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LEV Airflow FAQ's

Updated: Apr 20


Do I have to fit airflow indicators to all the hoods in the LEV system?


There is not a specific legal requirement to have airflow indicators or similar fitted to extraction. As an employer you do, by law, have to make sure your LEV system keeps working properly. One of the main reasons why LEV doesn’t function effectively is when airflow decreases and becomes inadequate resulting in ineffective control. This might be caused by a variety of reasons such as damaged ducting, blockages in the ducting etc.


One simple way of checking this is through the use of airflow indicators at the hood, this provides assurance that the flow-rate is maintained and that employees are adequately protected.

There are other ways of checking airflow such as using an anemometer, dust-lamp or smoke tracer (with the work process running), however, an airflow indicator is currently the only method that will show the operator or supervisor immediately if there's a problem, and HSE's LEV guidance HSG258 recommends that these are fitted.



How do I know that LEV hood airflow is adequate?


It is not possible to effectively gauge the velocity of air entering an LEV hood 'by hand'.

A suitable airflow indicator should make it easy to see whether airflow is adequate.



Do I have to fit airflow indicators?


It is not a specific legal requirement, but you should have some way of checking that adequate airflow is being maintained. If you decide to get airflow indicators, you should identify which LEV systems or parts of systems need to be addressed first.


Factors to consider in your decision include:

  • The risk of exposure

  • Whether the operator has to set the hood airflow

  • Whether other checks are practical

  • The cost

LEV suppliers can fit airflow indicators if requested.



Are airflow indicators the best way to check airflow for all types of hoods?


Not for all LEV. For instance, a manometer, measuring static pressure across the filter unit, can provide sufficient indication, for a simple LEV system consisting of a fan, an air-cleaner (e.g. filter), a duct and a hood.



What sort of airflow indicator should be fitted?


It depends on the level of potential health risks. If risk is low, a simple indicator will be appropriate. More hazardous substances and circumstances may require more sophisticated, and potentially more costly, indicators (e.g. with an alarm if airflow drops too low).


Whichever indicator is chosen, it will need to show clearly whether the airflow is adequate.


Example of a simple airflow indicator display


Green - Adequate airflow


Red - Inadequate airflow



Would airflow ‘tell-tales’ be good enough?


'Tell-tales' such as pieces of paper or plastic hung to bend in the LEV hood airflow, do not provide an effective indication of airflow and they are delicate and easily damaged.

In all but very simple systems, extracting low hazard substances, they will not be effective, adequate or suitable.



Do examiners have to label LEV systems that they test?


No - there is no specific legal requirement on employers or examiners to label LEV.

The law is that the employer must maintain LEV system performance and should also arrange a Thorough Examination and Test at least every 14 months.


The employer needs to know whether or not an examination has been done or when it's due, and so do supervisors and operators. Critically, they also need to know when a hood (or LEV system) has failed. Attaching labels is an effective way of easily providing this information.



Do examiners have to label LEV hoods tested?


HSE guidance recommends examiners label each hood with a test record. Alternatively, the test record label could be placed nearby, for instance, close to the system on-off switch. It should be clearly visible to the supervisor and operators.


Example of an LEV test record label







Do examiners have to put red labels on LEV hoods that they have failed?


HSE guidance recommends that a red 'Failed' label should be put on any hoods (or system) that has failed, to warn supervisors and operators directly and explicitly. This could be done by the examiner with agreement from the employer (client). Alternatively, the label could be issued to the employer's responsible person.


With the label, should come a short 'emergency' written report containing a clear description of what's wrong and a list of practical remedial actions.


Example of a "Failed" label






Once the employer has had the LEV hood or system repaired, a competent person needs to check that it is effective and adequately controls exposure. The 'Failed' label can then be removed.



Is there an alternative to labels?


Labels are recommended as a means of providing clear and simple indication that a hood/system is not functioning satisfactorily. Other means can be used, as long as it is clear to the employer and to the operators that the equipment requires rapid attention.



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If you have any questions that weren't covered in this FAQ section, or would like more information, Call us on +44(0)1563 546807 or click here to contact RCS.