg/m³ EC.

The lab report will include:

• Elemental carbon concentration (mg/m³) for each sample
• Detection limit (the lowest concentration the method can reliably measure)
• Uncertainty of measurement (typically expressed as a percentage or confidence interval)
• Pre- and post-calibration flow rates (confirming the pump operated correctly)
• Total sampling time and calculated air volume
• Quality control results (demonstrating analytical accuracy)
• Method reference (NIOSH 5040)

Choosing a NATA lab: Ensure your laboratory is NATA-accredited for NIOSH Method 5040 analysis. Accreditation means the lab has demonstrated technical competence and operates under quality assurance standards. It’s the gold standard for defensibility.

Step 7: Interpreting Results — Comparing Against the WEL

Results in hand, it’s time to understand what they mean.

The Australian Workplace Exposure Limit for DPM:

From December 2026, the 8-hour time-weighted average (TWA) WEL for respirable DPM (elemental carbon) is 0.01 mg/m³. This is a significant decrease from previous exposure guidance and reflects updated understanding of DPM health hazards.

Time-Weighted Average (TWA) calculation:

If your worker was sampled for the full 8-hour shift, their result directly represents the 8-hour TWA. If sampling was shorter (e.g., a 4-hour task), the lab result represents exposure during that period, but you must contextualise it:

• If a worker was exposed to 0.025 mg/m³ for 4 hours and zero DPM for the other 4 hours, their 8-hour TWA would be: (0.025 × 4 + 0 × 4) ÷ 8 = 0.0125 mg/m³

This calculation matters for compliance assessment.

Interpreting individual results:

• Below 0.01 mg/m³: Compliant with the WEL. The worker is adequately protected by current controls. Continue current practices and re-sample according to your DPM monitoring frequency schedule.

• Near the WEL (0.008–0.012 mg/m³): This is the critical zone. Due to uncertainty of measurement (typically ±20–30% for this analysis), results in this range mean you cannot be confident whether true exposure is above or below the WEL. Action required: Re-sample to confirm, or tighten controls immediately as a precaution.

• Above 0.01 mg/m³: Non-compliant. The worker’s exposure exceeds the WEL. This triggers mandatory control improvements. See Step 8 for reporting and recommendations.

Accounting for uncertainty of measurement:

Every analytical result has inherent uncertainty. A result of 0.012 mg/m³ with ±25% uncertainty means the true value is somewhere between 0.009 and 0.015 mg/m³. When results are near the WEL, this uncertainty becomes critical. Your NATA lab will provide uncertainty estimates; factor these into your decision-making.

Multiple samples and statistical interpretation:

If you’ve collected three samples (best practice), look at the pattern:
– All three below 0.01 mg/m³ → Strong evidence of compliance
– One above, two below → Investigate the circumstances of the high sample; consider re-sampling
– Two or more above → Clear exceedance; immediate action required

Step 8: Reporting and Control Recommendations

Results must be communicated clearly to management and workers — understanding who carries legal responsibility is critical; see our guide on WHS officer DPM monitoring obligations in Australia. This step also triggers the next phase of your DPM control strategy.

Preparing your assessment report:

1. Executive summary: Overview of exposure group, sampling dates, number of samples, key findings, and compliance status.

2. Sampling methodology: Document your preliminary assessment findings, why you chose this group, sampling strategy, and conditions during sampling.

3. Results table: Present all results clearly, including individual sample values, average, range, and comparison to the WEL. Cross-reference against our DPM compliance checklist for Australian workplaces to ensure all mandatory documentation elements are covered.

4. Compliance assessment: State clearly whether exposure is above or below the WEL and any uncertainty considerations.

5. Control recommendations: If results are above the WEL or borderline:

6. Engineering controls: Better ventilation, enclosed cabs with filtered air, DPM-generating equipment relocation
7. Operational controls: Reduce equipment operating time, improve maintenance (cleaner engines = less DPM), rotate workers to reduce individual exposure
8. PPE: Respiratory protection as a last resort, only when other controls aren’t feasible

9. Frequency of future monitoring: When to re-assess (often 6–12 months after controls are implemented to verify effectiveness)

10. Worker communication: A summary suitable for sharing with affected workers, explaining the results and any changes to their work environment or PPE requirements.

Legal and regulatory considerations:

• Keep all documentation: preliminary assessment, sampling logs, calibration records, lab reports, chain of custody documentation, and your assessment report. These may be requested during a regulator inspection or worker compensation claim.
• Notify workers of results. Most jurisdictions require this; it’s also ethical practice.
• If non-compliant, document what corrective actions you’ve taken and when. This demonstrates due diligence if a worker later becomes ill.

Step 9: When to Bring in a Professional Occupational Hygienist

Many organizations lack in-house expertise to conduct DPM assessments properly. There’s no shame in that—occupational hygiene is a specialized discipline.

Signs you should engage a professional:

• No expertise in-house: If your safety team has never conducted personal air sampling, the learning curve is steep. A professional ensures your first assessment is done correctly.
• Complex workplace: Multiple equipment types, varying shifts, seasonal variations, or unusual ventilation challenges benefit from expert analysis.
• High-risk operations: Mining, heavy construction, or large fleet operations warrant professional oversight.
• Regulatory scrutiny: If you’ve had regulator involvement or are in a high-compliance industry, a professional report carries more weight.
• Results near the WEL: When results are borderline, professional interpretation of uncertainty and recommendations for controls is valuable.
• Litigation risk: If there’s potential worker compensation or legal claims, a professionally conducted assessment is defensible.

What a professional hygienist brings:

• Expertise in exposure assessment strategy and sampling design
• Access to calibrated equipment and NATA-accredited laboratories
• Ability to interpret complex results and recommend proportionate controls
• Documentation and reporting that withstands regulatory or legal scrutiny
• Ongoing monitoring program design tailored to your workplace

FAQ

Q: How many samples do I need to conduct a valid DPM exposure assessment?

A: The AIHA recommends a minimum of three samples per exposure group to establish statistical reliability. This allows you to assess not just an average, but the range and consistency of exposure. If resources are extremely limited, at least two samples are better than one, though one sample is legally defensible only in very low-risk scenarios.

Q: Can I use area (static) monitoring instead of personal sampling to assess WEL compliance?

A: No. Area monitoring measures DPM at a fixed point in space; personal monitoring measures what an individual worker actually breathes. The WEL is a personal exposure limit. Personal sampling is the only legally defensible method for compliance assessment. Area monitoring is useful for identifying hotspots and assessing control effectiveness, but it cannot replace personal sampling.

Q: What if my results are slightly above the WEL but my uncertainty of measurement suggests the true value might be below?

A: You cannot assume you’re compliant based on uncertainty. The precautionary principle applies: if you cannot confidently demonstrate compliance, you must treat the exposure as non-compliant and implement controls. Re-sample after implementing controls to verify effectiveness.

Q: How often should I re-sample after implementing controls?

A: This depends on your risk assessment and regulatory expectations. Best practice is to re-sample 6–12 months after control implementation to confirm that changes have been effective. Once you’ve demonstrated sustained compliance (e.g., two consecutive rounds of sampling below the WEL), you may extend monitoring intervals to annually or every two years, depending on process stability.

Q: Do I need to sample every worker exposed to DPM?

A: No. You sample representative workers from exposure groups. Workers performing similar tasks under similar conditions can be grouped together, and you sample a subset of that group (minimum three samples per group). This is more efficient than sampling everyone while still providing data that represents the group’s exposure profile.

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Next Steps: Too Complex to Manage In-House?

Conducting a proper DPM exposure assessment requires expertise, specialized equipment, quality laboratory relationships, and meticulous documentation. If your organization lacks any of these elements, you’re at risk of invalid results or regulatory non-compliance.

Anitech Group’s occupational hygienists handle the entire DPM assessment process end-to-end: from preliminary site assessment and sampling strategy design, through equipment deployment and chain of custody management, to laboratory liaison and comprehensive reporting.

We ensure your assessment is defensible, compliant, and drives real protection for your workforce.

Contact Anitech for a DPM Exposure Assessment →

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Related Reading

• Complete Guide to Diesel Particulate Matter Monitoring in Australia
• DPM Workplace Exposure Limit: Australia’s New 0.01 mg/m³ WEL from December 2026
• NIOSH Method 5040 Explained: How Elemental Carbon Analysis Works