LEV Assessment: Back to the Shop Floor for Operations Director

Tue 29/08/2017 - 15:39

In the workplace, exposure to hazardous substances should either be prevented or adequately controlled. The purpose of an Local Exhaust Ventilation (LEV) system is to control the emission of such substances to the atmosphere as close as possible to the point of source, thereby preventing release into the workplace.  


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With a degree in Chemistry and a desire to be interacting with people and the practical working environment, David Gough, operations director, Built Environment Services, SOCOTEC, embarked on a progressive career in occupational hygiene over 20 years ago.

Occupational hygiene is all about the recognition, control and management of workplace health risks – from chemicals, biohazards and physical agents such as noise & vibration. Occupational hygienists use science and engineering to control risks to health, by designing out hazards and applying engineering controls to minimise exposures.

In the workplace, exposure to hazardous substances should either be prevented or adequately controlled.  The purpose of an Local Exhaust Ventilation (LEV) system is to control the emission of such substances to the atmosphere as close as possible to the point of source, thereby preventing release into the workplace.  To be effective, LEV must initially be well designed and constructed.  Over time, the performance of systems can deteriorate due to wear, blockage or damage.  Thus, regular inspection and testing is critical to ensure that control of exposure remains adequate, and this is one of the many occupational hygiene services that SOCOTEC provides.

Here, David talks us through the process at a major railway maintenance depot.


Interacting with the client and the varied nature of being on site was one of my favourite parts to being a research officer involved in occupational hygiene at the start of my career over 20 years ago. As Operations Director, I now manage a team of over 200 environmental professionals, including about 25 occupational hygienists, all engaged in helping clients comply with health, safety and environmental regulations, and I rarely get the chance to be involved in site work.  So, it was a welcomed task to go back to the shop floor and get involved first-hand with an LEV inspection and assessment.

Regulation 9 of COSHH requires all control measures to be properly maintained and the regular examination and testing of engineering controls including LEV.  In particular, an LEV plant provided to comply with Regulation 7 of COSHH should be examined and tested at least once every 14 months.  This particular system at the railway depot was installed to help control exposure to diesel engine exhaust emissions (DEEEs), generated from the running of Diesel Multiple Units (DMUs) in the maintenance shed. If working correctly and as specified, it should help to control exposure to DEEEs. 

We tend to carry out LEV assessments on railway depots in the daytime, where the sheds are quiet and train movements are minimised.  In the evening and early mornings, it would be almost impossible to carry out the assessment due to the frequency of trains entering and exiting the shed for servicing, and fume levels in the roof of the shed would be unacceptable. Nevertheless, we still need to ensure that train movements are suspended on the roads where we are working, and this forms part of our risk assessment and safe system of working.

Testing and Inspection

In order to undertake a visual inspection and perform test measurements, we need to access the LEV system in the roof of the shed using a Mobile Elevated Working Platform (MEWP).  Fortunately, my colleague and fellow hygienist, Chris, is a trained MEWP operator.

Visually, we are looking for damage to the ductwork, signs of blockage, holes in flexible trucking, etc.  Given the location of this system, high in the shed roof, damage is unlikely, but general wear and tear can still occur.

We use a variety of methods to measure the performance of the LEV system.  In this instance, we are using smoke tubes (to give a visual indication of performance), a micro manometer with a pitot tube for measurements in the ducting, and a thermal anemometer to measure face velocities at the LEV inlets. We take a number of readings at each point to gain a picture of the flow profile.

To assess the performance of the LEV system, the readings are recorded, flow rates calculated and then compared against the original specification of the system.  The HSE has issued comprehensive guidance on LEV and our reports and recommendations are based on this, and other, information sources. 

Old habits

When I’m on site, I also tend to look at the system from a visual perspective for evidence of system performance – such as accumulation of contamination in the workplace.  Even though I don’t spend as much time on site anymore, old habits die hard and it all comes flooding back very quickly!

For this system, the discharge point is on the side elevation of the shed, and I can see staining showing diesel fumes are being extracted from the workplace.  Depending on the process being controlled, emissions monitoring may be needed – this is where SOCOTEC’s MCERTS accredited stack emissions teams can step in – but they’re not needed in this case.

At this particular site, our teams have undertaken comprehensive DEEE exposure monitoring to assess the effectiveness of the control measures. As well as the LEV system, there are other considerations and actions which the client has implemented to control exposure, such as minimising engine run times.

Occupational Hygiene

Assessing LEV performance is just one aspect of occupational hygiene. For me, it’s the range of environments and industries that we get to work in and experience that makes occupational hygiene a fascinating career – I’ve been in hospital operating theatres assessing exposure to anaesthetic gases, motor manufacturing plants, flour mills, quarries, railway tunnels – this list is endless. And with it comes the satisfaction that I may have, in some small part, helped to protect workers from serious, and even fatal, illnesses caused by work-related activities and have helped our clients keep the workplace a safe environment for all who work there.

 Is there an area of occupational hygiene that interests you most?

 For more information, please get in touch.

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