WHY VENTILATION IS IMPORTANT IN OPERATIONS?
The article title appears to be purely technical but it has greater implications in Operations management. This is related to the safety of workers and the planners (top management) of operations must take into consideration the working environment as the prime factor for which effective ventilation system must be put in place. This not alone keeps workers healthy but also improves productivity and pre empts any accidents.
Ventilation differs from air-conditioning. The air conditioning, conditions the air by heating or cooling it or by using such other process. The ventilation merely supplies fresh air to the plant or removes vitiated air there from without in any way conditioning it. Moreover, control of temperature and humidity are the main parameters in air-conditioning making comfortable working conditions in an enclosed area say a room or office or a factory hall. The capacity to achieve required temperature or humidity is limited in ventilation. The difference is accentuated by the fact that, there are plants which specialize in the manufacture of ventilation equipment, while certain others exclusively manufacture air conditioning equipment. SKF India Ltd., Ventura Fabrication Pvt. Ltd., AndrewYule &Co and General Electrical Co and a few others manufacture ventilation and dust control equipment. Air-conditioning operations manufacture only air-conditioning equipment. Some of the reputed firms in air conditioning equipment field are Blue Star, Voltas, Carrier Aircon, National, Samsung, General Electric, Videocon etc.,
Types of Ventilation
Two types of ventilation are distinguished, depending on the purpose they serve. The two types are:
1. General ventilation, also known as dilution ventilation ; and
2. Local exhaust ventilation.
General ventilation is introduced to serve one of the two following purposes, viz.
(a) To keep the working conditions at acceptable comfort levels; and
(b) To keep contaminants in the air within safe limits.
(a) General Ventilation for Comfort Control:
General ventilation for comfort control is essential because, in certain plants, a lot of heat is liberated from structures, processes, lighting and people. These are called heat gains, which should be offset by ventilation to keep the inside temperature at the desired level A ventilation plant is sized to supply outside air so as to offset these heat gains, and the air supplied is distributed uniformly inside the factory. The outside air picks up the heat as it passes through the hot interior and helps to maintain a relatively lower temperature. In other words, the temperature of the outside air rises as it passes through the factory interior and the inside temperature of the air falls. However, it may be noted that in any well ventilated environment, the temperature is inevitably higher than the outside temperature; the degree of difference is beside the point. This is the essential feature of general ventilation.
General ventilation for comfort control is modified where a few workers are scattered over a relatively large area. Ventilation of the type described above would, therefore, be impracticable and wasteful. In such cases, local-area or spot-cooling ventilation is resorted to. This method involves directing high velocity air streams at that worker. Comfort is enhanced by the increased effects of convection and evaporative cooling. The effectiveness of this method depends on the temperature at which air is supplied and the velocity at which it is streamed at the worker. Here, high velocities will not be of much use if the temperature of the air stream is about 38 C and above.
(b) General Ventilation to keep Contaminants within Safe Limits or Dilution Ventilation:
It has already been pointed out that air contaminants are health hazards and that the purpose of any ventilation is to eliminate them completely or to hold their concentration down to safe limits, which are referred to as Threshold Limit Values (TLV). In dilution ventilation, attempts are made to flush the entire environment with ventilation of air; the airflow rate is calculated so as to restrict the contaminant concentration to permissible limits.
Dilution ventilation is advantageously used to control vapor from such organic (or industrial) solvents as benzene and carbon disulphide because they are relatively less toxic, and their generation rates are not too high. Dilution ventilation may also be used when the evolution of contaminants is reasonably uniform and is not confined to a few scattered locations. When the contaminants are highly toxic and the evolution rates are high, the ventilation or dilution flow rates, which are required to keep their concentrations within safe limits, become enormously so large that, dilution ventilation becomes uneconomical. In such situations local exhaust ventilation is best suited.
Local Exhaust Ventilation
Local exhaust ventilation is a system for preventing the contamination of factory air by withdrawing the contaminant at its source into a duct system for discharge to the building exterior (or air cleaner) In order to achieve this the process generating the contaminant is surrounded, as completely and effectively as possible by enclosures called hoods, booths which capture and convey exhaust air stream to an exhaust duct system. Local exhaust ventilation is resorted to, in plating tanks, cleaning stations, laboratory hoods, wood-working machinery and metal processes like buffing, polishing and grinding.
Though both the systems aim at contaminant control, there are differences between dilution ventilation and local exhaust ventilation. In dilution ventilation, contaminants are kept permissible limits; but they inevitably become a part of the environment. In the local exhaust ventilation, on the other hand, the contaminant is prevented from diffusing into the environment; it is captured at source and conveyed from the factory interior into the atmosphere. Local exhaust ventilation is more effective than dilution ventilation in controlling contaminants.
The starting point in the choice and design of any ventilation scheme is an assessment of all the relevant factors. If comfort control alone is desired heat sources and heat gains of all types should be assessed and a suitable ventilation system should be provided to allow sufficient air-flow to offset the heat gains. For dilution ventilation, the various contaminants should be identified and their generation rates assessed in order to determine ventilation air-flow rates based on permissible concentration levels. If local exhaust ventilation is desired, the identification of contaminants and a determination of their generation rates and locations constitute the starting point. The subsequent steps merely involve the determination of the flow rates and the selection of the necessary equipment.
In conclusion this article clearly indicates the importance of ventilation and of various hazards that occur in a factory. Proper and right ventilation not only prevent health hazards of personnel on shop floors but also considered by workmen as a good welfare measure or working atmosphere leading to one of the contributing factors for harmonious management worker relations.