Local Exhaust Ventilation (LEV) systems will have been designed by a competent engineer (ideally one who possesses a competency card through the Institute of Local Exhaust Ventilation Engineers (ILEVE), part of the Chartered Institution of Building Services Engineers (CIBSE)).

When such systems are designed the engineer involved will have taken into account the types of contaminants or hazardous materials involved (and the volumes being used) and the numbers of extraction points and positions where extraction is needed as well as any building limitations.

ILEVE competency cards demonstrate competency in 5 LEV related disciplines: Occupational Hygiene, Design, Installation Management, Commissioning, and Thorough Examination and Testing. A pass in any category is only achieved with appropriate Experience, Technical knowledge, Qualification and Submitted evidence. Full membership is only awarded after a minimum of 5 years' experience has been achieved.

Anyone wishing to alter an LEV system must ensure that this is only carried out in consultation with a competent engineer, as altering the system without competent advice could detrimentally impact the performance of the system and could put the users at risk.

Competent engineers upon completion of any modification will check if the system controls exposure effectively and will provide a full commissioning report which will be required for the next statutory test, as this data will be used as a baseline for measuring the system's performance. Departments who carry out this type of work on their own must provide a copy of the re-commissioning data either to the Estates Department, or must make this information available to the contractor who conducts statutory testing.

Departments must NOT alter LEV without consultation with a competent engineer.

Departments must also consider consultation with a competent engineer when wishing to change what the system is being used to extract unless the hazardous materials are of similar 'type'. If the materials are highly or extremely flammable (for example), or if using a corrosive material, or a contaminant that would warrant a full de-contamination post its use (such as lead, for example) and these were not what the system was originally designed to be used for, then a competent engineer must always be consulted.