Quarrying and aggregate production generate respirable crystalline silica throughout extraction, processing and transport. Exposure is continuous rather than task-bound, which changes how it must be measured and controlled.
Quarrying and aggregate production can generate respirable crystalline silica throughout the extraction, processing and transport of rock. The risk is not limited to visibly dusty activities: the finest particles are often invisible and may remain airborne long after larger dust has settled.
Stevin Rock and its sister company RAK Rock operate large-scale quarrying at Khor Khuwair in Ras Al Khaimah, producing limestone, dolomite and gabbro across multiple sites. Khor Khuwair in Ras Al Khaimah is among the region's major limestone quarrying operations, employing a substantial workforce across extraction, processing and logistics.
Respirable crystalline silica, commonly abbreviated to RCS, is the fine fraction of crystalline silica-containing dust that can penetrate into the gas-exchange region of the lungs. It normally consists of particles below approximately 10 micrometres, with the respirable sampling convention centred on much smaller particles than ordinary visible quarry dust.
Quartz is the crystalline silica form most likely to be encountered in natural rock and mineral processing. RCS particles cannot normally be identified by sight because the hazardous fraction is too fine to be individually visible.
A large visible dust cloud may indicate poor control, but the absence of a visible cloud does not establish that exposure is safe. Repeated inhalation can cause silicosis and is associated with lung cancer, chronic obstructive pulmonary disease and kidney disease.
Quarry operations repeatedly fracture, abrade, drop and transport mineral material. Each stage can create new particle surfaces and release a respirable fraction, particularly where dry material is processed at high energy or falls through an open transfer point.
Drilling: Drill bits break the rock face and can generate concentrated dust around the drill head, mast, collection system and discharge.
Blasting: Detonation fractures large rock volumes, while subsequent inspection, scaling and loading can disturb freshly created fine material.
Crushing and screening: Primary, secondary and tertiary crushers, vibrating screens and recirculation systems create dust through impact and abrasion.
Conveying and stockpiling: Transfer points, conveyor discharge, open belts, material drops and stockpile movement release fine particles.
Loading and haulage: Excavators, wheel loaders, dump trucks, loading chutes and vehicle movement on dry haul roads can repeatedly resuspend settled dust.
Job title alone does not determine exposure. The worker's proximity to the source, time spent outside protected cabins, condition of dust controls, wind direction and frequency of non-routine work can be more important than the nominal role.
Drill operators and drill assistants: may be exposed during drilling, rod changes, inspection and maintenance of dust collectors.
Crusher and screen operators: may encounter emissions around feed hoppers, discharge points, screen decks and blocked material.
Maintenance personnel: can receive high short-term exposures when opening equipment, changing filters, clearing blockages or working inside dusty enclosures.
Loader, excavator and haul-truck operators: may be exposed where cabins are open, poorly sealed or fitted with ineffective filtration.
General operatives and cleaners: may disturb settled dust through dry sweeping, compressed-air cleaning or manual handling of spillage.
Construction silica exposure is often associated with a recognisable tool and a defined task, such as cutting concrete for 20 minutes. Quarry exposure may instead arise from several large, continuous sources operating over an entire shift.
Quarry dust may contain a mixture of freshly fractured mineral, weathered surface material, road dust and deposited process dust. Exposure can be continuous or repeated across drilling, crushing, screening, transport and maintenance rather than linked to one short activity.
Wind direction, dry weather, vehicle movements and the position of the worker relative to several sources may change exposure considerably. The silica percentage depends on the mineralogy of the processed rock; total dust concentration alone cannot establish the RCS concentration.
Quarry workers may experience both a long-term background exposure and short, high-intensity peaks during interventions or breakdowns.
Personal breathing-zone sampling is the principal method for assessing what an individual worker inhales during representative work. Fixed-location monitoring can help identify sources and migration patterns, but it should not normally replace personal sampling when occupational exposure is being evaluated.
A calibrated personal sampling pump is attached to the worker and connected to a cyclone or other approved respirable-fraction selector. The sampling head is positioned within the worker's breathing zone, normally on the upper torso close to the nose and mouth.
Respirable dust is collected onto a suitable pre-weighed filter over a documented sampling period representing the work being assessed. The laboratory may determine respirable dust gravimetrically and analyse the crystalline fraction using X-ray diffraction or an appropriate infrared method.
The assessment should record tasks, time spent in and out of cabins, weather, material handled, control operation and unusual events that could explain the result.
Effective control begins by preventing dust from becoming airborne or separating the worker from the source. Respiratory protective equipment may be necessary for particular activities, but it should supplement rather than replace reasonably practicable engineering controls.
Water suppression: Apply correctly positioned sprays at drill heads, crusher feeds, discharge points, screens, conveyor transfers and haul roads without creating unsafe slurry or reducing product quality.
Enclosed, pressurised cabins: Use well-sealed cabs supplied with filtered, positively pressurised air, together with closed windows and maintained door seals.
Conveyor and transfer enclosure: Cover belts, reduce material drop heights, enclose transfer points and capture dust at locations where material changes direction.
Wet screening and conditioning: Introduce moisture before or during screening where the product specification allows wet processing.
Local extraction: Use correctly designed extraction and dust collection at enclosed crushers, screens, hoppers and bagging or sampling stations.
A quarry can have well-designed controls but still produce high exposure when sprays are blocked, cabin filters are overloaded or accumulated dust is disturbed. Control performance must therefore be inspected and verified under real operating conditions.
Avoid routine dry sweeping and the use of compressed air where vacuum cleaning or wet methods are practicable.
Keep cabin doors, windows and seals closed and replace intake filters at intervals based on pressure, loading and manufacturer guidance.
Plan crusher entry, screen changes, filter replacement and blockage clearance as high-risk tasks rather than treating them as ordinary maintenance.
Inspect water nozzles, extraction ductwork, conveyor covers and dust collectors for damage, blockage or loss of performance.
Repeat exposure monitoring after material changes, process modifications, increased throughput, control failure or evidence that exposure patterns have changed.
Drilling, blasting, crushing, screening, conveying and haulage each release a respirable fraction.
Time outside a sealed cabin and control condition matter more than the nominal role.
A dustier limestone operation can produce less silica than a cleaner quartz-rich one.
Opening equipment, changing filters and clearing blockages produce the highest short-term exposures.
Abu Dhabi's Occupational Standards and Guideline Values document (2016), Schedule A, includes crystalline silica as alpha-quartz and cristobalite, with a time-weighted average of 0.025 mg/m³ for the respirable fraction, classified A2. Its status needs stating precisely. Section 3.2 of that document says the Schedule A values shall be adopted as maximum allowable limits, while the document's own introductory note describes its standards and guideline values as non-mandatory requirements — and it sits in the Standards and Guideline Values class, not among the Codes of Practice, which the Abu Dhabi Public Health Centre describes as mandatory for all entities. The framework has since been renamed ADOSH-SF under that Centre, which now records the Standards and Guideline Values document as suspended and directs entities to comply with relevant local or federal standards in force. The value is therefore a published reference point, not an enforceable UAE limit. Requirements may also arise through federal provisions, emirate-level systems, free-zone rules, client standards and contractual obligations, so the applicable framework should be checked rather than assumed uniform.
Abu Dhabi Occupational Standards and Guideline Values (2016), Schedule A — recorded as suspended by ADPHC
No. Quarry dust is a mixture that may include coarse mineral particles, respirable dust and varying percentages of crystalline silica. The RCS concentration depends on both the amount of respirable dust in the air and the crystalline silica content of that respirable fraction. A very dusty limestone operation could sometimes produce less RCS than a less visibly dusty operation processing a more quartz-rich material.
Only when the cab provides effective separation from outside air. Protection depends on intact seals, positive pressure, suitable filtration, clean internal surfaces and doors and windows remaining closed. Exposure may rise sharply when an operator leaves the cab to inspect loads, connect equipment, clear material or work beside another dust source.
Area monitors are useful for mapping sources, evaluating control changes and identifying dust movement across a site. They do not necessarily represent the air within a particular worker's breathing zone. Personal sampling is generally required when the objective is to estimate individual occupational exposure.
There is no single frequency suitable for every quarry. Monitoring should be proportionate to the risk and repeated when representative information is lacking, previous results approach or exceed the applicable benchmark, or significant operational changes occur. Changes that may justify further sampling include new rock sources, higher production rates, different drilling methods, altered shift lengths, deteriorating cabin performance, modified water systems and major maintenance campaigns.