Ventilation Systems As Control Measures

Ventilation Systems As Control Measures

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

Types of Ventilation Natural General Dilution LEV

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

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

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

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

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

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

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

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

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

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

Simplicity Low original cost Large volumes of dilution air needed Employee exposures are difficult to control near source Advantage Disadvantage

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

Use of LEV • Major release (toxic) of localized sources of contaminants. • LEV consists of 4 parts: • Hoods (most important) • Ducts • Air cleaner device • Fan and motor

Use of LEV • The hood consists of 3 main types to contain and remove the air-borne contaminants. • Enclosures • Capturing hoods • Receiving hoods

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)

Conclusion • 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

Ventilation Systems As Control Measures