Air Filtration Across the Nation

May 7, 2008
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For years it has been recognized that carpets act as filters or traps for all kinds of filth, from soil and pet stains to a variety of chemicals. Even a clean water-damage event will begin to “reactivate” biological debris such as mold and bacteria.

While the extraction process will remove a great deal of this biological and chemical soup, the remaining portions are drawn to the surface. The drying process will reduce the weight of heavy, wet particles allowing them to become airborne. When an air mover is used, there is a tremendous amount of dirt and debris propelled into the air. Drying will also cause distress to any active molds or bacteria and will promote the release of spores.

I am astounded that HEPA air scrubbers are not used on practically every water-damage restoration. I know a lot of you will think, “Of course Larry thinks we should use air scrubbers, he works for a company that manufactures them.” True, but the IICRC S500 Standard certainly encourages the use of air scrubbers, and every remediation class I have attended, taught by a variety of qualified and independent instructors, has advocated their use. In fact, the only argument I have ever heard against their use is, “The insurance company won’t pay for them.” In some cases the insurance company may be adamant that they will not pay for air scrubbers, but in most of situations of which I am aware, the insurance company needs to be informed as to the reasons for their use.

If the structure is going to be occupied during remediation, there are several strong arguments. To fully understand the arguments, you need to know a little about the equipment.

Air scrubber, negative air machine, HEPA air filter and AFD (air filtration device) are fairly interchangeable terms for high-efficiency air cleaners. Today’s technology grew mostly out of the asbestos abatement industry. The basic negative air machine is an aluminum box about 2-feet tall and 2-feet deep (to accommodate a standard 24-by-24-inch HEPA filter) and about 3.5 to 4 feet long. It claims about 2,000 CFM of HEPA filtered air. The HEPA designation grew out of the atomic energy industry to filter out radioactive particles. In asbestos abatement these units would be set up to exhaust air from the containment area to prevent the spread of asbestos; hence the term negative air machine. Since the widespread use of asbestos in building materials has ended, the asbestos abatement industry started shrinking and began looking for opportunities in mold mitigation and remediation.

In the late 1990s mold was the hottest subject in the restoration industry. Million-dollar settlements and sensational stories of “deadly” black mold fueled the development of HEPA air cleaning devices for the restoration industry. At the same time, many chemical treatments were coming under fire, and the widespread use of biocides on every water loss was diminishing. Even though the hype eclipsed the threat, the mold frenzy brought attention to the practical applications of air cleaning to the restoration industry. Operating an air scrubber can only improve the air quality and remove airborne contaminates. An air scrubber accomplishes this without the potential liabilities of chemical treatments; its operation cannot cause harm by spreading toxins or disease.

Air is composed of gases, microscopic and sub-microscopic particles, and varying amounts of water vapor. The air particles can be solid or liquid, organic or inorganic, visible or invisible, and harmless or toxic. Air particle concentrations can be expressed in different ways, including: the quantity (number) of particles, the mass (size) of particles, and the weight (density) of particles. A cubic foot of “clean” air will contain over a million particles; “dirty” air contains well over 30 million particles. More than 95 percent of the total weight of the particles in a cubic foot of air will be found in less than 1 percent of the total quantity of particles. A dust arrestance rating on a filter refers to the weight of the particles collected. That is why a basic spun polyester furnace filter can carry an 80-percent arrestance rating and not capture even 50 percent of the largest particles of lung damaging dust.

The chart shows filter efficiencies and particle sizes. It also shows the range of sizes of several types of particles. You will notice that particles between 0.5 and 5 microns are considered “lung damaging dust.” This is because these particle sizes are small enough to get past the body’s natural filters and become trapped in the lungs. When inhaled, air particles between 8 to 10 microns are normally captured in the upper respiratory tract; particles between 2 to 8 microns are trapped in the conducting airways to the lungs and are cleared through swallowing or coughing. The particles smaller than 2 microns are normally drawn into the respiratory system and may be retained there. These particles cause the greatest concern to health professionals, and require HEPA-grade filtration for adequate removal.

Air particles between 1 to 10 microns will settle in still air; however, regular air currents can keep them airborne for substantial periods of time. Particles between 0.1 to 1 microns will eventually settle in perfectly still air, but remain airborne in normal conditions. Particles smaller than 0.1 microns behave like gas molecules and may remain airborne permanently. All of these particles sizes are outside human visual range. The operation of an air mover during remediation would be akin to a dust storm if our eyes were capable of seeing the particles. A HEPA media filter, by definition, removes 99.97 percent of 0.3-micron particles. To put that in perspective, a human hair is approximately 100 microns in diameter. Say that hair was a football field in diameter; 0.3 microns would be one foot. It is normally recommended that an air scrubber be sized to perform 4 to 6 air changes per hour on the affected area. That would allow a 500 CFM air scrubber to clean 2000 cubic feet of affected area.

Most HEPA air scrubbers have a multiple-stage filter design to prolong the life of the HEPA filter. These filters will remove virtually all hazardous airborne particles. The first-stage filter is normally a polyester media, similar to a furnace filter that removes larger particles and debris from the air. This low-cost filter should be replaced often and can be cleaned with a vacuum between replacements. The second-stage filter, if employed, is often a high-flow, 30-percent-efficient pleated media composed of a cotton/synthetic blend. This filter is designed to remove medium-size particles and prolong the life of the HEPA media filter. This filter is economical to replace and can be vacuumed to extend its life. HEPA filters are microglass paper, mini-pleat media and are the most expensive to replace.

The presence of hazardous airborne particles is inevitable. The question is if these particles will cause injury to the inhabitants of the structure. The individuals at the greatest risk are the very young, the very old, and those with allergies or with compromised immune systems. If you do not have this information for the job, you should get it. I would suggest that if I was being prevented from running an air scrubber on any water loss, I would make certain that someone signed a release relieving me of liability if someone got sick. Operating an air scrubber on a water loss protects your customers and your business. It demonstrates the standard of care you maintain for your company.

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