Guide to LEV systems

Local exhaust ventilation systems (LEV systems) are essential for keeping certain workplaces safe for employees. Industries such as food manufacturing, materials handling, chemicals, life sciences, pharmaceuticals, soft disposables, and general manufacturing, often have requirements for these due to the by-products and fumes generated during production.

lev systems example

Typical sources of hazardous substances include dust (e.g. flour dust in bakeries), mist (e.g. paint mist from spraying), fumes and gas (e.g. carbon monoxide) or vapour (e.g. solvents).

Under the Control of Substances Hazardous to Health (COSHH) Regulations, employers have a legal requirement to protect their employees from exposure to substances that could be harmful:

(1) Every employer shall ensure that the exposure of his employees to substances hazardous to health is either prevented or, where this is not reasonably practicable, adequately controlled.

According to COSHH, “where it is not reasonably practicable to prevent exposure to a substance hazardous to health, the employer shall comply with his duty of control under paragraph (1) by applying protection measures appropriate to the activity and consistent with the risk assessment.”

In simple terms, the employer must ensure adequate measures are in place to prevent workers being exposed to harmful substances. The most common and effective way of doing this is via an appropriately designed local exhaust ventilation (LEV) system.

What are LEV systems?

LEV systems remove harmful substances such as dusts, mists, gases, vapour and fumes out of the air.

An LEV system that has been appropriately designed and installed should extract air containing harmful contaminants, ensure they are contained and removed from any areas where people are working, and get rid of them safely.  

LEV systems design considerations

Good design is essential when it comes to choosing LEV systems. A system that is poorly designed and doesn’t meet the requirements of the facility can not only prove costly to fix, but also risks employee health.

The Health & Safety Executive has guidance available on the minimum requirements which must be taken into consideration when designing an LEV system, and it’s essential that these are followed to ensure the system is fit for purpose.

An experienced LEV system designer will ensure that the system includes:

  • Fit indicators (e.g. pressure differential gauges) that allow the operator to check the system is working as expected
  • Allowances for comprehensive training on how to use, check and maintain the system
  • A user manual which includes details of how the system works, maintenance, checks and testing, performance benchmarks and replacement parts
  • A logbook to allow the operator to record checks and maintenance

LEV systems are usually made up of five key elements:

  • Hood – this is where contaminated air enters the system
  • Duct system – pipework that safely carries the contaminants
  • Filtration – a cleaning component, typically a filter or scrubber, that removes the contaminants from the air
  • Air mover – a fan to power the system
  • Discharge – a safe point of air exhaust to discharge the contaminants
LEV system hoods

According to HSE guidance, the hood design is critical to the overall success of the LEV system and it must be suitable for the application.

Typically a hood will be one of three types:

  • Capture hoods – this type of hood “captures” or pulls the contaminant into the LEV system and away from the operative. Although this is one of the most used types, it must have sufficient airflow at the source in order to effectively capture the air and it’s important to consider the location of the hood in relation to the operative to ensure contaminants are effectively captured before they can be breathed in.

  • Receiving hoods – receiving hoods work in a similar way to capture hoods, with the key difference being that the source of contaminant has sufficient energy to make its own way into the hood without the need for additional airflow (typically the energy is provided by the heat or speed of the contaminated air).

  • Enclosures – enclosing hoods, also known as fume hoods, surround the point where contaminants are produced. They can either be completely or partially enclosed and are considered the most effective form of control when installed correctly.

An effective duct system is essential to successful LEV. The ductwork should be designed to ensure the air meets as little friction or resistance as possible and careful consideration should be given to the size of the duct and resulting duct velocity.

For example, air moving too slowly through the duct will allow contaminants to settle and eventually clog the duct, whereas air moving too quickly can create issues around power wastage, noise and can cause excessive abrasion and damage to the duct itself.

Experienced LEV systems designers should be able to ensure the system can achieve the required air flow rate using the least amount of power.


The type of filtration or air cleaning device will depend on the application and again, it’s important that careful consideration is given to the user requirements to ensure the option chosen meets their needs.

Types of cleaners include:

  • Fabric collectors – a popular example of this type are cartridge filters, which offer lower emissions and higher filtration efficiencies than standard bag filters for normal applications where the burden is not too high and dust is dry. They are commonly used in food production, pharmaceuticals and many other industries.

  • Centrifugal collectors – cyclone collectors being the most popular type and a common choice for woodworking operations or as pre-cleaners before fabric collectors.

  • Wet scrubbers – this type of cleaner uses liquid to force particulates from the air. There are many different types suitable for a variety of operations but often used in paper and pulp, tissue converting, board manufacturing, cooking/frying and metal machining environments. 
Air movers (fans)

Fans are an essential part of an LEV system and it’s important they are an appropriate size and type to effectively provide enough pressure to power the system and deliver the design flow rate.

Usually a centrifugal fan is the most suitable type as they can operate against a high resistance and have predictable performance curves that give stable extraction rates.


The discharge, or exhaust point, must be carefully considered as part of LEV systems design to ensure contaminants are disposed of safely and clean air is released into the environment. This includes considering its positioning and distance from employees and neighbouring communities.

LEV systems services

We offer a suite of LEV services, delivered by a team experienced in the challenges faced in the design of a bespoke industrial ventilation and filtration system.

Our LEV systems approach is in accordance with the world-leading American Conference of Governmental Industrial Hygienists (ACGIH). We work to ISO-9001 standards and we review constantly for energy-saving best practice. Recognised by the HSE, our methodology gives confidence to clients of compliance and effectiveness of our delivery.

LEV surveys 

We offer a thorough, custom examination LEV testing service, to ensure your LEV system is working correctly in line with COSHH. It is recommended that examination and testing is carried out at least every 14 months to ensure the continued effectiveness of your system.

We are also able to conduct workplace dust monitoring, including personal dust monitoring, to measure exposure levels and check against HSE guidelines. Our dust-in-air surveys address sampling and analysis to meet the needs of the specific type of workplace area required by HSE recommendations HSG258.

Unlike many survey providers, our expertise allows us to understand the practical application behind the results and provide recommendations.

Ventilation systems

We are globally recognised in the supply, installation and turnkey provision of ventilation systems. We are knowledgeable and compliant with all ATEX and DSEAR legislation and work only with world-class equipment manufacturers. Full instrumentation, installation, commissioning and maintenance is part of our core service, with bespoke control systems available as part of any project.

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An insight-led approach to solving dust issues at Andrex

Our team conducted extensive surveys to design a solution to this soft disposables manufacturer’s fugitive dust problem, coming up with a system that met production needs while satisfying ATEX/DSEAR requirements. 

Dust extraction systems

At FEG we install, design and commission fit-for-purpose LEV systems, providing cost-effective and reliable solutions from contaminant source to safe and efficient extraction.

Our industrial dust extraction system design is a holistic approach that takes into account the full picture of your facility. There is no “one-size-fits-all” approach and we will undertake extensive feasibility studies, surveys and assessment of your existing systems to ensure we provide a solution that works.

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