LEV Design and Testing for Woodworking Shops

Local exhaust ventilation is the primary engineering control for wood dust in timber operations and must be designed as an integrated system, not an afterthought. An effective LEV system consists of four components working together — hoods at each machine that capture dust at its source, ductwork that transports captured dust to the collection point, a fan that provides the airflow energy, and a filter or collection system that separates dust from the air stream before discharge. The hood is the most critical component because it determines whether dust is captured before it reaches the worker's breathing zone. Each machine type requires a specific hood design based on the nature and direction of dust emission — a table saw produces dust below the blade and above the blade in different patterns from a thicknesser that ejects dust from the cutter block in a focused plume. Generic or poorly positioned hoods fail to capture a significant proportion of emitted dust, regardless of the fan capacity available. The ductwork must maintain minimum transport velocity throughout the system to prevent dust settling and accumulation, which both reduces system performance and creates a dust explosion risk. For wood dust, the minimum transport velocity is typically 20 m/s in branch ducts and 23 m/s in main trunk lines, although system designers may specify higher velocities depending on dust characteristics.

Effective hood design varies significantly by machine type, and using the wrong hood design is the most common cause of LEV underperformance in woodworking shops. Table saws require extraction below the table surface and behind the blade guard, with the below-table connection typically carrying 70 per cent of the total dust volume. Thicknessers and jointers generate a concentrated dust plume from the cutter block that should be captured by a closely fitting hood around the cutter housing, with additional extraction at the chip breaker where applicable. Routers and spindle moulders require extraction integrated into the guard enclosure (Shaw guard or pressurised guard) with additional below-table extraction. Band saws require extraction at the lower blade guide area where most dust falls by gravity. Sanding machines require on-tool extraction for portable sanders and hood extraction for fixed belt and disc sanders. For CNC routers, extraction should be ducted to the machine enclosure with sufficient capacity to manage the high chip volume generated during high-speed routing. The critical principle is that the hood must be positioned as close to the dust emission point as physically possible, because capture velocity diminishes rapidly with distance — halving the distance between hood and source quadruples the effective capture.

The duct system connects machine hoods to the collection system and must be designed to maintain transport velocity while minimising static pressure loss. Undersized ducts create excessive velocity and energy waste, while oversized ducts allow dust to settle and accumulate, reducing system capacity and creating explosion hazards. Each branch duct should be sized for the airflow required at its connected machine, and the main trunk should be sized for the maximum simultaneous airflow from all machines likely to operate concurrently. Blast gates at each machine connection allow workers to close off unused branches, directing available airflow to active machines. However, blast gates are frequently left in the wrong position, causing either excessive velocity in open branches or insufficient capture at active machines when too many gates are open for the system capacity. Common duct system failures include excessive use of 90-degree elbows that create high pressure losses, flex hose connections that are too long or kinked, duct runs that pass through unheated areas where condensation causes dust accumulation, and inadequate clean-out access points for removing blockages. Every duct system should include labelled blast gates, pressure monitoring points at key locations, and clean-out access at every bend and junction.

WHS Regulation 2025 requires LEV systems to be examined and tested by a competent person at intervals not exceeding 14 months. This testing must verify that the system continues to perform as designed and that no degradation has occurred since the previous test. The competent person must measure capture velocity at each machine hood using a calibrated anemometer, static pressure at key points in the duct system using a manometer, transport velocity in duct sections using pitot tube measurements or pressure differential calculations, and filter system differential pressure and airflow. The test results must be compared against the system design specification and the minimum performance criteria needed to maintain worker exposure below the incoming 0.5 mg/m3 WEL. Any deficiencies must be documented with recommendations for corrective action, and the PCBU must implement corrections before the system is returned to service for production operations. Between formal 14-month tests, workshops should conduct daily visual inspections of ductwork connections, blast gate positions, and collection system operation, with weekly measurement of capture velocity at each machine hood using a simple smoke tube or anemometer check. These interim checks catch performance degradation before it progresses to a point where worker exposure exceeds the WEL during normal production.