SPECIAL CONTROL CONSIDERATIONS
The importance of thermal conditions to occupant comfort and the relationship to particular contaminants is well documented. The role of the HVAC system in delivering the required thermal conditions and meeting IAQ ventilation needs is a critical IAQ concern. The fact that the HVAC system is also a source of contaminants is a key consideration. Because of their unique characteristics and importance to IAQ, thermal comfort factors and ventilation are discussed separately in later sections.
Other control factors of particular concern are filter selection and maintenance, purchasing, and new construction/modifications design.
These areas are treated very briefly below from the management perspective. Filtration technology is also discussed in its own section.
Filter Selection and Maintenance
The primary purpose of filters is to reduce the contaminants in the airflow. The effectiveness with which they fulfill this purpose is determined by the type of air cleaner used, location in the system and the amount of air which passes through. The more effective the air-cleaning system is in removing contaminants from the already conditioned return air, the more that air can be substituted for outdoor air; thus, reducing the energy costs. The amount of filterable material that can be removed is determined by the volume of flow through the cleaner and its overall effectiveness.
The selection of an air-cleaning system is based on the contaminants to be removed, such as the size of particles, and any specialized needs that must be met. For example, a special air scrubber system is used to remove carbon dioxide (CO2) in the closed system of a nuclear submarine; however, its high cost and maintenance needs make it impractical for ambient conditions in commercial buildings. In other circumstances, the centrifugal cyclone separator is dependent on the density of the particles, their size and the density of the air. Since very small particles cause little aerodynamic drag in a moving airstream due to their surface area versus mass, cyclone separators only have application in settings where larger particle removal is required, such as dust removal in industrial plants.
Building HVAC systems typically rely on arrestance media filters and electrostatic air cleaners. The media filter is a porous material that strains out particles as air is forced through it. Media filters range from the more crude "duststop" filters still used in some warm-air furnaces to the high efficiency particulate arrestor filter (HEPA). The HEPA filter is highly capable of removing submicron particles, which is why they were called "absolute" filters early in their history.
The effectiveness of media filters changes as particulate matter builds up. If left alone, they gradually increase in collection efficiency.
That, however, is not a good reason to leave them unattended. As they clog, the flow rate decreases. Resistance from clogged filters reduces air flow and system efficiency and increases energy usage.
Electrostatic air cleaners (EAC) have demonstrated very high efficiency in removing particles in the range 0.01 micron to 5.0 microns.
The EAC acts by charging the particles passing through, causing them to be attracted to oppositely charged plates. The collected material must, however, be regularly removed from the collector plates. EACs operate best when absolutely clean. Build up on plates not only reduces effectiveness, but the units can become odor sources. In small installations, the whole filter is removed for washing. Larger EACs are designed with wash-in-place capability. These types of equipment are complex and require high levels of maintenance; thus, they are now only used in specialized applications, such as kitchen hoods.
Gases and vapors can be filtered using adsorbers or absorbers.
Activated carbon, with its large surface area due to voids within its structure, is a good example of this type of system. Adhesion of the gas molecules to the carbon removes the contaminants from the air. This process works fairly well on large molecular weight molecules, such as solvent (VOC) molecules, but does not do an effective job of removing small molecules, such as sulfur dioxide. For control of the latter compound and other more reactive gases, a potassium permanganate treated alumina pellet works better. A full range of sorbents, such as carbon, alumina and zeolite, can be treated with reagents to enhance their abilities to capture and retain specific chemical compounds.
The source of contamination can influence the placement of filters in the system. If the source of contaminants is the conditioned space, the air cleaner can be placed in the recirculating airstream or the mixed airstream. If the main source is outside, then outdoor air filtration is a primary consideration. Unless the staff has particular expertise in this area, it is wise to consult a specialist when filter design or modification decisions are needed.
Filtration and air cleaning can be a truly cost-effective and useful tool in IAQ prevention and mitigation. Yet, it is an under-utilized technology in the IAQ arena as the subject of filtration is complex, highly specific and , unfortunately, there are few generic non-biased sources of information. This is why the subject is covered more thoroughly in a separate section to provide the IAQ professional with a valuable in formation resource. Refer to the filtration section for further detail on application, product types, testing methods, and design techniques.
Caulks, sealants and adhesives have various levels of VOC emissions depending on the compound. Building, pipe and duct insulation with urea formaldehyde insulation or asbestos-containing acoustical, fireproof and thermal insulation can have an adverse effect on IAQ. Paints have highly volatile mixtures of VOCs and have high release rates during the short-term curing process. Many of the problems associated with these products can be avoided through selective purchasing.
The careful selection of construction materials and furnishings can help alleviate indoor air problems at the source; e.g., the level of formaldehyde emission from pressed wood products. Table 5-1 lists materials of particular concern that warrant careful selection procedures.
Materials of concern encompass site preparation, envelope construction, mechanical system and interior finishing.
Reference in the specifications to certain federal or industry guide lines can avoid major headaches later on, both figuratively and literally.
In purchasing materials directly or through the contractor, standards can be specified so that materials meet federal regulations. Manufacturer's Safety Data Sheets should be required of all vendors as per OSHA man date. But further, the MSDS data should be scrutinized closely for odorous or irritating components and the documents retained in an orderly reference system in case VOC complaints occur. An additional precaution is to ask that each chemical or material in a composition product be identified, and outgassing rates be provided when known.
New Construction/Renovation Design
All materials pollute, some a little, some a lot, but they all con tribute to a deterioration of the air quality. "Engineering out" materials and conditions known to have a particularly adverse effect on indoor air quality during new construction or renovation may prove to be the easiest control measure of all.
Tbl 1. Building Materials of Particular Concern
SITE PREPARATION and FOUNDATIONS
soil treatment insecticides
foundation waterproofing, especially oil derivatives
high levels of dirt and dust
caulking, sealants, glazing compounds and joint fillers
insulation, thermal and acoustical
fire proofing materials
INTERIORS and FINISHES
subfloor or underlayment
floor or carpet adhesives
carpet backing or pad
carpet or resilient flooring
wall coverings, both vinyl and fabric
Now that it has become evident that a building can be hazardous to one's health, the reduction of the potential hazards become a critical criteria of building design and construction. The ASHRAE IAQDG is an invaluable aid in designing acceptable IAQ into the building at the beginning because it integrates architecture with function and covers in depth all aspects of integrating IAQ into the design/construct process.
Put It in the Specs
The owner, who is ultimately responsible for the facility, can't assume an architect or an engineer fully understands the design and materials implications associated with indoor air quality. It is incumbent upon the owner to include sufficient direction in the specifications to obtain a facility that is energy efficient, aesthetically pleasing, productive and hygienically safe. Appropriate IAQ specifications offer a quality control opportunity, that can save millions in remedial measures, and could lessen legal liability.
Facility Siting, Foundations
Siting of a facility should consider potentially negative influences on IAQ; e.g., the quality of the soil, particularly in radon affected areas.
The proximity of roadways and vegetation may, depending on the type and placement, serve as a source of allergens and high particulate count.
The nature and location of polluting activities should affect design.
For example, exhaust near a localized activity may serve as an effective source control mechanism. If theatre or craft production, car repair work or maintenance operations are going to involve toxic gases or particulates from brazing, welding, cutting or soldering, then direct venting to the outside should be part of the design.
Precautions should be taken in new construction to thwart radon entry through slab plate penetration. Recommendations made by Brennan and Turner several years ago in "Defining Radon" still provide excellent control guidance. They recommended: (1) slabs and basements be poured with as few joints as possible and poured right to the wall; (2) wire reinforcement be used in slabs and walls to help prevent future cracks; (3) seams and perimeters be caulked with polyurethane; (4)
dampproofing, sealing and coating the walls be done to slow entry; and (5) sub-slab drains and several inches of #2 stone be placed below the slab during construction to provide sub-slab ventilation potential.
Thermal Comfort Design
In addition to the consideration given to the thermal environment and humidity, air flow patterns need careful HVAC designer attention.
Designers historically were concerned almost exclusively about temperature control. For years, humidity controls were ignored except in areas of extreme climate or special conditions. While we've provided "climate controlled" environments for rare books, masterpieces, and special documents for many years, we have only recently begun to recognize the importance of humidity in a comfortable, hygienically safe environment.
The role humidity plays in fostering/controlling contaminants is being more fully appreciated.
We have not progressed, however, in making sure that the outside air or the cleaned, recirculated air is actually reaching the occupants.
With the advent of sealed windows, occupants became totally dependent on the designer's understanding of air flow. To illustrate one renovation problem, we have only to look at the partitioned "open space" offices and schools of the 1970s where pockets of dead air have been created.
Ventilation Effectiveness Design
A more pervasive problem has been revealed in studies which found that most office buildings had both the supply air outlets and return air inlets located at ceiling level into a ceiling plenum. This placement can cause a short circuiting and poor distribution of air. As the air pours across the ceiling, half of the room-the half where the occupants are-is left with poor ventilation. This is exacerbated by poor louvre design and the part load operating condition of VAV systems.
An owner does not have to understand complex formulas on mixing efficiency to be able to spot grill work at the ceiling level and to see why the room still seems "stuffy" even with increased outside air.
Such designs also severely constrain the value of ventilation as a control measure. Ventilation effectiveness, the ratio of outside air reaching occupants compared to total outside air supplied to the space, determines the capability of the supply air to limit and control the concentration of the contaminants. Design considerations are implicit in the discussions of temperature, humidity and ventilation effectiveness found later in the guide.
The importance of providing access for maintaining all equipment can't be overemphasized. Failure to allow for maintenance access occurs entirely too often. The resulting horror stories are legion. For owners and managers, this should be a critical design concern.
Sources of contaminants and their controls, as discussed else where in this section and throughout the guide, suggest further design considerations. For example, the material on bioaerosols discusses the problems associated with the growth of microbials in the space, in the air handler, and in the distribution system. This is brought on by the improper maintenance and operation of systems that enables water and dirt to accumulate and promote this condition.
Bake-outs were frequently suggested early-on as part of the commissioning process to control VOC contaminants in new construction.
Elevated temperatures were thought to speed VOC emissions. The bake out was, therefore, expected to accelerate the off-gassing process prior to occupancy and thus reduce the pollution levels after the building is occupied. A bake-out was controlled by adjusting three parameters; the duration of the bake-out, the indoor air temperature during the bake out, and the ventilation rate during the process. In 1989, J. Girman and his colleagues reported reduction of selected VOCs as a result of the bake-out process. He also confided in verbal reporting that the research building suffered substantial physical damage to wall coverings, concrete foundation, and millwork. Researchers, headed by C. Bayer, at the Georgia Institute of Technology, later reported that total counts of VOCs were "about the same before and after the bake-out," but they found that numerous specific compounds had shifted to other totally new organic compounds. Bayer theorized that the higher levels of VOCs had transported to sorption sites and from these "sinks" re-emitted sometimes as new compounds. The bake-out process must be performed after the building is totally furnished and ready for occupancy. Yet, there must be no occupancy during the process. This creates tremendous financial burden to the owner who must delay the useful start time of the asset.
A successful alternative to bake out is the tactic of "flush-out." This employs as much mechanically induced outdoor air as possible during the final build-out when contaminant loads are highest. Flushing is per formed continuously around the clock for several weeks into the move-in and occupancy. One caution is that the technique is to be used only during mild low humidity seasons or with the refrigeration cycle operative to avoid humidity build-up in the space during off occupancy hours.
Finally, owners should keep their eye on emerging technology, particularly in the area of automated sensing controls and ergonomically correct furniture. Also, raised floor and underfloor distribution is adding to the ability of occupants to control discharge of supply air into their space while enhancing the overall ventilation effectiveness of the system.
New, more precise, and dependable sensing controls will allow much more accurate monitoring and response to specific constituents such as carbon dioxide. This will enable better demand control of ventilation levels that can be modified in response of varying occupancies. New heat-pipe technology is enabling more efficiency salvage of heat content of air discharged from the building. Newly developed high performance desiccant wheels based upon improved desiccants will aid in humidity control tactics without the use of CFC refrigerants. High flow and high capacity particulate filtration medias and fabrication techniques are making new high efficiency filters available that combine long life with low energy usage. Similarly, there are new developments in gas phase filtration employing sorbent imbedded fabrics that enable medium efficiency performance with lower cost and pressure drop. Improved air flow louvers are becoming available that can assure good air diffusion and mixing even at reduced velocities typical of part load conditions. Advances in UVGI (Ultraviolet Germicidal Irradiation) light bulbs and equipment have enabled the usage of this mechanism in HVAC equipment to control microbial growth on wetted coiling coil surfaces. Unfortunately, the process has limitations in a moving air stream to affect the air quality because of limited dwell time, according to research performed by RTI (Research Triangle Institute). There is also considerable funding emanating from Homeland Security that will bring about other rapid advances in contaminant monitoring and control materials and devices due to potential terrorism concerns.
Managers can't keep up with the state-of-the-art on all techno logical fronts. Keeping tabs on the continuing emergence of controls, equipment and software to satisfy IAQ needs, reduce energy usage, and optimize productivity and space utilization would be almost impossible.
The obvious benefits, however, warrant a thorough investigation of new products and technologies as construction/renovation project planning begins.
Though not an emerging technology, the process of commissioning is emerging as a critical component of successful completion of the construction process. It is even more critical in bringing remediation and renovation projects to successful closure. Described in ASHRAE Guideline 1, the process involves the aggressive overview of each stage of the construction project by a designated commissioning agent or staff person (not the contractor). From start to finish, the process is de signed to assure the conformance of the project to the design resulting in a building that performs according to intent. Along the construction pathway, the process reveals and remedies problems that normally get built-in and concealed only to emerge later as contributors to problems.
In commissioning of IAQ projects, both Milam and Woods both reported construction efficiencies to more than offset the cost.
CONTROL EVALUATION and MONITORING
Control management requires some evaluation of the steps taken.
The level of evaluation will vary with the condition(s) which caused the problem. With sick building syndrome (SBS), where the cause may never be identified, the cessation of complaints may serve as sufficient evaluation of treatment procedures. In the case of something as alarming as Legionnaire's disease, medical verification and a proactive program of analysis of water sources for Legionella may be warranted.
Following the treatment for SBS or BRI, a critical component of effective control management is monitoring. Monitoring may range from a simple oversight procedure that assures continued adherence to control practices, to intermittent or continuous atmospheric sampling and analysis methods.
Sampling and analysis for hazards may include area, personal, process, or duct sampling to determine characteristics of emission, level of exposure and operational conditions. Sampling and analysis procedures are usually very specialized, conducted by outside consultants and are expensive. It is an evaluation procedure generally reserved for extreme circumstance or research.
Currently, the most widely used monitoring approach to assure continued quality of the indoor air is monitoring carbon dioxide (CO2) measurements. As discussed previously, CO2 is frequently used as a surrogate for other contaminants. Except in instances where sources, such as vehicle exhaust, affect CO2 content, the concentration of CO2 in the outside air is fairly constant. With information about ambient CO2 levels outdoors and what is going on indoors, we can learn a lot about the effectiveness of the ventilation system.
If CO2 sensors are used to monitor concentrations, care should be taken to be sure they are sufficiently reliable and hold calibration. If they drift more than 100 ppm per year, then they will not offer a reliable reading nor accurate control if being used for variable demand controlled ventilation on a permanent basis.
CONTROL BY CONTAMINANT
The effectiveness of specific controls varies by contaminant. Ventilation as a control device, for instance, will not benefit and may aggravate certain contaminant situations. When the pollutant is known, controls should be contaminant-specific. Some control measures are required by law. In such instances, legal reference is made to the applicable law or code in the following discussion of controls by specific contaminants.
Asbestos Abatement methods are:
1) Operations and maintenance
The Asbestos Hazard Emergency Response Act (AHERA) is a federal law that specified acceptable abatement procedures. Some people falsely assumed that AHERA required asbestos removal. The law only required schools to exercise every effort to protect human health and the environment by "the least burdensome method." Financially, the least burdensome method seldom equates with removal. Furthermore, as the Harvard report, Summary of Symposium on Health Aspects of Exposure to Asbestos in Buildings, reminds us, "Removal itself is not without risk."
The threat of lawsuits prompted building owners to opt for removal; however, removal has the potential to increase, rather than decrease, indoor air concentrations. Removal and disposal exposes some workers to high concentrations of airborne asbestos. Owners may inherit an even greater liability through removal, for they are responsible by Federal Regulations for the asbestos at the disposal site for 40 years.
Abatement specialists, fully trained with appropriate credentials and experience, should be employed for asbestos detection, encapsulation, removal, disposal and air monitoring procedures. Owners should seek protection by having specialists bonded and insured. State counterparts of EPA and OSHA can help identify appropriately qualified contractors.
When reviewing contractor credentials, try to retain the services of specialists with experience in like facilities. Contractors, who gained their experience in schools, may not appreciate the difficulties to be found in government offices, hospitals, or multi-tenant high rise buildings where the HVAC system can't be shut down or the space totally evacuated during work.
Asbestos removal, when the HVAC is not shut off, presents a whole new set of conditions. Asbestos removal generates high levels of asbestos dust that may be transported in the HVAC system. Preplanning, by a team which includes a mechanical/HVAC engineer with asbestos expertise and an industrial hygienist, will help determine the precautionary steps to take; e.g., work area isolation, negative HEPA air filtration, personnel and area decontamination. It may be necessary to weigh the viability of the continued operation of the HVAC system.
OSHA guidelines for asbestos removal can be found in Title 29, Code of Federal Regulations, 1910.1001 and 1926.58, U.S. Department of Labor, Occupational Safety and Health Administration, 1993. It is management's responsibility to see that these guidelines are followed.
A review of microorganism and their sources suggests ways to control bioaerosols and microbial contaminants. Sources for biological growth include wet insulation, carpet, ceiling tile, wall coverings, furniture and stagnant water in air conditioners, dehumidifiers, humidifiers, cooling towers, drip pans and cooling coils of air handling units. People, pets, plants, insects, soil may carry biological agents into a facility or serve as potential sources. Frequently, bioaerosols settle in the ventilation system itself where viable spores and bacteria can colonize and grow. The inevitable dust inside duct work plus condensate moisture (often resulting from variations in temperature and humidity) can work together to turn these vast surface areas into breeding grounds for mold.
Because of numerous noteworthy and well publicized mold cases, mold has become the feeding frenzy of lawyers, investigators, and mitigation firms. Several high profile settlements involving celebrities and millions of dollars has fueled the tort litigation factions. Names like the Ballard Family, Erin Brockovich, and Ed McMann have become poster children of this issue and synonymous with huge multimillion-dollar settlements in mold litigation. Thus, mold has emerged as the building owners' scourge of the 21st century.
To show that this is almost a timeless exercise, the following quotation is a tongue-in-cheek distortion of scripture taken from Leviticus 14:33-59 with credit to Don Gatley, a noted IAQ expert in humidity control.
"The Lord also said to Moses and Aaron, when you come into the land of Canaan unto your people, when I might cause mildew to grow in a house in the land of your possession. Then he who owns the house and finds mildew, shall come to the Priest and indicate that he found mildew. The Priest will command the house to be emptied lest all that are in the house be declared unclean. Then he will go and examine at the mildew to see if the mildew is on the walls of the house with greenish or reddish spots, and if it might go deeper than the wall's surface. If these things are true, the priest shall go out and close the house for seven days. On the seventh day, he returns and if it has spread, then they must tear out the stones with the mildew on them, they should throw the stones away and put them at a certain unclean place outside the city. Then the priest shall cause all the inside of the house scraped round about and the people must pour all the plaster they scraped off the walls at a certain unclean place outside the city. Then the owner must take other stones and put them in place. They must cover the walls with new clay and plaster. Now, after new stones and plaster have been put in the house, the priest must go look. If after all of this he finds that the mildew has reoccurred, then the house shall be broken down completely, its stones, plaster, and timbers and they shall carry them forth to the unclean place outside of the city. and then they shall start over."
Although these biblical references were referring to Hansen's Disease (no relation to Shirley Hansen, the author of the original MIAQ) or other wise known as the feared and contemptible Leprosy, may seem like extreme and drastic myths, all one has to do is examine closely the mitigation tactics used on some notable Florida public buildings, which were rebuilt from the outside inward and again, inside outward at costs far in excess of initial cost. Furthermore, the cleanup process is following closely the tactics used in asbestos abatement, which increase the costs exponentially.
This is partly due to early guidance from the New York City Guideline on Assessment and Remediation of Fungi; the EPA Mold Remediation in Schools and Commercial Buildings; and the OSHA Guide to Mold in the Workplace. But also, the issue is being driven by the ex-asbestos contractors who are waiting in the wings ready to leap on buildings in trouble. This brings a new light to the cost effectiveness of prevention and control rather than waiting for the building to "break" before repairing it.
Most remedies and prevention tactics fall in the area of maintenance and preventive maintenance; e.g., cleaning filters and wet areas in the ventilation system; replacing water-damaged carpets, insulation; maintaining an average relative humidity between 30-60 percent; cleaning/disinfecting drain pans and coils; repairing water sources, etc. General cleanliness of the facility and the mechanical systems will satisfy many of these needs and it is important to note that "elbow grease" does not create or emit VOCs!
One of the most critical control issues for the prevention of microbial growth is the stringent and consistent control of moisture and relative humidity as mold growth is only the symptom of a moisture and / or humidity problem. This may require a reexamination of the outdoor air system, refrigeration capacity, coil selection, and control or operating schemes. Ultimate control may require dedicated humidity control equipment or strategies. The important consideration is to avoid the inappropriate dew point and thermal shock occurrences throughout the facility and the HVAC system that causes condensation where it should not occur-on walls, in gypsum board, in wall cavities, behind wall coverings, in building insulation, on vapor barriers-brought on in many cases by improper pressure relationships. There are few legitimate locations for water inside a building-a drinking fountain, a janitor's closet, a com mode bowl, a drain P-trap, and a condensate pan (and the latter is only to be a pathway-not a reservoir). Other sites or sources of moisture or water accumulation for whatever reason will result in "bad news" from a fungal growth standpoint.
While good quality filters will remove microbial contaminants, they will not do the job if the contaminants are generated downstream.
Stories are told of "rattling the cage," that is, disturbing the air conveyance system and increasing contaminant levels in occupied space four fold over outside air levels. Cleaning humidifiers, coil surfaces and drain pans are the most effective remedial actions for microbial contaminants generated downstream of the filter banks. The section on HVAC discusses bioaerosol-related maintenance in systems.
Filtration of bioaerosols is relatively easy as microorganisms fall in a particle size range that can be effectively trapped by a variety of filters.
Most microbial cells range from 1-20 µ with a few from 0.5-200 µ, all of which can be removed in a good quality filtration system. MERV 14 efficiency filters will remove most microbial particulates in the return or outdoor airstreams.
Biocides are sometimes recommended for cleaning ventilation systems. The American Conference of Governmental Industrial Hygienists Bioaerosol Committee recommends that no biocide be used in an operating ventilation system. Decommissioned HVAC systems can be cleaned with biocides provided all biocide is removed before the system is restarted. Risks associated with biocides may be worse than exposure to microorganisms. Also, biocides applied to interior surfaces must be registered with the EPA for application in an air stream. Remember that a chemical that can kill a cockroach, a bacterium, or a mold spore will not be gentle and soothing to human lung tissue.
The need to replace duct lining is seldom required. If it is, however, it is often cheaper and easier to replace the complete duct section rather than just the lining. EPA has published research that affirms that the process of duct cleaning may even worsen the problem of bio-contaminants in the occupied space. In addition, the new porous insulation duct liners have provided product modifications that make them more resistant to mold and more resilient to duct cleaning.
It remains that moisture control is the most cost effective prevention tactic when dealing with mold and bacteria. When and if mold occurs, remediation must be swift and thorough-starting with the correction of the water incursion. Delays, whether triggered by budget concerns, decision trees, priorities, or just "round-to-its," will magnify the negative impact on the structure, enhance exposures and related negative health effects of occupants or tenants, magnify cost of repairs and mitigation, and expand time delays to full productivity and usage of the space.
The remaining dilemma at the time of this writing is the is sue that there are no clear and definitive mold standards-the basic problem of "how clean is clean." The Occupational Safety and Health Administration has not established a Permissible Exposure Limit (PEL) for mold. Neither has the American Conference of Industrial Hygienists established a safe level, however, several states have recently enacted laws requiring licensure of mold consultants and remediators. The medical scientists have declared that there is no clear linkage between mold exposure and severe adverse health effects, yet concede that low levels of exposure can induce allergic reactions in susceptible individuals. This dichotomy mandates that the building owner take deliberate care and due diligence in selecting and managing the remediation team and his consulting experts.
This is because cleanliness targets are largely "expert" driven and getting in bed with the wrong expert will end up costing thousands of tests, months of productivity loss, and millions of dollars in laboratory and remediation fees to attain "clean." Thus, the targets for
"acceptability" must be mutually agreed upon between the experts and parties to the complaint before remediation commences-otherwise it does not ever end because "0" doesn't exist in the normal commercial building setting that is exposed to outdoor air. There is currently an ANSI approved standard for mold remediation from the Institute of Inspection Cleaning and Restoration Certification (IICRC) titled, "IICRC S520: Standard and Reference Guide for Professional Mold Remediation." Other organizations, such as AIHA and NADCA, have published documents that include guidance on mold remediation.
The best control of internally generated combustion products are efforts to maintain, properly adjust and carefully operate all combustion equipment. Vehicular exhaust from garages, loading docks, etc., constitute another major source of combustion products, that needs to be carefully managed and avoided.
The National Aeronautics and Space Administration (NASA) has published research that claims house plants can serve as living air cleaners for the volatile organic chemicals often found in combustion products. From a practical standpoint, it would require extensive foliage in a commercial building to measurably impact the overall level of pollutants. Plantings can also impose a negative IAQ aspect by providing sites for fungal growth due to aged potting soil and careless overwatering and spillage.
When unusually high levels of combustion contaminants are expected in an area, additional ventilation can and should be used as a temporary measure. Conversely, when the ventilation air is the source of contamination, as in peak rush hour periods, the outdoor air may be shut down according to ASHRAE Standard 62. Although carbon monoxide can't be filtered with current technology, other odorous and irritating outdoor pollutants resulting from combustion can be cleansed using engineered gas phase filtration systems. When combustion appliances are situated within the occupied zone, special care should be taken to avoid negative pressurization, which can cause back drafting of products of combustion into the breathing zone.
Environmental Tobacco Smoke
Even though most public buildings restrict smoking, this remains a significant indoor pollutant, especially in the hospitality industry such as restaurants and bars. Considering that over 20% of the adult population still smoke, the control of the problem contaminant remains a concern to the building owner or manager of facilities that contain smoking designated spaces. Thus, the proper management and control of ETS should be addressed.
The control and treatment of ETS generally falls into five areas:
(1) remove the source-eliminate smoking. Decrees to eliminate smoking are policy decisions with employee relation considerations.
However, the smoking curtailment proposed in the 1994 Proposed Ruling by OSHA, although formally withdrawn, prompted many state and local authorities to restrict smoking in public space. Thus, today most public buildings restrict smoking entirely or provide designated smoking areas. More recently, many states and local authorities have limited or eliminated smoking in hospitality areas.
(2) modify the source-relocate/separate smokers. Separating smokers will reduce, but not eliminate complaints about ETS from non smokers.
(3) dilution ventilation. Increasing ventilation may prove to be the most desirable option, but it is a very expensive one. Standard 62 requires increased ventilation for designed smoking areas.
Ventilation rates to satisfy ETS-related health concerns have not been established. ASHRAE 62 guidelines are designed to reduce tobacco smoke odor and discomfort or irritation, not necessarily reduce health risks.
(4) filter the contaminants. HEPA filters and electrostatic precipitators can remove the respirable particles of ETS smoke. Since both odor and irritation are mainly caused by the gaseous phase of smoke, this does not provide adequate control of the contaminant problem. Granulated filter media, such as activated carbon, or permanganate treated alumina or zeolite can collect much of the volatile component of ETS.
(5) isolate smokers and exhaust contaminants directly to outside. Establish a dedicated and designated smoking lounge. To assure smoke isolation, the space must be totally sealed from the public space; must exhaust its return directly to the outside; must maintain negative pressurization compared to the adjacent public space; must in crease ventilation supply air to a minimum of 60 cfm per smoker; and may supplement with recirculating air cleaners.
Through selective purchasing, materials can be obtained with lower potential formaldehyde off-gassing. Researchers have found up to a 23-fold difference in emission from the same products from different manufacturers due to different resins being used and /or pre-treatment to reduce emission levels. Contact and inquiries with dealers and manufacturers with regard to potential formaldehyde emissions rates prior to purchase is warranted and may result in materials with lower exposure levels.
The potential to significantly reduce the irritation from formaldehyde warrants a pro-active, preventive approach. Laminated products should have all exposed surfaces or unused "plug holes" covered with laminate or sealed.
Like other VOCs, out-gassing of HCHO can be lessened by venting the component, such as carpeting and fixtures in unconditioned ware house space prior to installation.
Barrier coatings and sealants might be used to reduce formaldehyde emissions. Researchers at Ball State University have tested various sealants on particleboard flooring and have found they are effective. Barriers, such as vinyl floor coverings, have reduced HCHO in residences up to 60 percent even with other HCHO emissions present. Barrier coatings and sealants pose their own IAQ problems and adequate ventilation should be maintained during application and until the strong odor fades. Prior to using sealants, notification to chemically sensitized people is recommended.
Formaldehyde is a difficult compound to filter because it does not sorb well onto the common activated carbons. The permanganate/ alumina type pellets control the contaminant very effectively. However, a high concentration and /or a high generation rate will consume the sorbent at high rates which can drive upward the air purification costs due to short life cycles.
The primary sources of radon in buildings with high concentrations is the pressure driven flow of radon soil gas. This pressure difference may be the result of indoor-outdoor temperature differences, prevailing winds, the mechanical ventilation systems and combustion devices that have a depressurizing effect on the building. Even buildings having positive pressure over-all may experience localized negative pressure on the footprint floor due to stack effect or the location of a primary mechanical room. There may also be foundation penetrations because of sumps, drains, or sewage collection. These are potential conditions to allow entry points for radon gas. Care should be take to assure that these penetrations are sealed and the footprint floor operates with positive pressurization so that ground derived gas is not pulled into the conditioned space.
The most effective means of controlling radon is to prevent it from entering the building. In radon areas, precautions should be taken to thwart radon entry. In existing buildings, sealing all cracks and openings around drains is helpful. Some studies have reported mixed success with this control procedure. Facilities with concrete block walls offer many, many avenues for radon entry. Sealing the block walls and ventilating the cavities have cut radon levels up to 90 percent.
In residences, mechanical ventilation of crawl spaces has proved to be very effective. Using fans to draw soil gas from beneath a slab in sub-slab ventilation has been shown to be 50 to 90 percent effective in reducing radon levels. In situations where a basement is fairly tight, pressurizing the basement can be effective. This relatively simple and inexpensive process has reduced radon concentrations 65-95 percent below radon concentration guidelines. As an alternative, increasing ventilation at the first floor level with exhaust out of the basement, as conducted by Wellford in his Pennsylvania study, proved to be effective.
General non-specific increased ventilation is frequently recommended in the literature as a way to reduce indoor radon concentrations. Repeated studies have found no correlation between radon concentrations and air exchange rates. In other words, just increasing air exchange rates in general may not work. Ventilation must be applied in a specific fashion to be effective as a control.
Several states require that those who engage in, or profess to engage in, testing for radon gas or the abatement of radon gas be certified or licensed. The state public health, radiation protection office or environmental agency can provide information as to whether such credentials are required; and , if so, provide lists of those who meet the requirements. The EPA's Radon Measurement Proficiency Report, which lists firms and laboratories that have demonstrated their ability to accurately measure radon in homes, may be available from the state. The state agency can usually provide guidance regarding the possibility of radon contamination and effective treatment in a particular geographical area.
The state can also offer counsel on the availability of effective detection devices and /or services.
Particles are the easiest contaminants to remove from the air stream. Media filters and electrostatic air cleaners are available for use in building HVAC systems. While more expensive to install and operate, high efficiency extended media filters, high efficiency particulate arrestor (HEPA) filters and electrostatic precipitators can remove respirable particulates from the air stream very efficiently.
Appropriate maintenance with scheduled cleaning and replacement of filters is essential. (For further information, see the section devoted to filtration.)
Volatile Organic Compounds (VOCs)
High concentrations of VOCs whether odorous or irritating are best controlled by dilution and , thus, increased ventilation is frequently used to reduce concentrations. Janssen, chairman of the ASHRAE committee that developed the original Standard 62-1989, indicated an effort to control these potentially harmful gases prompted the increase move from 5 cfm/person to 15 and 20 cfm/person.
Since increased ventilation is costly and marginally effective, source control tactics are the more cost effective especially with odor problems. For example, selective purchasing of construction materials, furnishings, maintenance and operational materials can avoid or reduce levels of VOC emissions. Metal shelving, equipment, appliances with a powder coated finish, rather than the conventional painted surface, offer essentially no off-gassing.
Materials, such as custodial cleaning materials, should be stored in well-ventilated places away from occupied areas and definitely not the mechanical rooms or closets that are in the return air pathway.
Time of use can be a key factor. Floor wax, for example, has a very high initial emission factor, which is followed by low-level steady state emissions. EPA research has shown floor wax emissions drop from 10,000 µg/cm2 to about 500 µg/cm2 in about an hour, and fall below 10 µg/cm2 in 10 hours. Purposeful activities such as pest control should be scheduled during non-occupied periods to lessen the risk of occupant exposure to harsh and potentially harmful chemicals.
Direct exhaust or additional ventilation should be used for activities known to have high VOC emissions, such as painting and varnishing. These activities should be conducted away from occupied zones whenever possible just as these activities should be restricted to periods of building operation when occupants are not present.
Because VOCs are usually present in relatively large initial concentrations, gas phase filtration is not normally a cost effective control mechanism. However, when used in conjunction with outdoor air purging techniques, excellent results has been demonstrated that are cost effective. Milam reported to an AIA Healthy Building Symposium dramatic reductions of TVOCs when employing gas phase filtration in combination with continuous flushing through the first six weeks of occupancy. The continuous 24 hr. flushing process reduced peak concentrations from over 12,000 micrograms per cubic meter, to an equilibrium target of less than 500µg. The facility has been monitored for over 10 years and low stable VOC concentrations have been maintained.
Tbl 2 offers a brief summary of primary control techniques for the major contaminants.
Tbl 2. Summary of Control Techniques by Contaminants/Sources
CONTAMINANT SOURCES CONTROL TECHNIQUES
Asbestos Furnace, pipe, wall ceiling insulation
1. Enclose; shield fireproofing, acoustical and floor tiles
2. Encapsulate; seal
4. Label ACM
5. Use precautions against breathing when disturbed
Bioaerosols/Mold Wet insulation, carpet, ceiling tile, Use effective filters to avoid build up of nutrients. Check and clean any wall coverings, furniture, air conditioners, areas with standing water. Be sure condensate pans drain and are clean. Tre
and cooling coils. People, pets, plants, with algicides. Maintain humidifiers and dehumidifiers, cooling towers, drip pans at
insects, and soil. Construction dehumidifiers. Check and clean duct linings.
components—wood and paper. Keep surfaces clean and dry. Remove visible mold.
Carbon Monoxide (CO) Vehicle exhaust, esp. attached garages; Check and repair furnaces, flues, heating furnaces; contaminated outdoor air. garage does not enter air intake. Avoid unvented kerosene heaters and exchangers, etc. for leaks. Use only vented gas appliances; tobacco smoke; malfunction- combustion appliances. Be sure exhaust from negative pressurization. Shut down outdoor air during bad peak periods.
Combustion Products Incomplete combustion process Use vented appliances and heaters. Avoid air
(NOx and CO) from loading docks and garages entering air intake. Check HVAC for leaks regularly, repair promptly. Filter particulates. Selective gaseous filtration. Avoid boiler exhaust.
Environmental Tobacco Smoke Passive smoking; sidestream and Eliminate smoking; confine smokers to (ETS) mainstream smoke designated areas; or isolate smokers with direct outside exhaust. Increase ventilation. Filter contaminants.
Formaldehyde Building products: i.e., paneling,, materials Selective purchasing of materials with (HCHO) with lower particleboard, plywood urea- lower formaldehyde emissions. Barrier formaldehyde insulation as well as fabrics coatings and sealants. New construction and furnishings. commissioning. Ventilation. Specific gaseous filtration. Selective exhaust.
Radon Soil around basements and slab on grade Ventilate crawl spaces. Ventilate sub-slab. Seal cracks, holes around drain pipes. Positive pressure in tight basements.
NOTE—Increased ventilation does not necessarily reduce radon levels.
Volatile Organic Compounds Solvents in adhesives, cleaning agents, paints, Avoid use of solvents and pesticides indoors.
(VOCs) fabrics, tobacco smoke, linoleum, pesticides, If done, employ time of use isolation.
gasoline, photocopying materials, refrigerants, Localized exhaust near source when feasible.
building material Selective purchasing.
Rigid MSDS control.
Selective gaseous filtration.