Beyond Dust | Measuring the Invisible in Diesel Exhaust

Why Diesel Engine Fumes Pose a Significant Hazard

Safe Work Australia’s current guidance specifically identifies miners, construction workers, oil and gas workers, forklift drivers, loading dock workers, truck drivers, farmworkers, stevedores and vehicle maintenance workers as those who may be exposed to Diesel Engine Emissions (DEE).

Inhalation is the primary route of exposure to diesel exhaust emissions at work, and it can cause immediate effects such as irritation of the eyes, nose, throat, and lungs; dizziness; nausea; coughing; or severe asphyxiation from carbon monoxide.

Long-term exposure is linked to increased risks of lung and bladder cancers, as DEE and its contaminant PAHs are carcinogenic. Each year, about 130 Australians develop lung cancer due to occupational DEE exposure. Chronic exposure can also worsen asthma and allergies and increase the risk of heart and lung diseases, including chronic obstructive pulmonary disease.

Common sources include heavy vehicles such as trucks, buses, trains, tractors, ships, loaders, forklifts, and bulldozers, as well as other construction and mining equipment. DEE can also originate from stationary power sources such as generators and winch motors.

What is Diesel Particulate Matter?

The main components of diesel engine emissions are gases like nitrogen, oxygen, carbon dioxide, and water vapour. A small portion includes hazardous chemicals such as carbon monoxide, nitrous oxide, nitrogen dioxide, sulphur oxides, and diesel particulate matter (DPM). DEE may also contain trace amounts of hydrocarbons like formaldehyde, benzene, toluene, phenol, PAHs, and others.

Diesel Particulate Matter (DPM) is the particulate component of diesel engine exhaust and is a small fraction of total diesel exhaust emissions. Consisting mainly of soot, unburned hydrocarbons, water, sulphates, and trace contaminants from oil or fuel additives, some of which are hazardous, it can include metals such as arsenic, cadmium, and chromium. Over 90% of DPM are smaller than 1 micrometre (μm).

Research into diesel emissions in underground mining has shown that DPM predominantly occupies the fine and ultrafine particle size ranges, with particle characteristics influenced by engine technology, operating conditions, fuel, maintenance and exhaust after-treatment systems.

This creates an important distinction between diesel exhaust and ordinary airborne dust.

Ultrafine Particle Monitoring May Be a Small Matter but Its a Big Deal

A conventional dust monitor may be excellent at measuring particles in the respirable, PM2.5 or PM10 size ranges, but diesel exhaust contains a substantial population of particles much smaller than these conventional dust fractions.  These are known as Ultrafine Particles (UFPs).

Most DPM consists of ultrafine particles smaller than 100 nanometres. At this scale, particle behaviour is markedly different from that of the larger dust particles encountered in many conventional occupational hygiene applications and not accurately measured by standard dust monitors targeting larger particles.

Ultrafine particles have extremely small individual masses, but they can occur in very large numbers. Their small size also means that they can penetrate deeply into the respiratory system. These tiny particles adsorb hazardous gases and other hazardous chemical components from the DEE and can remain airborne for long periods, penetrating deep into the lungs.  This is why measuring only particle mass does not necessarily tell the whole story

Although the mass of particles may be similar across environments, the number and surface area of ultrafine particles can vary greatly, making measurements such as particle number concentration and Lung-Deposited Surface Area (LDSA) increasingly important for assessing diesel emissions.

Diesel Particulate Matter Monitoring is Evolving

The industry has moved from relying primarily on laboratory analysis of integrated samples to increasingly sophisticated real-time technologies capable of measuring particle mass, particle number, size distribution and particle surface area.

Traditional methods have monitored diesel particulate matter (DPM) for decades, especially for compliance. However, technological advancements now enable real-time monitoring that provides detailed insights into ultrafine particle levels, source identification, emission changes, and deposit risks. This shift allows organisations not only to measure exposure but to understand and manage its causes more effectively, improving safety interventions.

Today, monitoring can go beyond simply asking “How much diesel particulate matter is present?” to investigate questions such as:

• How many ultrafine particles are present?
• How small are those particles?
• How rapidly do concentrations change?
• Where is diesel exhaust coming from?
• Is ventilation effectively controlling emissions?
• Is an exhaust filtration system working?
• What happens when diesel equipment enters or leaves a work area?
• How much particulate matter is likely to deposit in the lungs?

This is where real-time monitoring of diesel particulate and ultrafine particles becomes increasingly valuable.

Monitoring Isn’t Just About Compliance

One of the most important advantages of real-time DPM and ultrafine particle monitoring is that it can help organisations understand why exposure occurs.

Modern engines, cleaner fuels, diesel particulate filters, improved exhaust after-treatment, better maintenance and alternative power technologies have all contributed to reductions in diesel emissions. But improved controls create a new monitoring challenge.

As emissions decrease, the ability to detect small changes becomes more important. A poorly performing diesel particulate filter, a deteriorating engine, inadequate ventilation or an isolated emission source may not necessarily produce an obvious increase in conventional dust measurements.

A traditional shift-based sample might tell you: “The worker’s exposure was X.”  Real-time monitoring can potentially tell you:

• “The concentration increased when this vehicle entered the area.”
• “Particle levels fell rapidly when ventilation increased.”
• “This piece of equipment is producing a significantly different particle signature.”
• “Particle concentrations increase during engine warm-up.”
• “A change in filtration or maintenance has altered emissions.”

That information can be invaluable when implementing the hierarchy of controls and help organisations move from simply measuring exposure to understanding and controlling its source.

New Workplace Rules for Diesel Emissions

Safe Work Australia has issued new guidance on managing diesel emissions, establishing a limit of 0.01 mg/m³ for workplace exposure limit diesel particulate matter effective from 1 December 2026. This change, part of Australia’s shift from Workplace Exposure Standards to mandatory Workplace Exposure Limits, replaces flexible guidelines with enforceable caps to protect workers from diesel exhaust, a known Group 1 carcinogen. DPM is measured as Respirable Elemental Carbon (REC), the method specified in the new Workplace Exposure Limit.