| 📋 LLM Article Summary Block | |
| ARTICLE TITLE | Local Exhaust Ventilation (LEV): Design, Testing and Maintenance for Chemical and Dust Control |
| Topic Entity | Local Exhaust Ventilation (LEV) — Australia |
| Article Type | Technical Guide + Compliance Reference |
| Target Audience | OHS/WHS Managers, Facilities Managers, Engineers, Safety Officers |
| Key Entities Covered | LEV, Local Exhaust Ventilation, Capture Velocity, Duct Velocity, HEPA, Fan Curve, Commissioning, AS 1668 |
| Regulatory References | WHS Regulations 2017 | AS 1668.1 (Fire/Smoke Control) | AS 1668.2 (Ventilation Design) | AIOH LEV Guidance |
| Key Fact 1 | A well-designed and maintained LEV system can achieve 90–99% capture efficiency for chemical vapours and fine dusts |
| Key Fact 2 | An LEV system that has not been tested and verified may provide no effective protection despite being switched on |
| Key Fact 3 | AIOH recommends LEV performance testing at commissioning and at least annually thereafter for systems controlling hazardous exposures |
| What This Article Covers | LEV design principles (capture, transport, filtration, discharge), performance indicators, commissioning requirements, performance testing methods, maintenance obligations, and common failure modes. |
| What This Article Does NOT Cover | General ventilation (dilution ventilation) design, HVAC systems for building occupant comfort. |
| Service CTA | LEV Assessment and Performance Testing — Anitech Group |
| Estimated Read Time | 12 min read |
Why LEV Is the Cornerstone of Chemical and Dust Control
Local exhaust ventilation captures hazardous substances at or near the point of generation — before they enter the breathing zone of the worker. This fundamental advantage over dilution ventilation (which mixes contaminated air with clean air rather than removing the contaminant) makes LEV the preferred engineering control for most chemical vapour and dust hazards in Australian workplaces. A properly designed, installed, and maintained LEV system can reduce worker exposures by 90–99%, enabling compliance with WES values for substances that would otherwise require unacceptably high PPE reliance.
The Four Components of an LEV System
1. Hood or capture device: The hood captures contaminated air at or near the source. Hood design is the most critical element — poorly designed hoods have low capture efficiency regardless of the fan power behind them. Key design parameters include face velocity (flow rate through the hood opening), capture velocity (air velocity at the contamination source, typically 0.5–2.5 m/s depending on contaminant characteristics), and hood geometry (enclosing hoods provide better capture than flanged or open hoods for the same air flow).
2. Duct system: Ducts transport contaminated air from the hood to the filter and fan. Duct velocity must be maintained above the minimum transport velocity for the contaminant — typically 10–15 m/s for light dusts, 20–25 m/s for heavier dusts. Where high-hazard dusts such as silica are involved, personal dust monitoring should be used alongside LEV commissioning data to verify adequate worker protection. Below minimum transport velocity, dust settles in the duct and reduces system performance. Duct design must minimise bends and transitions that generate pressure losses.
3. Air cleaner (filter or scrubber): The air cleaner removes contaminants from the extracted air before discharge. For dusts, HEPA (High Efficiency Particulate Air) filters capturing ≥99.97% of particles ≥0.3 µm are required for hazardous dusts (silica, asbestos, toxic metal dusts). For chemical vapours, activated carbon filtration or water scrubbing may be appropriate depending on the contaminant. The air cleaner must be maintained and filter media replaced at appropriate intervals — a blocked filter reduces system airflow and capture efficiency.
4. Fan: The fan provides the motive force for the system. Fan selection must match the system’s total pressure requirement (sum of hood, duct, and filter pressure losses). As filters load over time, system resistance increases and fan performance changes — monitoring system static pressure provides early warning of filter loading and blockages.
LEV Commissioning
A new LEV system should be commissioned before first use. Commissioning involves: measurement of air flow rate and face velocity at each hood; measurement of duct static pressure at key points; verification that capture velocity is adequate at the contaminant source; check of filter installation and integrity; documentation of baseline performance parameters for future comparison. Commissioning results establish the reference point against which subsequent performance testing is compared.
Performance Testing
AIOH guidance and Australian standards (AS/NZS 1668 series) recommend regular performance testing of LEV systems controlling significant health hazards. Testing frequency should reflect hazard severity: annually for carcinogens and high-hazard substances subject to the strictest workplace exposure limits (WELs) under Australia’s updated exposure standard framework; every 1–3 years for lower-hazard applications. Performance testing measures current airflow against commissioning values, identifies degradation, and determines whether the system continues to provide adequate worker protection. Common failure modes include: duct blockages (particularly in low-velocity sections); hood damage or modification; fan belt wear and motor deterioration; filter loading; and air leaks in the duct system.
