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1. The need for clean air
2. The Case for Electrostatic Filters
3. About Welding Fumes
4. Odour and its removal
5. Particle Size Chart
6. Classification of Air Contaminants

1. The Need for Clean Air

The Air Surrounds Us

The atmospheric air is part of us and is here to stay; but what is the Quality of air that we breathe day and night? Society’s future is uncertain, at best, unless we heed the experts and commit ourselves to clean the atmosphere. The earth is like a spaceship in that it is surrounded by the troposphere which extends about seven miles up. All the air that is available to everything living on this planet is contained within those seven miles. No fresh air can enter and no polluted air can escape. It must be used over and over again to eternity and each year it is becoming more and more polluted from industrial wastes, contaminants from automobiles and from those pollutants formed by nature such as pollen, mold spores and germs. Basically the problems of air pollution will continue to increase as the population continues to increase and the earth will become like an overpopulated spaceship. It is no more practical to clean the outdoor atmosphere than it is to heat or cool it. That is why the air must be cleaned inside of buildings where people live, work and spend their leisure hours.

Air and its effect on our Health

Over the last two or three decades doctors and scientists have demonstrated the harmful effects of more and more airborne contaminants.

Cigarette smoke is perhaps the best known example, with doctors initially suggesting that smoking could be injurious to the smoker's health, and then more latterly, that cigarette smoke could harm anybody who breathed it, whether or not they smoked themselves. It has been said that a barman working in a typical smoky bar inhales the equivalent of 15 cigarettes a day. 

In industry the list of declared unhealthy contaminants has grown, while the permitted exposure to them has decreased.

Across the World , governments have endeavoured to legislate towards a healthier atmosphere in the workplace-with varying success, for the legislation needed to cover specifically all aspects of industrial and commercial air pollution would be impossibly complex. What is important, however, is their recognition that a problem exists and the spirit of their intentions that something should be done about it.

The Factories Act calls for ‘All practicable measures' to be taken to prevent workers from inhaling dust, fumes or other impurities Vague as these provisions may seem, they do represent a definite requirement for a factory owner to protect his employees from known specific dust and fume hazards and, ideally, any other dust and fumes which might be injurious.

Offices are not covered by the Factories Act . While no specific requirements are set out as in the Factories Act, it still does call for ventilation by circulating fresh or artificially purified air. It is worth noting that the term office' is used to describe a host of other rooms in industrial and commercial buildings and, significantly bars and restaurants  as well.

There is no legislation which says specifically 'you must install some kind of air cleaner', but there is a strong awareness by all right-minded persons of the need to protect employees in all situations from airborne pollution, and failure to install a readily-available solution such as an air cleaner could weigh against a company.

Employee Relations

Of course, it makes sense to keep the air clean whether or not the Health and Safety Inspectorate is banging on your door.Employees who are healthy are more efficient than those who spend their days feeling uncomfortable. Staff don’t turn up for work at all. A simple example is of those millions of people whose asthma, hay fever or other bronchial complaints are aggravated to an unbearable level by breathing pollen grains during the summer.

It would be unreasonable for any Health and Safety Inspector to take action against a company whose employees were made to suffer by this natural phenomenon. In fact, one of the legally accepted methods of improving ventilation-opening a window- could make the situation worse.

But an air cleaning system which effectively removed the pollen from the atmosphere would not only make things better, it could make the workplace the most desirable place to be in all day.

Customer Relations

But there is another class of people to whom the benefits of a dust and fumes free atmosphere are equally, some might say even more, important: customers. Any company whose customers visit its premises must be aware of providing the right, dare one say atmosphere in which to do business.

A customer may be a representative of one company visiting another and needing to be impressed; he may be a member of the public forced to sit in a small crowded waiting room and become increasingly irritated by the delay.

Or He may be a customer in a bar, or restaurant where his time on the premises may be directly related to the money he spends.Keeping the air sweet means keeping the customer sweet.

While making the air more pleasant for people to breathe has both tangible and intangible benefits, there are other
practical aspects of air cleaning which can be translated into hard cash.

Clean Air and Materials Reclamation

In machining shops the air is inevitably contaminated with lubricating oils. These are clearly a health nuisance and must be removed. But they are also expensive commodities, and cannot lightly be dissipated. Our air cleaners designed for this application are able to remove the airborne oil, allow it to coalesce,  collect it to be recycled.

Product Contamination

Heavy industrial pollutants may ultimately settle out of the air of their accord - all over the product. And every manufacturer knows the headache of polluted product when it reaches his customer's quality control - or the general public.

Cleaning and Decorating Costs

Pollutants will also settle out on the walls, the floor, hard-to-reach ceiling members, processing machines, people - anything within the factory. And while an engineering factory is expected to exhibit a degree of grime, cleanliness standards are being pressed ever higher.

Translate this into a commercial environment and the cleaning factor becomes more substantial. We have all seen bars with white walls and white ceilings that are not white. They are covered with a nasty yellow-brown deposit from cigarette smoke. (It is a sobering thought that what you see smeared on the walls, feeling sticky to your touch, may also be liberally coating your lungs).

This build-up of tar needs removing at regular intervals, and that costs money. Cut down the tar build-up and you cut down redecoration costs.

In addition, the routine cleaning work, such as cleaning optics, mirrors, polished glasses and so on can be reduced.
So there is a directly attributable financial benefit from keeping the air clean in a bar, and that is in addition to the increase in trade which follows the creation of a more pleasant atmosphere for the customers.

The benefits do not stop here. Assuming that the bar needs some form of smoke clearing system, our electronic air cleaners will show substantial savings over other alternatives that might be considered for installation, or already be installed.


2. The Case for Electrostatic Air Filtration

There is no effective competition to Our electronic air filter. But there are other commonly used ways of clearing the air whose drawbacks need explaining.

Natural ventilation

The oldest, cheapest and simplest method is to open a door or window to let in 'fresh air'. This form of ventilation is uncontrollable, not related to the problem in hand, and likely to cause more discomfort from draughts than it attempts to alleviate. It is also likely to let in air which is as polluted as the air you are trying to let out.

Mechanical filters

The effectiveness of any air cleaning apparatus should be rated against the type of contamination it sets out to trap. Unqualified claims for effectiveness are meaningless: for instance a road-roller could be rated 100 per cent effective - if its job was stopping traffic!

A mechanical filter can be very effective, for a while, against large contaminant particles, but it won’t trap the smaller particles, which in fact make up 9 per cent of all airborne contaminants. Allowing for a degree of latitude, a mechanical filter could be said to be 5-10 per cent effective in trapping all airborne particles. Using the same criteria, an electrostatic air cleaner will trap 70-95 per cent of all particles.

Powertech Fumekiller / Dustkiller , in fact uses mechanical filters as pre-filters in its electronic air cleaners, removing the larger particles and enabling the electrostatic section to operate without hindrance in its more important job of removing the particles which are too small for a mechanical tilter to catch.

A word is needed about what big and small particles are. The size of airborne particles is normally measured in microns. A micron is 0.001 mm, or about 1 /25400 in. A pencil dot is around 50 microns across.

Mechanical filters will trap particles of about 5 microns and bigger. These particles are just about visible without the aid of a microscope, and include such things as cement dust, pollen, fly ash and some bacteria.
Smaller particles, which will pass through a mechanical filter but will be trapped by an electronic air cleaner, include oil smoke, tobacco smoke, cooking oil smell, some viruses, carbon black, welding fumes, fine fly ash and ground talc.
The smallest particle which can be trapped by an electrostatic air cleaner is around 0.01 microns (about 1/10,000 the diameter of a human hair) which is 500 times smaller than the smallest particle that can be caught by a typical mechanical filter.

Mechanical filters are reasonably efficient at filtering large particles out of the air. But the more efficient they are, the less efficient they become, as the dirt they have removed collects in the filter mesh and gradually reduces the filter area left to catch more dirt. After a while the filter is too clogged to be effective and often has to be thrown away.

There is no effective competition to Our Fumekiller / Dustkiller electrostatic air Filters . But there are other commonly used ways of cleaning the air whose drawbacks need explaining. Electrostatic air filters don’t trap the dirt particles directly across the airflow like a mechanical filter, but the particles are deposited on the collector plates in line with the airflow, so there is a much less noticeable build-up of resistance.

The collector plates eventually need cleaning, and then it is a simple task to remove them, wash the dirt off and put them back. Some of the industrial units have their own automatic washing systems built-in.

Extractor fans

The third approach adopted for clearing the air is not to attempt to clean it, but just to blow it outside with a fan. This is clearly unacceptable in many situations where the fan is blowing out air that has been heated, replacing it with air from outside that has to be heated, only to be blown back outside again.

It can be shown that up to 80 per cent of the cost of heat wasted in this way can be saved by recycling the heated air through an electronic air cleaner rather than wasting it with an exhaust fan. This is another direct financial benefit to add to those achieved on reduced cleaning and decorating bills.

In an industrial context, while not necessarily having any directly harmful effect on the environment, a policy of exhausting contaminated air outside into the atmosphere could cause bad feeling between a factory and its near neighbours.

There are other drawbacks to extractor fans. One is that the more air they are able to move, the noisier they are, which is particularly disadvantageous in commercial installations. But more importantly they have to be bigger and therefore noisier - than the fan which moves the air through an electrostatic air filter because, in ideal ventilation terms, they are working back to front.

The tendency of extractor fans to draw air from sources of least resistance, such as through open doors, is the cause of at best a slight draught under doors, and at worst, a corridor of air moving from door to fan, between two banks of unaffected stale air.

Of course, the air circulation of a fan or an air cleaner depends largely on how it is sited . Let's investigate how an electrostatic air filter system is much better to use than an extractor fan for the removal of airborne contamination. A general principle of ventilation states that a fan will influence the surrounding air greater on the outlet side of the fan than on its inlet. This is because you can control the outlet air far easier than you can the air entering the fan. Taking the principle a step further, a fan will blow air 30 times farther than it will draw. Consider the following example and figure. 

If we measure the air movement in any direction on the inlet at dia. (2 ft.) away from the face, we will find that it will be only 400 FPM. However we will have to measure 30 dia. (60 ft.) away to read the same 400 FPM velocity.This is why we want to blow air in a definite pattern with our electronic air cleaning system. In many cases, an extractor fan simply, will not move the air.


3.About Welding Fumes

The potential hazards of welding operations include metal fumes, toxic gases, and ultraviolet and infrared radiation. Fume particles are formed from vaporization of molten metal. They are very fine in size, generally one micron or smaller, and may join together to form larger particles. Fumes can be sampled by drawing air through a special filter at a controlled rate. The adverse health effects of overexposure to welding fumes and gases include chronic or acute systemic poisoning, metal fume fever (a short-term painful ailment with symptoms of fever and chills), pneumoconiosis (lung disease due to accumulation of mineral or metallic particles), and irritation of the respiratory tract.

The welding fumes produced at welding operations depend primarily on the composition of the metals being welded and the welding rods. When the base metal is iron or steel, with welding rods of similar composition the main component of the fume will be iron oxide. When welding on stainless steel, fumes containing nickel and chromium may be produced. Welding on plated, galvanized, or painted metals may generate fumes containing cadmium, zinc oxide, or lead. In addition, welding rods can generate fluoride in the fume as well as free silica, depending on the composition of the welding rod coating. In summary, welding processes may generate many different metal fumes and other toxic components. It is important that the hazards of a welding operation be controlled properly. Toxic gases that arise in welding include carbon monoxide, nitrogen dioxides, and ozone. If welding or cutting operations are conducted in the presence of chlorinated hydrocarbons, such as the form of solvents either on the metals or in the air, hazardous concentrations of phosgene and hydrogen chloride, which are highly toxic irritant gases, may be produced.

In addition to the health hazards of metal fumes and toxic gases, welding operations involve the hazard of burns from flame arc, molten metal, and heated surfaces and also that of metal splatter. Welding operations in general require face neck and eye protection for the welder - against sparks, splatter of molten metal, and the radiations (ultraviolet, inflared, and intense visible) of the arc or flame. Normally this means that a welder will wear a welding hood, or helmet, though in some cases gas welding may properly be done with adequate goggles, gloves, and other protective clothing of neck and arms. 

Normally, good local or general ventilation is required to control exposures to the metal fumes and gases of welding operations. The most effective control is local exhaust ventilation in which an exhaust hood is placed near the welding arc or flame, and the contaminants are drawn away from the welder's breathing zone. The system may consist of moveable exhaust hoods, flexible and stationary ducts, a powered fan, and a fume or dust collector. It is important that, during the welding operation, the exhaust hoods are placed or set so that welding fumes are not drawn across the worker's face or into the breathing zone. Welding in confined to spaces such as tanks, cabs of mobile equipment, and large shovels may be especially hazardous and requires additional ventilation.If you have any questions about this or any other occupational health matter, feel free to ask us.


4. Odour Removal with Electrostatic Air Filters

Odors are gases which are concentrated enough to be sensed by our olfactory system (nose). These gases can either be diffused in the air we breathe or absorbed on the particles. contaminating the air we are breathing. The sense of smell is extremely sensitive to minute concentration of gases.

Chloroform can be sensed when only one molecule is mixed with 36 thousand air molecules. This means that if just a few odorous gas molecules are allowed to circulate, the odor can still be detected by the human sense of smell. 

Electronic air cleaners help reduce odours because
1. Some odour molecules collect on the particles which are removed by the Electronic Air Filter.
2. The low level of ozone produced by the air cleaner oxidizes some odor molecules.

6.Classification of Air Contaminants

Composition of the Atmosphere

Under natural circumstances, the air we breathe contains (by volume) approximately 78% nitrogen, 21 % oxygen and trace amounts of argon, neon, helium, krypton, hydrogen, nitrous oxide and xenon as permanent gases. Variable gases in the atmosphere are water vapour (0 to 7% by volume), carbon dioxide (.03%) and much smaller amounts of methane, carbon monoxide, ozone, ammonia, nitrogen dioxide, sulphur dioxide and hydrogen sulphide. The atmosphere is also a host to natural atmospheric impurities in the form of particles and gases that originate from wind erosion, sea spray evaporation, volcanic eruption and biological processes such as sporing and pollinating.

Definition of Air Contaminant
When a substance enters the atmosphere in large enough quantities to disrupt the natural balance of gases and permanent atmospheric impurities in the air, it is a contaminant (or pollutant). Air contaminants may be chemically organic or inorganic; their sizes range from submicroscopic and microscopic substances to those which are visible to the human eye (macroscopic). The effect which a contaminant has on the environment may range from toxic to harmless. The response of living things to a given contaminant often depends on the sensitivity of the individual organism.

Air contaminants may be particles or gases. A particle is a solid or a liquid that has definite physical boundaries; a gas does not have specific physical limits for it can expand indefinitely. Particles and gases acting together as contaminants are sometimes called 'dispersoids' and solids and liquid particles suspended in a gas are often referred to as 'aerosols'.

Measurement of air Contaminants by Size, Count and Weight

The unit of measurement used to describe the size of particles and gases is the micron.One micron equals one-millionth (1/1,000,000 or.000001) of a metre; 25,400 microns equal one inch.

An average diameter of 10 microns is considered to be the dividing line between visible and invisible particles. An electron microscope can resolve particles down to 0.005 micron in diameter. If air currents do not aid their suspension, visible particles greater than 10 microns in diameter settle quite rapidly because of gravity. The visible particles, however, constitute a minor percentage of the particles in the air.

Particles less than 1 micron in diameter has so little mass that gravity has negligible effect on them.

On a particle count basis over 99% of the particles in a typical atmosphere are below 1 micron in size . . . even clean country air will normally contain over 1,000,000 particles per cu ft2.

The weight of a particle increases proportionally to the cube of its diameter. Even though particles about 0.01 micron make up 80% of ihe number of particles in the atmosphere, they contribute only 1 % of the weight of all particles for a specified volume. It is particles ranging from 1 to 10 microns in diameter that contribute the majority of the weight for air contaminants.

Types of Air Contaminants
The following classification of air contaminants into types is based on the physical state of the contaminant (solid, liquid or gas) and the normal physical state of the material from which it originates.

Dusts are minute solids projected into the air by the breaking apart of large solid masses or simply by the scattering of pulverised material. When natural forces such as wind, volcanoes and earthquakes produce excessive amounts of atmospheric impurities in the form of dusts and flyash they become contaminants. Mechanical processes that create dusts often include crushing, grinding, demolition, blasting, drilling, shovelling, screening and sweeping.

Dust explosions can be produced when organic or mineral dusts are exposed to a source of ignition in an enclosed area. The high concentration of organic dust in flourmills and grain elevators is a prime example of locations where dust explosions might occur. Often a primary explosion occurs from the ignition of a small amount of dust. This can dislodge large accumulations of dust on horizontal surfaces, which produces a larger secondary explosion.

Generally, dust clouds require high temperatures, a sufficient amount of dust, an adequate supply of oxygen and an enclosed space for ignition. Explosive dusts are potential hazards whenever the dust escapes uncontrolled to disperse in the atmosphere or settle on horizontal surfaces such as beams and ledges.

Fumes are very fine solids formed by the condensation of vapours of combustion from materials that are normally solid. Metallic fumes such as iron, copper and zinc oxide are generated from molten metals and usually occur as oxides because of the chemically reactive nature with the available oxygen in the air. Fumes which are permitted to age are said to ‘flocculate' into clusters of larger size.

Pollen which comes from weeds, grasses and trees is responsible for hay fever and some allergies. Although ragweed pollen ranges from 15 to 25 microns in diameter, most pollen grains vary widely in size and their weight varies according to the relative humidity.

The pollen count is determined by exposing an adhesive-coated glass plate outdoors for 24 hours and then counting calibrated areas under the microscope. Daily pollen counts reported during the hay fever season represent the number of grains found on 1.8 square centimetres after 24 hour exposure of the glass plate. However, the pollen count per cubic yard may vary from 2 to 20 times the number found on the calibrated gravity slide depending on grain diameter, shape, specific gravity, wind velocity, humidity and location of the collecting plate. Hay fever sufferers may notice their first symptoms when the pollen count is 10 to 25. In some localities the pollen count may reach 1,000 during the peak of the hay fever season depending on the methods used for counting the pollen.

Airborne Micro-Organisms are frequently a public health hazard because they cause diseases. Commercial enterprises may be further concerned because mould or yeast, which range from 1 to 10 microns in diameter may cause product loss. Wild yeast, for example, can use the air as a transfer medium to destroy a batch of beer or wine. Also some industries involved in rnedical, space and computer technology need to develop their produces in environments free from airborne micro-organisms.

Most micro-organisms become airborne by their attachment to dust particles. Bacteria derived from the soil are likely to be spore formers, minute unicellular organisms that are capable of surviving in hostile environments. Other airborne bacteria, especially within closed occupied spaces, often originate from droplet nuclei caused by such actions as sneezing. The concentration of microorganisms in the atmosphere varies over a wide range from a few to several hundred per cubic foot of air.

Mists are liquids dispersed into very small droplets. Atomizing, spraying, chemical reactions, bubbling gases through liquids or allowing a gas to escape from a liquid under pressure are all ways to produce mists. Sneezing constitutes a mist which contains some contaminants that are micro-organisms.

Smokes are extremely small, solid and/or liquid particles produced by incomplete combustion of organic substances such as tobacco, wood, coal, oil and other carbonaceous materials. Although a distinction is made in technical literature between soot, carbon particles, flyash, cinders, tarry matter, unburned gases, and gaseous combustion products, smoke is often used in place of all these terms. Smoke particles vary considerably in size, the smallest being much less than 1 micron, often in the range of 0.1 to 0.3 micron.

Smog implies an air mixture of smoke, mists and fog particles of such concentration and composition in the air that they impair visibility and may be irritating and harmful. While smog composition varies widely between different locations and at different times, the term is often applied to the haze caused by sunlight-induced photo-chemical reaction involving the materials in motor car exhausts. The most common chemical constituents of this haze are varying amounts of nitrogen compounds, hydrocarbons and ozone. Smog is often associated with temperature inversion in the atmosphere which prevents the normal dispersion of air contaminants.

Gases are actually formless fluids which tend to occupy a space or enclosure completely and uniformly. Proper temperature and pressure control may be used to liquify or solidify gases. Gas molecules are less than 0.0001 micron in size. Typical man-made gas pollutants of the atmosphere are carbon monoxide, sulphur oxides, hydrocarbons and nitrogen oxides.

Fogs are usually formed by the condensation of a vapour from a material that is normally a liquid. Condensed water vapour in the atmosphere is a common occurrence of harmless fog.

Radioactive Pollutants present distinctive problems because the concentration at which most such materials are hazardous are much lower than hazardous concentrations of ordinary pollutants. The properties of radioactive material which may be a particle or a gas and can be removed from the air by filters and absorption traps, must be distinguished from the radiation given off by the material. Radiation may be composed of alpha, beta or gamma particles.

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