Indoor air quality has become a major issue affecting employers, employees and Government bodies in all working environments throughout the United States. In offices and commercial eating/drinking establishments in numerous states, cigarette smoking inside the building is forbidden with violators facing hefty fines and other penalties.

Industrial facilities are likewise under scrutiny to clean the air not only in office areas but also on the factory floor. Concerns over clean air in the workplace are well founded. Many airborne contaminants common to the manufacturing operations are proven to be carcinogenic agents causing human cancer, or are currently being examined as suspected causes of cancer. Other airborne contaminants such, as dust and fibers, are known to damage the respiratory system.

As an environmentally concerned manufacturer, you face some difficult challenges with new and tougher clean air regulations. Legislation is pending which will toughen the standards and mandate compliance.

What are the types of industrial air contaminants?

Air contaminants can be either 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.

The unit of measure to describe the size of particles is the micron. One micron equals 1/25 th on an inch. The dot on the letter (i) would equal 397 microns. The opening on a common needle would equal 749 microns.

Smoke is composed of extremely small (.01 to 1 micron), solid and /or liquid particles produced by incomplete combustion of organic materials such as wood, coal, oils and tobacco.

Dusts are minute solids propelled into the air by the process of breaking apart larger solid masses or simply by scattering of pulverized material. Manufacturing process that creates dusts include sand blasting, grinding, crushing, drilling, screening, painting, shoveling and sweeping. Dust explosions can occur when organic or mineral dusts are exposed to a source of ignition in an enclosed area.
Mists are liquids dispersed into very small droplets. Coolant (oil or water based) for screw machining centers creates mist particles in the 0.2 to 5 micron range. Atomizing, spraying, chemical reactions, or allowing a gas to escape from a liquid under pressure are all ways to produce mists.

Fumes are very fine solids formed by the condensation of vapors. Metallic fumes such as copper, iron, zinc oxide are generated from molten metals.

Gases are formless fluids which tend to occupy a space or enclosure completely and uniformly. Gas molecules are typically less than .0001 micron in size. Common manmade gas pollutants are carbon monoxide, sulfur oxides, hydrocarbons and nitrogen oxides.

Vapors are the gaseous state of a substance which are either a liquid or a solid in their commonly known state. Vapors develop from substances as gasoline, benzene, mercury, kerosene and iodine.

In addition to their ability to pollute, gases and vapors also present a fire and explosion hazard.

How do you select the best air cleaning system for your specific application?

The following factors need to be considered when selecting the right air cleaning equipment to meet your needs:

  1. Type of contaminant generated by the process
  2. Concentration of the contaminant
  3. Required airflow (cfm) to produce the desired results
  4. Source capture versus ambient collection
  5. Required filtration/adsorption efficiency
  6. Maintenance preference
  7. Operating expenses
  8. Cost considerations (equipment cost and installation)

What technologies do you have to choose from for air cleaning applications?

Particulate filtration can be broken down into two categories, Electronic Air Cleaners and Mechanical Air Cleaners. Vapors/ Gaseous filtration is accomplished by use of adsorption filters such as activated carbon.

ELECTRONIC AIR CLEANERS - Two-stage electrostatic Precipitators (ESP)

Two Stage electrostatic precipitators were invented by Dr. Gaylord Penny in the 1930’s. Since that time they have been used extensively in industry for particulate removal down to 0.01 microns.

Two-stage electrostatic precipitators are composed of two sections- a charging section and a collection section. The charging section uses ionizer wires to impart a positive charge to the incoming pollutants; the charged fields are then drawn to the collector section where the positive particles are collected on the negative charged plates. Clean air is then re-circulated to the work space.

The electronic air cleaner maintains a relatively high efficiency on particles in the range of 0.01 to 1 micron.

The electronic air cleaner creates a low pressure drop which greatly minimizes fan horse power. This translates into energy savings when compared to media cleaning systems.

The primary filters can be cleaned and re-inserted for years of use with no costly filter replacement costs.

MECHANICAL FILTRATION DEVICES - Cartridge Collectors, Media Air Cleaners and Cyclones

Cartridge Collectors use pleated paper, polyester or a blend of paper and polyester filter cartridges to clean the air. Most cartridge collectors incorporate a reverse pulse system to automatically clean the cartridges on line. Cartridge cleaners offer high efficiency (99% at .5 micron oparticle size. Selecting the right size unit is easily done by using a simple air to cloth ratio based on the type of contaminant. The advantages of Cartridge collectors are reduced maintenance/downtime, high capacity for heavy concentrations of particulate and high efficiency. The disadvantages are the need for compressed air to pulse the solenoids, the units physical size, and a much larger blower system is required.

Media Collectors- Self contained media collectors are the simplest form of a filtration device. The two main components are the filter section which is usually made up of a pre filter and a primary filter and a motor and blower system to draw the air through the media filters.

Dirty air is drawn through the pre-filter where large particles are collected. Smaller particles are then collected in a higher efficient primary filter section. A variety of filter efficiencies are available depending on the application. As the filter become loaded the filter becomes more efficient in capturing smaller particles but the dirty filter allows less air to pass through the unit. When the reduction in airflow causes a decrease in the effectiveness of the air cleaner the filters need to be replaced. Typically, the pre-filters will need to be replaced more often than the primary thereby increasing the life of the more expensive primary filter.

There are many options for media air cleaners, ranging from 35% efficient cubes up to 99.999% DOP HEPA filters. Because of the wide range of efficiencies, there are many applications for media cleaners where the particulate is dry. Media air cleaners can also be used in mist applications if a special oil mist filter is used along with impingers.

The advantage of media air cleaners are the relatively low cost to buy and install, very little maintenance and large choice of filter efficiencies. The disadvantage is the cost of filter replacement and they require a higher horse power motor to operate thus use more power than electrostatic air cleaners.

CYCLONES - Cyclones or dry centrifugal collectors whirl the air stream into a vortex. Particles down to 5 microns in diameter are driven to the perimeter of the chamber and settle to the bottom of the collector. The efficiency of the cyclone is largely dependent on the air flow through the collector. Particles 5 microns in diameter and larger may be removed from the air stream at an efficiency up to 70%.

The advantage of the cyclone is the high holding capacity of the contaminant and low maintenance. The disadvantages are that they are big and take up a lot of floor space. They are expensive to buy and operate but are effective on large particles like fly ash and wood dust.


Early pollution efforts concerned particulate removal because particles are more easily visible. However, Electronic and mechanical filtration removes only particulate and lets gaseous vapors through.

Today, adsorption filters are commonly used in conjunction with particulate filters to address both gaseous and particulate air contamination.

Activated carbon is the most common adsorbent filter media because it effectively captures a wide variety of gases and vapors that are common to industrial environments. Typically, these compounds have a high molecular weight and gases with a high boiling point, such as benzene, xylene, toluene, methylene chloride and methyl ethyl ketone.

There are a variety of specially impregnated activated carbons available for gases lower molecular weights which cannot be effectively adsorbed by activated carbon such as formaldehyde and ammonia.

One of the most common questions asked in carbon applications is, “How often will I have to replace the carbon”? The only to answer this is by simple air sample testing. At Air-Filtration Systems, we can provide an organic vapor monitor or you can simply send us a sample which we will have tested to determine replacement cycle for your applications generation rate.

What is the best way to eliminate air contaminants inside my facility?


If you are able to locate capture hoods to collect the smoke, mist, dust, powder etc. as close as possible to the point of generation (usually within approximately 18” to 24”) it will draw the particulate to the filtration equipment and keep it from permeating throughout the internal area of your facility. Source capture techniques or individual breathing respirators are needed when the contaminant poses a respiratory hazard to the employee.

Portable air cleaners are a good example of source capturing pollutants as they are a self contained system including a capture hood, hose/ducting, air cleaning filtration equipment and a fan/blower to draw the contaminant away from the employees.

A good source capture system can also be designed by implementing a complete self contained system utilizing an inlet plenum at the intake of a stationary air filtration unit (could be hung from the ceiling, wall mounted, on a stand etc.). Ducting and/or flexible hoses are then run from the inlet plenum to the source(s) or collection points where a good hood design then insures adequate pick-up of the pollutant. Hood design, duct sizing and proper sizing of the equipment can provide excellent collection at multiple sources. Obviously, the filtration equipment utilized is important as some types of filtration are better suited for certain materials depending on a number of parameters.

Four important considerations for designing a good source capture system are:

  1. Capture Hood
  2. All Ducting (intake plenum, ductwork, hoses etc.)
  3. Filtration Unit
  4. Air Flow Generator

Let our experienced personnel at Air-Filtration Systems help in designing a system that will meet or exceed you expectations.


If you are not able to capture the contaminant at the source, then the next best solution is to ambient clean by locating one or more units within the facility and creating an airflow pattern that will circulate the air to insure it is drawn into the air filtration equipment. This method is sometimes referred to as general background cleaning in addition to ambient.

Some reasons why ambient cleaning may be required are:

  1. In some welding or grinding applications, it may be impossible to source capture as there may be multiple points of generation and it would be cumbersome to run ducting over a large span that may be temporary and subject to re-location.
  2. Sometimes there may be obstructions such as overhead cranes which would make ducting impracticable or impossible.
  3. Employees are sometimes reluctant to use the source capture arms as they may need to reposition them frequently which may be cumbersome and impede their productivity.
  4. There may be too many points of generation that would make source capturing way too expensive and unaffordable.

In designing a good ambient collection system one must consider the size of the space to be cleaned, the type and amount of contaminant being generated and the internal ventilation system parameters that may enhance or obstruct the air flow pattern employed.

Probably the biggest mistake made in a new design is under sizing the job and installing fewer air cleaners than needed to the job. Cutting corners to save money will almost always result in reduced effectiveness of the equipment and costly maintenance issues. Sizing and proper placement of the air cleaning equipment is critical in insuring optimal performance and satisfaction. For this reason, we recommend that you call us for a free copy of our sizing and locating guide at Air-Filtration Systems. Let us help you select the best equipment for your application, the proper number of units needed and an air flow pattern that will produce optimal results.