COSHH (LEV) Requirements

Looking after your LEV

Once a system has been specified and provided then there is ongoing maintenance and checks that need to be monitored to ensure the LEV system stays effective in controlling the hazardous materials.

When a LEV system is provided or installed it will be often be balanced and then commissioned. Balancing the system ensures the airflow is even and steady across the LEV system. This can be simply setting the right speed on the extraction unit or fan to setting blast gate and control dampers in the ducting. The commissioning will test the system and prove it works to the designed specifications and legal bench marks.

Once the system is balanced and commission responsibility for its continuing maintenance is passed to the system owner. The system owner legally has to continue to check the system periodically to ensure it is working within the original design parameters. These checks will need to be recorded in a system log book and annually the system will need to be Thoroughly Examined and Tested by a qualified inspector.

It is important to know what to check and how the system should perform to ensure it is still effective.

Performance Velocities

The capture velocities and transport velocities are the two primary gages of airflow. There are legal bench marks that these two velocities need to meet and should have been measured and proven as part of the system specification and commissioning.

But once the system is in use these airflows should be monitored. The simplest way to monitor these is using an airflow indicator. These are analogue or digital devices that show a visual indication that the airflow is still running and mount to the duct work. A small pipe is inserted into the duct and, if the airflow is on, a visual indication is given. In analogue gages this is usually a needle pointing to a green zone. In digital indicators an LCD screen usually shows an arrow or cross depending if the air flow is running or not.

However, airflow indicators are just that, an indication that there is airflow – nothing more.

For a closer look then the airflows can be checked with an anemometer which takes the air speed. To check the airflows, it is important to know the bench marks.

Capture velocities are the air velocities required at the source in order to effectively capture the contaminate cloud and draw it in to the hood. These are commonly referred to as face velocities.

The table below shows the required bench marks as detailed in HSG258 Controlling Airborne Contaminates at Work.

Contaminate Cloud Release Example of Process Capture Velocities
Still air with little or no energy Evaporating, mist from electroplating tanks 0.25m/s to 0.5m/s
Fairly still air with low energy Welding, soldering, liquid transfer 0.5m/s to 1.0m/s
Moving air with moderate energy Crushing, spraying 1.0m/s to 2.5m/s
Turbulent air with high energy* Cutting, abrasive blasting, grinding 2.5m/s to 10m/s

*these types of cloud are difficult to control using capturing hoods.

Capture hoods with large faces, such as the opening of a fume cabinet will need to be tested as averages across its face. This is done at 9 points across the face of the opening or hood.

Transport velocities refer to the air volume through the duct work. In order to carry the dust through the system and to either the extraction unit or out to the exhaust duct. If the airflows are too low for the size of the duct or the type of contaminate being extracted then dust can drop out of the air flow in the duct and pile up at places such as:

  • Long horizontal runs of ducting
  • At low points in the system
  • At junction's where the duct diameter increases
  • After junction or bends
  • When conveying different sizes of dust such as in wood dusts
Type of Contaminant Indicated Duct Velocities
Gases and Non-Condensing Vapours Minimum of 5 m/s
Condensing vapours, fume and smoke Minimum of 10 m/s
Low or medium density, low moisture content (plastic dust, saw dust) fine dust and mists) Minimum of 15 m/s
Process dust (cement dust, brick dust, wood shavings, grinding dust) Around 20 m/s
Large particles, aggregating and damp dusts (metal turnings, moist cement dust, compost) Around 25 m/s

As the system is used, natural wear and tear, blockages and saturation of filters can all affect the systems airflow.

Electronic System Monitoring

Many recirculating filtered systems have electronic monitoring systems that monitor airflow, filter conditions, run times, face velocity and more.

Many of these also include airflow indicators and “low flow alarms” that sound if the system performance drops to low.

Some systems will include filter monitors. For dust particulates these often take the form of differential pressure gages. These measure the air flow on one side of the filter. As the dust filter blinds, the air will back up on side of the filter as it struggles to get through the dust layer. Once the air pressure on one side gets too high or too low then an alarm will trigger, normally as a flashing light or audible alarm.

Monitoring a carbon filter is a little more difficult as even when the filter is saturated the air will flow freely through the filter. This means the air exhausted through the filter needs to be measured for the amount of contaminates making through the filter.

This can be done in varying degrees of success depending on the type of vapour or gas being filtered. For example, solvents are easy to monitor using a Volatile Organic Compound (VOC) monitor but more specialist equipment is often required for vapours like acid and alkalis.


If your LEV system has filters these will also need to be checked. Many large filtration systems have cleanable filters in the form of vibration systems (often referred to as shakers) or with internal air systems (reverse pulse jet). Many of these systems can be set to automatically activate when the extractor is turned on or off but some require manual activation.

If the extract unit has disposable filters then these will also need to be monitored and changed as they become saturated. Many systems have filter monitoring systems built in or as an optional extra and, where possible, these should always be used.

How to dispose of disposable filters is down to your local authority as it depends entirely on what contaminates are being held in the filters.

Care should always be taken when changing saturated filters and proper PPE should be worn to avoid contamination from the saturated filter.

Filter monitoring, changing or cleaning should be part of your regular LEV checks. It is recommended spare disposable filters are kept in stock so that when a filter saturates it can be quickly changed. Filter changes should be recorded in the system log bog.

A common cause for LEV systems to fail their annual thorough examination and test is saturated filters with no spare filters available at the time of the test to change out. If an LEV system fails due to a saturated or worn filter then it will be deemed unsuitable for use until the filter is replaced or cleaned. This can also then incur the costs of a re-test.

They System Log Book

The system log book is an important aspect of any LEV as it is used to record the regular checks, maintenance, replacements and repairs. Log books can be generic or specialised but all should contain:

  • Schedules for regular checks and maintenance
  • What checks and maintenance has been carried out
  • Record of these checks, any maintenance, repairs and replacements
  • Checks of operator compliance with the correct use of an LEV system
  • The name of the person whom made these checks and dated when the checks were made

Various components of the LEV system should be checked regularly. Each aspect will need degrees of checking daily, weekly and monthly. Items include:

  • Hoods, including airflow indicators, physical damage and blockages
  • Ducts, inducing damage, wear and partial blockage
  • Dampers – positioning
  • Air cleaner, including damage, failure alarms
  • Filter changes/ condition
  • Air mover, including power consumption, noise or vibration
  • Maintenance carried out
  • Replacements made
  • Planned and unplanned repairs
  • How operators have been using the LEV
  • Enough space to report the results alongside each item
  • Signature of designated person and date

The log book will also show a record of the annual Thorough Examination and Test.

LEV Thorough Examination and Test

All LEV systems are legally required to be checked every 14 months in a Through Examination and Test as per COSHH Regulation 9 to the stipulations cited in HSG258: Controlling Airborne Contaminates at Work.

This is commonly referred to as an LEV check. The LEV Check is broken down in to three stages.

Stage 1: A Thorough visual and structural examination to verify the LEV is in efficient working order, in good repair and in clean condition.

Stage 2: Review of the technical performance to check conformity with commissioning or other sources of relevant information.

Stage 3: Assessment of the control effectiveness.

There are several elements to each stage that need to be completed and verified. Once the test has been completed the examiner will either issue a pass or a fail.

If the system passes then a report will be issued detailing what the LEV examiner found. There may be notifications or actions that require attention in the future, such as wearing that has not yet become bad enough to fail the system but will require attention to prevent the system from failing in the future.

If the system has failed the LEV check then it should not be used and should be repaired immediately. The LEV report will stipulate why the system has failed and what needs to be done to bring the system back to compliance.

These repairs should be enacted immediately. Once the repairs have been affected then the system will need to be retested to ensure the repairs have been carried out properly.

The LEV examiner should enter the date and result of the thorough examination and test into the system log book.


As with every stage of LEV implementation, knowing what is legally required once the system has been handed over to the system owner is vital to ensure the system remains effective and compliant during its life time.

Failing to properly monitor and maintain a system can be costly. Systems may end up needing extensive repairs or even completely replacing. There are also the legal ramifications. Failing to maintain an LEV system and properly record it and have it thoroughly examined and tested could result in being in breach of Health and Safety Law. This could expose people to unnecessary health risks and have further impacts in the forms of official warnings, fines and, in extreme cases, prosecution.

Monitoring and checking a system is easy and can be done by a designated competent employee “in house” and annual thorough examinations and checks are not expensive and can be carried out by most LEV providers.

Vodex Extraction Services

Vodex Ltd has over 30yrs experience in handling fume extraction and we offer a whole range of extraction products for fumes and vapours. We have worked in a very wide range of applications. As always if you need any further information, have any questions or just want to chat about your application or requirements then please feel free to contact us. Its really easy to do.

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