What Are Engineering Controls?

Engineering controls physically separate workers from hazardous dust or reduce the amount released into the air. They form an important part of the hierarchy of control and should be considered before relying on respiratory protective equipment.

Common engineering controls for silica and construction dust include:

• On-tool dust extraction.
• Water suppression and wet-cutting systems.
• Local exhaust ventilation.
• Extraction booths and enclosed processes.
• Suitable industrial dust extractors.
• Air-filtration and air-scrubbing systems.

The controls selected must be suitable for the material, task, equipment, working environment and expected level of exposure.

On-Tool Dust Extraction

On-tool extraction is one of the most effective ways to control silica dust at its source. It involves connecting a suitable dust extractor directly to a power tool.

On-tool extraction may be fitted to equipment such as:

• Grinders.
• Cut-off saws and disc cutters.
• Drills and breakers.
• Sanders.
• Chasing and routing tools.

The tool should have a suitable extraction hood or shroud positioned close to the point where dust is created. The extractor then captures the dust before it can enter the worker's breathing zone or spread across the work area.

Every component must be compatible and correctly connected. An unsuitable shroud, loose connection, damaged hose or weak extractor can significantly reduce the effectiveness of the system.

Choosing a Suitable Dust Extractor

The dust extractor must provide sufficient airflow and capacity for the tool and task. For construction dust, an M-class extractor will normally be the minimum suitable classification, while an H-class extractor may be required where the risk assessment identifies the need for a higher level of control.

Domestic vacuum cleaners are not suitable for collecting silica or other hazardous construction dust. They may have inadequate filtration and could release fine dust back into the workplace.

A suitable extraction unit should have:

• The correct dust-classification rating.
• Enough airflow for the connected tool.
• Compatible hoses and connectors.
• An appropriate filter-cleaning system.
• A safe method for collecting and disposing of dust.
• A dust-capacity warning or airflow indicator where required.

Water Suppression and Wet Cutting

Water suppression reduces the amount of dust that becomes airborne during cutting, grinding, drilling and similar processes. Water is applied at the point where the tool contacts the material.

The water binds with the dust particles and helps keep them on the surface rather than allowing them to disperse into the air. This can substantially reduce the amount of respirable crystalline silica released.

Water suppression is commonly used when working with:

• Concrete.
• Blocks and bricks.
• Paving materials.
• Stone.
• Tiles and other silica-containing products.

The water must be supplied at a sufficient and consistent rate. Simply wetting the material before work begins may not provide adequate control throughout the task.

Managers must also control the resulting slurry, prevent slip hazards and consider electrical safety when water is used near powered equipment.

Local Exhaust Ventilation

Local exhaust ventilation, commonly called LEV, captures dust close to where it is generated and carries it away through a controlled extraction system.

LEV systems may include:

• Extraction hoods.
• Capture arms or receiving hoods.
• Ductwork.
• Filters or dust collectors.
• Extraction fans.
• Discharge arrangements.

LEV is frequently used in workshops, factories, production facilities and other fixed working environments. For the system to be effective, the hood must be properly positioned and the airflow must be sufficient to capture the dust.

LEV should be designed, installed and commissioned by competent people. It must also be maintained, thoroughly examined and tested at the legally required intervals.

Extraction Booths and Enclosed Processes

Dusty operations can sometimes be isolated inside an extraction booth, enclosure or separate controlled area. This helps contain the contaminant and prevents it from spreading to other parts of the workplace.

Enclosures may be suitable for:

• Fixed production processes.
• Stone and concrete finishing.
• Cutting or grinding operations.
• Automated processes.
• Tasks that repeatedly produce high levels of dust.

Access should be restricted, and the enclosure should be designed so that dust cannot escape when materials or waste are removed.

Tool Maintenance and Dust Reduction

Well-maintained tools can help reduce unnecessary dust production. A blunt blade, worn drill bit, damaged cutting disc or poorly operating tool may take longer to complete the task and generate additional dust.

Maintenance arrangements should include:

• Pre-use equipment checks.
• Inspection of blades, discs and drill bits.
• Replacement of worn or damaged components.
• Checking extraction shrouds and guards.
• Following the manufacturer's servicing instructions.

Damaged or defective equipment should be removed from service until it has been repaired or replaced.

Air Scrubbers and General Air Filtration

Air scrubbers and filtration units can help remove residual airborne dust from enclosed work areas. They may be useful during refurbishment, maintenance or other work undertaken inside buildings.

However, general air filtration captures dust only after it has escaped into the workplace. Air scrubbers should normally support source controls rather than replace on-tool extraction, water suppression or LEV.

The equipment must have suitable filters, sufficient capacity for the room and an appropriate position that encourages effective air movement.

Inspecting and Maintaining Engineering Controls

Engineering controls will only remain effective when they are properly used, inspected and maintained. Employers should establish suitable arrangements for checking their condition and performance.

Routine checks should cover:

• Filters and filter-cleaning mechanisms.
• Extraction hoses and connectors.
• Hoods, shrouds and guards.
• Airflow indicators and warning devices.
• Water supplies, pumps and spray heads.
• Dust-collection bags or containers.
• Fans, ducts and extraction units.

Filters must be cleaned or replaced safely in accordance with the manufacturer's instructions. Extraction units must also be emptied without releasing collected dust back into the air.

A system that appears to be running may still provide inadequate protection if its filter is blocked, its hose is damaged or its airflow has fallen.

Checking That Silica Dust Controls Are Effective

Managers and supervisors should regularly observe dusty work and check whether the selected controls are performing as expected. Warning signs of ineffective control may include:

• Visible dust escaping from the tool.
• Dust collecting around the worker.
• Damaged or collapsing extraction hoses.
• Reduced airflow or extractor warning signals.
• Blocked water jets or an inadequate water supply.
• Dust leaking when the extractor is emptied.

Work should stop if essential engineering controls fail or no longer provide adequate protection. The task should not restart until the controls have been restored and shown to be effective.