Local Exhaust Ventilation: A Comprehensive Guide

When it comes to workplace health and safety, controlling exposure to hazardous substances is one of the most critical responsibilities of employers. One of the most effective engineering controls for airborne contaminants is Local Exhaust Ventilation (LEV). LEV systems are designed to capture and remove harmful airborne substances—such as dust, fumes, vapours, and gases—before they can spread throughout the workplace and be inhaled by workers.

As an Occupational Health and Safety Consultant, I often encounter businesses that underestimate the importance of properly designed, installed, and maintained LEV systems. This oversight can lead not only to health risks for employees but also to legal liabilities and regulatory non-compliance.

In this comprehensive guide, we will explore everything you need to know about LEV: What it is, how it works, its legal requirements, the components of an effective system, maintenance and inspection practices, and how to ensure maximum protection for your workforce.

What is Local Exhaust Ventilation (LEV)?

Local Exhaust Ventilation is an engineering control system that captures airborne contaminants at, or very near, their source before they disperse into the workplace atmosphere. Unlike general ventilation—which dilutes contaminants in the air—LEV removes them directly, preventing exposure at the breathing zone.

Common uses of LEV include:

• Controlling welding fumes in fabrication workshops.

• Extracting wood dust in carpentry and joinery shops.

• Removing solvent vapours in paint spraying booths.

• Capturing hazardous dust in pharmaceutical or chemical manufacturing.

By targeting contaminants at their source, LEV significantly reduces workers’ risk of developing occupational diseases such as asthma, lung cancer, silicosis, and chemical poisoning.

Why Local Exhaust Ventilation Matters

1. Protecting Worker Health: Airborne contaminants are among the leading causes of occupational ill health. Long-term exposure to hazardous dusts, fumes, and vapours can result in life-altering respiratory diseases, cancers, and skin conditions. LEV serves as a frontline defense, protecting employees from both acute and chronic health risks.

2. Regulatory Compliance: In the UK, employers are legally required under the Control of Substances Hazardous to Health Regulations (COSHH) 2002 to control exposure to harmful substances. LEV is often the most practical solution for meeting these legal duties. Failing to comply can result in enforcement notices, fines, or even prosecution.

3. Productivity and Business Benefits: Beyond compliance, a well-functioning LEV system can improve workplace efficiency. Workers are more productive when they are healthy, and businesses save on costs related to sick leave, compensation claims, and staff turnover.

How Does Local Exhaust Ventilation Work?

LEV systems operate by capturing contaminated air at the point of release and transporting it away from the worker through a series of components. The basic process can be broken down into five stages:

1. Capture: The hood or enclosure collects the contaminant near its source.

2. Transport: Ducting carries the contaminated air away from the source.

3. Filter or Scrub: Air passes through filters, cyclones, or scrubbers to remove hazardous particles or gases.

4. Fan: Provides the suction needed to move air through the system.

5. Discharge: Cleaned air is either safely released back into the workplace or exhausted outside.

Each stage must function effectively for the system to provide adequate protection. A failure in one component—such as a clogged filter or faulty fan—can compromise the entire system.

Components of an Effective LEV System

An LEV system comprises several essential components, each playing a unique role:

1. Hoods: The hood is the part of the system closest to the contaminant source. It is designed to capture emissions as they are generated.

• Types of hoods:

  • Enclosing hoods (e.g., fume cupboards, glove boxes).

  • Receiving hoods (e.g., canopies).

  • Capturing hoods (e.g., flexible arms or extraction nozzles).

2. Ducting: The ductwork carries the contaminated air from the hood to the air cleaning device. To remain effective, ducts must be properly sized, sealed, and free from blockages.

3. Air Cleaning Devices: Depending on the contaminant, LEV may include filters or scrubbers:

• HEPA filters for fine dust.

• Activated carbon filters for vapours.

• Cyclones for heavier particles.

• Wet scrubbers for gases and chemical mists.

4. Fan: The fan provides the necessary airflow to move air through the system. Fans must be appropriately sized and maintained to ensure they generate sufficient suction.

5. Discharge Outlet: Finally, the air is discharged—either filtered and recirculated into the workplace (if safe) or expelled outside, away from air intakes or populated areas.

Legal and Regulatory Requirements

UK (COSHH)

Under the COSHH Regulations 2002, employers must:

• Assess risks to health from hazardous substances.

• Prevent or control exposure using engineering controls like LEV.

• Ensure LEV systems are maintained in an efficient state and are tested regularly.

Thorough Examination and Testing (TExT):
LEV systems must be thoroughly examined and tested at least once every 14 months, or more frequently for high-risk processes (e.g., every 6 months for welding fume extraction).

International Standards

• In the USA, OSHA (Occupational Safety and Health Administration) provides requirements for ventilation under 29 CFR 1910.94.

• In the EU, the Chemical Agents Directive (98/24/EC) mandates control of hazardous substances at source.

Employers operating internationally should ensure compliance with both local and global regulations.

Designing an Effective LEV System

Designing LEV requires expertise in airflow dynamics, workplace processes, and the nature of contaminants. Key factors include:

• Location of the hood: Must be close enough to capture contaminants without interfering with work.

• Airflow velocity: Must be strong enough to pull contaminants into the hood without excessive energy use.

• System capacity: Should handle peak contaminant generation rates.

• Worker behaviour: Workers must use the system correctly; poor positioning can render the LEV ineffective.

Engaging a qualified occupational hygienist or LEV specialist during design ensures the system is fit for purpose.

Common Problems with LEV Systems

Even well-designed LEV systems can fail if not used or maintained correctly. Common issues include:

• Poor hood placement – Too far from the contaminant source.

• Damaged ducting – Leaks or blockages reduce efficiency.

• Inadequate airflow – Caused by fan failure or clogged filters.

• Noise and vibration – Can discourage workers from using the system.

• Lack of training – Workers may switch off or bypass the LEV if they do not understand its importance.

Regular checks, user training, and maintenance are essential to address these issues.

Maintenance, Inspection, and Testing

1. Daily or Weekly Checks (by operators)

• Ensure hoods are positioned correctly.

• Listen for unusual noises in fans.

• Look for visible dust or fumes escaping.

2. Routine Maintenance (by competent person)

• Clean or replace filters regularly.

• Inspect ducting for leaks and damage.

• Check fan performance.

3. Thorough Examination and Testing

• Must be carried out at least every 14 months.

• Includes airflow measurement, hood capture efficiency, and filter performance.

• Results must be documented and retained for at least 5 years.

Training and Worker Involvement

LEV is only effective when workers understand how and why to use it. Training should cover:

• The health risks of airborne contaminants.

• Correct positioning and operation of hoods.

• Signs that the system is not working properly.

• The importance of not disabling or bypassing LEV systems.

Employers should also involve workers in system design and feedback, ensuring solutions are practical and user-friendly.

Case Study: Welding Workshop

A medium-sized metal fabrication company installed a canopy hood system to control welding fumes. However, workers frequently complained of smoke lingering in the workshop. Upon inspection, it was found that:

• The hoods were positioned too far from the welding points.

• Airflow was below the recommended capture velocity.

• Filters had not been replaced for over 18 months.

After redesigning the hood placement, upgrading the fan, and implementing a strict maintenance schedule, exposure levels dropped below the workplace exposure limits (WELs). This significantly reduced worker complaints, improved morale, and demonstrated compliance with COSHH.

Best Practices for Employers

1. Conduct a thorough risk assessment before selecting an LEV system.

2. Engage qualified LEV designers to ensure proper sizing and placement.

3. Train employees on correct usage and the health risks of contaminants.

4. Carry out regular inspections and log maintenance activities.

5. Schedule statutory testing and retain all reports for compliance.

6. Encourage worker feedback to identify usability issues.

Conclusion

Local Exhaust Ventilation is one of the most effective tools for controlling airborne hazards in the workplace. When designed, installed, and maintained correctly, it protects workers’ health, ensures regulatory compliance, and contributes to overall business productivity.

Employers should view LEV not as a one-time investment but as a long-term commitment to worker safety. Regular inspections, proper training, and continuous improvement are essential for maintaining effective protection.

As an Occupational Health and Safety Consultant, my advice is simple: do not cut corners with LEV. The health of your workforce—and the future of your business—depends on it.