Indoor Pollutants (1981)

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Id CONTROL OF INDOOR POLLUTION The quality of the environment in a building is inherently dependent on the design and operation of the building ' s environmental control system. Several factors that af feet the des ign and operation of control systems are identif fed in Chapter A, including human activities and geographic and building characteristics . Optimally, control systems are designed to maximize human comfort, and it is essential to know the acceptable ranges for environmental characteristics {comfort and air~qual~ty factors). Some constraints that must be imposed on control systems are related to cost and energy consumption. As a result of the application of these constraints, the goal of maximal comfort in usually compromised. The ranges of conditions within which control systems operate are usually based on codes and standards that have been developed and promulgated to protect the health and welfare of occupants. This chapter begins with a review of codes and standards that pertain to indoor pollution. Codes and standards have been developed as prescriptive guidelines based on consensus, but, as energy conservation and operating cost become more important, the need for evaluation of control-system performance increases . Cr iteria of system acceptability are also changing-codes and standards are becoming oriented more toward performance, and life-cycle costs are receiving more attention. Changes in the attitude toward environmental control present several cliff iculties . Feedback control for acceptable indoor air quality is recognized and needed, but the availability of reliable and inexpensive controllers is seriously limited. Performance-oriented standards ham not been widely accepted by contractors and enforcement officials, ~~:;suse of barriers in technology transfer and increased costs of implementation and liability. And economic decisions based on life-cycle Casting have not been accepted by contractors and building developers, who have resisted because of a lack of incentives, such as amortization periods and all:~*ance of pas"-through of operating costs, and because of the high cost of capital. Appendix B considers energy, environmental, and economic factors and presents a method for providing acceptable control of indoor air quality at acceptable costs of money and energy. 450

451 VENTILATION CODES AND STANDARDS .. Control of indoor environments in residential and commercial buildings to achieve what Is termed ~comfortable. or an ~acceptable. thermal quality requires approximately one-third of the total annual energy consumption in the United States.6S An additional 10% may be required to maintain conditions that are acceptable for occupants in industris1 facilities. Ventilation systems have been reported to require as much as 501 or 601 of the fatal enerav consumed in building. 5. SO 7 ~ ~ For energy conservation, rather arbitrary changes in building codes and standards are being proposed. Is Reduction of ventilation in residential, commercial, and industrial buildings could jeopardize the health, safety, or welfare of those who occupy them. Reduction of energy consumption is a necessary but insufficient step in the development of acceptable building energy management programs. Also required in the maintenance of environmental conditions that are not deleterious to the occupants Or harmful to property. These conditions include spatial, thermal, illumination, and acoustic qualities of the environment, as well as the gaseous and particulate qualities of the air. Ventilation is the historically and currently practical means of providing acceptable indoor air quality. To protect the health, safety, and welfare of the general public, building codes have been adopted and enforced by local, state, and federal government agencies. These codes generally specify minimal acceptable ventilation cr iter is to be maintained In the buildings . Note that Ventilation air, ~ as used here and elsewhere in this document, refers to outdoor air or recirculated, treated air. Compliance with building codes is usually the responsibility of licensed professional engineers and architects during design. Responsibility for compliance during operation often is vague, if specified at all. After a building has been designed and constructed, the owner or manager usually assumes responsibility for maintaining the quality of the indoor environment, and there is normally no official enforcement. State and local building codes are normally based, directly or with modification, on one of three model building codes published in the United States: The BOCA Basic Building Code ~ s ~ ~ of the Building Officials and Code Administrators International (BOCA); the Uniform Building Coder' of the International Conference of Building ort~czals (ICBO): and the Southern Building Code55 of the Southern Building Code Congress International, Inc. (S8CCI). Building codes are usually derived from standards that have been promulgated by authoritative bodies, such as the American National Standards Institute (ANSI), the National Fire Protection Association (NFPA), and the American Society for Testing and Materials (ASTM). Other organizations that publish standards for the building industry are the American Society of Heating, Refrigerating, and Air- Conditioning Engineers (ASHRAE), the American Society of Hechanica1 Engineers (ASME), the Illuminating Engineering Society (IES), the

452 American Concrete Institute (ACI), the Air Conditioning and Refrigeration Institute (ARI), and the Sheet Metal Contractors Association (SMACHA). (In preparing proposed procedures for listing voluntary standards bodies for federal agency support and participation, the Department of Commerce held discussion. with come 3 7 voluntary standards bodies. 62) Standards published by these organizations are usually developed by a consensus method and are known as .voluntary standarde. or ~consensua standards. 62 ,' Voluntary standards are usually adopt - , after periods of open review, as guidelines of recommended practice or minima performance criteria by which an organization may govern itself. However, a voluntary standard may become mandatory if it is adopted within legal document-, such as government standards or building codes. Standards also are developed in response to state or federal laws. These are known an Mandatory standards. ~ 2 ~ ~ and are promulgated in the form of state or federal regulations after they have been subjected to public hearings. Agencies responsible for the promulgation and enforcement of mandatory standards relevant to the building industry include the Department of Housing and Urban Development (BUD), the Department of Health and Human Services {D~S, formerly the Department of Health, Education, and Welfare, or DREW), and the Department of Energy (DOE). BACKGROUND By selecting the site, size, shape, and orientation of housing, man has nearly always take- advantage of natural ventilation for thermal and air~uality contra ventilation requirements in buildings have been specified since ice eighteenth century. The early history of the development of ventilation codes and standards has been reviewed by Nevins,.' Klaus et al.,32 and Arnold and O'Sheridan, Incest As shown in Figure IX-1, ventilation rates increased from 4 cfm/person in 1824 to 30 cfm/person in 1895. A minimal requirement of 30 cfm/person dominated design of ventilation systems during the first quarter of the twentieth century, as evidenced by the fact that in 1925 the codes of 22 states required a minimal ventilation rate of 30 cfm of outdoor air per person. 32 A major change :n ventilation standards resulted from experimen"1 work reported by Yaglou et al. '. in the 1930~. These studies recognized the importance of controlling indoor air quality, as well as ventilation-air quantity, and reported ventilation rates in cubic feet per minute per person required to provide ~odorfree. environments as functions of available air space per person. It should be noted that these ventilation rates were bared on the assumption that outdoor air of resin air ~ ~ was odorf tee. The Yaglola studies, conducted under controlled experimental conditions, have served as the primary reference in codes and standards for the last 40 yr . However, because of the cliff iculty in accurately estimating occupancy and the lack of feedback control methods for

453 30 O 25 co A: Al 20 LU z~ 1 5 o - ~S 10 by - _ - _ _ i,_ ASHVE R - tuirarmna r' 1 / Tred~old (t824) 0 1825 1850 1875 19~00 1925 1950 1975 1980 YEARS Accepted Rquiranen~ \ Subject to R~lustion ; - ;8 for ~ ASA Standard Yaglou (1938) ASHVE Requirement ASHRAE Standard 82-73 (1973} Current Revaluation FIGURE LY-1 Historical development of ASHRAE Standard 62-73 After Klauss et al.

454 ventilation, many codes and standards, including several now in e f feet, ~ ° ~ ~ 2 ~ ~ - 7 a have specif fed ventilation requirements as room-air changes per hour, rather than exchange rate per person. Theoretically, these or iter ia should be synonymous, but they are not . When ventilation rates are specif fed as room-air changes per hour, sensitivities to spatial dimensions and occupancy are lost. For example, 5 air changes per hour (ach) in a theater with a 20-ft (6.1-m) ceiling height and a sparse occupancy of 100 ft2 (9 .3 m2) of floor area per person would result in 161 cfm {79 L/s) per person, whereas the same room-air exchange rate and occupancy in a classroom with an 8-ft {2 . 4-m) ceiling would mean 67 cfm {32 L/~) per person. Bowever, at full-load occupancies of 10 ft2 (o.g m2) per person in the theater and 20 ft (1.9 m2 ~ per person in the classroom, 5 ach would result in 17 cfm (8 L/s ~ per person in the theater and 13 cfm ~ 6 L/s ~ per person in the classroom. Thus, at less than full-load occupancies, the ventilation rates per person would exceed the values shown in Figure ~X-2, whereas at full loads, the ventilation would be insufficient to provide ~odorfree. air. The inherent problems associated with specifying air changes per hou r have been recognized in some standards for several years . In 1 946, the Amer ican Standard Building Requirements for Light and Ventilation, AS3.1, was published by the American Standards Association (ASA) with primary criteria in cubic feet per minute per square foot of floor area. A A revision and update of A53.1 was published in 1973 by ASHRAE with primary criteria in cubic feet per minute per person. ~ The latter standard was adopted by the ANSI (formerly ASA) in 1977 and has been designated ANSI Standard B194 .1. For the f irst time in a ventilation standard, Standard 62-73 provided a quantitative def inition of Acceptable outdoor air ~ and specif fed conditions under which recirculated air could be used. Both minimal and recommended ventilation rates were specified in the ASHRAE standard to accommodate fuel economy (minimal values) or comfort in odorfree environments (recommended values). Energy savings at design surmer and winter conditions resulting from minimal ventilation rates specified in Standard 62-73 have been estimated to range f rom 27 to 81% for various occupied spaces, compared with rates in Standard A53.1. 'I In response to demands for energy-ef f icient buildings, ASHRAE developed a new standard, which was published in 1975: Standard 90-7S, Energy Conservation in flew Building Design. ' Through a contract with DOE, the National Conference of States on Building Codes and Standards, Inc. (NCSB0S), undertook, with the three n~odel-code groups recognized in the United States, to write a model Code for Berry Conservation in New Building Construction. ~, This roodel code was based on ASlIRAE Standard 90-75 and is generally considered to be its codified counterpart. By 1980, legislation either had been parsed or was being considered by 45 states for energy-conservation regulations based on these two documents. ~ ASHRAE Standard 90-75 was expected to reduce energy requirements in new buildings by 15-60%, 12 but efforts to promulgate the standard resulted in a conflict with Standard 62-73. Standard 90-75 stated that the ~minimum. column in Standard 62-73 for each type of occupancy

455 30 - z ° 25 - :~: - ~ 20 cat go to - 15 10 s _ _ _ _ O l I 0 100 \ \ Theater \ ~ \.o~ ~0', occupancy - 10 f t2tperson . classroom occupancy 2 - 20 ft /person MI N I MUM YENTI LATION FOR ODOR-EREE SPACE AStlYE RECOMMENDATIONS (1936) ~0z i; AVERAGE SOCIOECONOMIC STATUS 200 3iO0 400 500 AIR SPACE PER PERSON ( ft3) FIGURE IX-2 ventilation rates resulting f ram the Yaglou studies .

456 .shall. be used for design purposes. This statement in Standard 90-75 effectively deleted the Oregon mended. column in Standard 62-73 and caused serious concern regarding the possibility of insufficient ventilation in new buildings. For example, when smoking was allowed in a room ventilated at the minimal rate of 5 cfm ~ 2 .4 L/s ~ per person, the carbon monoxide concentrations approached the limits specified by the EPA primary ambient-air quality standards, and particle concentrations exceeded the proposed limits by a factor of 30-60. i2 .. There is still controversy about what are acceptable concentrations of pollutants and ventilation rates. In January 1981. ASERAE adopted Standard 62-1981' in an effort to resolve some of the problems with Standard 90-75 and to reflect newer design requirements, equipment, systems, and instruments. A comparison of the newly revised Standard 62-1981, Standard 62-73, and the obsolete Standard A53.1 is shown in Table IX-1. Several major revisions have been made in an effort to resolve the apparent conflict between operating ventilation control systems for energy savings and operating them for protection of the health and comfort of the occupants. · The quality of outdoor air to be used for dilution and control of indoor air pollution has been defined, not only in terms of the EPA pr imary standards, but also in terms of other recognized guidelines and professional judgment. · values for minimal and recommended ventilation rates have been replaced with required values for smoking and nonsmoking areas. Nonsmoking areas have proposed values similar to the existing minimal values, and those for smoking areas are similar to or greater than the values currently recommended . · A method has been specified that will determine the amount of recirculation air required to compensate for allowable reductions in outdoor air. The amount is determined as a function of air-cleaner e f f iciency . · The operation of mechanical ventilation system during periods of occupancy is specified as a function of the source of indoor pollutants . · An alternative method specifies both objective and subjective criteria for indoor air~quality, but the method of achieving control is left to -fine discretion of the operator. With the advent of performance criteria for indoor pollutant control, conflicts between various codes and standards could became more intensive. IMPLEMENTATION OF CODES AND STANDARDS Ventilation codes and standards have been published by several agencies and organizations. As ~ result, the designer or operator of a system has the responsibility of reviewing the relevant documents and then deciding which of them apply. In many canes, the values in these codes and standards will not be consistent. Thus, it can prceent a

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458 challenge to the building designer and operator to select a ventilation rate that will meet the requirements of all relevant codes and standards. Under these circumstances, the usual procedure has been to select the largest value that would satisfy the requirements of all the codes and standards. Because of recent concerns regarding energy consumption and costs, some regulations have been promulgated or proposed that are in direct conflict with those promulgated to protect the health or comfort of occupants; an example is the 1977 Assembly Bill 983 of Wisconsin, Ventilation Requirements for Public Buildings and Places of Emplownent. Bill 983 would have eliminated mandatory minimal ventilation requirements specified in the state building code (i.e., 5 cfm per person} during the period October 1 to April 1 of each year. Building owners would have been allowed to close or otherwise regulate outside-air intakes to conserve energy during these periods. Bill 983 was passed by the 1977 General Assembly and vetoed by the governor; the veto was overridden by the Senate and sustained by the Mouse. This legislation was reintroduced as a rider to an appropriations bill in the 1979 General Assembly . I t was later amended to allow reduced ventilation only through adminstrative action; in that form, it passed . The state Department of Industry, Labor and Human Relations, previously responsible for ventilation requirements, will administer the law. A summary of the most commonly cited ventilation codes and standards is shown in Table IX-2. Several model codes and ASHRAE Standard 62-73 may be applied to each of the nine functional categories of buildings listed in Table IX-2.S° Other voluntary and mandatory standards are shown as they apply to particular functions. It should also be noted that the NCSBCS model Code for Energy Conservation in New Building Construction was developed with the three model-code groups and applies to all functional categories. I' This model code specif ies ventilation rates for energy calculations as the minimal values in Standard 62-73 0 The ASHRAE standard, in turn, defers to other standards or codes when they have precedence and require higher ventilation rates. Domicile" - As indicated in Table IX-2 ~ the two primary sources for ventilation requirements are ASHRAE standards ~ ~ and the HUD Minimum Property Standards IMPS) . ~ ~ ~ ' ~ Both nets of standard" are considered voluntary, but may become mandatory under 'specific conditions--Standard 62-73 when adopted as part of a state energy code, and the MPS if housing is financed through the Federal Housing Administration (E~A). Ventilation rates for various spaces throughout private dwelling places are specif fed in Standard 62-73 as 5-20 cfm/per~on {minimum) and 7-50 cfm/person (recommended). The higher rates are for bathrooms and kitchens and are for intermittent operation. The MPS also set intermittent exhaust rates in kitchens and baths at 15 and 8 ach, respectively. The 1979 revisions of the MPS allow ventilation by

459 TABLE LX-2 Sources of Ventilation Codes and S&candards for Occupied Spaces Buil di ng-Funct ion Cat egory - Domictle: place of residence, such as a single-family dwell- ing, multifamily dwelling, public housing, rowhouse, apartment, or con- domi nium Educat tonal: but ld- ing used f or class- rooms or instruction Laboratory: building - used predominantly for research and diagnostic work, and not necessarily for instruction Medical: building used for health-care facilities, such hospital, clinic, medical center, sani- tarium, day nursery, infirmary, orphanage, nursing home, or mental-health institu- tion Voluntary Standards ASHRAE6 ~ 9 MPS 490069 MPS 4 9107 ° ASHRAE 6 ~ 9 I IAR guide jade 2 Mu ASHRAE ASHRAE6, 9 MPS 49207 Office: such buildings ASHRAE6'9 as used for offices, Civil administration. Or radio or tele- vision station Public assembly: build- - ASHRAE6'9 ing where groups can meet for such f unc- tions as theater, restaurant, cafeteria, retail store, art gallery, museum, bank, pos t of f ice, court- house, assembly hall church, dance hall, coliseum, passenger terminal, or library Mandatory Standards l 9 CFR 1.1, 197974 29 CFR 1910, 197972 H~ 79-1450068 Model Buildlug Codes BOCig UBC SBCCI 55 NCSBCS17 B()C2~15 ~ 16 ItBC 9 SBCCI55 NCSBCS 17 ~9 UBC SBCCI55 NCSBCS1 7 BoC~15 ~ 16 use 9 SBCC155 NCSBCS17 ~,oC,15, 16 UBC SBCCI55 NCSBCSi7 15,16 Usc SBCCISS NCSBCS17

460 liable IX-2 (coned ) But l di ~-Funct ion Category - Rehabilltation: non- . healt in-care bu ildi ng used for instruction, but not of the regi- n~ented classroom type; pertains more to read just~nt, such as jail ~ prison, refo rmo story, or half-way houses Warehouse: but 1 di ng used for storage of materials and sup- plles, such as stor- age facility, msin- tenance faclli ty, garage, airplane hangar, or bus barn Industrial: such . buildings as factories, assembly plants, foundries, mills, power plants, eelephone-exchange facllitie~, water and waste~water treatment plants, solid-refuse plants, zoos, greens houses, aviaries, arboreta - , or others requiring environ- mental control for process control Voluntary Standards ASHRAE ~ 9 ' ASHRAE 6, 9 ASH~69 9 Handatory Standards os~72 osHA72 Model Building Codes BoCtI5,16 UBC SBCCI55 NCSBCS17 SOCKS 5,16 UBC SBCCI55 NCSBCS17 BoC,15, 16 UBC SBCCI 55 NCSBCSl 7

461 infiltration rates of 0.5 ach and natural ventilation through operable windows, which must have a total area of at least one-twentteth of the floor area of the room. ANSI/ASaRAE Standard 62-1981 specifies 10 cfe (5 L/~) per room for spaces other than bathrooms and kitchens, for which values are set at 50 and 100 cfm {24 and 47 L/~} per room, respectively. Although the ventilation rates are specified differently in these voluntary standards, the results are intended to be equivalent. Moreover, the 1979 revisions to the t'PS and the values in Standard 62-1981 are in close agreement with values recommended internationally. 23 IS Educational Facilities The mechanical-ventilation rate for classrooms is specif fed in Standard 62-73 and in the model codes as a minimum of 5 cfm/per son for a full-load occupancy of 20 f t2/per son . However, the minimal supply-air rate (i.e., ventilation plus recirculation) is specified as 10 cfm/per~on in Standard 62-73 and 15 cfm/person in the model codes. Natural ventilation is specified in the model codes as that obtainable through operable windows with areas one-twentiett~ of the floor areas; Standard 62-73 specifies minimal and recommended natural-ventilation rates of 10 and 10-15 cfm/person, respectively. Standard 62-1981 specifies required ventilation rates of 5 cfm (2.5 L/~) and 25 cfm (12 . S L/s ~ per person for nonsmoking and smoking areas, respectively, in classrooms. Laborator id Specific controls for ventilation in laboratory spaces are required for protection of the health and comfort of laboratory personnel and for the preservation of specimens and critical experimentation conducted in the facilities. A differential in air pressure may be required between laboratory areas and public spaces, such a. meeting rooms and reception areas, to protect the general public. Thus, the nature of ventilation control is more complex in these facilities than in mos t other indoor environments . Toxic and hazardous materials used in the laboratory must be controlled to within the limits prescribed by OSEA.72 Control may be by isolation or enclosure of the pollutants, dilution, or air~cleaning, but OSHA does not mandate a particular control method. This type of standard has become known as ~ performance standard. ~ Indoor areas in which substances suspected of being carcinogenic are used or where recombinant-DNA research i8 conducted must be kept under negative static pressure relative to the surrounding areas. 6' 72 Local exhaust and clean makeup air Lay be used for pressure control, but the exhaust must be decontaminated before discharge. Also, ~experiments,. procedures, and equipment that could produce aerosols must be confined to laboratory hoods or glove boxes. 72

462 When laboratory animals are used in experiments, their care and well-being must also be maintained. The Animal Welfare Act74 specifies many procedures for the care and handling of the animals, but is vague and nonspecific about environmental control in the laboratory or the cage. .. The standards published by the Institute of Laboratory Animal Resources ~ VICARS of the National Research Council are somewhat more specific in ~recommending. ventilation rates. However, these standards often require 10-20 ach with 100% outside air, which is energy-intensive, and the use of 100% outside air may have little or no impact in the cage microenvironment. ·2 ASHRAE Standard 62-73 specif ies 15 cfm/person as minimal and 20-25 cfm/person as recommended ventilation rates for spaces without animals. With animals, the minimal rate is 40 cfm/person and the recommended rate is 45-50 cfm/per~on. These outdoor-air requirements may be reduced by two-thirds for mechanical ventilation systems with adequate particle filtration. Standard 62-1981 specifies ~ required ventilation rate of 10 cfm (5 L/s) per person for nonsmoking areas and recognizes that other standards may override this rate.' Medical Facilities Ventilation and control of biologic contamination in medical facilities, especially in some hospital treatment areas, have been the subject of much research since the middle of the nineteenth century. 13 36 The Health Resource Administration (HRA) publishes requirements`' that must be maintained if federal funds (i.e., Hill-Burt~n funds) are used for new construction or major modifications. Since 1969, these regulations have allowed recirculation in sensitive areas, such as operating rooms. However, changes have occurred in the specif fed number of air changes per hour of supply air and the percentage of outside air. 13 Currently ERA allows recirculation of air in all areas of hospitals, with the following restrictions: " · In sensitive areas, 'such as opera~cing rooms, two air f liters are required--a prefilter and a final filter, rated at 25% and 90% efficiency, respectively, according to ASERAE Standard S2-76.4 · Each space in which inhalation anesthetic agents are administered must be supplied with a separate scavenging system for exhausting waste anesthetic gases. · Appropriate air-pre"sure relationships must be maintained with respect to adjacent areas. Change" specified in the minimal requirements of construction and equipment for hospital and medical facilities.' allow reductions of up to 25% when specif ic rooms are unoccupied, provided that the specified pressure relationships are maintained when they are occupied. When thin feature is used, positive provisions, such as an electric interconnect between the ventilation system and room lights.

463 must be included, to ensure that the specified ventilation rates are a utomatically resumed when The rooms are reoccupied . Standard 62-73 specifies ventilation rate. for hospitals and n urs ing and convalescent homes in terms of minimal and recommended cubic feet per minute per person and allows reductions in the use of outdoor air to one-third of the -specified values when mechanical ventilation is used. Standard 62-1981 specifies required ventilation rates for patient rooms an 35 cfm (17 . 5 L/s ~ and 7 cfm (3 . ~ L/s ~ per bed for smoking and nonsmoking spaces, respectively. In other hospital areas, Standard 62-1981 values are per person for nonsmoking spaces and are similar to the minimal values previously specif led. As shown in Table IX-3, the ventilation and total air-supply rates specif fed in BRA 79-14500 are generally greater chart those specif fed in ASHRAE Standard 62-73 or 62-1981. 7t The ventilation rates specified in MPS 4920 ' ~ are primarily in terms of allowable inf titration rates and exhaust rates for kitchens and patient-room lavator ies . Other Nonindustr ial Spaces The ASHRAE standards ~ 9 are primary sources for ventilation rates for off ices, public-assembly buildings, and rehabilitation facilities. Currently, no other standards are generally used in the United States. In Standard 62-73, ventilation rates are specified as minimal and recommended rates per person with reductions in outdoor air of one-third of the specified values allowed for mechanical ventilation, if adequate filtration is provided. Standard 62-1981 specifies ventilation rates as required for smoking and nonsmoking areas with reductions in outdoor air allowed for mechanical ventilation as a function of filter efficiency. SUMMARY State and local building codes usually are based on one of the three model-code documents. These become legal documents when adopted by appropriate government agencies. The ventilation rates specified in the building codes are usually derived from standards, such as those published by ASHRAE. Traditionally, other mandatory standards have taken precedence over a building code when the values in standards exceeded those in the building code. However, model energy-connervation codes have been promulgated by the model-code groups, and there can now be conflicts in required ventilation rates between codes and mandatory standard". With the advent of indoor-pollutant criteria, the conflicts could become more extensive, because method" of pollution control that do not require the traditional ventilation rates may be used.

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465 RECOMMENDATIONS The general public is not aware of the distinction between ventilation control and indoor air~quality control. The techniques and terminology used in air~quality control and ventilation design, operation, and codes should be described in clear and consistent language. We recommend that professional and government organizations coordinate to establish a model code for indoor air quality that would meet health, energy, and economic criteria. Responsibility for enforcement of acceptable control of indoor air quality should be defined for various building categories. E:nforc~ent procedures should be considered with respect to building oonatruction and building operation. AIR DIF=SION COWL Air is supplied to ventilate an enclosed space (i.e., a room or group of rooms in a building} for two main reasons: · To maintain acceptable oxygen concentration and to dilute (and remove) carbon dioxide and other contaminants for safety of the occupants {and sometimes to provide a differential in sir pressure as required by building codes or standards ~ . Ventilation air flow rates are specified in codes and standards. ~ It should be noted that supplying the specified or mandated rates for ventilation does not guarantee adequate dilution or removal of contaminants if the air is not uniformly diffused throughout the occupied space. ' To provide a thermally controlled environment that is acceptable to the occupants. An acceptable thermal environment has been defined as one in which at least 809 of the occupants clothed normally and engaged in sedentary or near-sedentary activities would express thermal comfort, which is defined as That condition of mind which expresses--eatisfaction with the thermal environment.. s Depending on the activity and typical clothing of the occupants, the combination of---air temperature, mean radiant temperature, relative humidity, and air velocity must be appropriate for the occupants to feel comfortable (see Chapters IV and VII) . 24 IS 52 Conventionally, air diffusion control has been designed and installed to meet the criteria for thermal comfort, with the assumption that the air~quality criteria will be met simultaneously. AI R DIFFUSION EQUTPMEtlT The supply air for ventilation is usually treated at ~ central location (i.e., filtered and conditioned for an appropriate dry-bulb and dew-point temperature! and then distributed by ~ duct 8y8t" to the intended space. The amount of air supplied to each space 18 controlled by the terminal units of the duct system.

466 Four types of terminal unite are only available:' grilles. slot diffusers, celling diffusers, and perforated ceilings Grilles, which can have different configurations (e.g., adjustable bar grilles, fixed bar grilles, stamped grilles, and variable-area grilles), are usually in a high sidewall position, in ~ perimeter installation, or in the ceiling. The air from ~ high sidewall position is thrown across the ceiling and drops toward the floor as it traverses the room. From a floor or sill grille, the air is directed vertically upward along the perimeter walls to which the airstream adheres, owing to tbe Coanda effect. (The Coanda effect can be defined as the ability of a jet to cling to a curved or deflected surface while increasing its mass flow rate along the flow path.20) When grilles are installed in the ceiling, curved vanes deflect the air along the ceiling so that the Coanda effect causes the airstream to follow a horizontal distribution. A slot diffuser is usually installed in long continuous lengths in several different locations similar to those described for grilles. Ceiling diffusers usually are series of rings or louvers (not necessarily circular} that direct the air~tream across the ceiling. In perforated ceilings, the air is contained in a supply plenum above the ceiling and delivered through holes or slots in the ceiling material. AIR DIFFUSION CRITERIA l The velocity of the air is important--if the appropriate velocity is exceeded, conditions can become drafty and thus uncomfortable. s' The force of the air supplied must be such that it stirs the air already in the space so that mixing is accomplished, to reduce the variance of air properties, both thermal and chemical, throughout the space. However, complete mixing of the air in the space is seldom achieved. In some cases, especially when there are high ceilings (i.e., commercial or institutional spaces), various zones can be identified as occupied and unoccupied spaces. There is little thermal and respiratory exchange between people and the air above head level, and the space between head level and the ceiling is called Unoccupied space.. Uniform mixing of the air is necessary for the comfort of those in the occupied 'space, but is not needed in unoccupied space. Because there may be incomplete mixing of the air in the unoccupied space, the chemical and thermal composition may be noticeably different from that of the occupied space. Nonuniform mixing may be caused by the type and location of the terminal units selected for the space or by such deficiencies as: · Direct air flow from the terminal supply unit tO the exhaust or return air grilles that bypasses a part (or most) of the occupied space. ~ ~ · An air circulation pattern that causes secondary air currents where the supplied air does not have sufficient force to cause complete mixing, thus leading to air stratification within the enclosure.

467 Mathematical models to determine the effective mixing rate that occurs in a space bave been proposed, but extensive research is still needed to obtain reliable methods to quantify mixing. 33 .. ·2 l' When mixing in an occupied space is nonuniform, comfortable conditions cannot be ensured for the occupants in the stagnant (secondary flow) zones. To minimize nonuniform mixing, the loca~cion, type, and size of the terminal units must be selected correctly. There are very few definite criteria to make this selection for a particular application, but the concept of air~diffu~ion performance index (ADPI) .. is commonly used to characterize a terminal unit. The ADPI is based on subjective responses to drafts. The effective draft temperature (~) is determined from the loce1 velocity (Vx), in feet per minute, and the difference in dry-bulb temperature, in degrees Fahrenheit, between the local point (tx) and the control temperature (tc): ~ ~ (tx ~ tog - 0.07 - 301. The ADPI is the percentage of the total number of measured points that have effective draft temperatures of -3.0 to +2.0°F and local velocities of 70 ft/min or less (see Figure IX-31. ADPI values have been experimentally calculated for typical applications of terminal units as a function of the airflow characteristics from the units and the thermal loads of the spaces {see Tables IX-4, IX-5, and TX-6 and Figure ~X-43. From the values listed in Table IX-4, types and sizes of terminal units can be selected to provide acceptable mixing in the occupied space. The ADPI, although practical, may not yield the best selection in all cases. Several points should be considered: · The location of the exhaust outlet influences air movement only in a small zone near the outlet itself . Thus, the ADPI does not depend on the location of the exhaust outlet. 43 However, there are studies ~ s ~ ' that have shown that different locations of the supply and exhaust units cause different patterns of airflow, some of which may be unstable and some unacceptable for thermal comfort. · Airflow patterns are different during heating and cooling cycles . Commonly, the same terminal unite are used for both situations. Thus, the cool air from a ceiling diffuser would drop into the occupied space, but hot air supplied by the same terminal mixes to provide thermal comfort of the occupants. However, the ceiling location may not be appropriate for a heating situation, inasmuch as the hot air supplied by the ceiling diffuser would tend to stay near the ceiling, owing to buoyancy; this results in air stratif ication near the floor. A similar situation may occur when the terminal units are placed low in the occupied space; the hot-air supply tends to rise and affect the whole room, whereas the cold-air supply tends to stay low, thus poss ibly caus ing development of a stagnant layer near the ceiling . Therefore, for spaces where both heating and cooling are needed, care should be taken to ensure that the terminal unit will have an appropr late ADPI in both Situations . · Calculation of an ADPI assumes that steady conditions exist and that the room has no airflow obstructions. Some attempts }Zaire been made to study the effects of obstructions in the Scrupled space, ~ ~

468 80 \ c I_ E 60 - C~ O 40 > ILL ~ 20 x _ _ ~ ,, it, / A/ Z1 / / / A/ i/ / / / / / I ~ -6 ~ -2 0 2 4 DRAFT TEt~llPERATURE Dl Ff ERENCE (tX - tC),°F FIGURE IX-3 Comfort criteria used to evaluate the airs dif fusion perf ormance index (ADPI ~ . = ~ . _ SPREAD — \ OR 0P V£RTI=L CROW SE=ION \ - SPREAD _ t job' TERMINAL VE LOCKET ENVELOPE ANGLE Of DISCHARGE \~ Plow' VIEW FIGURE {X-4 Airstream characteristics. permission from Nevinn. 43 Reprinted with

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470 TABLE IX-5 Definitions of Airstream Characteristics Throw: Horizontal distance measured from plane of supply diffuser to farthest point of airstream center line at which airstream velocity equals selected velocity, i.e., terminal velocity (T50 if terminal velocity is 50 ppm or Tloo if terminal velocity is 100 f pm) . Spread: Divergence of airstream in horizntal or vertical plane. Drop: Dif fuser Type - High-sidewal1 grille Circular ceiling diffuser Sill gr ille Ceiling slot di f fuser Light troffer diffusers Perforated, louvered celling dif fusers aReprlnted with permission from Nevins.43 Vertical distance between center line of terminal unit and point to which throw is measured. TABLE IX-6 Characteristic Dimensions for Different Air Diffusers a Characteristic Length Distance to wall perpendicular to jet Distance to closest wall or intersecting air jet Length of room in direction of jet f low Distance to wall or midplane between out- lets Distance to midplane between outlets plus distance f ram ceiling to top of occupied zone Distance to wall or midplane between out- lets

471 but more research is needed to analyze the effects better. Moreover, actual conditions in the occupied space (i.e., normal working conditions} may be very different from those predicted by the ADPI method, because the obstructions, people, and appliances in the space may cause a different air pattern. · ADPI relater comfort to local air temperature and local air velocity as they deviate from a ~etpoint suitable for providing thermally comfortable conditions. This setpoint must be established by other methods, such as percentage of people dissatisfied (PPD}, 24 MU thermal sensation index, 52 and standard effective temperature (SEA) . 2S All these methods determine the proper combination of ambient air temperature, relative humidity, mean radiant temperature, and air velocity that must exist in the room as a function of the occupants ' activity and clothing. CONCLUSIONS Currently, air-diffusion systems are designed for two main purposes: to supply ventilation air according to type of room and intended use, as required by codes; and to locate supply-air terminal units and def ine setpoints on the basis of occupant comfort, which depends on thermal factors. RECOMMENDATIONS Interactions between thermal factors and mass factors (i.e., concentrations of water vapor, odors, and other gaseous contaminants and suspended particles) that influence the comfort or health of occupants must be studied, and the results must be incorporated into the design procedure. The measurement of air quality in a space is still quite difficult. 26 It is recommended that research be conducted to provide design guidelines for the selection and placement of air-supply and -return units that will ensure both the mass air quality and the thermal air quality required in a space under conditions of use. AIR CLEANING EQOIYME:N~ The pr inc iples that govern the process of cleaning a ir to improve its quality for use indoors are similar to those for industrial processes to remove effluent gases before discharging exhaust air to the atmosphere. However, these processes and the equipment involved to process air for ventilation are radically different from their industr ial counterparts .

472 LOCATION OF I~R-AIR COWS l As shown schematically in Figure IX-5, the location of sir-cleaning equipment in a ventilation system will vary with the type of ~y8~ and its application. (Strategies for control of indoor pollutants are discussed in the final section of this chapter. ~ First, if the concentrations of contaminants in outdoor air are unecceptable, the outdoor air must be cleaned. Second, recirculated air from occupied spaces must be cleaned to achieve the Awe quality as specified for the outdoor air used for ventilation. Third, special ventilation systems, such as fume hoods, nay use air~cleaners in the supply and exhaust airstreams. TYPES OF AIR-CLEANERS An air-cleaner capable of controlling particulate, vaporous, and gaseous contaminants does not exist. Filters and electronic cleaners are used to remove airborne particles from ventilation air; and commercial and institutional facilities may use wet collectors. Viable biologic particles are usually removed by special filters, electronic air-cleaners, or wet collectors; in some cases, ultraviolet (W} lamps may be used to inactivate the viable contaminants. It should be noted that W radiation is used to kill bacteria, but not to remove them from the airstream. Filters and electronic air-cleaners are not effective for removing gases or vapors. Sorption devices are usually selectee to remove these contaminants from the airetream. If both particles and gases or vapors must be removed, air-cleaners first remove the particles, then the gases or vapors. In Some critical applications, such as hospital operating rooms, a ~final. filter may be required to remove residues Or particles sloughed from the gas-re~oval devices..' Devices for Particle Removal . Airborne particles are commonly removed by mechanical filter units that Bee one or a combination of the following mechanism: 22 . · Inertial impingement {impaction): An abrupt change in direction of the airatream causes airborne particles to collide with the filter fiber. This method of collection is most effective with larger particles. · Interception: This method of collection is ~ special case of impingement in which a particle collides with a fiber, independently of inertia. This method nay be more effective than impingement at low velocities. · S training: Airborne particles are captured as they attempt to pass between two adjacent fiber-. · Diffusion: Very small airborne particles are driven to the filter fiber by random molecular bombardment by air molecules e This method is most effective for the Tallest particles e

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474 The relationship between filter efficiency and particle size is shown in Figure ~X-6. The effectiveness of diffusion is greater for smaller particles, whereas the effectiveness of impingement, interception, and straining is greater for larger particles. Thus, a characteristic performance curve, similar to the upper curve in Figure IX-6, shows a minimal effectiveness of a f ilter to remove a given particle size. 2 ~ The performance of a mechanical f liter is usually expressed in terms of its particle removal eff iciency, its loading capacity, and its resistance to air flow.28 Removal efficiency may be expressed as a function of the mass, physical or aerodynamic size (e.g., Stokes diameter), or number of particles removed. 28 S. A relationship among these efficiencies can be expressed mathematically but the filters must be tested to express the appropriate efficiencies numerically. Although many test methods for evaluating f ilter ef f iciencies have been published, I' 3. S. those generally accepted for indoor environments in the United States are ASHRAE Standard 52-76 for mass and size efficiencies. and MIL Standard 282 for number efficiency. 'I A method for rating the loading ~ i . e ., dust-holding ~ capacity is also specified in ASHRAE Standard 52-76. Both standards result in single value ratings. MIL Standard 282 specif ies a means for rating the efficiency of DOP (dioctylphthalate) produced by a special generator i-n removing O . 3-mn particles . ASHRAE Standard 52-76 ~pecif ies a means for rating the size removal ef f iciency of a f liter challenged with a standardized ~aunospheric dust. ~ A Weight arrestance. (i.e., mass removal eff iciency) procedure specified in ASlIRAE Standard 52-76 results in a s ingle value rating for a f ilter challenged with a Synthetic dust. ~ This dust is used to rate the dust-holding capacity of a filter (i.e., the amount of dust a filter can retain before a specified pressue drop is reached). A major shortcoming of these standards is the lack of def ined procedures to rate mass, size, and particle removal eff iciencies as functions of particle size. The other character istics necessary to rate the performance of mechanical jeers are the air flow rate at which the efficiencies are determined ~ .. the air pressure drops imposed by the f liter when it is clean and when it is fully loaded. Both standards specify procedures for determining these characteristics. Characteristics for several types of mechanical filters are summarized in Table IX-7. Mechanical f liters are used for three kinds of applications in which the three types of removal efficiencies are required: · Filte_ ~ used to remove the largest and heavies t particles f rom an airstream are usually rated by weight efficiency (see Table ~X-71. They are often described as low-eff~ciency filters and are used as upstream prefiltere to remove some of the load before the final filters' or to protect such mechanical devices as fans and heat-exchangers. Probably the most con Ron use for thin type of f ilter is in residential furnaces and central air-conditioning system. · Medium-ef f iciency f ilter", usually rated by ~ ize or dust-spot efficiency,. are used when smaller particles must be removed from the air. They are more expensive than low-efficiency filters. They are

475 100 10 Cal at lo - C~ ~ t J o MU J - 6 o,ot 0.1 _ 0.001 _ 0.0001 0.001 1 / ~ O - ran Perforn - nce ~ coot/ Is, ~2~/ / ~ ~ 0,._ O~/ ~ _ , 0.01 0.1 PARTICLE SIZE,,um 10 FIGURE DY-6 Filter efficiency as a functioylof particle size tor a typical impingement filter. Adapted from Crawford.

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477 often used with prefilters to extend their useful lives. They are also specified for sensitive areas in hospitals" and are used for removal of tobacco smoke or for protection of materials from soiling. · High-efficiency particulate air {HEPA) filters are rated by number efficiency " and are used when ~absolute. filtration in required. These f liters were originally developed for industrial applications and are generally used in nuclear reactor facilities and for cleanroom applications. HERA filter. are expensive and are therefore normally protected by pref ilters . Medical facilities use them in isolation wards, pharmacies, and surgical suites. KNAPP- 51 73) In these areas, it is often necessary to test the filters after installation. Test procedures developed for some of these applications are available in the literature. KNAPP- 193-213) Small HERA filters have recently been used to create Clean-air zones,. especially about the heads of allergic persons during sleep. Air is drawn through the filters and distributed from headboard emission ports as a discrete laminar-flow field. 8' Claims of removal of various inhalant allergic substances and reduction in associated problems have been ~de; however, the effect on removal of biogenic particles r equines more study. It should be noted that mechanical filters are effective only when the particles remain airborne in the ventilation system, and particles f rom an occupied space must be transported to a f il~cer in the system (Figure IX-51. Particles that have settled are a residual source of contamination if re-entrained. In removal or cleaning of filters, care must be exercised to minimize re-entrainment and exposure of maintenance personnel. Electrostatic precipitators are also commonly used to remove airborne particles. The precipitation process consists of providing an electric charge on the particle, establishing an electric field, and removing the particle from the precipitator. .~(P. 192} Electrostatic precipitators, used for outdoor pollution control, typically are of single-stage design and use a high direct-current (d-c) voltage (20-100 kV) to produce a negative corona {see Figure TX-71. The corona generated provides the necessary charge to particles f or the elects ic f ield to cause them to dr if t to the collecting electrodes . Electrostatic precipitators, which are used only for cleaning ventilation air, are designated as Electronic air-cleaners. Three types of electronic air-cleaners are commonly used for control of particulate matter in residential and commercial environments: · Ionizing-plate typo: These devices are typically of the two-stage design, as shown in Figure IX-8. A high d-C voltage (e.g., 12 kV) produces a positive charge on the airborne dust, which is Men precipitated on the collection plates. The positively charged corona is less effective as a particle-collector than the negatively charged, but produces much less ozone.

478 High Vol Cage dc power supply (20-100 kY)! Col lection Electrodes (Pipe) 1 _ - Gas Flow E1 ectri Cal consul ator ~ I ~ ~ Gas Flow .H _ Discharge Electrode (wire) Lion Path and path of charged dust particles ~ ;, ~ . ~- O~Z weight Collected Dust Single Stage FIGURE L1-7 Schematic of a 8iDgle-8tage tyire and pipe ) electrostatic precipitator. After Oglesby a" Nichols.

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480 Charged-media, nonionizins ty=: A dielectric filtering medium (e.g., '3lass-fiber mat or cellulose mat) is supported on or in contact with an alternately charged and grounded gridwork (e.g., +12 kit d-c) . Airborne particles are polarized in the resulting f ield and electromagnetically attracted to the f ilaments of the f ilter . · Charged-media, ionizing the: Airborne particles are charged by positive ions from a discharge electrode. The charged particles are then collected on a charged filter mat downstream from the ionizer. The performance of electrostatic precipitators is often evaluated in terms of the Deutach equation:.' ~ ~ 1 - expl-Aw/Ql, where n ~ particle removal efficiency, A ~ ares of collecting surface (m2), Q ~ gas volume flow rate {~3/~), and w - migration velocity of particle (m/~. This equation can only approximate the actual removal efficiency. Manufacturers often publish performance data on removal efficiency, particle size, and an empirically derived migration velocity (called precipitation rate parameter,. wp}~(P. 211) Unlike the migration velocity (w), the parameter w includes effects due to rapping losses ~ i.e., for industris1 precipitatora), gas flow distribution within the precipitator, particle size distribution, and dust resistivity..~(P 244) ~ ~r4F~^ ~^ ~~- · -~i-~1 electrostatic precipitator is shown in Figure TX-9. Conversely, the performance of electronic air-cleaners is not ~ ~~_~- - ~~~ ~—~ ~ -`r^~~ usually rated in terms of the Deutsch equation, but rather in terms of dust--pot efficiency. or the DOP method." Their performance compares favorably with that of medium- to high~efficiency mechanical air filters, and their major advantage is the low resistance to air flow, compared with that of mechanical filters. However, this low resistance can be a disadvantage, if they are not installed so that there is uniform air velocity at the entrance of the cleaner. As shown in Table ~X-8, cc~mpromises are often required with respect to removal efficiency, pressure drop, and space limitation when selecting electronic air-cleaners. E1= ctronic air-cleaners are often used for the same applications as described for medium-c ff iciency and BEPA f ilters and normally require the six;; type of prefiltering as mediums to high-efficiency mechanical f ilte,^ to remove larger particles. Special care is needed in serv:~;~ng, and any of three method. is acceptable: . Removal of collection plates or charged media, washing with a detergent, and drying before reinstallation. This method is most common for residential units and small commercial applications. · Washing of collecting plates in place with an integre1 washer. This method is commonly used in larger commercial installations . · Collection of dry agglomerates dislodged from the collection plates. An automatic replaceable-medium f ilter is usually used for this purpose in large and small commercial installations (see Figure ~X-81.

481 100 >,` 50 it - c' - ~L Let o - Lo J J o Cat to 1 _ 1 1 1 3 4 5 O t 2 PARTICLE DIAMETER, Am 6 FIGURE X-9 Typical removal efficiency of electronic air-cleaner. After ASHORE.

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483 There are some problems to be considered with electronic air-cleaners. There is a potential hazard associated with the high voltage at the ionizing electrode, collection plates and charged media; ~ ozone can be produced by the high voltage, even with the positive corona; AMP- 196) s. and soiling can be caused by charged dust particles that penetrate the air-cleaner. ~ ' 5 Disinfection with Germicidal Ultraviolet Radiation . Airborne contagion may be controlled with germicidal W radiation produced by mercury-vapor discharge lamps. Modern germicidal lamps can be made of glans that blocks radiation in the ozone-producing range, but transmits the germicidal rays of 254-n~ wavelength. This radiation is effective in disinfecting most pathogenic airborne bacteria and iruses, provided that the relative humidity does not exceed 70~; but it is less effective against fungi. Direct exposure to germicidal W radiation causes superficial skin and eye irritation, fading of fabric colors, and browning of plant leaves. The W source must therefore be placed so as to prevent direct exposure . Usually, this is accomplished by irradiating the air above the heads of occupants. The W lamp fixtures are relatively inexpensive to install and operate. Frequency of maintenance depends on dustiness of the environment . For example, in room installations with cold cathode tubes, yearly cleaning and biennial replacement are ordinarily adequate. Upper-air irradiation is provided by lamp fixtures mounted on the wall or suspended from the ceiling at a height of about 7 ft. si Occupants of the room are protected from direct exposure to W radiation by baf fles . The effectiveness of disinfection depends on good mixing of the air in the upper and lower portions of the room; thus, stratification for energy conservation may be counterproductive for contamination control with W irradiation. However, the concentration of airborne organisms in the breathing zone in a uniformly mixed space can be reduced to one-tenth to one-fifth that in the absence of W radiat ion . Upper-air irradiation is well suited to rooms with high ceilings if strati f ication is prevented, such as classrooms . Success in blocking the spread of measles has indicated that inactivation of measles virus with W radiation is feasible. Improved W lamps are being developed, but the modern trend toward low ceilings in home '3 will seriously limit the applicability of upper-air W irradiation. W irradiation of . air in supply-air ducts is technically easy, because intense radiation can be used there without hazard to people. The amount of radiation required depends on the size of the ducts and the supply-air flow rate.t' " When air is recirculated within the ventilation system, W irradiation is very useful to reduce the concentrations of infectious organisms or droplet nuclei throughout the areas supplied by the forced-air system. W irradiation in the ducts cannot stop the spread of infection in the room of a person with an infectious disease. When the source of infection is in the roam. the

484 concentration of infectious droplet nuclei i. relatively high. Therefore, W irradiation in required in the room itself, or other methods of contamination removal may be required. Devices for Gas and Vapor Removal Gas and vapor molecules cannot be effectively removed f tom airstreams by the mechanical and electrostatic principles so far described. Sorption is generally used for gas or vapor . removal; there are three basic mechanisms, as described by Lieser: Is · Absorption: Penetration of molecules of the pollutant into the sorbent material (i.e., absorbing phase), which may be either solid or liquid. An example is absorption of nitrogen dioxide in a wet air-scrubber . · Adsorption on external surfaces: Physical or chemical f ixation on f ree surfaces . Examples of physical adsorption include f ixation of noble gases or nitrogen on nonporous solids, such as aluminum oxide, graphite, ionic crystals, and metal foils. An example of chemical adsorption (chemisorption) Is the uptake of carbon monoxide on transition metals, such as iron and nickel. · Sorption on internal surfaces and in Cores: Physica} adsorption or chemisorption fixation on internal surfaces or within pores of porous solids. Capillary condensation with);' pores and occlusion of molecules or ions also occur. Examples of these sorbents are silica gel, aluminum hydroxide, activated carbon, clay minerals, and molecular sieves. An application of this mechanism would be radon sorption on activated carbon. Although absorption is an important gas- or vapor~removal mechanism for industrial and military applications, IS it is seldom used for environmental control in residential or commercial buildings, but is used to control odorous gases or vapors. Adsorption is a dynamic process in which the net rate of adsorption is expressed as: ~ ~ net rate of adsorption ~ (ks - d), where s rate of bans fer of gas molecules to the adsorbent sur face, k ~ fraction of molecules retained on the surface, and d ~ desorption rate. Because d increases with amount adsorbed, the performance of adsorption devices is not usually rated in terms of efficiency, but rather in ter'es of adsorption capacity and penetration time.35 37 6t Adsorption capacity is usually measured in terms of the amount (graces, moles, or cubic centimeters) adsorbed per gram of solid adsorbent as function. of the partial pressures of the adeorbates at constant temperature. (isotherms). Adsorption can be classified as physical, chemical, surface, or internal. Lieser'5 has reported on var iations in adsorption ef f iciency as functions of relative partial pressure. Because the adsorption process i" dynamic, specification of the adsorption capacity is not sufficient to describe the effectiveness of the process. A measure of its Resorption rate or its correlate, the

485 penetration time, is also necessary. Penetration time has also been described as the duration of adsorbent service before Saturation. ~ ~ and the breakthrough time,. or Time in which the maximum permissible concentration will not be exceeded. ~ ~ ~ Methods described by Turk ~ ~ can provide a means to evaluate the dynastic performance of sorption devices that is consistent with those used to evaluate the performance of particle removal devices. Standard test methods for evaluating the effectiveness of gas and vapor removal devices are not yet available in the heating, ventilating, and air-conditioning (HVAC) industry in the United States. However, some standard test procedures have been developed in western Europe. ~ ~ The development of such a standard in the United States has recently been initiated by ASHRAE. The conventional method of selecting gas and vapor removal equipment has been to define the potential sources of contamination, describe the problem to equipment manufacturers, ask for equipment specifications, Sometimes ask for a per formance guarantee, and, less f requently, ask that the equipment be tested for compliance after it is installed (H. E. Burroughs, personal communication ~ . Performance of gas and vapor removal equipment depends on several factors: 'I concentration of the sorbate in the airstream, total surface area of the adsorbent, total volume of pores small enough to facilitate condensation of the adsorbed gases, presence of other gases or vapors (e.g., water vapor) that will compete with the adsorbate for a place on the adsorbent, physical and chemical characteristics of the adsorbate (weight, electric polarity, size, and shape), and electric polarity of the adsorbent surfaces. Activated carbon consists mostly of neutral atoms of a single element and presents a surface with a relatively homogeneous electric charge. But oxygenated absorbents (e.g., activated alumina, silica gel, and molecular sieves) contain nonhomogeneous distributions of electric charges and are polar . Oxygenated adsorbents have considerably greater selectivity than activated carbon and have much greater preferences for polar than for nonpolar molecules. Thus, oxygenated absorbents are more useful for separation of pollutants, and activated carbon is generally more useful for overall decontamination. Because oxygenated absorbents hate a strong af f inity for water vapor, which is highly polar, they are essentially ineffective for direct decontamination of moist air. 6~ To enhance adsorption, the adsorbent may be impregnated by other substances. Enhancement is achieved by chemical conversion of the pollutant by the impregnant to harmless or adsorbable products, the impregnant's functioning as a continuous catalyst for oxidation or decomposition, and the impregnant 's functioning as an intermediate catalyst. ~ ~ Table IX-9 shows some examples of adsorbents and pollutants and the mechanisms of action . Except for formaldehyde, ammonia, and perhaps mercury, the pollutants 1 issued may be found more commonly in the industrial environment. But this table illustrates the broad range of vapors and gases that might pollute the impregnated adsorbents. Note that activated carbon impregnated with sodium 'sulfite and activated

486 TABLE LX-9 Adsorbent Impregnationsa Adsorbent Impregnant Fo11~t Action Activated Bromine Ethylene; other Conversion to dibro- carbon alkenes mice, which remains on carbon Lead acetate Hydrogen sulfide Conversion to lead sulfide Phosphoric acid Adonis; aoines Neutralization Sodium silicate Hydrogen fluoride Conversion to fluorosilicates Iodine Mercury Conversion to mercuric iodide Sulfur Mercury Conversion to mercuric sulfide Sodium sulfite Fo~aldebyde Conversion to addition product Sodium carbonate Acidic vapors Neutralization or bicarbonate Oxides of copper, Oxidi sable gases, Catal ysin of air chromium, inclutlng re- oxidation vanadium, etc.; duced sulfur com- noble metals pounds, such as (palladium, hydrogen sulfide, platinum) COS' and mercaptans Activated Potassium penman- Easily oxidizable Oxidation alumina ganate gases, especially formaldehyde Sodium carbonate Acidic gases Neutralization or bicarbonate 8Reprinted with permission from Turk.

487 alumina impregnated with potassium permanganate are both effective in adsorbing formaldehyde. This point is important, because formaldehyde has been found indoors in concentrations above those considered acceptable by some European standards and ANSI/ASERAE Standard 62-1981. Gas-cleaning devices with the required impregnated adsorbents are commercially available in the United Stated for use in residential and commercial buildings. For example, activated carbon does not adsorb carbon monoxide, but a combination of a desiccant (silica gel) and an oxidation catalyst, Hopcalite {a mixture of cupric oxide and manganese dioxide), has been reported to be effective,,5 although the Hopcalite must be kept scrupulously dry. Preconditioning of the adsorbate can be used to enhance gas- or vapor-cleaning. ' ~ Some of the techniques are as follows: . Use of a particulate prefilter to reduce loading of the adsorbent. · Concentration of the adsorbate (e.g., by pressurizing the system). · Removal of moisture from the airstream by dehumidification to a relative humidity below 50%. · Cooling of the airstream to below 38°C (100°~. Some of these techniques may be more energy-intensive than reducing pollutant concentration by dilution ventilation. Thus, limitations to the enhancement potential must be considered, including: · Penetration time through the adsorbent is inversely proportional to the air f low rate and the concentration or vapor pressure of the adsorbate. IS l} · Resistance to air flow (i.e., pressure drop) increases with the air flow rate or velocity, the mesh size of the adsorbent, and the thickness of bed. · Adsorption capacity decreases as the temperature or relative humidity of the airstream increases. IS Servicing tehniques for gas and vapor removal equipment include replacement or regeneration of the sorbent and are similar to those for replacing mechanical f liters . The sorbent may be contained in panel- like trays, canisters, or pleated retainers. Discarding old sorbent and replacing with new is normally cost-effective. if the penetration time exceeds a month and the sorbate concentration is low (as in residential air-conditioning systems) or if the '3orbent requires impregnation. However, in some large SAC systems, such as in airline terminals, where the. adsorbate concentrations are relatively high (penetration times relatively short) and impregnated sorben~cs are not required, regeneration may be cost-effective. Regeneration is accomplished primarily by thermal methods, but techniques with ionizing radiation and chemical activation are also available. ~ ~ 2 Regeneration may be accomplished on site, or the sorbent may be returned to the manufacturer for processing, as i. usually done for a jr-conditioning applications .

488 SUMMARY Air-cleaning devices for residential and commercial applications are commercially available. However, no single type of air-cleaning process is available that can control particle., gases, and vapors . Therefore, it is necessary to rely on multistage systems to obtain the desired control, if all three types of contaminants are to be removed. These systems consist of combination. of mechanical f ilters, electronic air-cleaners, and gas and vapor removal devices. The system can be used as components within central air-conditioning systems or as uni tary appl lances ~ fan-f ilter modules ~ . Voluntary standards exist in the United States for methods of rating performance of par~cicle-removal devices, and corresponding standards for gas- and vapor-removal devices are now being developed. However, no standards provide procedures for rating performance of fabricated or assembled air-cleaning subsystems, whether they are installed as components or used as unitary appliances. Some effort toward predicting dynamic performance of gas-cleaning from liquids has been reported," but dynamic modeling of indoor air~quality control systems has received little attention. Many of the air-cleaning control devices impose substantial resistance to air flow (i.e., system pressure drop). This resistance requires additional energy consumption. Costs of installing and servicing these devices must also be considered. Thus, optimization techniques should be considered to decide between alternatives that will provide acceptable indoor air quality, energy consumption, and life-cycle costs. . STRATEGIES FOR CONTROL OF INDOOR POLLUTION The demarcation between healthful and unhealthful air is not well def ined . Although air~quality standards exist for outdoor air and for the industrial environment, few standards directly address the indoor, nonindustr ial environment (see Appendix A) . Occupants of indoor environments are expected to be exposed to long-term low concentrations and intermittent high concentrations of pollutants. Control strategies des igned to limit indoor concentrations must consider the possible time dependence between exposure and effects, as well as the specifics of source configuration and contaminant characteristics (i.e., Gas versus particles, reactivity versus nonreactivity, molecular weight, particle size) . Five general control strategic- (see Table IX-lO ~ have been identified and may be applied in indoor environments: ventilation, source removal, source modification, pollutant removals and education. These strategies may not be mutually exclusive S combinations, such as source modification plus ventilation, may be preferred in some situations. This section briefly discusses these strategies and tabulates the relative effectiveness of some of them for various contaminants . More details on controls are provided in Chapter IV, w ith respect to individual contaminants or sources .

489 TABLE IX-10 Indoor-Pollution Control Strategies Control by Ventilation A. General ventilation 8. Spo t ~ zone or local) zed ~ ventilation C. Infiltration II. V. Control by Source Removal A. Material or product substitution B. Restrictions on source use, sales, and activities by type of indoor facilities Control by Source Modification Change in combustion de Sian Material substi tution A. B. C. Reduct ion in emission rates by intervention of barriers Control by Air~C1eaning (Pollutant Removal) A. Particle filtering B. Gas and vapor removal C. Passive scavenging or abs orption Education A. Consumer inf ormation on products and materials B. Public information on health, soiling, productivity, and nuisance ef facts C. Resolution of legal rights and liabilities of consumer, tenant , manufacturer, etc., related to indoor quality

490 Ventilation is the principal means of controlling residential indoor pollution by dilution with outdoor fresh air. (See Figure ~X-lO for schematic of SAC system for nonresidential building. ~ Outdoor air is brought in and dilutes the indoor-generated pollution. This strategy is in conflict with energy conservation, in that the heat and humidity of the displaced indoor air are not conserved. Control by dilution requires a well-ventilated indoor ~pace; energy conservation requires reduction in the amount of unconditioned air brought in f rom outdoors. Optimal air ventilation must be estimated, or energy must be conserved and indoor quality preserved without reducing ventilation rate. Heat-exchangers provide the technologic capabilities to conserve energy while not substantially reducing the ventilation rate. Control of indoor air quality in many buildings depends on the HVAC system. Maintaining acceptable indoor air quality has not yet been a design feature of H\tAC systems (see earlier sections of this chapter). The American Society of Heating, Refrigerating, and Air~Conditioning Engineers has recently included indoor air quality as additional design and operating criteria for SAC in its new ventilation standard. 2 The use of SAC systems a" a means of controlling the quality of indoor . . — air Is pron~s~ng. H~AC systems can be divided into several categories, as listed in Table IX-ll. Each category has advantages and disadvantages that broadly define the characteristics of the individual system. ~ Potentially, the mass concentration and thermodynamic requirements can be met by any of several ILIAC systems. However, proper design will optimize equipment selection and component conf iguration and the functional and economic requirements of a building 's HVAC system. Table IX-12 indicates typical applications for var foes SAC systems . Local exhaust--e .g ., forced ventilation near a known or well-clef ined source of indoor pollution--~s widely used in industr ial environments and to a lesser extent in residences. Control is achieved by exhausting the pollutant at the source to the outdoor environment. Examples of such residential use are bathroom vents and vents over cooking and heating facilities. It is important that exhaust air not be re-entrained into the build ing . Some areas in a structure may have unique requirements for spot ventilation for example, positive- and negative-air-pressure zones. Exhaust fans may be required to control moisture and odors in bathrooms without windows. Kitchens and kitchen stoves usually have some form of filtered, Invented forced draft for contaminant control, and Invented range hems with charcoal filters have really become popular. These may be effective for grease, odors, and owner large molecules, but not for removing carbon monoxide and other small molecules. Fur~chermore, the filters are somewhat expensive and in normal practice are not changed often enough to be reliable. For these reasons, the Invented range hood cannot be considered a reliable pollution control device. A further problem with the use of spot-ventilation exhaust fans in airtight houses is that too much powered exhaust reduces the natural draf t in the furnace vent and can cause combustion products f tom the furnace to be drawn into the living space. Spot ventilation or exhaust ts not provided for gas stoves, gas ovens, small gas water-heaters, and

491 Exh - Damper fen . ,, _ Exhale Air Oueide Air _~'x" ~ Air /////// for Air Recireulmion Air from _ , _ Owed ~ Span - SLIPPIY Fen Inlet Damper Filters' - sting, Cooling Coils FIGURE ~t-10 Schematic of conventional heating, Ventilating, a" air~condi~ioning (~AC) air-supply system for nonresiden- tial buildings. Air to Occupied Speo

492 TILE {X-11 Air-Handling Sy8tem8 Category Description Advantages Disadvantages All air Atwater Provides all required Dense le and latent heat-exchange capac- ~ ty in air supp lied by the system both air ant water distributed to space to provide required heat ing and cool ing 1. Centralized location of all major equipment 2. Removes ma jor coapo- nent ~ f roe condi tioned area 3. Greatest potential for use of free cooling Flexib illty under varied operating con- ditions Easily adapted to heat recovery 6. Optimal distribution for air motion control 7 0 Suitab le f or large makeup-sir require- ments Adaptab le to automatic seasonal changeover 9. Adaptable to winter humidif teat ion 1. Individual room tem- perature control , 2. Plexibllity under war fed operating con- ditions 30 Low distr ibution space requirement 4. Reduced central equip- 2. ment space requirement 5. Horsepower savings by 3. using water instead of air 6. Reduc t ton in f an power req ul recent s dur ing occupied period 7. Can eliminate cross- contamination 8. Icing lif e of compo- nents 1. Additional duct clearance require- ments 2. Additional fan energy required f or perimeter load during unoccupied hours 3. Air balancing cliff icult 4. Accessib ility to terminal devices required 1. Low primary air quantities make design of two-pipe system crietcal f or proper lnter- mediate-season control System changeover can be complicated Usually limited >o perimeter spaces 4. Controls tend to be more complex 5. Secondary air flows create high asin- tenance requirements 6. Primary air supply usual ly cons tent Primary air provides all dehu~ldif ica- tion, 80 low~dew- point air t8 pro- vided 8. Not able to handle hig~exhaust applications

493 Table {X-~l (coned) De script ion Category Description Advantages All water Provides space required for heating ant cool- lng by distributing ho t and chit led wa ter to terminal units Vnltary Packaged system that can provide heating and cooling 1. Plexib ility for atapta- tion to many building conf figurations 2. One of lowest-f irst- cost central-perimeter systems 3. Easy to retrofit to existing structures 4. Low system distribution requirement ~ 5. Low cross-contamlcation potential 6. Individual room control with quick response to varying loads 7. No seasonal changeover need be required 1. 2. Individual room control Indlvidual air distri- bution control 3. Heat ing and cool ing i n- dependent ly controlled b y zone 4. Individual ventilation air control 5. Usually space-saving 6. Usually low installation costs Usually lower initial costs 8. Allows zone shutdown Disadvantages - 1. Inadequate rela- tive-humidity control 2. No positive venti- lation f or many types of designs 3. Througi2-the~wall units may be unsatisfactory in appearance on out- side of building 4. Two-pipe sys teas require seasonal changeover i. Maintenance and service work re- quired in occupied space 6. Filters, cot 15, and condensate drain 1 ines must be kept clean to limit b ac ter ial grows h 1. Limited opt ions available for size and control 2. Limited capability for exceptionally high or exce pt ion- ally low relative t~u~idi ty Acoustics must b e care f ul ly con- sidered 4. Maintenance in occupied space requi red 5. Exterior building aesthetics may be aff ected 6. Higher operating costs

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495 pace-heaters fueled with gas or oils therefore, large runts of carbon dioxide and water vapor are introduced indoors. The indoor-pollution problems caused by the lack of spot ventilation or exhaust in single-fa~nily residences are only now being studied. The information is inadequate to assess the magnitude of the problems or to define the amount of ventilation air needed to abate the pollutants produced by these sources. Source removal is the most effective means of controlling indoor pollution. Examples of source removal are nonsmoking areas and prohibition of urea-formaldehyde foam insulation and kerosene heating units for indoor spaces occupied by people. These strategies are more effective when substitute products are available and less effective when they rely on enforcement to ensure compliance. Where source- removal strategic. modify human behavior, conflict with consumer preference, or involve an economic penalty, they are less likely to be adopted by regulatory bodies. The adverse effects of indoor con~caminant exposure must be well established in the public perception. Public debate centered on the restriction of smoking in public places illustrates the controversy that surrounds source-re~val strategic" for maintaining indoor air quality. However, when material or product substitution is not disruptive or expensive, source removal is clearly the strategy of choice. Tt is obvious that these decisions should be made early in the design stage" of new facilities. If a material or product already in use is determined to be hazardous. removal may still be the strategy of choice. Source removal has been applied in the removal of lead from house paint both in the produce and by paint removal. A current widespread effort to remove all asbestos from school buildings is another example of the source-removal control strategy. Cost consideration must be carefully compared with the likely benefits in reduced health risks and property damage and with other imputed benefits. Source removal may cause a displaced problem, such as occupational exposure during removal or a hazardous-waste disposal problem. These and other factors must be carefully considered before the institution of a program to remove an existing source. Air-cleaning devices have been used in large indoor commercial, industrial, and institutional environments to eliminate or reduce indoor pollutants. This strategy has not been widely used in residences, because the devices are expensive to buy and operate and can be bulky and noisy. Small commercial electrostatic precipitator-, ion generators, sir filters, and gas absorbers (charcoal filters) are used to remove contaminants in some indoor environments. Many of these devices are advertised to provide particlefree and odorfree clean indoor environments. The efficiencies of these devices need to be evaluated by independent organizations. Source modification is an alternative to source removal. The objective of source modification is to reduce the rate of pollutant emission into the indoor environment. Source modification includes maximizing the efficiency of gas cooking and heating facilities that reduce emission of some pollutants. Coating of lead-ba~ed paints and asbe~to--containing building materials to seal the surface and prevent emission is effective and practical. Coating radon- and formaidehyde-

496 emitting surfaces is promising and warrants further study. A source should not be modified when it can be assumed that the codification will cause emission of a different contaminant. The spraying of surfaces that are formaldehyde-emitters may itself constitute a source of indoor contamination. Table IX-13 summarizes control strategies available for several types of pollutants. The table identifies strategies proved effective in controlling a pollutant, but interactive effects must bee considered if several pollutants are to be controlled simultaneously. mis requirement and the complexity of control strategies lead to the necessity of an overall systems designer. Control of indoor contaminant concentrations by dilution with outdoor air will continue to be a major control strategy. Direct control of the ventilation system based on indoor contaminant concentration is the best means of achieving the optical compromise between energy conservation and pollution control. Some provision is needed to add or conserve moisture. }bones in cold climates need to conserve humidity in the indoor sir in winter and reject as much water as possible to the outside in super. Simple energy-conserving means for this kind of moisture control are not yet available, but the latent heat associated with moisture movement can represent substantial energy that is not conserved. New ventilation control strategies are needed. Positive ventilation with heat recovery should be introduced in the building industry. Past practice fixed the temperature of the mixed sir {outside air plus recirculated air). This simplified comfort control. but usually resulted in excessive energy loss. A floating mixed-air temperature based on outside-air temperature can provide closer control of the ventilation sir and energy savings. New sensors for optimal control of ventilation should be developed. Although laboratory instruments can measure the concentration of Tonne indoor pollutants, often these instruments are too bulky, too expensive, too complex, and generally not suitable for extended, unattended use that might be required in measuring indoor environments . Greater emphasis should be placed on controlling specific pollutants at their sources. Co~bustion-generated pollutante-- including carbon dioxide, water vapor, carbon monoxide, and nitrogen oxide-can be removed at the source. New inexpensive, 11, and uncomplicated pollutant control devices are also needed. New construction materials must be examined carefully for undesirable environmental effects. The efficiency of each control strategy must be studied both in laboratory and under ~real-life. conditions. As indicated earlier, systems approach may be required in large structures however, less elaborate and inexpensive means of Controlling contamination in indoor residential environments are conceptually possible, are needed. and can become practicable. Some indoor pollution problems can be controlled through the marketplace choices of an educated consuming public. The general public must be informed of the sources of indoor contaminants and the - the a

497 0 0 v v o a: L' a o - o ~ 0 1 o x a ~ A: ~ ~ a - ; o E" 0 ~ so :- v a, I: o a ~ c} :: o ~ ~ o a ~ ~ o a, ~1 v o I: a ~ 0 =e e ~ ~ ~ o Cot ~ 0 V ~ 0 0 C _. I _ V 0 - ~ ~" C, :. v 0 V A: 0 X I I: o V o ~ 0 v D — CO ~ To 1 V 0 1 s0—_ t~,4 0 ~ _ C ~ ~ Z == == =~" ~ 1 1 1 1 1 1 ~ ~ ~ ~ ~ Z ~ Z 00 CL Z ~ V" ~ : 60 C ~ g ~ ~ ~ 00 ~ ~ Y ~ e ~ ~ ~ Z . ~ ~ ~ :^ :' 0 0 :' O ~ e~o 0 C D C ~ h ~ ~ ~ ~ a: ~ Z ~ Z ~ ~ ~ ~ V ~ ·. ~ V l: b E C c K 111 ~ = O C ~ ~ b ~ 0 ~ ~ l , o ~ 0 a ~ b E _ ~ 1# V ~ ~ ~ ~ ~ ~ 60 ~ ~ C :' ~ ~ ~ V ~4 b e e ~ ~ e ~ ° ~ ° C 0 ° 0 e X I b S § ~ b 0 0 C E 08 C C C O O 811 _ b _. V 4, | O ~ O ° .e ~ ;~) ~ ° ~ ~ x: ~ ~ ~ v ~

498 adverse consequences of acute and chronic exposures. It must be informed about the cost and effectiveness of various control options and the efficiencies of commercially available air-cleaning equipment. The public should be informed of its legal r ights with respect to product liability. The obligation and rights under purchase and lease agreements pertaining to healthful indoor environments for residential, commercial, and public places must be defined. Education provides easy and inexpensive steps that help to improve indoor air quality. Such steps include reduction in indoor smoking, ban of potentially harmful indoor sprays, use of proper paint, changes in daily routines to evoid exposing all family members to pollutants, and the like. The efficiency of this control strategy cannot be estimated, but most would agree that only a properly educated public can require steps toward ~mp~ementlng one or more combinations of the other control strategies. Public-interes~c organizations, public utilities, professional societies, trade and manufacturing associations, and government agencies all have a responsibility to ensure that the public receives factual information related to indoor contaminants. REFERENCES 1. American National Standards Institute. Constitution and Bylaws of the American National Standards Institute. New York: American National Standards Institute, 1978. 16 pp. 2. American National Standards Institute, and American Society of Heating, Refrigerating and Air-Conditioning Engineers. ANSI/ASHRAE Standard 62-1981. Ventilation for Acceptable Indoor Air Quality. New York: American Society of Heating, Refrigerating and Air Conditioning Engineers, Inc., 1981. 48 pp. 3. American Society of Beating, Refrigerating and Air-Conditioning Engineers. ASK RAE Handbook and Product Directory. 1979 Equipment, pp. 2.1-2.8. New York: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., 1979. 4. American Society of Heating, Refrigerating and Air-Conditioninq Engineers. ASHRAE Standard 52-76. Method of Testing Air-Cleaning Devices Used in General Ventilation for Removing Particulate Matter. New York: American Society of Beating, Refrigerating and Air~Conditioning Engineer-, Inc., 1976. 5. American Society of Heating, Refrigerating and Air~Conditioning Engineers. ASERAE Standard 55-74. Thermal Environmental Conditions for Human Occupancy. New York: American Society of Beating, Refrigerating and Air~Conditioning }engineered, Inc., 1974. 12 pp. 6. America--: ~ Gaiety of Beating, Refrigerating and Air~Conditioning Engineers RESERVE Standard 62-73. Standards for Natural and Mechanical Ventilation. New York: American Society of Beating. Refrigerating and Air Conditioning Engineers, Inc., 1973. 17 pp. 7. American Society of Beating, Refrigerating and Air~C;onditioning Engineers. ASERAE Standard 90-7S. Energy Conservation in New Building Design {Section 123. New York: American Society of Heating, Refrigerating and Air~onditioning }engineers, Tnc., 1977. 11 pp.

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