Achieving Healthy Indoor Air
Report of the ATS Workshop: Santa Fe, New Mexico, November 16-19, 1995

	OVERALL INTRODUCTION

In 1988, the American Thoracic Society and the American Lung Association convened an interdisciplinary workshop on improving indoor air quality (IAQ) and health. The workshop was prompted by the emerging literature on the health effects of air pollution, and by the need for a critical review of the evidence on control strategies directed at the adverse health consequences of indoor air pollution. The focus of the 1988 workshop was primarily on specific pollutants; also addressed were source control and building-related problems. A workshop report was published in 1990 in the American Review of Respiratory Disease (1). The target audience for the workshop included the many health professionals providing clinical care to patients with respiratory diseases, the American Lung Association and its constituents, and the wide range of other professionals concerned with indoor air quality.

In the ensuing years, our understanding of the adverse effects of indoor air pollution on health and comfort has broadened, supplying a stronger framework for developing and implementing control strategies. During these years, the array of professionals offering commercial services related to indoor air quality has grown steadily, as have the types of products and services advertised as improving indoor air quality (e.g., air cleaners, vacuum cleaners, radon measurement and mitigation, and air duct cleaning). Products with low emission rates of volatile compounds are available, and homes can now be designed and constructed to offer lower concentrations of pollutants than in the past.

Health problems linked to indoor air quality have persisted, however, and the scope of the health concerns has broadened. We continue to identify buildings with occupants who are affected by building-associated illnesses, and we have learned that these outbreaks may reduce productivity and perhaps result in costly litigation. The number of people who report responding adversely to environmental contaminants has increased, with many receiving the label of "multiple chemical sensitivity," for which the World Health Organization has recently suggested an alternative term: "Idiopathic Environmental Intolerance." Changing patterns of infectious disease have brought new concerns. Tuberculosis, a waning disease at the time of the last meeting, has returned, and multi-drug-resistant organisms are becoming more prevalent, particularly in inner cities. Substantial time is spent today in often-crowded microenvironments such as airplanes and day care, where there is enhanced opportunity for disease transmission.

In response to these dynamic changes since 1988, the American Lung Association and the American Thoracic Society convened a second workshop in 1995. Additional sponsoring organizations included the American Academy of Allergy, Asthma and Immunology, the American Academy of Pediatrics, the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE), the Centers for Disease Control and Prevention, the U.S. Environmental Protection Agency, and the National Association of Home Builders Research Center, Inc. Attendees represented the broad range of professional disciplines concerned with indoor air quality and health: architects, engineers, building diagnosticians, physicians, public health professionals, facilities managers, lawyers, and others. The target audience for the report was construed as broadly as in 1988.

The charges to the workshop participants reflected the changes in the problems and in the evidence base between 1988 and 1995. Solutions to problems and the technology developed to improve health and comfort through better indoor air quality received greater emphasis. After an opening session that addressed the concept of healthy indoor air, five different working groups were convened, and during the three days of the meeting they focused on: (1) problem-solving: design, construction, and operation of buildings; (2) source control; (3) ventilation; (4) air cleaning and treatment; (5) potentially susceptible populations. This workshop report provides summaries of the five groups' responses to these charges, and includes overarching recommendations. The report also provides a general background for readers on the conceptual basis of healthy indoor air and on institutional jurisdiction for various dimensions of indoor air quality. A brief description is included of the complex factors in the design and construction of a building that affect the air quality within the building as it is commissioned, and the diverse factors that determine air quality in a building during its use.

What Is Healthy Indoor Air?

The meeting began with a discussion of the key elements in the concept of healthy indoor air, with Richard Diamond, Thad Godish, William Cain, Ronald White, and Jonathan Samet reviewing and addressing component issues related to architectural design, the residential environment, irritation, public health, and clinical medicine, respectively.

Diamond described the multiple perspectives from which architects may approach indoor air pollution. In the traditional "one-point" perspective, architects view their work primarily for its visual impactarchitecture as artwith little concern for occupant comfort and health. A more pragmatic or "two-point" perspective recognizes that architecture has aesthetic value but also needs to reflect a broader range of functional considerations such as providing for human needs, allowing construction within budget, and avoiding costly litigation. The architect assumes that conventional practice will provide acceptable conditions for occupant health and comfort. A third, more comprehensive, perspective, advanced by Levin (2) and others, adds to the previous perspective a fully integrated "ecological approach," incorporating explicit concerns for a building's effects on the health of its occupants and on the environment.

Godish began by referring to the difficulty of defining "healthy air." He then discussed the characteristics of residential environments that pose unique issues: the large number of buildings and the diversity of environments, ownership status (owned or leased), diversity of construction characteristics, the limited complexity of building systems, and special exposure concerns. Godish emphasized diversity and the frequency of problems in manufactured housing. With regard to exposure, he pointed to the length of time spent at home; the diversity of the exposed population, which includes infants, children, the elderly, and persons with underlying illness; particular exposures such as radon, formaldehyde, environmental tobacco smoke, and releases from craft activities; and the limited potential for dilution through ventilation.

Cain noted that the effects of irritants may or may not be predictable. Although body odors and environmental tobacco smoke (ETS) have predictable effects, other agents may not affect everyone in a uniform way. He commented that, for irritation, the response reflects the additive contributions from the individual agents. He noted that ventilation approaches have been based largely on odor control, and he considers that since this odor-based approach has been generally successful, it should not be abandoned. He advocated for research to support a mass-balance approach and raised the problem of funding sources.

The presentations by White and Samet emphasized the broadness of the concept of health. Implied in the World Health Organization definition of health is a need for considering a wide range of responses to indoor air pollution, including irritation and symptoms. Samet noted the substantial burden of clinically diagnosed disease associated with indoor air pollution.

In the discussion prompted by these presentations, and during subsequent open discussions at the workshop, there were reminders that comfort in indoor environments reflects not only indoor air quality but the thermal environment, lighting, physical stressors, and diverse psychological and social factors.

A Conceptual Framework for Considering Indoor Air Quality and Health

Indoor air pollutants are linked to health responses through a sequence that moves from emission by the source through exposure, dose, and ultimately to the health response, as illustrated in Figure 1. This model, designed by the conference participants, simplifies a complex set of interactions but indicates the critical points at which control strategies have effects. The schema points to the central role that source control should play in any control strategy. Air cleaning and treatment can lower concentrations and thereby reduce exposures, and time-activity patterns can be modified to limit source use and exposures. Ventilation reduces pollutant concentrations through dilution. The materials selected in the design phase may determine the potential for future adverse health effects, depending on associated emission rates. As a building is used, new and unintended sources may be introduced and the original design ventilation may be either inadequate or compromised by inadequate maintenance. This model also acknowledges the range of susceptibility in the population.

View larger version (11K): [in this window] [in a new window]   Figure 1.   Sequence of health responses linked to indoor air pollution.

General Recommendations

On issues transcending the charges of the individual working groups, the workshop participants offered a series of general recommendations reflective of the interdisciplinary nature of the group.

Exposure reduction. Many products have been developed to benefit indoor air quality, including room and central air cleaners and low emission products for construction and furnishing. It is doubtful that experimental data from controlled clinical trials will become available for most of these products, and observational data, if available, may be difficult to interpret because of the multiplicity of factors determining responses to indoor environments. However, there still exists a need for recommendations concerning the purchase and use of these products. Persons seeking relief from health problems associated with indoor air quality may turn to health providers, the American Lung Association, or other organizations for guidance when considering the purchase of products promising health benefits. Even though there are no data on most specific products, the workshop participants considered that reduction of exposures could be generally recommended. Persons seeking relief from problems related to indoor air quality or attempting to minimize risk for developing problems can be counseled that using products that reduce exposure is reasonable. They need to be aware, however, that purported health benefits may not follow and they should balance costs and potential benefits.

Interdisciplinary meetings. The 1988 and 1995 workshop participants were multidisciplinary in background and reflective of the broad range of professionals concerned with indoor air quality. As at the previous meeting, the 1995 participants commented on the lack of similar meetings and of venues for multidisciplinary interactions. Participants recommended that the American Thoracic Society and the American Lung Association take the lead in conducting regular interdisciplinary workshops that promote in-depth discussion of key and timely issues.

Institutional interactions. Institutional alignments related to indoor air quality were also discussed. A specific focus of discussion was the development of ventilation standards by ASHRAE; the standard-setting process continues without formal participation from organizations concerned with clinical illnesses of individuals and with public health, although persons with health backgrounds have served on the ASHRAE committee that developed the ventilation standard and on other ASHRAE committees. The group encourages discussion of ASHRAE's unique role regarding ventilation and indoor air quality and involvement of other organizations such as the American Thoracic Society and the American Public Health Association. The possible role of governmental agencies should also be explored.

Voluntary guidelines. There was discussion on establishing voluntary guidelines for indoor air quality practices for use in commercial buildings. The participants agreed that these guidelines already existed in the Environmental Protection Agency/NIOSH's Building Air Quality guide and that the real issue was the adoption of these good indoor air quality practices. To promote their use, the participants recommended bringing together a group similar to the Building Air Quality Alliance initiated by the EPA, which would implement a voluntary program by encouraging building owners and operators to adopt good indoor air quality practices through opportunities and incentives.

Communication. The group commented on the lack of effective strategies and processes for educating the public about indoor air quality. The American Lung Association has produced printed and video documents, but no process is in place for communicating with the public systematically and comprehensively at key times of need-to-know such as during the design or purchase of a home. The participants encourage the development of strategies for assuring consumer understanding of options and consequences as key decisions are made with regard to residences.

Needs for research. Like participants in the previous workshop, the 1995 attendees lamented the lack of information in key areas. They expressed concern about product marketing that promises health benefits without appropriate data, as absence of data handicaps those formulating recommendations on the use of such products. These large gaps in our understanding of control strategies reflect the regrettable lack of funding for research on indoor air quality. The workshop participants encouraged the American Lung Association to advocate for increased funding for indoor air research, to urge manufacturers of products related to indoor air quality to support research, and to seek a mechanism for contributing to research on indoor air quality in general.

This report is intended for professionals in a variety of fields who need to increase their understanding of how a building's indoor air quality affects its inhabitants and what can be done to eliminate or reduce potential adverse reactions to pollutants in indoor air. It is a workshop report and presents the findings of the participants. Anyone who is interested in a more in-depth treatment of the topics discussed or of other dimensions of indoor air quality should refer to the list of recently published general references at the end of the document. These references provide information on the health effects on indoor air pollution, not a topic of this report. A number of comprehensive references have been published, and the proceedings of the Triennial Indoor Air Conferences offer invaluable coverage of the subject.

Organization of This Report

The five sections of this document reflect the tasks of the meeting's five working groups. The first section provides basic information on how a building's design, construction, and operation affect the quality of its indoor air, how to prevent air quality-related problems, and how to address them when they do occur. The section that follows looks at sources of indoor air pollution and identifies strategies for minimizing or eliminating potential risks. Section three deals with ventilation as an approach to managing indoor air. It explores how a building's inhabitants are affected by the quality of its ventilation system. The fourth section discusses air cleaning and filtration and the impact of these technologies on improving indoor air quality. The fifth and final section is a brief overview of selected populations who, for various reasons, appear to be especially susceptible to the adverse effects of indoor air pollution.

	PROBLEM SOLVING IN THE DESIGN, CONSTRUCTION, AND OPERATION OF BUILDINGS: THE RELATIONSHIP TO INDOOR AIR QUALITY

This section considers two aspects of indoor air quality (IAQ) as it relates to commercial and residential buildings: (1) how buildings are designed, constructed, and operated to achieve low concentrations of pollutants and prevent problems from occurring; and (2) how to mitigate problems related to indoor air in buildings when they do occur. Delivering and operating a "healthy building" is key to health and comfort. It begins with an extensive discussion of the design, construction, and operation of buildings. An understanding of the complex sequence that leads from design to building use is essential for preventing and diagnosing problems.

Current Nonresidential Design and Construction Practices: Description and Deficiencies

The quality of a building's indoor air reflects in part the processes by which it is designed and constructed. Current practices, each with advantages and disadvantages, have not consistently delivered buildings and building systems that perform as designed reliably over a building's lifetime. These performance deficiencies often lead to indoor air quality problems. What follows is a review of two common design/construction delivery practices for nonresidential buildings in use today, each with many variations.

Design/bid/build. The design/bid/build approach is by far the most common practice in most areas in the country for institutional and large commercial projects. In this approach, the owner retains an architect who takes the lead through the design phase. The architect typically hires consultants to design specific elements of the building such as structural, mechanical, electrical, and plumbing systems. Once the design is complete and documented by plans and specifications, it is let out for bid by general contractors. After award of the project, the general contractor usually subcontracts most or all of the construction to specialty subcontractors. Because the bid documents are in the form of plans and specifications, this approach is commonly referred to as the plan & spec' approach by contractors.

There are several variations of the plan & spec' approach. The general contractor may be selected before or during design on a fixed-fee basis. The contractor is then brought on to assist in developing some design details as well as to control and ultimately guarantee the budget. In another variation, a construction manager is hired by the owner to oversee both the design and construction process and to ensure that the owner receives the lowest possible price. The plan & spec' approach has two key elements: the designers are independent professionals (architects and consulting engineers), and all or most of the subcontractors who build the building and its systems are selected based on low bid.

Design/build. In the design/build approach, the designers work for the contractor. A design/build general contractor firm, for instance, would have its own architectural and structural engineering staff; a design/build heating, ventilation, and air conditioning (HVAC) contractor firm would have its own mechanical engineering staff. On occasion, instead of in-house designers, contractors retain local architects or consultants. The contractor may also be selected based on low bid using a performance specification as the basis of design. This approach shares many of the characteristics of the plan & spec' approach and there is a potential to compromise quality to save costs.

A dichotomy has developed in the building industry that can adversely affect occupational health. On the one hand, increasing litigation in the construction industry has indirectly encouraged design professionals to take less responsibility for the ultimate product of their work (the building), leaving many construction details to the contractors. On the other hand, the emergence of more sophisticated HVAC systems and control systems has made competence in design, construction, operation, and maintenance even more important. Minor deficiencies in one aspect of the building defeat excellent performance in other areas.

Attempts have been made to change these processes, but none offers a complete solution. Possibly, the most encouraging attempt has been the design/build approach in which the designer is employed directly by the contractor. This organizational approach eliminates the separation of design and construction responsibilities and should improve the design as well as reduce costs because of the close contact between designer and builder. However, this approach places the designer, who is licensed and professionally responsible, in a potentially compromising role.

The Integration of the Project Team

The need for communication among stakeholders increases as project development objectives become more sophisticated and increasingly demanding of interdisciplinary discussion. If possible, a commitment to design team integration should be made at the outset of the project. Each stakeholder then has a role and can contribute to the project development. What follows is an idealized approach showing how indoor air quality issues can be identified and addressed throughout the design and construction process.

In the Project Planning Phase, a commitment is made by the owner or developer to a project schedule, budget, and design team that will provide for indoor air quality requirements. The schedule should provide adequate time for airing-out of new construction materials and for commissioning building systems before occupancy. Project feasibility studies and assembly of the design team involve consultation with all relevant participants in the process. A design team should be selected on the basis of proven indoor air quality experience as well as commitment to integration of stakeholders into the design process. Budgeting fully anticipates both capital and holding cost requirements of additional time, expertise, and specialized systems or materials to address indoor air quality requirements.

In the early Site Planning and Design Stage, the architect and the building owner or developer define the site, parking, landscape, and future area requirements. Together with the landscape architect, they evaluate options for landscape areas to enhance the outdoor air requirements. Previous land use evaluation and testing for soil contaminants may be undertaken. The location of parking areas and vehicle access areas relative to building openings and air intakes is identified as an issue for consideration as the building mass is developed. The mechanical engineer contributes information on HVAC options and develops filter and air-cleaning options, assuring the quality of outdoor air to be used for ventilation. The site and the building need to complement each other and to be designed to work together to optimize IAQ.

During the Overall Architectural Design Stage, the building owner/developer, the architect, and the mechanical engineer work together to develop the most appropriate building form and preliminary window design strategies in conjunction with an overall environmental control concept covering ventilation, thermal control, lighting, and acoustics. Locations of building openings are related to vehicle access and parking areas to minimize pollutant entry.

Pollutant-generating activities located within the building are identified and separation/ventilation strategies are developed if needed. Wherever there is a potential moisture source, ventilation and dehumidification should be adequate to protect against microbial growth. Regardless, attention to dehumidification is needed throughout the building. Smoking lounge requirements and locations are determined, if necessary.

The building envelope, including roof, walls, doors, windows, and floor, is developed. Depending on ambient air quality, as identified in the previous stage, operable windows are considered by the architect, and their potential impact on the HVAC system is assessed by the mechanical engineer. The building owner/developer considers reasonable occupant use and interlock or pressure control requirements, if any. The envelope and structural materials are selected with input from the architect, the building owner/developer, the structural engineer, and the mechanical engineer.

Once the overall building and site have been selected, Ventilation and Climate Control Strategies are developed by the architect, the building owner/developer, the mechanical engineer, and the landscape architect. Outdoor air dilution depends on ambient air quality as affected by perimeter trees, shrubs, and landscape materials. Air intakes, exhaust locations, air cleaning, and space air distribution are developed by the mechanical engineer in conjunction with the team. Heat recovery systems and microbial development control strategies are considered at this stage. Strategies related to ventilation rates, filters, cleaning, and air distribution are selected, and a choice is made between using either ducted or plenum return air.

In the Materials Selection and Specifications Stage, the team explores source control options. Low-emitting materials for the envelope and the interior finishes are selected wherever possible. Materials that might support molds are reduced and design strategies are developed to ensure that moisture does not accumulate. Strategies are designed to reduce off-gassing of materials in the enclosed spaces; to manage any condensation in HVAC systems; to ensure proper curing of concrete before covering; and to generally address issues of indoor air quality and make them part of the construction contract and of the operations and maintenance plan. The contractor, if available, is invited to assist in the development of the specification and selection of materials. Ideally, future building operations and maintenance staff would be involved to ensure that specification strategies are practical and will be implemented during the building operations and handover stage.

During construction, the issue of Product Substitution may arise. A contractor may make a request to substitute a product that carries consequences for indoor air quality performance. This can present a temptation to owners for cost-cutting because these substitution requests are made in isolation; the consequences for indoor air quality may not be fully apparent.

The Construction Process and Initial Occupancy Stages involve the entire team. Some decisions regarding the commissioning of the building are made at this time, but comprehensive plans and the commissioning process should begin with design. The importance of special ventilation during construction and of avoiding premature occupancy is clearly communicated to the contractor and the building owner/developer to ensure indoor air quality throughout construction and occupancy phases. The HVAC system is handed over to the building's operations and maintenance staff with a hands-on training session to ensure the building will be operated to maximize potential performance.

A recent and successful development in the management of IAQ is the System Commissioning Process. Commissioning is a formal process verifying that systems have been installed and are operating as designed. It involves a comprehensive review of design drawings to ensure that systems meet design intent and are readily maintainable, inspections to ensure that systems and equipment are installed per the design documents, and testing of all equipment and control systems. Several case studies have shown that a formal commissioning procedure can be highly effective (3).

The cost of building commissioning may be erroneously perceived as high and as a reason for not implementing commissioning of HVAC systems in commercial buildings. In fact, experience with commissioning to date has clearly demonstrated its financial advantage (3). Savings are realized from the reduced need for corrections of deficiencies late in the construction process and during the early occupancy period. Further savings, in some cases shown to be quite dramatic, have come from reducing energy costs in new buildings. Because the commissioning process provides complete documentation of systems and training of building operators, design intent is more likely to be executed in a fully commissioned building. A recent study in Switzerland found that symptom prevalence in occupants varied inversely with how closely building ventilation rates conformed to the original design (4). Documentation of design intent and commissioning, therefore, can be cost effective by reducing problems and their severity and by reducing lost work time from absenteeism because of building-associated illness or by contributing to optimal worker productivity.

Mitigating IAQ Problems in Commercial Buildings

The management of indoor air quality in an occupied building often starts with simple preventive measures and may include more advanced technological approaches as needed.

Housekeeping procedures. Indoor environments are continuously contaminated with dirt and dust tracked in by building occupant's footwear, from dust in the supply air, and from dust sources in the building, such as office machines and paper handling, by spillage, by residues, and from other sources. Proper housekeeping prevents build-up of dust deposits, and thus is a most important measure in controlling secondary dust sources. To date, there are very few scientific attempts to demonstrate an effect of cleaning on occurrence of Sick Building Syndrome (5).

Building entrances designed to minimize track-in of dirt may consist of grilles followed by removable, washable mats. The mats should be washed at regular intervals. If an office room is disturbed by computer cables, printer paper boxes on the floor, or other obstacles, the cleaning staff cannot carry out the cleaning job as effectively as intended in the time assigned; untidy workplaces may interfere with cleaning and thereby affect IAQ.

The building owner should take care in selecting a cleaning contractor and phrasing the final contract. Proper cleaning contributes significantly to the expenses of running a building, whereas insufficient cleaning results in an unacceptable environment. The customer should specify the degree of cleanliness to be maintained and the cleaning loads placed on rooms. The professional cleaning contractor then can design a cost-effective cleaning procedure while considering other factors such as types of room surfaces and accessibility. The contractor should specify how the proposed cleaning procedures along with quality assurancewill be documented. Special emphasis should be put on carpets, particularly in rooms with high person/dirt loads.

Cost-effective cleaning consists of a carefully chosen combination of cleaning agents, tools, and machines applied in a specified cleaning program. The program should specify the method by which an object is cleaned and how frequently. The cleaning contractor should document procedures for selecting the least toxic cleaning agents to do the job. Cleaning personnel should be properly trained, as improper use or dosing of cleaning agents may degrade surfaces. Use of cleaning agents can be reduced by more frequent inclusion of dry mopping methods. Occupants should be informed about cleaning programs specified for each room in a building.

Computer-supported quality control procedures are available, based on subjective assessment of the quality of the cleaning (6). Assessors select a random sample of cleaning objects for inspection and count the number of "failures" such as spots, heel marks, greasy fingerprints, and visible dust deposits. The procedures can only help to assess if a given cleaning procedure has been followed, not if the quality is appropriate in relation to the indoor air quality.

A comprehensive approach to evaluating the quality of cleaning, including a method for on-site measurement by non-specialist personnel has been proposed (6). The method is applicable to nontextile surfaces and measures the degree of surface soiling by the percentage of surface area covered by particles (see Table 1). Proposed guidelines for the quality of cleaning, based on what is reasonably achievable, are as follows:

1. Baseline quality. The potential dust sources can readily be controlled to this level by using appropriate cleaning methods.
2. Improved quality.
3. Indoor environment quality. Surface cleanliness can be maintained by the best currently used cleaning methods and programs. Control of secondary dust sources at this level does not imply that sick building symptoms will not occur. The limits specify the levels not be exceeded during the period between cleanings. The cleaning contractor selects appropriate cleaning methods and frequencies.

Commercial IAQ assessments. To increase assurance that commercial buildings offer thermal, air quality, lighting, and acoustic conditions conducive to health and comfort, periodic assessments of spaces should be conducted by trained facilities staff. One readily available document that can be used by the staff for this purpose is the EPA's Building Air Quality Manual (7). Although its procedures do not require quantitative measurements or formal surveys of occupants, they can be implemented with the expectation of achieving reasonable assurance that occupant exposures are "acceptable" according to applicable guidelines (8). If a higher level of assurance is required, then quantitative and simultaneously obtained system performance, human response, and exposure measurements should be obtained and evaluated against a rigorous and established protocol.

Commercial system performance assessments. To carry out periodic systems assessments, ASHRAE's Guideline 1: System Commissioning and Guideline 4: Operations and Maintenance Manuals are useful (10, 11). These procedures demand extensive knowledge of building systems and may require additional training for staff or the services of a competent test and air balance (TAB) outside contractor. If system performance is deficient, a system performance assessment should be conducted using a comprehensive protocol. Air flow should be measured and compared with the original TAB report. However, if there have been modifications to the building structure, use, or occupancy, the original design TAB specification must be evaluated and modified if needed. A third party should direct and evaluate the TAB assessment or provide assurance of the competency of the selected firm.

The "healthy" building should include sensors for real-time monitoring of supply and return air flow. Cost can be reduced by placing the sensors within the fan, eliminating the need for a large expanse of straight duct to minimize turbulence and provide accurate measurements.

The transfer of HVAC building operations and preventive maintenance. In this step, information on operations and preventive maintenance is transferred from the designer and constructor of the facility to the owner and/or tenant operating the facility. The approach to the transfer varies widely. At one extreme, the owner/operator is simply handed instructions from the equipment manufacturers without any operator training. At the other, systems are formally "commissioned," including thorough system inspection and testing and careful on-site training of the operators. Detailed approaches to accomplishing this hand-off are covered in ASHRAE's Guideline 1: System Commissioning and Guideline 4: Operations and Maintenance Manuals (10, 11). At a minimum, wall displays of the HVAC system should be provided in mechanical rooms and should include a brief description of the HVAC systems that serve the facility and of the ASHRAE design standards used. Basic assumptions should be given, including the maximum number of human occupants that each HVAC system was intended to serve and the major pollutant sources in the ventilated areas. The information should also include the basic central operating sequence and the schedule for preventive maintenance.

Evaluation of current HVAC performance. Many facilities lack any routine evaluation of the ongoing performance of HVAC systems. A few states, through state OSHA regulations, do require periodic maintenance and verification of performance. One prudent approach to ensure proper performance is to conduct periodic audits of HVAC systems and to maintain records of these audits by an identified, responsible person.

If problems are found by the HVAC audit, a careful diagnostic procedure by trained professionals (i.e., mechanical engineers and HVAC control contractors) should be conducted and appropriate corrective actions taken. If the problems have come from changes in the pattern of occupancy in the area that the system serves, modifications may be needed in the design of the system.

Proactive maintenance. Proactive maintenance is far-reaching; it includes inspection for cleanliness and operations, cleaning, and filter replacement. Some procedures should be carried out seasonally and others annually. Property owners should arrange for periodic in-house or contracted maintenance service for HVAC systems.

HVAC system correction during commercial maintenance procedures. The previous section outlined typical inspection processes and the steps usually needed to determine if HVAC systems are functioning properly. Perfunctory maintenance and inspection processes, usually performed for the sake of economy, may not reveal latent indoor air quality problems, and almost always fail to assure the comfort of building occupants. The maintenance process requires diagnosis, planning, documentation, and communication with building management to assure achievement of adequate IAQ.

The qualified maintenance technician should be able to identify defects in design or installation and also to diagnose and correct items that reflect mechanical or electrical failed uses. Attempts should be made to initiate elements of "predictive" maintenance. Examples include vibration measurement of rotating devices, insulation resistance integrity of HVAC system motors (including compressors), and periodic overall airflow and water-flow measurement. Failure of HVAC systems, although sometimes instant and possibly catastrophic, is often gradual and predictable. Actual repair and remediation techniques are well documented (11) and will not be detailed here.

Preserving IAQ during building renovation. A high potential for compromising IAQ exists during building renovations, as the renovations may generate pollutants and alter ventilation. These problems may be minimized by conducting IAQ design and procedural reviews with a specific IAQ control agenda and by retaining a qualified IAQ industrial hygienist with engineering experience, or a consulting engineer with industrial hygiene and IAQ experience, to review design and implementation plans. Building personnel should be informed, and an IAQ industrial hygienist could be appointed to administer the IAQ plan. Further steps to reduce IAQ problems include renovating in off-hours, sealing off construction spaces, and ensuring that particles and gases are satisfactorily controlled. Some renovations may necessitate removing personnel from the area being renovated and the surrounding areas.

IAQ correction during renovation or remodeling operations. During renovations and remodeling operations, occupant exposures can occur; therefore a decision is needed before the process begins on whether occupancy should continue. The three critical steps in the detection and remediation process, should harmful agents be liberated, are communication, evaluation, and remediation.

1. Communication. The communication process begins with immediately alerting the administrator of the IAQ response plan that an incident has occurred. The report may originate with the party causing the incident or from facility occupants. In the communication process, delay in notification should be minimized, regardless of concerns about culpability. The plan should emphasize that reports of possible incidents should be taken seriously and action should be immediate.
2. Evaluation. Upon notification of an IAQ incident during building renovation, it is imperative that the administrator of the IAQ response plan evaluate options rapidly and conservatively. All options, ranging from containment, vacating the area, and requests for third party assistance (i.e., local HAZMAT forces), should be considered and implemented on a timely basis.
3. Remediation. After communication, evaluation, termination, and containment, potentially harmful sources should be pursued vigorously and completely. Entry of particles, fumes, or vapors should be ended by use of approved direct contact measures (i.e., cleaning, vacuuming, etc.), or concentrations reduced by appropriate approved ventilation measures. All contaminants should be mitigated without transferring the problem from the area undergoing renovation to another area. Professional third-party review of these measures is encouraged to assure that complete and correct measures are undertaken.

Competent and trained staff. The healthy building has a competent and trained staff that is cognizant of the IAQ implications of HVAC maintenance. Even a well-designed building can have poor IAQ if maintained poorly. Modern HVAC equipment such as boilers, chillers, fans, and pumps, can be quite sophisticated, often incorporating sensitive electronic components. The equipment may be integrated with a variety of controls, including pneumatic, electronic, and direct digital control (DDC) devices. In larger buildings, and even in some medium-size buildings, these controls may be managed with a computerized and automated system. Thus, without extensive and continuous hands-on training, maintenance staff may be unable to operate the building properly. Appropriate hands-on training and complete operations and maintenance manuals should be provided.

Current Residential Design and Construction Practices: Description and Deficiencies

Design and delivery. Designing and building small residential buildings, especially single-family houses, contrasts markedly with the process for other types of buildings. Houses are "designed" once and built many times, in different locations, on different types of foundations, and with diverse modifications. The use of stock plans from plan books is widespread, whereas custom homes designed by an architect and incorporating systems designed by engineers are a small minority. Typically, the "design team" is a single person. The builder may also be the developer and may use employees to perform some services that would ordinarily be subcontracted. Expertise in identifying and avoiding potential IAQ problems may be lacking.

Builders of speculative housing build for an anonymous buyer whose tastes are assumed based on overall perceptions about buyers and experience with previous buyers. There are always exceptions, but few home builders see upgrading IAQ as a significant marketing opportunity, nor do they see failure to incorporate IAQ upgrades as leading to buyer complaints or call-backs. As a result, IAQ upgrades are likely to be incorporated voluntarily in new homes only where their incremental cost is very small, the measures are prescriptive in nature and understandable to the nonspecialist, and/or the changes are beneficial and marketable for reasons aside from their impact on IAQ.

Design and delivery of combustion equipment. The design/ delivery phase can have significant influence on the exposures to combustion emissions in residential structures. All combustion devices should be ventilated effectively, and major combustion devices such as furnaces should be isolated from the interior space. In designing venting systems, one should consider the interactions of all the devices acting on the house airflow system. Vented appliances are designed to have combustion emissions released to the outdoors when operated normally. Back-drafting may bring combustion products into the house because of a malfunctioning venting condition.

Radon control. New homes built in areas with high radon potential should be designed and constructed to facilitate remediation if elevated radon levels are found after occupancy. Radon-resistant construction features include a permeable layer underneath the basement floor slab or slab-on-grade; a polyethylene membrane above the subslab layer prior to pouring the floor slab; a vent stack extending from below the floor to above the roof, and electrical wiring to facilitate installation and activation of a fan to depressurize the layer below the slab. A set of prescriptive requirements for radon control along these lines has been added to the 1995 Council of American Building Officials (CABO) One and Two Family Dwelling Code, so this type of construction should become more common (12).

Surface drainage. It is standard practice to slope the ground away from foundation walls to provide positive drainage of surface water and discharge from downspouts. However, as this soil must be placed after the foundation wall is poured or erected, proper compaction of the fill is critical if the final grade is to be maintained. If the fill is not fully compacted, it will settle around the foundation wall and eliminate positive drainage away from the home. In that event, the likelihood of a damp basement or crawl space, or even of major leaks at the basement floor level, is greatly increased, facilitating growth of microorganisms and subsequent IAQ and other problems.

Multifamily buildings. Multifamily buildings represent nearly a quarter of new housing construction stock and 18% of the new residential construction since 1990 (13) in the United States. As building types, they fall between other residential and commercial construction. The population in this housing stock has a higher proportion than single family housing of renters, lower income, and minority group members, but notas popularly perceivedelderly residents. The two main issues relating to indoor air quality and the design and construction of apartment buildings are the provision of mechanical ventilation systems and the lack of attention to details to prevent moisture penetration.

Ventilation systems are typically required in large apartment buildings to exhaust air from kitchens and bathrooms. Outdoor air is typically supplied through the corridors, where it enters the apartments through the gap under the door. However, because of noise complaints from the tenants on the top floors, the roof exhaust fans are often shut down.

New apartments are often required by code to have direct supply and exhaust at each apartment. There is no evidence from the field on the efficacy of these systems. Because of the conflicts over reducing energy costs and the provision of ventilation air, ventilation systems in multifamily buildings are often run intermittently, if at all. Apartment building managers and owners may not perceive ventilation as critical, and it may be given low priority in the maintenance and operation of the building, unless tenant complaintsusually regarding cooking smells from other apartmentsare frequent. Unlike single-family housing where infiltration and natural ventilation have been used to provide adequate air entry, the patterns of air flow in multifamily buildings are quite complex; depending on the height of the unit and the wind direction, some apartments may not receive any natural infiltration.

Moisture inspection and repair. Moisture is a major problem in multifamily buildings, because of the configuration of units. Balconies are prime locations for rain penetration, and flat roofs may be ineffective in preventing water entry. Coupled with the frequent lack of maintenance, moisture entry in apartments can lead to water-damaged materials. Another source of moisture in apartments is the use of unvented gas stoves and ranges for space heating. In large multifamily buildings, tenants are often billed directly for their electric space heat, but the gas stove is typically metered centrally and the tenants are not billed for their individual consumption. The tenant realizes the economic benefit of using the "free" gas heat, but the unvented stoves produce a great deal of moisturein addition to the combustion gasesthat frequently results in condensation on walls and other surfaces.

Entry mechanisms. (1) External leakage. There are two entry paths through which moisture can enter the residential environment. The first is leakage through the building shell, either through the roof, walls, windows, doors, or other building structures and components. The second is through paths below grade slabs and walls. (2) Internal leakage. Another cause of water presence within the home is internal leakage or overflow (i.e., pipes, basins, tubs, appliances) or condensation of internal moisture on cold surfaces. Moisture condenses at a temperature known as dew point. Expressed in units of temperature (degrees), the dew point varies with the temperature and the relative humidity within a space. For example, if a home environment is kept at 75° F and 50% relative humidity, any surface lower in temperature than 55° F will cause condensation to occur. Thus, cold window surfaces can promote condensation with subsequent water damage and mold growth at window sashes within and on the surface of adjacent walls. This problem is most likely with single-pane windows or thermally unbroken window frames in cold climates. Installation of furnaces directly onto concrete floors may also promote mold growth as dew-point condensation occurs during the summer. Leaving a small gap between furnace and floor can solve this problem. The manufacturer's installation instructions should be consulted for more information.

Preventive maintenance and inspection checklist. The workshop participants' recommendations for homeowners' checklists for periodic inspection and repair as required, to prevent leakage and sources of condensed moisture within the home are shown in Tables 2 and 3.

Moisture control in the home. Remediation is generally a two-step process undertaken once the presence of water has been detected. The first and obvious step is to prevent further damage by correcting structural defects, repairing leaks, correcting drainage, and managing internal sources.

The second step involves repairing the damage. Mechanical deterioration, spalling, rot, component separation, and delamination generally require the conventional correction techniques of removal, patching, and/or replacement. Hidden surfaces should be fully exposed to examine moisture entry or deposition sites for signs of mold or bacterial growth. These contaminants are usually readily identifiable by color, texture, or odor, and, once identified, they need to be removed.

Inspection and maintenance of residential HVAC systems. HVAC systems that are poorly operated or maintained can cause significant indoor air quality problems by not providing proper environmental conditions of temperature or humidity, or by contaminating living areas through malfunction. Most HVAC systems in homes are not designed to clean air by removing particlesother than very large particlesand gases. A list of tasks designed to prevent operating and maintenance problems is given in Table 4.

HVAC remediation in the home. This section deals with remedial procedures to be employed once signs of HVAC malfunction are detected.

Remediation is again effected in two steps. First is the determination of a design or installation deficiency, or a maintenance problem such as improper heating system flue sizing, installation, or slope. Common deficiencies also include improper pitch of the air conditioning condensate pan with inadequate drainage and inadequate disposal of collected air conditioning condensate (e.g., piping condensate to the space under a basement or crawl space floor slab). Improper filter size installation permits bypass of dust particles and their reintroduction into the house. Once a deficiency is identified, then the second steprepairing the damageshould take place.

HVAC maintenance issues. Low airflow, odors, and discomfort can result from blocked filters or obstructed or closed air ducts. Humidifiers require frequent cleaning during the humidification season, and can themselves be significant sources of microorganisms. In combustion appliances, fuel-air ratios can be incorrect, resulting in incomplete combustion, and leading to a release of carbon monoxide or carbon particles. In older systems, heat exchange surfaces may deteriorate or become punctured, liberating products of combustion into the space. A preseason service contractor or utility checkup of a heating system should identify many of these defects.

Control of residential renovation processes. To assure that occupants will not be adversely affected by renovations generating dust, particulates, or vapors, the space under construction should be physically isolated from the rest of the residence, and air from the isolated space should be exhausted. The supply and return ducts of the heating and air conditioning system that serve this area should be sealed with 6-ml polyethylene sheeting and the ducts kept clean during construction. If the existing HVAC system will be reconnected to the renovated or remodeled space, the capacity of the system must be adequate to provide the required/desired thermal and air quality control throughout the residence (14, 15).

Other IAQ Problem-Solving Issues

Emission tests. To eventually establish emission guidelines, architects, purchasing agents, and general consumers will require both accurate emissions testing and an understanding of the health effects of emissions. Emissions from a great variety of materials have been measured using controlled chamber tests. American Society for Testing and Materials (ASTM) Standards for chamber testing have been established and emission rates are usually reported as "steady state" in mass (microgram or milligram) per square meter per hour. These studies have been conducted at national and private facilities in North America and Europe. Results depend on the test condition's temperature, humidity, and volume flow rate. Emission rates are shown to depend on material preparation, preconditioning, and age. For example, emissions from paints vary with drying rates, number of layers, and composition.

We know substantially less about the emission rates of materials under conditions of actual use. Only recently has a standardized method for in situ testing of emission become available (16, 17). Although "as used" conditions are more relevant from the point of view of the occupant, tests of this type will not provide a readily useful way to discriminate among components. Standardized laboratory testing, along with modeling and health evaluation, does provide an objective evaluation scheme to compare among products.

Product labeling. Modern building materials and products may have complex chemical formulations and release volatile organic compounds (VOCs). There is a substantial body of literature and general experience that associate elevated mixtures of VOCs with symptoms (18). Products are often used on a daily basis in homes and offices, and population exposures are ubiquitous. Aging of materials and/or reactions with gases (i.e., ozone) may continue the release of VOCs or aldehydes. Emission rates and composition vary among specific products and sometimes among batch productions.

In the long-term, it may be cost effective to reduce emissions from building materials and equipment. Reduction is accomplished by product/component reformulation and process/ production controls. Removal or reduction of these and other sources avoids total reliance on ventilation to achieve a safe indoor air quality. Broader societal gains potentially include conservation of petroleum chemical stocks, reduction of photochemical compounds, and conserving of energy.

A study of the olfactory properties can also be helpful in understanding the sensory emission of building materials (19). Recently, Jensen and coworkers (20) compared the perceived (relative) odor intensities with chemical emission data from 13 linoleum products. Multivariate analysis of the data revealed that two principal factors could explain 68% of the odor intensity variation. The factors were aliphatic C₆-C₈ acids and C₅, C₇, and C₁₀ unsaturated aldehydes, respectively. The GC/sniffing analysis of emissions and the above approach appear to be a powerful combination to identify odorous VOCs.

The Danish indoor climate labeling system. Denmark uses a labeling system that rates VOC emission from building materials according to impact on comfort and health (21). The system unifies chemical emission testing over time (months) (including a standard room and mathematical modeling of the emission profile, when necessary), and health evaluation. The Danish system focuses on comfort and includes odor annoyance and mucous membrane irritation, with plans to add other material characteristics (e.g., fiber release). Two design criteria were set: the labeling system shall be easily comprehensible, and, at the same time, operational and dynamic. The parameter used for labeling is the time value t(C_mi) required for emissions to decay to a point at which room concentrations would be below the indoor relevant values, C_mi of VOC_i, presently based on either odor detection thresholds or mucous membrane irritation thresholds. The time value, t(C_m), is a measure of the duration during which new building material may increase exposure, as well as the probability of indoor air quality problems. Odor thresholds are used because they generally are at least one order of magnitude lower than mucous membrane irritation thresholds. The system may also be used for single VOCs when a specific health end point has been reported. In addition, the system has a built-in safety procedure for sensory testing over time, thus providing sensory emission profiles (intensity and acceptability) by the use of a special chamber and a panel of judges (22). The evaluation should be performed at approximately the same time as the chemically determined time value. Several building products have now been labeled by this process.

The Canadian experience. To help builders, architects, and sensitive persons who are intending to build and renovate, the Canada Mortgage and Housing Corporation has compiled a reference guide on building materials (23). Product listings for residential construction materials were gathered that contain information on health effects from two sources: existing or published health information and experiential information based on the experiences of perceived environmentally hypersensitive persons on exposure to these materials.

It should be noted that incentives to protect the environment such as recycling materials may not be compatible with efforts to improve indoor air quality. The incorporation of recycled materials can introduce new pollutants into the indoor environment, e.g., recycling rubber tires. Although the landfill burden is reduced, using them in such products as carpet underpads results in an increase of emissions from rubber inside buildings. The applications of recycled materials must be carefully selected. Recycled celluloseprimarily newsprintis used in chemically treated slurry for insulation in residential construction. In hot and humid climates, this can provide a microbial growth site, as the composite is closed in with gypsum prior to complete dryout. There is also potential outgassing from the chemical fire retardants used in the slurry to meet fire code restrictions

Strategies to encourage product labeling. For labeling to be useful to decision-makers, including consumers, architects, interior designers, engineers, and building owners, it must be relevant to design-condition parameters and also must identify the classes of contaminants of concern. For target products to reduce VOCs, labeling should probably be kept to a very simple pass/fail standard. Behind this label, additional standardized, independently tested information should be available to those charged with special construction of low-emissions buildings for sensitive populations or for specific climate conditions. Information on the VOC emission rate should show a simple quantitative analysis tool that relates square feet of installation to cubic loads. Any quantitative standard relating to the performance calculation method should recognize the inherent difficulties in assessing total surface areas of all materials specified for buildings and the relatively limited practical application of this method for most types of construction. If the quantitative analysis standard is simplified, it is more likely to be used in ventilation load calculation.

Supply-type strategies for reducing VOC emissions from building materials can complement demand-type strategies such as product labeling. One approach is to provide an incentive to reformulate or modify products by, for example, revising the current system for reporting and regulating emissions at the point of manufacture so that downstream emissions are also considered, thereby regulating total emissions instead. Under this approach, manufacturers who could demonstrate reduced emissions at the point of end-use could take credit for emissions reductions in their Toxic Release Inventory filings and pollution prevention strategies. This could shift the emissions from locations where effective ventilation is problematic to locations where exhaust systems designed to eliminate large amounts of emissions are present, and reduce the overall burden of dealing with released chemicals while effecting greater reductions of population exposures. A variation of this approach would be to foster development of voluntary industry standards for VOC release on a product-by-product basis. Although this approach has some appeal and follows the current cooperative trends, results to date have been mixed. Substantial improvements in woodstove performance have been made. However, labeling for carpets lack specificity and sensitivity and consequently has limited usefulness for architects and consumers.

Recommendations

The problems in indoor air quality resulting from the common practices of building design, construction, commissioning, and maintenance/operation are not likely to improve without involvement of other stakeholders. A potentially important player in the solution of indoor air quality problems is the insurance industry. Not only is the insurance industry a major holder of commercial building investment property but its business encompasses workers' compensation and tort liability coverages. To date, workers' compensation claims for building-related illness are limited by physicians' inability to identify building-related etiologies for asthma and hypersensitivity pneumonitis in individual patients; lack of familiarity of infectious disease physicians of the workers' compensation coverage for Legionella pneumonia among employees; and infrequent claims of financially significant, permanent impairment for sick-building syndrome. Nevertheless, the financial incentives for insurance companies may increase as a function of public and medical professional recognition and the shift from workers' compensation to third party liability claims against manufacturers, building owners, and ventilation contractors.

In a climate of litigation, another opportunity for intervention/prevention regarding indoor air quality is during lease negotiation, which could include specifying building performance for indoor air quality. In the short run, marketing of indoor air quality performance may provide a competitive advantage for building owners and a health/productivity advantage for tenants/buyers seeking commercial or residential property. In commercial property transfers, financial interests could include indoor air quality inspections both for system design and postdesign performance. Such inspection is routine for termite infestation in some parts of the country, for asbestos in some older commercial properties, and for radon in residential property in some locations. Thus, extension of due diligence with respect to broader indoor air quality concerns is perhaps feasible in order to increase incentives to address indoor air quality by building owners.

Several professional organizations show substantial activity regarding indoor air quality because of membership involvement in problem-solving or prevention. The leading group in impact is ASHRAE, as its standards become the basis of building codes in many localities. However, the process by which standards evolve is driven by consensus among various interested parties, and public health is not necessarily the driving principal. Other professional groups with substantial educational or standard setting activities include the Building Owners and Managers Association (BOMA), International Facility Management Association (IFMA), American Institute of Architects (AIA), American Industrial Hygiene Association (AIHA), and the American Conference of Governmental Industrial Hygienists (ACGIH). The ACGIH Bioaerosols Committee does not believe that quantitative standards with respect to bioaerosols are feasible given current measurement methods for most bioaerosols and the dearth of exposure-response relationship information.

Several trade associations may develop or have developed an interest in indoor air quality because such concerns are critical to their business and protection from liability. These include the North American Insulation Manufacturers Association, the Air-Conditioning and Refrigeration Institute, the North American Duct Cleaners Association, the National Air Filtration Association, the National Association of Home Builders, and the Association of Home Appliance Manufacturers. These trade associations should have a substantial interest in needed research on etiologies of indoor air quality complaints, along with their resolution, and prevention. Certainly, individual companies have occasionally taken aggressive roles in IAQ investigation teams because of attribution of IAQ problems to their products.

Employee representatives have taken a role in motivating attention to indoor air quality for specific groups of employees. Examples include service, teacher, and government employee unions. With the absence of accountability for indoor air quality, the role of an educated public in motivating change is important. Approaches are needed for informing the public, possibly beginning with school curricula.

Finally, government at federal, state, and local levels is an important stakeholder regarding indoor air quality. Government buildings account for a significant number of office buildings in the United States, and government workers are among the major groups affected by poor indoor air quality. Aside from productivity concerns in an era of government downsizing, the government has substantial agency commitment pertinent to indoor air quality regulation, investigation, and research. The obvious federal agencies include the General Services Administration (GSA), the Occupational Safety and Health Administration (OSHA), the National Institute for Safety and Health (NIOSH), the Centers for Disease Control and Prevention (CDC), the Department of Defense (DOD), the Department of Housing and Urban Development (HUD) and the Department of Energy (DOE). State and local governments also have the burden of governmental employee complaints and the responsibility for public health investigation of complaints from nongovernmental workers, including the substantial source of problems in schools. There is perhaps room for an educational partnership between government agencies and trade associations that can lead to favorable changes for indoor air quality. In this regard, NIOSH and CDCwith respect to communicable disease in hospitals, schools, and other community facilitiesmay be able to take leading roles as nonregulatory agencies.

	SOURCE CONTROL

Source control is essential to achieving healthy indoor air quality. The methods used for source control vary according to the pollutants and range from complex and costly solutions (e.g., earth removal in the case of severe radium contamination) to relatively simple remedies (e.g., not smoking in the home). This section includes recommendations for the general population and some recommendations for special populations. A provides a list of recommendations for reducing the number of particles in the indoor environment to minimize the negative health effects of indoor air pollution. As possible, statements in this section are referenced to the literature, but some recommendations are based on professional judgment, absent published data. The pollutant sources addressed include moisture, building materials and products that emit VOCs, pesticides, household products, and other point sources and particulates. Specific sources well-covered elsewhere in the literature and in the previous workshop such as environmental tobacco smoke, radon, asbestos and lead paint, did not receive extensive consideration by this working group (24, 25). For radon, asbestos, and lead paint, the Environmental Protection Agency offers guidance (26).

Moisture

Moisture underlies some of the most common indoor air quality problems. For example, high relative humidity allows house dust mite infestation to occur, and water damage and water reservoirs facilitate proliferation of microbes. Water incursion can also lead to structural degradation of building and ventilation system components, which can result in further indoor air quality problems.

Associations between moisture problems and health effects. Moisture-related health problems are diverse, including allergic diseases, infection, and complaints of musty odors. The allergic diseases affected by moisture include allergic rhinitis and asthma, with house dust mites and building-associated fungi as possible moisture-related triggers for those diseases. Hypersensitivity pneumonitis, a less commonly recognized immunologic lung disease, has occurred in endemic form in buildings with contaminated spray water humidification, water-damaged materials, and visible bacterial or mold growth. Apart from physician diagnoses of asthma and hypersensitivity pneumonitis, epidemiologic studies document that indicators of residential dampness are associated with respiratory symptoms in children (30).

Contaminated reservoirs from which water is entrained into indoor air can produce bacterial infection, with Legionella pneumonia as the prototype. Legionellosis has been attributed to diverse sources, including cooling towers, hot water heaters, shower heads, and whirlpools. Pontiac fever, a febrile syndrome, is also associated with exposure to aerosolized Legionella bacteria. Immunocompromised persons are at risk for fungal infection from saprophytic fungi in indoor air (31).

Sources of moisture. The primary source of moisture-related problems is usually in the building envelopein the walls, roof, and foundation of the structure. A major area of concern is the failure of the water-proof roof membrane. Leaks typically occur at the junction of the roof and the wall parapet. Any opening in the exterior envelope (e.g., vents, flashings, skylights, doors, windows) is a potential site for the entry of moisture. As mentioned previously, balconies and overhangs are also well-documented areas of moisture entry. Deterioration and ultimate failure of sealing materials such as grout, caulking, and other sealants can lead to moisture entry. The location and the installation of the vapor barrier in the building envelope are critical in preventing future moisture damage, particularly moisture condensation in the walls. Sub-grade leakage from rain, irrigation, and ground water all speak to the need for careful design and construction of basement walls and foundation drainage.

In addition to moisture introduced from outside the building, there are also numerous indoor sources of moisture, including unvented combustion equipment, as well as activities such as showering and cooking. Good design should provide ventilation for areas where indoor moisture levels can be high. People, pets, and plants are sources of indoor moisture, as are indoor pools, spas, and fountains.

HVAC equipment is a frequent source of moisture problems because of inadequate disposal of condensate from condensation on pipes and ducts and from cooling coil condensate drainage and carry-over. Standing water in humidifiers, evaporative coolers, cooling towers, condensers, and air washers may become a source of contamination. Water damage, whether caused by flooding from broken pipes or natural flooding, may also lead to moisture damage of materials.

Moisture mitigation strategies. Drying affected areas and materials is a first step in tackling moisture-damaged areas. Identifying the sources of recurrent moisture can help determine strategies for remediation, whereas repairing the damaged area may not address the underlying reasons for the moisture. In the case of moisture damage, all water-damaged porous materials such as carpets, insulation, acoustic materials, and ceiling tiles, should be removed and replaced.

Inadequate dehumidification capacity of HVAC systems may lead to moisture problems as well. HVAC equipment should be designed and installed so that reservoirs of stagnant water can drain as intended; for example, drain pans and sump pumps should be sloped to drain. A critical design requirement is that all systems have easy accessibility to allow for routine inspection and maintenance; individual interior components of systems must be easily accessible as well.

Building Materials

Building materials that are potential sources of indoor pollutants include particleboard, adhesives, glues, sealants, wall coverings, paints, stains and varnishes, cabinets, tile grout, plasters and cements, furniture, draperies, carpeting, and plastic laminates. The principal pollutants from these materials are volatile organic compounds (VOCs) and semivolatile organic compounds (SVOCs). Emissions from building materials are typically maximal at the time of installation and retrofitting, and outgassing decays over a period of weeks or months. Thus, building materials are more likely to be sources of problems during initial occupancy.

Associations of exposure to VOCs with health effects. VOCs are ubiquitous in indoor air, although they are also found outdoors. They can be characterized by their indoor/outdoor concentration ratios. For typical indoor-related VOCs, the ratio is larger than 1. Concentrations of indoor VOCs may be characterized by substantial variation both in time and in space, depending on the source dynamics and the building attributes. Indoor concentrations are typically below Threshold Limit Values (TLV) levels and airway irritation thresholds, but often above odor thresholds.

Links between VOC concentrations and complaints about indoor air quality and symptoms have been postulated. However, the etiology of complaints and symptoms is likely complex and multifactorial, and characterizing the contributions of VOCs may be difficult. Effects of VOCs might follow directly from inhalation of gases, but VOCs may also have effects by binding to particles. Particles, in particular, floor dust, can act as carriers of VOCs and SVOCs. Exposures to VOCs and SVOCs might thus occur through deposition of particles on the skin, as well as by inhaling the compounds themselves.

Mechanistic hypotheses have been advanced that ascribe a role to VOCs in causing symptoms in building occupants. Thus, responses have been proposed as consequent to: (1) total exposure to VOCsadditivity of individual VOCs is proposed so that a mixture might have adverse consequences even though individual VOCs are present at concentrations well below TLV values; (2) specific irritants, e.g., formaldehyde or acrolein, underlie the effect; (3) VOCs in combination with other pollutants (particles) or other elements of the work environment combine to produce adverse effects; (4) physicochemical properties of the VOCs such as acidity, basicity, or effects on surface tension of the eyes tear film are responsible; (5) odors trigger symptoms; (6) reactive species formed by chemical reactions in indoor air are responsible.

Furthermore, in most indoor environments, pollutants other than VOCs are present, such as ozone, nitrogen oxides, and particles with VOCs adsorbed on their surfaces. In addition, other factors affecting responses to air pollutants such as thermal climate and psychosocial dynamics of the workplace should be considered in a holistic manner (18).

The VOCs emitted from building materials may originate from different types of pollutant sources. Primary pollutant sources emit free (nonbound) VOCs. The primary VOC pollutants are generally of low molecular weight. Chemically or physically bound VOCs may also be relevant to health. Hydrolytic decomposition may also result in release of VOCs, as may oxidative degradation and reemission of adsorbed VOCs.

Specific Building Materials

Carpets. The benefits of carpets include acoustic control, soft surface, protection against trauma, thermal insulation, durability, attractiveness, and resilience. However, carpets can be reservoirs for allergens and growth environments for house dust mites and molds. To date, these concerns about carpets have related to their uses in homes, offices, and schools, and particularly to their being sources of biologic particulate antigens. Carpet underlays may also be VOC emitters, and the adhesives used for commercial installations to subsurface have a potential to release VOCs. There is also concern that carpet cleaning can be a source for indoor pollutants, as can fumigation of carpets.

The issues below relate primarily to special populations (32).

1. Reservoir for allergens. House dust mites are unavoidable in climates of high and moderate humidity. The carpet is not the primary means of exposure but provides a reservoir for infestation of bedding in homes and for the generation of airborne particulates with vacuuming and human activity. For animal dander from household pets, carpeting is the major reservoir from which particulate antigen can be generated by human activity. Approximately 30% of American homes have one or more cats and 40% have one or more dogs, with more than 60% having one or both types of animal (33).
2. Growth environment for house dust mites and molds. Dirt accumulates over time, rendering the carpet a favorable medium for the growth of molds. Carpets in basements, bathrooms, and other areas prone to moisture are likely sources of molds. Carpets laid on concrete slab-on-grade are also subject to trapping of moisture below the carpet, which is a potential source of microbial contamination.
3. Cleaning and fumigation. Carpet steam injection cleaning is less likely to leave large amounts of residual moisture than carpet shampooing, but it may leave carpets damp, contributing to mite and mold growth. Both methods may leave residual chemicals, so products should be carefully selected. Waterless processes are chemically based, and more information on the potential health effects of these products is needed. Vacuuming can contribute to the load of respirable particles in the air. This loading can be avoided by using equipment that is directly exhausted outside (i.e., central vacuum systems), with a HEPA filter or a double electrostatic bag.
4. Chemical emissions. Numerous VOCs, including 4-PC (4-phenyl cyclohexene), toluene, and styrene, have been identified as released from carpets. These emissions originate from the latex backing and the numerous chemical treatments applied to the carpet fibers such as those for soil and stain repellency, antistatic, and pest resistance. Chemical emissions are higher when the carpet is newly installed, and then diminish with time: it may be prudent, therefore, to increase ventilation at the time of installation. As carpets age, the reservoir effects in No. 1 above predominate.
5. Odors. Carpets act as efficient sinks for odors generated from human activities such as cigarette smoking and cooking. Solvent emissions from painting and other maintenance activities can be adsorbed by the carpet fibers and reemitted.
6. Carpet underpads and adhesives. Carpet underpad materials also contribute VOCs. The underpad also serves as a reservoir for dirt from the top or moisture from below when laid on concrete. Underpads deteriorate in time, turning brittle and becoming sources of particulates. The underpad selected should be stable and have minimal emissions. Commercial installations typically use adhesives. Mechanical installations using tacks or fasteners on soft subfloor surfaces or Velcro-type tapes on concrete or hard surfaces are preferable. Water-based adhesives have fewer emissions than solvent-based adhesives.

Wall vinyls. These materials are VOC emitters, as may be the adhesives used to mount them. If a durable wall surface is needed and a latex-based paint is not acceptable, a water-based commercial grade coating should be used instead of vinyl wall covering.

Paints, stains, and varnishes. Interior water-based paints can substitute for oil-based paints as their VOC emissions tend to be lower, although emission decay may be much slower. In cases where water-based paints are not appropriate, special durable, washable paints have been developed for the market. There are numerous labeling and manufacturer's information sheets available for guiding the consumer. In some instances, odorless stains and varnishes are available. Stored paints in enclosed spaces such as garages may affect indoor air quality and should be recycled rather than stored or disposed of improperly.

Drywall. Drywall is a fairly inert substrate and an acceptable finish material from the IAQ perspective. Installation and finishing generates particles. When drywall is being taped and sanded in occupied buildings, all ventilation ducts should be sealed, as should openings to occupied areas.

Ceiling tiles. Suspended ceiling tile systems may form the underside of the return airflow in an institutional or commercial building. The top surface of the ceiling tile is typically covered with one coating of sealant to offset the potential for fine particulate dusting. Sample tiles should be examined carefully to assure that the sealant coat is effective. Where the return air plenum has an exposed steel structure sprayed with fire retardant materials, care should be taken to ensure that the spray-on material has enough cementitious content to maintain proper binding and prevent contamination of the return air plenum. Fully ducted return air systems using sheet metal ducts are preferable to using ceiling cavities as the air plenum.

Cabinets and other uses of particleboard. Cabinets made of particleboard or medium-density fiber board (MDF) manufactured from urea-formaldehyde resin can be sources of formaldehyde and other organic compounds. Emissions are of less concern if solid hardwood is used, but higher costs are involved. If particleboard or MDF are used, all surfaces and edges should be laminated to encapsulate the emissions. Alternatively, several coatings of a low-odor acrylic sealant can be used. Composite wood in substrate applications such as flooring system reinforcement is a potential source of formaldehyde and other VOCs; carpet over pressed wood subfloor will still allow the emissions to pass through. Other subfloors such as construction-grade plywood, manufactured with phenol-formaldehyde resin, have lower formaldehyde emissions than does particleboard or MDF, and should be selected.

Adhesives, glues, and sealants. These can be sources of aliphatic hydrocarbons, aromatic hydrocarbons, chlorinated hydrocarbons, ketones, and esters. Exposures should be minimized by vacating the premises and increasing ventilation during and after application. Use of these products may be reduced by mechanical connections and cementitious grout compounds. Alternatively, low emissions products are available and consumers should use manufacturers' product information in making their selections.

Plastic laminates. Plastic laminates are typically used in the finishing of counter tops, cabinetry, elevator cab interiors, door surfaces, and washroom partitions. Laminates are unlikely sources of emissions; they can, as stated previously, seal the emissions from the substrate (usually particleboard or MDF). Emissions, however, will escape from unlaminated surfacesthe undersides, backs, edges, and holes for adjustable shelving. All surfaces should be laminated or sealed, or alternates for application should be considered. Solid wood products could be used for cabinetry and doors, whereas metal partitions are recommended for washrooms, mirrored glass and fabric installations for elevators, and ceramic tile, stainless steel, or natural stone for counter tops.

Furniture. Furniture made of composite wood can be a source of formaldehyde and other emissions. Upholstered furniture can also be a source of formaldehyde emissions. The emissions can come from the fabric covering, chemical finish on the fabric, the foam upholstery, or composite wood base. It can also support mite growth and be a reservoir for mite and animal dander allergens. For persons prone to or having allergic diseases or asthma, it may be prudent to consider limiting the amount of upholstered furniture in their home.

Pesticides Used In or Around the Home

All pesticideswhether herbicides, insecticides, or fungicides, depending on their targetare intended to control pests. The active ingredients are semivolatile, whereas inert ingredients and carrier solvents may have varying volatility and content. The inert ingredients may themselves be as or more toxic than the active ingredients. Of the many pesticides that are in use today, we know the acute and chronic health effects of only a small fraction.

Herbicides applied on lawns and termidicides applied around foundations can enter the house in soil gas, in the same manner that radon enters the house. These chemicals therefore potentially can contaminate indoor air of homes. The termidicides used have been the persistent organochlorine insecticides such as chlordane, and contamination of some houses has been demonstrated (34). Direct application indoors exposes the occupants to the volatile ingredients and residues. Exposure may occur through inhalation of particles on which these semivolatiles are adsorbed.

Homeowners may want to explore methods of controlling pests without the use of pesticides. Some pests, notably silverfish and carpenter ants, are bioindicators of moisture in the house. The first line of control of these insects is to control moisture. Cockroaches can be baited or trapped, and, when combined with meticulous sealing of entry points, disruption of food supply and cleaning offer effective control. Sticky or mechanical traps can help to control other common pests. For termite control, a successful method not employing large amounts of pesticides is to prepare baits containing a gram of a chitin inhibitor; this can control colonies of termites occupying several hectares (35). Fewer chemicals are used, and they are targeted to the pests with less potential harm to the environment and the occupants.

Household Products, Office Products, and Other Point Sources

Among the many different products used inside homes, offices, and other nonindustrial buildings, those that may introduce contaminants into indoor air include cleaning agents, polishes, paints, deodorizers, and even pens and marking pens. Other potential sources are personal care products, moth balls (pesticides), and adhesives. These sources are ubiquitous and are frequently used in large quantity. A 1986 Danish database study shows that more than 60,000 tons (12 kg/person) per year of cleaning and maintenance products for hard floor covering and furniture alone were used from more than 700 different products in Denmark. Some of these