Dust Monitoring

What is the difference between respirable and inhalable dust?

Inhalable dust is the fraction of airborne particles that can be breathed in through the nose and mouth — it includes larger particles up to 100 microns. Respirable dust is the fine fraction (typically below 10 microns) that penetrates deep into the gas-exchange region of the lungs. Respirable dust is the more hazardous fraction because it reaches the alveoli where it can cause pneumoconiosis (dust lung disease), including silicosis, asbestosis, and coal workers' pneumoconiosis. Annexure 2 of the Regulations for Hazardous Chemical Agents, 2021 sets limits for specific agents and for general particulate, and the general particulate value only applies to dust that contains no asbestos and 1% or less crystalline silica. For crystalline silica itself (quartz and cristobalite), the respirable limit is 0.1 mg/m³ for OHS Act workplaces, and 0.05 mg/m³ for mines since GN R.6053 of March 2025.

How is personal dust monitoring conducted?

A worker wears a personal sampling pump on their belt, connected to a sampler head positioned in their breathing zone (within 30 cm of the nose and mouth). For respirable dust, a cyclone sampler separates the fine fraction; for inhalable dust, an IOM (Institute of Occupational Medicine) sampler collects the total inhalable fraction. The pump runs for a full shift (typically 6–8 hours), drawing air through a pre-weighed filter. The filter is re-weighed after sampling, and the mass gain divided by the air volume gives the concentration in mg/m³. This is the gold-standard method for measuring actual worker exposure.

What is dust fall-out monitoring and when is it needed?

Dust fall-out (deposition) monitoring measures the rate at which dust settles out of the air onto surfaces, using open buckets placed at the site boundary and in the surrounding area. It's expressed in mg/m²/day. Dust fall-out monitoring is used for community impact assessment — it tells you whether dust from your operation is depositing on neighbouring properties. The National Dust Control Regulations, 2026 (GN R.7335), which replaced the 2013 regulations on 31 March 2026, keep the limits at 600 mg/m²/day for residential and 1,200 mg/m²/day for non-residential areas over 30 days, but change the method from ASTM D1739 to SANS 1137 and allow the authority to require a dustfall programme as part of your dust management plan without any exceedance having occurred. Sampling points must cover sensitive receptors such as schools, clinics and surface water.

How often should dust monitoring be conducted?

Personal exposure monitoring should be conducted at least annually for workers in similar exposure groups (SEGs) where dust is a significant hazard, and more frequently if exposure levels are near or above the OEL, or after process changes. Under the Regulations for Hazardous Chemical Agents, 2021, agents with a maximum or restricted limit in Annexure 2, which includes crystalline silica, must be monitored representatively at least every 24 months, and only an approved inspection authority may do the air monitoring. As a practical screening rule we treat results above half the limit as significant and increase the frequency. Ambient dust monitoring (PM10, dust fall-out) is typically continuous or monthly, depending on the method and the authorisation conditions. We design the monitoring frequency based on your risk profile and regulatory requirements.

What is crystalline silica monitoring and why is it important?

Crystalline silica (quartz) is a component of many mineral dusts — in mining, quarrying, foundries, construction, and ceramics. When respirable silica dust is inhaled, it causes silicosis, a progressive, irreversible and potentially fatal lung disease. The respirable limit is 0.1 mg/m³ (8-hour TWA) under the Regulations for Hazardous Chemical Agents, 2021, and 0.05 mg/m³ for mines since GN R.6053 of March 2025. Monitoring requires a respirable dust sample analysed for quartz and cristobalite by X-ray diffraction (XRD) or Fourier-transform infrared spectroscopy (FTIR). A total or inhalable dust result cannot tell you your silica exposure, because the general particulate limit only applies to dust with 1% or less crystalline silica. Where exposure is significant, medical surveillance (chest X-ray and lung function testing) must follow.

Do you conduct the physical sampling or advise on the programme?

We design the monitoring programme, interpret the results, and provide the strategic recommendations. For the physical sampling, we work through our approved inspection authority (AIA) partner and SANAS-accredited laboratories, because the Regulations for Hazardous Chemical Agents, 2021 allow only an AIA to carry out workplace air monitoring. This separation ensures the data is defensible — the sampling is done by accredited field technicians, the analysis by an accredited laboratory, and the interpretation by experienced hygiene professionals. We also verify that the sampling equipment was calibrated and that chain-of-custody documentation is complete, because data without these quality assurances is not defensible.

How does dust monitoring link to medical surveillance?

The link is explicit in the regulations. Where personal dust monitoring shows significant exposure, medical surveillance must follow — typically annual lung function testing (spirometry) and, for crystalline silica exposure, baseline and periodic chest X-rays (interpreted to the ILO classification). The monitoring data determines who needs surveillance, what type, and how often. Without monitoring data, you cannot demonstrate that your medical surveillance programme is risk-based — it becomes a generic checklist, which is neither defensible nor cost-effective.

Two silica limits, and which one applies to you

South Africa now has two limits for respirable crystalline silica. Workplaces under the OHS Act, such as foundries, brickworks, stone fabricators, glass and ceramics plants and construction sites, work to 0.1 mg/m³ as an 8-hour time-weighted average under Table 2 of the Regulations for Hazardous Chemical Agents, 2021. Mines work to 0.05 mg/m³ after GN R.6053 of 28 March 2025 amended the mining exposure limits.

The split matters most for contractors. A crushing or earthworks contractor working on a mine is measured against the mining limit on that site and the OHS Act limit on its next job. If your monitoring strategy uses one limit for every site, some of your results are being judged against the wrong number.

Why a low total dust result can hide a silica problem

The general particulate limit in Annexure 2 only applies to dust that contains no asbestos and 1% or less crystalline silica. Most rock, sand, concrete and brick dust contains far more than that. So a total or inhalable dust result that looks comfortable tells you nothing about silica, which is the hazard that causes silicosis and is classified as carcinogenic.

To measure silica you need a respirable sample collected with a cyclone at the correct flow rate, analysed for quartz and cristobalite by X-ray diffraction or infrared spectroscopy. Both methods are accepted for this analysis in South Africa. If your last survey only reports total dust, it did not answer the question that matters.

How often, and who may measure

Crystalline silica is a maximum-limit agent in Annexure 2, so under the Regulations for Hazardous Chemical Agents, 2021 it must be monitored representatively at least every 24 months, and only an approved inspection authority may carry out the air monitoring. In practice, re-survey sooner whenever you change a process, material, machine or shift pattern, and increase frequency for any group whose results sit above half the limit.

On mines, the Mine Health and Safety Council set a milestone that by December 2024, 95% of individual silica measurements should be below 0.05 mg/m³. That is a useful benchmark for any silica-exposed operation, mine or not: look at how many individual results, not averages, clear the lower number.

Dustfall monitoring under the 2026 regulations

Fence-line dustfall is a separate programme with separate rules. The National Dust Control Regulations, 2026 changed the method from ASTM D1739 to SANS 1137 and gave operations with existing plans six months to switch, a window that closes at the end of September 2026. The limits stay at 600 mg/m²/day for residential areas and 1,200 mg/m²/day for non-residential areas over 30 days, with no more than two exceedances a year in non-consecutive months.

What has changed is when you need it: an authority can now require dustfall monitoring as part of your dust management plan without an exceedance having occurred, and the sampling points must cover sensitive receptors such as schools, clinics, daycare centres and surface water.

Why being under the limit is not the same as being safe

South African researchers reviewing silica exposure data have pointed to a study in which about 19% of miners developed silicosis even though measured concentrations were below 0.1 mg/m³. The mining limit has since been halved, and we treat the OHS Act limit as a ceiling rather than a target. A defensible programme shows results well below the limit, controls at the source, and medical surveillance that picks up disease early in the workers who remain exposed.