text: Local exhaust ventilation addresses the issue of avoiding the contamination of indoor air by specific high-emission sources by capturing airborne contaminants before they are spread into the environment. This can include water vapor control, lavatory effluent control, solvent vapors from industrial processes, and dust from wood- and metal-working machinery. Air can be exhausted through pressurized hoods or the use of fans and pressurizing a specific area.<br />A local exhaust system is composed of 5 basic parts
  # A hood that captures the contaminant at its source
  # Ducts for transporting the air
  # An air-cleaning device that removes/minimizes the contaminant
  # A fan that moves the air through the system
  # An exhaust stack through which the contaminated air is discharged
  In the UK, the use of LEV systems has regulations set out by the Health and Safety Executive (HSE) which are referred to as the Control of Substances Hazardous to Health (CoSHH). Under CoSHH, legislation is set to protect users of LEV systems by ensuring that all equipment is tested at least every fourteen months to ensure the LEV systems are performing adequately. All parts of the system must be visually inspected and thoroughly tested and where any parts are found to be defective, the inspector must issue a red label to identify the defective part and the issue.
  The owner of the LEV system must then have the defective parts repaired or replaced before the system can be used.