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November 19, 2014

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Local exhaust ventilation: not enough protection

Prof. David Fishwick’s blog on occupational asthma made a clear case for reducing inhalation exposure. This blog picks up on this theme and deals with local exhaust ventilation, the most common method of reducing inhalation risk.

Local exhaust ventilation (LEV) is used to protect workers’ health by removing airborne contaminants before they enter their breathing zone. Unfortunately, LEV frequently fails to offer adequate protection and in truth, the majority of systems I see can be improved; some only require minor modification but many need fundamental redesign.

There are many reasons why LEV fails to protect but before these are discussed we need to take a step back and recognise that LEV fits into a hierarchy of controls. There are steps to consider before LEV is applied. For example, you may be able to significantly reduce exposure by substituting a substance for one that is less hazardous, potentially removing the need for LEV. If this is not possible there are other steps which should be considered. For example, can the process be modified to reduce airborne emissions? Or can the process be adapted to make it easier to apply LEV?

Many employers and employees are over optimistic about LEV capabilities (especially the capture performance of ‘flexible arms’). The assumption is often that if LEV has been applied to a process, it will automatically control airborne exposure – this is wrong. The LEV hood has to match the process. The ‘wrong’ type of hood or a poor hood design are common reasons for failure of control.

How do you ensure you get the right system?

It is important to think about controlling exposure as more than simple just buying and installing equipment. Effective exposure control measures consist of a mixture of control ‘hardware’ (engineering control) and work practices (working procedures and methods). Therefore it’s important when purchasing LEV to prepare a specification document that contains information that a potential LEV supplier needs to know. The type of information that is essential includes the:

  • contaminant to be controlled
  • source, speed and direction of the contaminant
  • work process requirements
  • how the worker will carry out the job, and

The specification document should also include an exposure benchmark or other test(s) to help demonstrate control success – essentially your LEV system should be commissioned. Commissioning tests should include technical performance information, including measurement data (e.g. air velocities, static pressures). These are required to demonstrate that the system meets the design specification and they also provide a baseline to compare with future measurements. But importantly the commissioning tests should demonstrate that the LEV system can help control exposure rather than simply create random or directional airflow which may or may not influence exposure. This may be demonstrated using a mixture of qualitative (e.g. flow visualisation using smoke) and quantitative (e.g. personal sampling) testing.

Once you have an LEV system you should ensure that the supplier provides you with a user manual containing information on how to use and maintain the LEV system. This should also detail what tests and checks need carrying out during the statutory ‘annual’ thorough examination and test.

Carrying out these steps may appear to be an expensive and time consuming alternative to buying an ‘off the shelf’ solution but it’s these early steps that result in cost effective LEV systems that actually work and protect workers’ health.

More information can be found on the HSE LEV web page and for training on practical management of LEV see the HSL webpage.


What makes us susceptible to burnout?

In this episode  of the Safety & Health Podcast, ‘Burnout, stress and being human’, Heather Beach is joined by Stacy Thomson to discuss burnout, perfectionism and how to deal with burnout as an individual, as management and as an organisation.

We provide an insight on how to tackle burnout and why mental health is such a taboo subject, particularly in the workplace.


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