Things Required in Environmental Sanitation | Environmental Engineering

The following points highlight the top two things required in the environmental sanitation. The things are: 1. Ventilation and 2. Lighting.

Thing # 1. Ventilation:

The process of removing used air or vitiated air by fresh air from buildings is called ventilation in buildings. This can be done by natural method or artificial method.

Objects of Ventilation:

The following are the objects of ventilation:

(i) To remove the used air from the buildings,

(ii) To supply oxygen for humans in the buildings,

(iii) To remove the excessive moisture,

(iv) To cool the body of humans and remove the excessive heat,

(v) To prevent the suffocations of theatres, assembly halls and other public meeting places,

(vi) To cool the surrounding objects and freshen the atmosphere inside the buildings.

Composition of Air:

The atmospheric air mainly consists of oxygen and nitrogen. But certain impurities are always present in the air.

The composition of air is as follows:

The purest sea or mountain contains 20.999 volumes per cent of oxygen. In the overcrowded halls it is as low as 20.65.

Carbon dioxide is obtained by combustion, purification, fermentation, fog and respiratory processes of animal life. The quantity of carbon-di-oxide is decreased by vegetation, rain and high winds. If the percentage of CO₂ increases up to 1.5 it will produce nausea, depression and headache. If it becomes 2.5 percent, it will extinguish the candle. The presence of 5 per cent by volume of carbon dioxide causes fatal accidents.

Out of other impurities present in the air, the carbon monoxide is the most poisonous, it is formed by the imperfect combustion of carbon and cast iron stoves give it off in considerable quantities.

Combustion and Respiration:

The quantity of oxygen is reduced and carbon-dioxide increased by combustion and respiration. When coal is burnt, it gives off carbon-di-oxide, carbon monoxide and other impurities. Similarly during respiration and breathing an average adult gives off 0.017 cu. metre per hour carbon dioxide.

Each cubic metre of gas on burning also gives 0.017 cubic metre carbon dioxide. Therefore, combustion and respiration continuously impure the atmosphere which should be continuously freshened by proper ventilation.

Quantity of Air Required:

In the previous article, it has been stated that an average adult gives off 0.017 cu.m carbon dioxide per hour. Under average conditions air contains 0.04 percent of CO₂. If in the standard of purity 0.06 percent of CO₂ is allowed, an adult will make 85 cu.m impure per hour, because he will add up 0.02 per cent of CO₂ per hour.

The following table gives the quantity of air required per head per hour:

During the design of buildings, sufficient care should be taken so that each person may get fresh air and there should be no suffocation in the buildings. Table 1.3 gives the air space required for the design purpose.

Comfort by Ventilation:

As previously stated that the efficiency of work depends on the freshness received by ventilation, light, suitable atmospheric temperature and humidity. There is no hard and fast rule which can define the comfort. Now a days the efficiency can be increased by air conditioning. I.S.I. has recommended the following dry bulb and wet-bulb temperatures for optimum air-conditioning.

Systems of Ventilation:

The systems of ventilation can be broadly classified as under:

(1) Natural System

(2) Artificial System:

(a) Plenum System

(b) Vacuum System

(c) Balance System

(d) Air-conditioning.

A good ventilating system should have the following characteristics:

(i) It should be possible to control the incoming and outgoing air from the rooms.

(ii) It should freshen each and every corner of the room and there should be no stagnant pockets left.

(iii) It should only allow the entrance of fresh air free from dirt and excessive moisture.

(iv) It should avoid the draught for which the maximum velocity of air should not be more than 16 metres per minute.

(v) It should draw sufficient quantity of fresh air which is necessary for preventing stagnation.

(vi) It should also allow the control over the room temperature which should not decrease or increase than that required for comfortable working and living.

(1) Natural System:

For ordinary buildings natural system of ventilation is mostly used. In this method natural forces are used for the removal of foul air and admittance of fresh air in the buildings through ventilating inlets and outlets respectively.

When air is heated, it expands and rises, therefore the air which is given off by the body, starts rising upward and is collected below the ceiling of rooms or apartments. This can be taken out by the ventilators of properly designed ventilation outlets. The fresh air is admitted in the buildings through doors, windows or properly designed ventilation inlets.

The efficiency of natural ventilation depends on the wind velocity and the difference in the specific gravity of the inside and outside air of the apartments. As the cold air on fresh air has less specific gravity than the warm foul air, therefore, it should be drawn inside the room sufficiently below the ceiling. The height of the sill of the windows should be sufficient high from the floor level so that the current of wind may not hit the sleeping.

Persons in the room and giving them a sense of draught. In tropical countries, the windows are provided on the windward as well as on the leeward side. These windows will admit air only when they are open, therefore in some better places fan lights are provided above or below the windows as shown in Fig. 1.1.

The position and the inclination of the fan-light should be such that the fresh air should drive off all the foul air from the room as shown in Fig. 1.2.

In case of sloppy roofs ridge ventilators may be provided as shown in Fig. 1.3.

In very cold, countries it is not possible to keep open the doors and windows for the natural ventilation purposes. In such places properly designed ventilation inlets (Fig. 1.4) and ventilation outlets (Fig. 1.5) are provided. These inlets should be placed at suitable places about 2 m above the floor level on the side of fire-place.

The inlets should also be so arranged as they can draw pure fresh air from the atmosphere. Dirts and other organisms should not be collected in them; and they should be self-cleaning.

The position of ventilation outlet directly depends on the position of ventilation inlet. In cold countries the fire-place is the natural outlet. In few places ventilating flue pipes are used as outlets. These pipes are also most suitable for ventilating basements and other small rooms of the buildings. The outlets should get their motive power by heat or exhaust, otherwise, they will act as ventilating inlets and will draw cold air from the atmosphere.

(2) Artificial System:

(a) Plenum System:

This system is mostly used in cold countries and comprises a complete ventilation and heating unit.

It includes:

(i) A filter of air washer.

(ii) A heater warmed by hot water, electricity, steam or gas.

(iii) A centrifugal fan for forcing the warm air.

(iv) A system of distributing ducts connecting every room to the building.

When centrifugal fan starts, it draws air through the air inlet, which is first filtered and then heated up to the required temperature. The fan forces the warm air through duct, which reaches in all the rooms through the openings of ducts kept in the ceilings. When air enters the rooms, it increases the inside pressure due to which foul air forced out through the outlets.

This system is also used during the construction of tunnels for ventilating them.

(b) Vacuum System:

This system is mostly used in cinema houses, assembly halls, hotels and other public buildings. In this system, the foul air is forced out from the rooms or halls by means of exhaust fans, exhaust pumps or other suitable means due to which partial vacuum is created in the halls. 

When the partial vacuum is created by expelling foul air, the fresh air starts coming through doors, windows and other ventilation inlets. This is very good and cheap system for tropical countries under favourable conditions.

(c) Balance System:

This is combination of plenum and vacuum system. In this system pumps or centrifugal fans are fixed in the bottom which continuously supply the fresh air, while the foul air is also continuously forced out by means of exhaust fans. This system is very efficient but very costly.

(d) Air-Conditioning:

The atmosphere in the modern cities and towns contains dirt, smoke, fumes in addition to noise caused by the traffic, industries and business area. In such atmosphere, it is necessary to get comfort for relaxing purposes or for concentrating retention. All these problems have been solved by air-conditioning in modern days in which all the doors, windows and ventilators are kept closed.

The air-conditioning may be defined as the process of controlling temperature, humidity, distribution of air and simultaneously removing dirt, bacterias and toxic position from the air. In other words, the air-conditioning is the method of providing comfort and healthy atmosphere to increase the efficiency.

The air-conditioning process is the development over plenum system.

Its complete cycle has the following stages:

1. Removal of dirt and other objectionable things by passing the air through air cleaner filter or washer.

2. Cooling or heating the air by refrigerator coils or heating coils respectively.

3. Adjusting the humidity of air by adding moisture in summer and removing moisture in winter or rainy season, by passing air through Humidifier.

4. Forcing of conditioned air-through ducts by fans or pumps and distributing it in rooms.

1.6 shows the process of air-conditioning diagrammatically.

For washing or cleaning air, dry or viscous type of filters are used. Dry filters are more common which are made of close gained paper, cloth or felt. After long use when these filters are clogged, these are cleaned by vacuum method or discarded and new filters are used. In viscous type filters the air is passed through course grained materials coated with viscous oils which absorb the dirts of air. In modern air-conditioned plants electric precipitators are used for cleaning the air.

The cooling air is done by passing the air over cooled surface of metal coils, which are cooled by passing volatile refrigerant through them. These coils are cooled by refrigeration plants.

The heating of air is done by passing, the air through furnace or coils heated by passing hot water or steam through them. Now-a-days the coils are heated by electricity and heating elements are kept inside the coils.

The desired humidity of air is kept by passing it through humidifier. If the humidity of air is less as in summer it is passed through spray of water, while passing, it absorbs required moisture from the water. In some cases, steam can be mixed in the air before passing it through filter in controlled way.

In air-conditioning machines it is done by atomizing water by means of compressed air. If the humidity in air is more, it is reduced by condensation is done by absorption or adsorption method.

The circulation of conditioned air is done by forcing it through ducts by means of pumps or fans. In case of small units ducts may not be provided and the air-conditioning machine is fixed on the wall of room directly.

But in case of big halls, cinemas, hotels and offices one central air-conditioning plant is provided in one room and ducts to various rooms and various points in the hall are laid, which distribute the conditioned air. Fig. 1.7 illustrates the central system of air-conditioning.

Recirculation:

It is the method of passing conditioned air after use again through the air-conditioning plan. After operating air conditioners sometimes the room temperature becomes low than atmospheric temperature during summer and higher in winter.

Therefore, it will be economical to operate air conditioner if the room air is again circulated. This process is known as recirculation. The quantity of air to be recirculated will depend on so many factors. This recirculated air is mixed up with the fresh air as already shown in Fig. 1.6.

If the difference between the room temperature and the atmospheric temperature is more than 8° C, it will give temperature shock to the person leaving or entering the room, causing home to feel chill suddenly which is harmful for health. Therefore, to avoid this trouble, the difference in temperature should not be kept more and the lobby or corridor should be provided having an intermediate temperature between the room and the atmosphere.

Thing # 2. Lighting:

Everybody knows about the importance of light. It is as important for the life as the fresh air. Without light it is not possible to pull on the life. If the plants are deprived of light they cannot grow. Light plays a vital role in the growth of human and other living beings.

The lighting can be classified as:

(i) Sunlight or natural light

(ii) Assisted natural light or reflected sunlight.

(iii) Artificial light.

(i) Natural Light:

The sun’s light is composed of seven colours, which can be separated by passing it through a prism of glass. If the light is splitted, the band of colours will have blue, red, yellow, green, violet and orange. The ultra-violet rays present in the sunlight are very good disinfectantive and kill the disease bacteria.

These rays also purify the blood, increase the health, and give the power of resistance to disease. That is why now a days in cold countries the people have started taking sunbaths. Therefore during the construction of new buildings, care should be taken that each room should get the natural light, directly at any time during the day.

The position of doors and windows should be such that sufficient solar light can enter in the buildings. In long and narrow rooms it is better to provide windows in the end walls. The total area of doors and windows should not be less than 1/10th that of the floor area of the room preferably it should be 1/7th of the floor area. The location and area required by the doors and windows also depend on the climate of the country. In hot area less numbers are required than in colder countries.

While locating the windows in institutions or office-buildings care should be taken that light should enter in such a way that it may not cause glare and obstruction in the usual work. This is necessary because if the light is coming from behind the shadow of the body will come in front.

If the light is coining from the right sight the shadow of the hand will come on the writing table. If the light is coming from the front it will cause glare and obstruct the worker and increase strain on the eyes. The intensity of the light should also be such that it should be comfortable for the persons to do their work i.e. it should not be too bright or dim.

(ii) Reflected Sunlight:

Practically, it is not possible to construct buildings in such a way that each room may get sufficient natural light directly, due to adjacent high buildings. Similarly in the basements and other interior rooms, some arrangements should be made to get natural light if not directly then at least indirectly or by reflecting it. The reflected or diffused sunlight can be obtained in various ways.

If the walls of the external rooms are painted white or in light colours, their walls will reflect light in the internal rooms. In case of multistoreyed buildings which are constructed side by side the assisted light can be obtained in the lower stories by well-designed windows which reflect it.

In foreign countries Luxfer prisms are used in the building for obtaining reflected light. Fig. 1.8 shows some of these methods. In the case of basement for obtaining natural reflected light there are various methods, few of them are illustrated in Fig. 1.9.

(iii) Artificial Lighting:

In large buildings it is not possible to get the required intensity of light at every point. Similarly during nights, cloudy weather and closed rooms, artificial lights are required. In olden days it was obtained by burning candles and lamps, but now a days electric light is used almost everywhere for this purpose.