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Occupational safety course.doc
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2.3. Ventilation systems

Ventilation system is combination of methods and equipment aimed to secure workplace atmospheres, which are as free as practicable from hazardous contaminants and abnormal meteorological condition. A ventilation system works to extract contaminated or heated air from work area and input the fresh one.

Ventilation is classified as following.

By air circulation it’s classified into natural and mechanical ventilation, combined (together action of natural and mechanical ventilation).

By direction of airflow – input, extract, input and extract ventilation.

By location - general ventilation, local ventilation and combined ventilation.

By time of operation – regular and emergency ventilation.

2.3.1. Natural ventilation

Natural ventilation is classified as organized and disorganized one. Disorganized ventilation provides input and extract of airflow depending on direction and force of the wind and temperature of inside and outside air. It consists from infiltration and airing.

Infiltration is input air leakage through voids in windows and doors. Opened doors and windows make airing.

Organized natural ventilation is called aeration. It’s arranged through ventilation opening in the walls to input the air, ventipane in the roof or top section of the building to extract the air. Deflectors mounted in ventilating shaft and vent tube improve effectiveness of ventilation.

Natural ventilation is cheap and easy to operate, however input air is not previously purified and may be contaminated.

2.3.2. Mechanical ventilation

Mechanical ventilation defers from natural one in capability to purify extract air before its ejecting into the atmosphere, catch airborne contaminants and provide air conditioning in the workplace. Besides, it makes possible to arrange air intake for input ventilation in the least contaminated zones of an enterprise or even beyond it.

General ventilation provides air free of contaminants and conditioning in whole work area. It’s applied to extracting overall heat with the air that has no toxic emission, and also when it’s impossible to use local ventilation for technological reasons.

If gases or vapors spreading in the work area are denser than air general ventilation should provide 60% air extract from lower zone of area and 40% - from upper one.

Input and extract ventilation with general input and local extract from the place where contaminants are emitted is the most practicable for occupational condition.

In work area, which atmosphere contains great quantity of gases, vapors and dusts extract ventilation should be 10 % greater than input one, what prevents pushing contaminants from that area into the neighboring.

Ventilation system can use for input not only outside air but also air of the work area after its purification. Such repeated use of the air is called re-circulation recommended in cold year period to keep warm inside.

Local ventilation as the general one can be input and extract.

Local ventilation is performed as airflow shower, air and air-heated curtains used for focused air input.

Airflow shower is aimed to protect workers from overheating in hot workshops, air and air-heated curtains prevent work areas from incoming of outside cold air.

Local extract ventilation works by means of extract hoods, panels etc. It should provide maximum catch of contaminants with minimum quantity of extracted air.

To choose appropriate ventilation system they consider characteristics of harmful emission (temperature, vapor density, toxicity), worker position in the workplace and technology.

Emergency ventilation is installed in the work areas where harmful or explosive gases may be rapidly evolved into the air in great quantity. Gas generator and compressor areas are referred to such work areas. Emergency ventilation is only extract.

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