1. Local Exhaust Ventilation

2. Local Exhaust Ventilation (LEV)
Operates by removing a contaminant at the point of generation and ducting it away in an air flow to a safe place

3. LEV Components Exhaust outlet Ducting Fan and motor
Hood or exhaust outlet
Filter or purifying system

4. Ducting As straight as possible Bends or angles should be gentle
Should be well supported
Ample access ports should be provided for cleaning (think MEMS)
Provision for testing duct pressure via water gauges or access points for air flow meters

5. Filter or Purifying System
Care must be taken to see that correct type of filter is used e.g. cyclones are not suitable for very fine particles
Owing to the dynamic nature of cyclones and the resultant generation of static electricity the potential for dust explosions is very high

6. Ventilation Fans and Motors
Fan must have sufficient power to cope with normal working but have sufficient margin to deal with overload situations

7. Exhaust Outlet
Exhausted air must be away from any air inlets, otherwise a cyclic pollution system is produced
Variation in wind direction must not reduce exhaust efficiency
Exhaust noise must be controlled

8. Fume Cupboards Type of LEV widely used in laboratories
Large ventilated box
Consists of enclosed chamber accessed through vertical sliding sash
Kept under negative pressure by a fan
Prevents back release of contaminant

9. Multihood Extraction Systems
Often convenient to extract from different locations via hoods linked to a common extraction system
Size of ducts must be selected to distribute total airflow amongst the several hoods

10. Maintenance 14 months if installed as a control measure under COSHH
Transport velocity (anemometer)
Capture velocity
Static pressure
Clean/change filters
Maintain fans