Dust exposure is one of the most common occupational hazards across construction, manufacturing, and industrial sectors. Yet not all dust behaves the same way in the body. Understanding the difference between inhalable and respirable dust is fundamental for selecting the right control measures, equipment, and monitoring methods.

What Are Inhalable and Respirable Dusts?

Dust in the workplace is typically classified by particle size. Inhalable dust refers to larger particles that enter the nose and mouth during breathing. These are generally up to around 100 micrometres in diameter. Respirable dust, on the other hand, is made up of much finer particles that can penetrate deep into the lungs and reach the gas exchange region called the alveoli. These are usually below 5 micrometres.

The key takeaway is that inhalable dust mainly affects the upper respiratory system (nose, throat, and upper airways), while respirable dust poses a greater risk for long-term lung diseases such as silicosis and chronic obstructive pulmonary disease.

Health Impacts of Different Dust Fractions

Inhalable dust exposure can cause irritation, coughing, and inflammation of mucous membranes. Certain substances such as wood dust or flour dust can trigger occupational asthma. Respirable dust presents deeper health concerns because once particles reach the alveoli, they can cause scarring or fibrotic changes that permanently damage lung tissue. Crystalline silica, for example, is a well-known culprit for severe respiratory illness.

Measurement and Control Approaches

Control measures depend on which fraction poses the highest risk. Air monitoring equipment is often fitted with size-selective sampling heads to target inhalable or respirable fractions. Dust extraction systems, filtration, and personal protective equipment (PPE) are all designed with these classifications in mind. A Class H vacuum with HEPA filtration is generally required when working with respirable crystalline silica or lead dust. For general site clean-up of coarser particles, a Class M vacuum may suffice.

How Dust Classification Affects Daily Practice

Knowing the distinction ensures better compliance with exposure limits and helps select appropriate engineering controls. For instance, COSHH regulations specify Workplace Exposure Limits separately for inhalable and respirable fractions. Employers should review Safety Data Sheets, check extraction system performance, and ensure that fit testing for respirators corresponds to the actual risk profile of the dust generated.

Practical Takeaways

• Assess the main dust sources and particle sizes before selecting control measures
• Match vacuum and filtration class to the dust hazard level
• Use air monitoring to confirm compliance with exposure limits
• Train workers on inhalable vs respirable risk awareness
• Review controls regularly under COSHH or equivalent standards

Understanding how inhalable and respirable dusts differ helps teams take targeted action rather than relying on a one-size-fits-all approach. It ensures not only compliance but long-term worker health protection.