Controlling Chemical Emissions: Local Exhaust Ventilation (LEV)

1. Controlling Chemical Emissions: Local Exhaust Ventilation (LEV)

2. What is an LEV? • A Local Exhaust Ventilation System (LEV) is: • An Engineered Control system intended to reduce occupant exposure to airborne contaminants. • A mechanical system comprising: • An Air Mover. • Air Cleaner. • Series of interconnecting and Discharge Ductwork. • Capture Hood(s), Booths,

3. Simple LEV, Fig. 1

4. LEV Design Principles • The Air Mover. • Air Cleaner. • Hoods/Booths. • Interconnecting/Extract Ductwork.

5. Benchmark & Control Requirements • LEV requirement is dictated by the following factors: • Acceptable Concentration Levels (Benchmark/ppm). • Concentration Levels being produced, as determined by: • Degree of the Hazard (Hazard Band). • Magnitude of the Source (S, M, L). • Volatility (L, M, H).

6. Types of LEV Hoods:

7. Types of LEV Hoods……..

8. LEV Design Principles……. • Capture Hoods, Booths…… • Should be located away from drafts. • Drafts can shift the rising Chemical plume away from the capture Hood, especially if it is slow rising.

9. LEV Hood Effectiveness/Efficiency

10. Walk-in Booths

11. Managing ‘The Wake’ Effect

12. ‘Push–Pull’ VentilationJet of air pushes low velocity contaminated air into Capture hood.

13. Capture Zone

14. LEV System Engineered to Match Exposure

15. LEV Design Principles……. • Extract. • Momentum and buoyancy. • ‘Air boundary layer’: • Recirculation eddies. • Wind direction. • Downward wake. • Replacement Air so as to maintain Space/LEV pressure balance. • Clean source and/or conditioned prior to being introduced into the space. • Make up air must not introduce drafts.

16. Multi-branch LEV System, Fig. 2

17. Achieving LEV Design Intent • Installation of the LEV system must be in strict accordance with design. • Testing, adjusting, balancing (TAB) and commissioning must be carried out by competent personnel. • Verify or establish design conditions, including: • Airflow. • Hood Face Velocities. • Fan speed & power consumption. • System Pressure Drop. • Air Cleaner pressure drop. • Space IAQ before and after TAB. • Tab results will form the basis for periodic evaluation/verification of system performance.

18. Operator Protection

19. Operator Protection

20. Regulations/Legal Responsibilities……… • Under HSW Act: • Employer has HS duties to themselves, employees and others who may be affected by their work processes. • LEV providers (supplies, installs, commissions and/or tests)are responsible to the end users who are meant to be protected by such systems. • COSHH (Control of Substances that are Hazardous to Health) Regulations include: • Employers must assess the degree of exposure and the risk to their employees, devise and implement adequate control measures, and check and maintain them. • Employees must use the control measures in the way intended as instructed. • Employers must ensure that the equipment necessary for control is maintained in an efficient state, in efficient working order, in good repair and in a clean condition. • Employers must ensure that thorough examination and testing of their protective LEV is carried out at least every 14 months (or as otherwise stipulated), other controls at suitable intervals and must review and revise ways of working so that controls are being used effectively. • PUWER (Provision & Use of Work Equipment Regulations: • LEV as work equipment should be suitable for its intended purpose, maintained for safety and conform at all times with any essentila requirements that applied when first put into service.

21. Regulations/Legal Responsibilities……… • MHSWR (Management of Health & Safety at Work Regulations) 1999: • An employer should be competent for Health and Safety purposes or employ or obtain advice from competent people. • People are seen as competent where they have enough training and experience or knowledge and other qualities to enable them to properly assist in undertaking the measures referred to. • Others include The Machinery Directive (2006/42/EC); The Supply of Machinery (Safety) Regulations 2008 (SMR08); ATEX Directive 94/9/EC; DSEAR (Dangerous Substances & Explosive Atmosphere Regulations 2005.

22. LEV Competence • Professional Competence can be achieved by qualifications obtained through: • ILEVE (Institute of Local Exhaust Ventilation Engineers). • RoHS. • CIBSE.

23. Benchmark & Control Requirements • LEV requirement is dictated by the following factors: • Acceptable Concentration Levels (Benchmark/ppm). • Concentration Levels being produced, as determined by: • Degree of the Hazard (Hazard Band). • Magnitude of the Source (S, M, L). • Volatility (L, M, H).

29. Exposure Reduction • Example: • A Hazardous substance, rated as CHIP R- 20,21,23,24 will be a Band C Hazard. • Bench Mark exposure is 0.5 to 5ppm. • If Medium amount and medium volatility Liquid, exposure is 50 to 500ppm. • Exposure reduction necessary = 1000 fold (to achieve bench mark of 0.5 – lower value).

30. REFERENCES:1. Local Exhaust Ventilation – Engineering Control 2002. IAQ Guide3.