Ventilation Systems As Control Measures

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Ventilation Systems As Control Measures

• Dr. Lim Jac Fang
• Doktor Kesihatan Pekerjaan
• JKNSabah

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Introduction

• A good and effective ventilation system is
  necessary in a workplace which have processes
  that emit air contaminants such as dust, fumes,
  mists or vapours.
• Substitution or enclosure method
• Simple, cheap and effective

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Types of Ventilation

• Natural
• General
• Dilution
• LEV

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Natural Ventilation

• Natural movement of air entering and leaving
  openings such as windows, doors, roof ventilators
  as well as through cracks and crevices of a
  building
• Heated air rises, cool air below

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General Ventilation

• A method of improving or maintaining the quality
  of air in the work environment with airflow
• A room or an entire building is flushed by
  supplying and exhausting large volumes of air
  throughout the area

• Supply or forced ventilation
• 2. Exhaust or induced ventilation

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Dilution Ventilation (DV)

• DV consists of general ventilation
• Uncontaminated outside air inside air
  diluting and reducing the concentration of air
  contaminants to acceptable levels to which a
  worker can be safely exposed for eight hours a day

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LEV

• Capture or contain contaminants at their source
  before they escape into the work room environment
• System consists of one or more hoods, ducts, air
  cleaner and a fan
• LEVs remove contaminants rather than just dilute
  them

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Use of Natural Ventilation

• Not suitable for processes which emit dust,
  fumes, mists or gas
• Rooms for chemical storage
• 25 of floor area
• Half the ventilating area should be between floor
  level and a height of 2.25m from the floor

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Use of Dilution Ventilation

• DV is usually applied to the control of
  contaminants in situation meeting these criteria
• To control vapours (organic) from low toxicity
  solvents
• To control contaminants released over such a
  large area or in such a manner that LEV is
  impossible, impractical or prohibitively
  expensive

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• Small quantities of contaminants released into
  the work room
• Rate of contaminant release should be reasonably
  constant to avoid inadequate dilution during
  periods of peak contaminant release
• No corrosion or other problems from the diluted
  contaminants in the work room air

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• Sufficient distance from the worker to the
  contaminants source to allow dilution to safe
  levels

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• DV is prohibited control emission of very toxic
  air contaminants e.g., formaldehyde or other
  carcinogenic chemicals
• For effective DV, the exhaust outlet and air
  supply must be so located that all the air
  employed in the ventilation passes through the
  zone of contamination

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• Avoid re-entrance of the exhausted air.
• The advantages and disadvantages of DV are as
  follows

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Advantage Disadvantage

• Simplicity
• Low original cost

• Large volumes of dilution air needed
• Employee exposures are difficult to control near
  source

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Use of LEV

• The most effective means of controlling air
  contaminants is to capture and remove the air
  contaminants at their source with LEV and to
  prevent them from being carried away by air
  currents into the breathing zones of the worker

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• Major release (toxic) of localized sources of
  contaminants.
• LEV consists of 4 parts

• Hoods (most important)
• Ducts
• Air cleaner device
• Fan and motor

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• The hood consists of 3 main types to contain and
  remove the air-borne contaminants.

• Enclosures
• Capturing hoods
• Receiving hoods

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Conclusion

• Ventilation an effective way to control toxic
  air contaminants if substitution or enclosure
  method of control is not possible
• DV reduces contaminant concentrations by diluting
  them with fresh air. (not for toxic emission)

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• LEV capture or contain contaminants at their
  source before they are dispersed in the workroom
• LEVs need to be maintained, inspected and tested
  regularly to ensure that it is performing
  adequately

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• Thank You!