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Commercial and Educational Ventilation
Heating, Ventilating and Air-Conditioning Systems in Commerical and Educational Buildings

Heating, Ventilating and Air-Conditioning Systems in Commercial and Educational Buildings Overview Ventilation rates for offices and schools Problems with ventilation systems Temperature and humidity problems Poor outside air quality Chemicals Infectious diseases Recirculated air Inspection of ventilation systems Correcting ventilation problems Cleaning of air ducts Overview Inadequate ventilation is a significant problem associated with poor indoor air quality (IAQ). Ventilation is the process of bringing fresh clean air into the building and exhausting stale indoor air out of the building. This is often done by a heating, ventilation, and air-conditioning system called a heating, ventilating and air-conditioning (HVAC) system. The HVAC system controls the temperature of a building as well as the humidity levels. In addition to controlling temperature and humidity, HVAC systems can also control odors and dilute pollutants inside the building. Some studies estimate that approximately 60 percent of all indoor air problems are due to ventilation. Of this 60 percent, 30 percent are a result of air contamination, 20 percent from inside the building and 10% from outside.¹ If there is not good ventilation, pollutants can build up inside the building and result in indoor air complaints. A National Institute of Occupational Safety and Health (NIOSH) study blamed about half the cases of indoor air pollution on poor ventilation.² According to a report from the US Government Accounting Office, an estimated 20 percent of all schools in the United States have indoor air problems and 25 percent have unsatisfactory ventilation. In addition, 36 percent of all school officials rated their facility's heating and ventilation systems as a "less than adequate building feature."³ Having good ventilation systems can decrease the number of indoor air complaints and health problems caused by poor air quality. A study by the Walter Reed Institute of Medical Research found that absentee rates in poorly ventilated buildings are 50 percent greater than in well-ventilated buildings.⁴ Several studies have shown that the number of building-related symptoms (BRS) [also referred to as sick building syndrom] is 40 percent to 50 percent lower among office workers six months after moving into buildings with good ventilation systems. In a study in Quebec City, researchers showed that this large decrease in the number of SBS complaints was maintained three years later. In this study, one of the reasons for the fewer SBS problems was that in the new building the copying machines were in separate rooms away from workers. Another reason was the smoking area had its own exhaust system so that contaminated air was not recirculated throughout the building.⁵ Nevertheless, poor ventilation can also affect the quality of work that one does. In a recent Danish study, researchers found that typists in offices with clean air had six percent more output than typists in other offices.⁶ There are many different parts to an HVAC system. These parts include furnaces or boilers, chillers, cooling towers, air handling units, exhaust fans, ductwork, filters, steam (or heating water) piping, dampers, louvers, cooling coils, drip pans, registers, and grills. All of these parts need to be kept clean, free of debris and mold, and in good working condition in order to provide good quality air to the building. In addition, it is important that the location of the air intake units be considered. It is possible for rooftop units to pull pigeon and other bird droppings into the HVAC system as part of the outside "fresh" air brought into the building. This increases the chance of people inside the building developing lung infections such as histoplasmosis or psittacosis. Intake units located near building exhausts, parking lots, loading docks, or busy highways increase the chance of bringing into the building vehicular exhaust, carbon monoxide, VOCs, and particulates. Intakes located near or downwind of cooling towers increase the risk of Legionella bacteria entering the air supplies of buildings. Ventilation Rates for Offices and Schools Ventilation rates are measured in cubic feet per minute or cfm and guidelines are written in cfm per person. The guidelines that are often used for ventilation rates are provided by an organization called the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). ASHRAE recommendations are voluntary standards that only become enforceable when a state or locality adopts their standards in their building codes. In the United States, there are no federal laws requiring a minimum amount of fresh airflow into buildings. The Society's guidelines have changed over the years. One of the first recommendations to improve indoor air quality was in 1836 when Tregold calculated the minimum amount of outdoor air needed for miners to be 4 cfm.⁷ In 1895 ASHRAE adopted a recommendation of 30 cfm to reduce the spread of disease, especially tuberculosis. In the early and mid 1900's, building ventilation standards called for about 15 cfm of outside air for each building occupant. The purpose at that time was to mainly reduce body odors in the building. Early ventilation recommendations for schools were first proposed in the early 1900s in Massachusetts and New York. These states recommended 30 cfm per student. States began realizing that by bringing in fresh outdoor air, they were able to reduce the spread of respiratory infections. Because of the 1973 oil embargo, however, the amount of outdoor air for ventilation was reduced to 5 cfm per occupant. This was considered necessary to save energy as long as there were no major sources of pollutants. Another action that was taken to conserve energy around that time was that buildings were "tightened up" to prevent leaks and new buildings were built with windows that did not open. This tightening of the building along with reduced ventilation rates began causing discomfort and health problems in building occupants. The pollutants inside had no way to get out and began to build up. This became known as sick building syndrome, more properly referred to now as building-related symptoms. The Society presently recommends 20 cfm of outdoor air per person for office spaces and conference rooms, and at least 15 cfm of outdoor air for other nonresidential environments such as school classrooms. However, this may not be enough. In a study of 399 workers in 14 mechanically ventilated office buildings in Helsinki, Finland, the researchers found that outdoor air ventilation rates below 32-53 cfm increases the risk of building-related symptoms.⁸ In France, as compared to the United States, buildings are required to have three times more ventilation and two times more soundproofing, while using half as much energy.⁶ However, it is not enough to just increase the amount of outdoor air. In a study of 1838 buildings, the ventilation rates were increased from 20 cfm to 50 cfm for two weeks without the occupants knowing about the increase. However, this increase in ventilation rates did not change the workers' perceptions of the air in their offices or decrease the number of building-related symptoms complaints received.⁹ Another well-controlled study has shown that increasing the supply of outdoor air does not affect workers' perceptions of their office environment or their reporting of symptoms considered typical of building-related illness.¹⁰ From these studies, it would appear that increasing the ventilation rates does not make any difference. However, there is a variety of factors that need to be considered such as the layout of the space. For example, offices that use partitions to divide the space into individual cubicles are also creating barriers to adequate air reaching everybody. The activities going on inside the building are also important since indoor air pollutants are increased by activities such as photocopying, smoking or handling paper. Problems with Ventilation Systems Often problems with ventilation systems occur because the building is being used for a different purpose or has more people in it than were originally thought of when it was designed. First, look at these factors to see if they might explain some of the problems that may be happening: How was the building originally intended to function? For example, if the building was originally built as a factory with an open design, there may be ventilation problems if that open space is broken up with walls and partitions. The activities going on in the building may also be different than originally conceived. Is the building functioning as designed? What changes in building layout and use have occurred since the original design and construction? Find out if the HVAC system has been reevaluated to make sure it reflects the current use of the building. When there are changes, there may be indoor air quality problems. For example, there was one building built in the early 1960s in Bonn, Germany that consisted of three naturally ventilated sections. Until the mid-1980s, the building was used by a pharmaceutical company. Some parts of this building were used for production and storage of pharmaceutical products. When a new company took over the building, they converted this production and storage space into offices. Later there were complaints of indoor air problems. Upon investigation, researchers found that the people who were complaining about indoor air problems were in the same areas that had at one time been the production and storage areas. These areas had been converted to office space without regard to the prior use of these parts of the building.¹¹ When one study looked at HVAC problems in several buildings, they found the following problems¹²: 70 percent had inadequate amounts of outside air 50 percent to 70 percent had inadequate air distribution to the parts of the buildings where people worked 60 percent had inadequate filtration to remove outdoor pollutants 60 percent had standing water in the system which had the potential for microbial growth 40 percent with visible mold and fungus growing on the insulation 20 percent with malfunctioning humidifiers 75 percent had inadequate maintenance programs Mechanical ventilation systems in large buildings are designed and operated not only to heat and cool the air, but also to draw in and circulate outdoor air. If they are poorly designed, operated, or maintained, however, ventilation systems can create indoor air problems. Ventilation problems are the biggest cause of indoor air quality problems: 75 percent do not get enough outside air; 65 percent have problems distributing the air to all occupants (partitions and other obstacles that may block supply and return vents); 60 percent have improper filtration; 75 percent have inadequate maintenance of the air handling system; and 45 percent have microbial contamination.¹³ Some of these problems are due to poor initial design, outdoor vents or dampers closed to "save energy," inadequate maintenance of dampers and control linkages, and obstructed outdoor screens on the air intakes. There may also be fans that have been inoperative for a number of years or filters that have not been changed on a regular basis. Some of the other problems in the ventilation equipment itself include: Condensate in pans and ductwork. This can lead to microbial growth such as bacteria, slime, algae, and mold. Fiber glass being shed by a fiber glass interior duct lining. Fiber glass was used as a liner in buildings built in the late 1970s and the early 1980s in order to reduce noise from the HVAC fans and for thermal insulation. After several years, these linings begin releasing fibers. For example, there was an office in Richmond, Virginia in which workers thought they were suffering from insect bites for several months. When somebody was brought in to check out the problem, they found that some filters were missing and loose fiber glass was being blown through the vents onto workers. As soon as the filters were installed, their skin cleared up.⁴ Fiber glass that is dirty and becomes wet can be a source of mold growth. Mold spores from this growth can become airborne and distributed throughout the occupied spaces of buildings. Broken dampers can prevent outdoor air from being brought into the building. Pneumatic controls that do not work properly can determine whether a sufficient amount of outdoor air is being brought into the building. Poor quality filters can reduce the efficiency of the mechanical system in distributing air. They can also allow dirt, particles, pollen and other debris to enter the building. Filters that become clogged with dirt can become sources of mold and bacterial growth. These mechanical problems can create these following indoor air concerns: Temperature and humidity problems Poor outside Air Quality Chemicals Infectious diseases Recirculated air Temperature and Humidity Problems Though temperature, relative humidity and air movement have usually been considered "comfort" factors, there is increasing evidence that these factors are important in building-related symptoms as well as sickness-related absence.¹⁴ Not everybody is going to be happy with the temperature in a building. Age, gender, job activity, clothing, and physiologic differences all affect individual preferences in desired temperature. Since people differ on what temperatures they find comfortable, the recommendations from ASHRAE are designed to satisfy 80 percent to 95 percent of the building occupants. That is not always done. In one study, over half of the office workers surveyed said that the office temperature needed to be improved.¹⁵ Because there are often comfort problems in workplaces where there are complaints about indoor air quality, thermal control of the indoor environment should be the first thing investigated when investigating indoor air problems. The temperature range recommended by ASHRAE is from 68°F to 78°F, but it seems that temperatures higher than 75.2°F will usually increase complaints about indoor air quality and may increase building-related symptoms. For example, in one study the number of people reporting headaches increased from 10 percent to 60 percent when temperature was raised from 70°F to 76°F. Other building-related symptoms, including skin problems, showed similar effects.¹⁵ In addition to physical symptoms, temperature differences can also affect work performance. For example, moderate heat can reduce reading speed, typewriting, and the kind of logical thinking required for mathematics by up to 30 percent.¹⁵ However, it is not just environments that are too warm that are a problem. Studies have also show that moderate cold can reduce manual speed, sensitivity, and dexterity by up to 20 percent.¹⁵ However, air temperature alone does not determine thermal comfort. Both temperature and humidity are very important measures of IAQ since they directly influence the perceptions of the occupant as to comfort and health. For example, humidity levels that are too low (below 20%) can result in buildup of static electricity, complaints of eye and throat irritation, dry skin, and other problems. Static electricity can be a problem since it can result in unpleasant electric shocks if someone encounters a metal object. In addition, sparks created by static electricity may damage computer circuits. Because of problems like these, dryness is one of the most common complaints about indoor air. High humidity levels can also cause problems such as equipment corrosion and microbial growth problems. At high humidity levels, occupants tend to describe the air quality in a room as "stale" and odors can be detected more often. For example, in a study of 20 panelists in Finland, researchers found that humidified air was perceived as being stuffier and having more odors than non-humidified air.¹⁶ But the big problem with high humidity levels is that it may cause condensation on walls, floor, ceilings, and even air ducts on which mold may grow. In addition, dust mites thrive in humid environments. Poor Outside Air Quality Ventilation systems can bring in pollutants from outside. Examples of pollutants that may be brought in from outside include: Smog Elevated mold spore or pollen levels during certain seasons: Naturally ventilated buildings are not always better. One study showed that the levels of fungi and pollen were much greater in a naturally ventilated building than in an air-conditioned building. This is because the HVAC system in the air-conditioned building prevented these contaminants from getting inside. The HVAC system also diluted the indoor concentration of mold and pollen that were already inside.¹⁷ Vehicle exhaust from cars in underground garages or from forklift trucks on nearby loading docks Legionella or other bacteria Stale indoor air being exhausted from the HVAC system: This can happen when the exhaust vent is too close to the air intake vent Many variables can influence the outside levels of pollutants. These include: Outside concentration of the pollutant Seasonal and daily variations Climatic factors such as temperature, humidity, wind, rainfall and surrounding vegetation Chemicals There are several hazards that may be associated with HVAC systems. These include: Chemicals used to treat water used in the HVAC system. This is especially true of water treatment additives into the water that is made into steam in a boiler. The chemicals in this steam get into the supply air. ASHRAE/ANSI 62-2001, Ventilation for Acceptable Indoor AIr Quality, says that steam is the preferred method of humidifying indoor air; therefore, steam is replacing water humidification systems in newer buildings. These systems can be sites for the growth of mold and bacteria. Chemicals in the ductwork. There may be VOCs found in the duct liner, duct sealing caulk, and/or neoprene gasket. For example, one type of duct liner is coated with a phenol formaldehyde polymer, hexamethylene tetramine. Another kind of duct liner is coated with a resin made of phenol-melamine-formaldehyde. These kinds of linings can emit VOCs that can get into the air and be distributed throughout the ventilation system if they are exposed to ozone gas (like from a photocopier). There is usually not a problem with them emitting VOCs unless they encounter ozone. This is because of an oxidation reaction between the ozone and the chemicals. One study showed that emissions from materials in the HVAC system were responsible for 80 percent of all the indoor emissions of VOCs in that building.¹⁸ Improper venting of combustion products. For example, smoking rooms should have a dedicated exhaust system so that environmental tobacco smoke is not carried to other parts of the building. Ventilation in these rooms should be 60 cfm per smoker in the room. Of course, the best way to reduce exposure to these chemicals is to not allow smoking in buildings at all. Refrigerant leakage. Improper use of biocides, sealants, and/or cleaning compounds. Leaks such as natural gas or propane leaks that accidentally get pulled into the ventilation system Chemicals from activities going on in the building. These depend on what type of work is being done in the building and can include ozone, pesticides, lead, and VOCs. Infectious Diseases People are more likely to catch infectious diseases in buildings without enough ventilation. When someone coughs or sneezes, they spew a fine mist of droplets that contain an aerosolized virus. If there is not enough ventilation to blow away and disperse the infectious organism, the virus can stick to desks or to doorknobs and live for several hours. Therefore, if someone sneezes close to you and the air is not moving, you have a good chance of becoming infected. Bacteria and Fungi There should not be any problems with HVAC systems that are well designed, well maintained, and properly installed. For example, even a properly designed condensate drain system will malfunction and hold water if the pan is not correctly pitched when installed. If they are well maintained, these systems can even improve the quality of indoor air by filtering out mold and pollen that may be present in high concentrations outside and by maintaining proper humidity levels so that mold and fungi do not thrive inside. In one study, even though there was more fungus (mold) collected in the dust of buildings that were mechanically ventilated compared to those that were naturally ventilated, there was less fungus (mold) in the air of mechanically ventilated buildings compared to naturally ventilated ones.¹⁹ However, if HVAC systems are not properly cleaned and maintained, over time a lot of dirt can accumulate in the ducts and form an ideal breeding ground for fungi and bacteria. Then these microbes may get into the air supply and be blown throughout the building, possibly causing health problems. For example, at two office buildings in Rochester in 1984, a fungus got in the ventilation system. About 1,000 people were exposed to the fungus, which caused an outbreak of hypersensitivity pneumonitis. Of those exposed, 115 got sick. Though the company spent millions trying to get rid of the fungus, they ended up having to replace the entire ventilation system.⁴ Bacteria and fungi found in HVAC systems can also trigger allergies, cause infections, and be the source of outbreaks of building-related illnesses such as Legionnaires' disease. High levels of microbial pollutants have been found on many parts of HVAC systems including: Cooling coils Filters Drip pans Humidification systems Cooling towers Ductwork: Ducts can be a particular concern if they are lined with a fiber glass lining since these types of linings can retain moisture. Fiber glass sheets were commonly used for lining the interiors of air supply ducts and air handler compartments of buildings from the early 1960s through the late 1980s. Fiber glass sheeting is an excellent moisture retainer. In laboratory experiments, fiber glass liner has retained moisture for up to 16 days.²⁰ As dust gathers in the ducts, mold will begin growing in it. Some inspectors have found mushrooms several inches tall growing inside ventilation systems! Recirculated Air In an effort to save energy, there has been as much as a 50 percent decrease in the amount of fresh air brought into some buildings. Some of the HVAC systems in some buildings were not even designed to let in as much fresh air as they should. Recirculating stale air can lead to problems. For example, in a study of 1144 workers in three different office buildings in Paris, the workers in the buildings with HVAC systems that were supplied by 30 percent fresh air had slightly higher building-related symptoms complaints than workers in buildings that were naturally ventilated. Recirculating too much stale air can raise contaminants (i.e. dust, human bioeffluents, and VOCs) to unhealthy levels. In a study of soldiers during the 1982-1986 period there were 2700 more hospitalization rates for acute respiratory disease hospitalizations among occupants of modern barracks that used mostly recirculated air (95 percent was recirculated) as opposed to old barracks with windows and ceiling exhaust fans (50 percent was recirculated).²¹ Recirculation can also happen if special vents do not exhaust to the outside like in bathrooms or smoking rooms. Inspection of Ventilation Systems Some of these problems can be found by having the HVAC system inspected. Some of the things that an inspector may do are: Examine the system, possibly using a fiber-optic borescope. This tool can help visualize and videotape the inside of ducts. Take ventilation measurements to make sure that enough airflow is going through the system. Sample for things such as microbial contamination, dust or fiber glass If you are going to investigate your ventilation system, make sure to follow these suggestions: Look to see if each room has an air supply. If windows cannot be opened, there should be two vents: a supply vent that blows fresh air into the room and an exhaust vent that moves stale air out. Supply vents may be found near windowsills and exhaust vents may be in ceilings. Look to see if the vents are dirty. If so, a more efficient filter on the HVAC system may be needed, but the system would need to be checked first to make sure that it is powerful enough to blow air through a filter like a HEPA. See if the air is actually moving in the room. Put a strip of paper at the opening of each vent. The paper should flutter out for supply vents and be drawn into exhaust vents. Look to see if any of the vents are blocked. Often things like partitions, file cabinets, desks, and many other things may block a vent and interfere with airflow. See if the supply and exhaust vents are too close together. If they are just a few feet apart, the incoming air may immediately get sucked into the exhaust and leave the room with stale air. Check to see if printing and copying machines have adequate exhaust. It is preferable to have these types of machines in their own room with good exhaust and away from people. If you choose to have an investigator come in to do an evaluation, only hire someone who specializes in IAQ investigations. Be sure to check the person's references. Anyone claiming to be a professional should be able to provide references of similar projects they have successfully completed. They must know what to look for in evaluating an HVAC system. Since most IAQ problems involve the HVAC system, make sure that the person actually looks inside it. Knowledge of environmental microbiology. Many IAQ problems involve microbial contamination so they should be familiar with how to evaluate these kinds of problems. The inspector should put more emphasis on their inspections than on their tests. Somebody who crawls around parts of the system and talks to people about problems is more valuable than somebody who just takes measurements with fancy equipment. Correcting Ventilation Problems Simply increasing the ventilation rate may not resolve IAQ problems. There are several reasons for this:²² Research findings show that IAQ complaints and building-related symptoms are caused by many things not related to the air like personal, occupational, and psychological factors. For example, some people are more sensitive or susceptible to the problems that cause indoor air problems. There may be enough airflow, but it may not be reaching its target due to problems like blocked vents. Do not put up things that might restrict air movement such as putting furniture over air vents. The best ways to control indoor air pollutants from being distributed throughout the ventilation system include: Control pollutants at the source: This is the most effective strategy for maintaining clean indoor air. If installing an HVAC system, make sure that: The HVAC system is properly designed for the needs of the building. This includes making sure there is enough ventilation for the number of people expected in the building and that ventilation rates are high enough given the activities that are going to be conducted in the building. Air supply vents are not too close to building exhaust vents. Supply vents are placed away from outdoor sources of pollution such as: Loading docks Parking and heavy traffic areas Chimneys Furnace, kitchen, or bathroom exhausts Trash dumpsters Conduct proper and regular HVAC inspection, cleaning, and maintenance. Click here for a detailed checklist recommended by NIOSH, including the following: Make sure that vents are open, fans are on, and filters are cleaned on a regular maintenance schedule. Change air filters regularly. In many schools, air filter efficiency ranges from 10 percent to 40 percent. These are not good enough to minimize dust levels and they do a poor job of removing pollen from the air. Filters should be upgraded to 85 percent filters, but an HVAC engineer should be consulted first to make sure that the equipment can handle this kind of filter. Use air cleaners that are part of the HVAC system. However, this should only be in addition to controlling pollutants at the source and properly maintaining the HVAC system. These air cleaners should include high efficiency filters that can remove some of the particles in the air. However, these filters will not be able to remove any of the gases or vapors unless the filters are specially treated with something like activated charcoal. In addition, the blower on the HVAC system must be designed to be powerful enough to blow air through a high-efficiency filter. Many HVAC systems have low efficiency filters that are only designed to prevent dust from damaging the blower fans. Make sure that air intake vents are open, clean, and far from air pollution sources such as kitchen exhaust vents, truck-unloading areas, and smoke stacks and clear of other sources of contamination such as pigeon droppings. Check the exhaust system to make sure that air can adequately be exhausted from the building. Properly maintain and clean humidification and dehumidification systems to prevent the growth of harmful bacteria and fungi. This includes things like making sure there is no water in the drain pan. Failure to properly treat the water in cooling towers to prevent growth of organisms, such as Legionella, may introduce such organisms into the HVAC supply ducts and cause serious health problems. Frequently inspect and clean the heating and cooling coils, cooling tower, and drip pan to prevent microbial contamination. Wall-mounted fan coil units are often found in educational facilities. These units are frequently not well maintained. This often results in dirty coils, dirty condensate pans, and dirty or missing filters. Ensure that air dampers are clear of obstruction and operating properly. In educational facilities, supply grilles are often blocked by books or papers. Inspect and clean as needed the inside of air handling units Inspect fan motors and belts Regularly inspect and clean air humidification equipment and controls Inspect and clean as needed air distribution pathways and variable air volume (VAV) boxes. Maintain building temperatures and humidity levels within the recommended range Ventilate the building with at least 20 cfm unless occupant activities are such that higher ventilation rates are needed. ASHRAE/ANSI Standard 62-2001 says that mixed air (fresh and recirculated) should be distributed uniformly throughout the area where occupants work and that it should reach their breathing zones. Install local exhaust ventilation to remove pollutants from areas where they may build-up such as rest rooms, copy rooms, and printing facilities. If the ducts have fiber glass liners that have gotten wet, the North American Insulation Manufacturers Association (NAIMA) recommends that they be removed and thrown out as soon as possible to prevent mold and fungi from growing on them. This is because it is so hard to properly clean these ducts. In one study, they were able to clean the ducts, but the same level of microbial contamination returned in just six weeks.²³ Clean air handlers yearly and ducts every 5 to 10 years or as needed. Use the best possible filtration that your system can handle. Have individually controlled ventilation systems for each worker. When workers in one study had control of their ventilation system, there were a lot fewer complaints about indoor air problems. When workstations that had individual climate control systems were examined, researchers found a wide range of temperatures and airflows.²⁴ More than 60% of the occupants in one study said they had no control over their thermal environment of their workstation. Only 1% said they had "complete control." Self-reports of health symptoms seemed to decrease with an increased amount of control over thermal environment.²⁵ In offices where people could individually control the temperature, there was a 34 percent reduction in sickness due to building-related symptoms. People who had windows in their offices that could be opened were 25 percent more likely to lose workdays due to building-related symptoms than those who did not have windows that opened. Investigate all indoor air complaints right away. A NIOSH form to assist with this may be found at www.cdc.gov/niosh/pdfs/complain.pdf. Cleaning of Air Ducts There is currently no hard data that shows that cleaning air ducts improves indoor air quality. The EPA/NIOSH publication, Building Air Quality Guide,²⁶ places its emphasis on prevention. Any HVAC system that is clean and dry should work well and provide enough quality air for good indoor air quality. All parts of the HVAC system, including the ducts, should be kept in proper working condition. Poorly maintained, poorly operated, "dirty" air handling units, and dirty air ducts create poor indoor air quality and increase operating costs by using more energy. If duct cleaning is needed, the following recommendations should be followed: Any duct cleaning should be done when people are not in the building in order to prevent exposure to chemicals and excess dust. Avoid application of biocides, sealants or other chemical treatments. Choose consultants and air duct cleaning specialists with experience and training in cleaning office building HVAC systems. Make sure proper methods are used. In one study, Florida International University researched which of three commercial HVAC duct-cleaning processes was most effective in reducing the level of airborne particulate matter. They found the most effective method to be the "air sweep" in which compressed air blows out dirt and debris, which is collected by a vacuum system.²⁷ NIOSH/EPA recommend that this type of cleaning also include gentle, well-controlled brushing of duct surfaces or other methods to dislodge dust and other particles. Duct cleaning that relies only on a high velocity airflow through the ducts may not get good results since there may be caked on dirt on the edges that gets missed. This type of power brushing should use HEPA (high-efficiency particle arrestor) filtered vacuum cleaners since dust may go through the filters of regular vacuum cleaners or shop-vacs. The only downside is that this method cannot be used on inaccessible ducts. Methods that are not recommended are: Using sealants/encapsulants?these may cause more problems in the end. None of these techniques has been proven to stop microbiological growth nor have many of these materials been evaluated for their potential health effects on occupants. In addition, the use of sealants may void the fire safety rating of the ductwork. Truck-mounted vacuum or portable high power vacuum?this also does not work. No matter how powerful the vacuum is, the airflow at the edges of the duct is minimal. If the vacuum is too powerful, it can cause the duct to collapse or develop a leak. The use of biocides?this can expose all the building occupants to these chemicals. There is some question about whether any of these techniques use enough biocide to actually kill the bacteria, germs, or mold that may be present. Deodorizers may provide a fresh smell, but they are not meant to provide any real control of the underlying problem. They add chemicals. Careful cleaning and sanitizing of part of the HVAC system, such as coils and drip pans, can reduce microbiological growths. Before using sanitizers or any cleansing agents, carefully read the directions on the product label. Once cleaned, these components should be thoroughly rinsed and dried to prevent exposure of building occupants to the cleaning chemicals. Where possible, vacuum equipment or fans should be used during cleaning and sanitizing to make sure that vapors and dust are exhausted to the outside and do not enter parts of the building where people may be. Any water-damaged or contaminated materials in the ductwork, such as fiber glass, should be removed and replaced. Even when such materials are completely dried, there is no way to guarantee that all microbial growth has been eliminated. After the duct system has been cleaned and restored to use, a preventive maintenance program will prevent the recurrence of problems. 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