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In practice, there is little to distinguish the control of contaminants from their treatment and mitigation. Treating an existing problem through mitigation or remediation is often the same exercise as preventive measures taken to control or avoid it in the first place. and once treated, the same actions become control procedures to prevent a recurrence. Some preventive actions, of course, can be taken that are not available in remedial treatment. Building design is an example. The full recognition of the importance of designing for IAQ acceptability is recognized and more fully elaborated in the ASHRAE Indoor Air Quality Advanced Design Guide (IAQDG) published in 2009.

Unless specifically mentioned, as in the new construction discussion, prevention and control strategies will be considered as one and the same in the following discussion.


Managing indoor air quality requires a basic understanding of toxicity and hazard. These terms are frequently used incorrectly in the press. They are not synonymous. Every substance is toxic to humans in some manner, or to some degree, even orange juice. A toxic substance becomes hazardous by intensity of the dose, the length of exposure or the manner in which it is introduced into the body. Few would fear orange juice in a glass, but no one would want it injected into his or her blood stream.

Hazard is actually a measure of risk or the probability that an unwanted event will occur. Hazard is usually measured in severity or magnitude. It is a product of toxicity and exposure (or dose). Exposure is usually defined as acute when it is intense for short duration, and chronic in the case of low level over a long period of time. Control procedures reduce or eliminate the level of toxicity, the dose, or both; thereby, reducing the hazard or risk.


In the process of controlling a contaminant, if it can't be eliminated, then some gauge of acceptable level is desirable. Building owners and facility managers, in most instances, simply do not need to know all the particulars about acceptable levels, measurement techniques, or the jargon that goes with it. When management gets embroiled in a serious problem, they soon learn more than they ever wanted to know about that particular pollutant.

Fortunately, about 80 percent of the problems associated with in door air quality can be identified with a walk-through inspection using simple diagnostics and an experienced and educated eye. Extensive testing is used in approximately 20 percent of the SBS investigations and the definitive cause is found in most but not all of those. The difficulties associated with investigations, as discussed in the preceding section, help explain why some cases are never resolved completely.

Testing for contaminants clearly meets the test of diminishing returns: it is progressively more expensive while the possibility of positive results declines.

The difficulties inherent in measuring contaminants, the limited talent available to analyze findings, and the high cost of measurement argue for an effective control and prevention program. Since such a large percentage of the problems can be found in a relatively simple walk through, control opportunities are relatively easy to identify.

Many only take a little common sense. If investigations and interviews, for example, reveal three findings: (1) occupants experience and report the symptoms associated with bioaerosols; (2) the area was recently flooded; and (3) the carpet got wet, the logical answer is: "replace the carpet." The alternative, in almost every case, would be to go through an exceedingly costly and elaborate process of testing for bioaerosols, only to end up with a recommendation: "replace the carpet" after the delay of several weeks of increased exposure and reduced productivity.


To accommodate occupant needs, building owners and facility managers must recognize the multiple purposes of controlling the quality of indoor air. First of all, federal requirements for specific contaminants must be met. Furthermore, satisfying guidelines that do not have the force of law may still be financially and legally prudent as a defense against negligence in potential lawsuits.

The underlying purpose in all control procedures is to be sure the indoor air:

• maintains the quality needed for safety and health;

• satisfies comfort and productivity needs; and

• is as cost-effective and energy effective as possible.

The variability of organizational and occupant needs further com plicate control procedures. The "status quo" is never static. As facility managers and operating engineers have long recognized, seasonal variations call for accommodations in air conditioning (heating and cooling) and in lighting. In fact, controls to meet these needs vary from day to day, even hour to hour. Similarly, air quality needs may vary by tasks and the scheduling of those tasks. For example, VDT use may be much greater at the end of the month. Or, copiers may suddenly be used extensively just before the big meeting.

Obviously, operators could be run ragged trying to meet every little variation. The goal is to avoid rigidity in implementing control strategies and to allow sufficient flexibility and resiliency to meet these variables. As more sophisticated automated systems emerge, their sensing/control devices will facilitate more subtle responses to individual needs and conditions.

Control Methods

Methods for controlling fall into only three categories: (1) elimination at the source(s)-source control; (2) dilution with less contaminated air-ventilation; (3) extraction with some type cleanser-filtration. They can be further broken into more precise measures of design, operation, or maintenance to help identify the needed control actions. Many control procedures were first developed in the industrial workplace. While industrial hygiene and safety considerations are beyond the purview of this guide, some tactics are mentioned here because of their carry-over implications to other occupational settings. The following listing pro vides greater detail on the wide variety of tactics available for prevention and control of contaminants. Considerably more detailed guidance is available in the ASHRAE IAQDG, especially in regard to availability and evaluation of low-emission materials and the selection of appropriate filtration and air cleaning equipment.

1. Elimination-the complete removal of; (a) the biological agent, (b) a toxic substance, (c) a hazardous condition and /or, (d) the source.

Elimination procedures include maintenance actions to re move the breeding grounds for bioaerosols, the removal of friable asbestos, the banning of smoking, or the use of air cleaning devices at contaminant sources.

2. Substitution-the deliberate purchase or use of less hazardous materials; e.g., pesticide selection, the purchase of low emitting furnishings or building materials, the selection of latex/water based paints over oil-based paints wherever possible. Review of MSDS information will aid in the selection of low out-gassing product. Partly driven by the initial "Carpet Dialogue" with EPA, the Carpet Institute has developed a Green Label program that reports out-gassing data on carpeting products. Driven further by the Green Building and other labeling trends, such as "GreenGuard," other product manufacturers are providing testing data and additional content information that is helpful in selecting "indoor environmental friendly" products.

3. Isolation-containment, encapsulation, shielding, sealing, timing, and the use of distance are all means of isolating a contaminant or a source from exposure to humans. Distancing may be accomplished through location and /or time of use. Examples of isolation controls include painting or insect treatment during unoccupied hours, asbestos encapsulation, and removing ornamental plants from the facility before spraying with pesticides.

4. New construction/renovation design-many design steps can be taken to prevent problems from occurring including ventilation effectiveness, thermal comfort, lighting, the selection of building materials and maintenance needs. Filter selection and access, for example, is an often overlooked but critical design consideration.

Procedures to commission a new building, including extensive air purging or "flush-out" and occupancy schedules, should be considered. (See section on bake outs later in this section.)

Modifications to buildings to be avoided include changes that restrict original air flow design, such as partitions in an open space facility, or changes that increase heat and contaminant load beyond HVAC capabilities.

5. Product or process change-while borrowed from industry, change in process controls have applications in other settings. Component design to reduce emissions might be used, for example, to affect the way a Zamboni machine is exhausted at an ice rink.

6. Housekeeping and dust suppression-actions that keep surfaces clean of contaminants, prevent their re-dispersion, and /or eliminate personal contact entirely are important control measures.

Some very common place controls are windbreaks, care in pre venting vacuum cleaner leaks, improved vacuum cleaner bag performance to HEPA level for example, and efforts to contain/ isolate dusty sources, such as printers and paper shredders.

Walk-in contaminants should also be addressed and some excellent guidance is presented in the ASHRAE IAQDG under the section dealing with Track-off systems at entrances.

7. Maintenance and work practices-specifications for the proper work procedures to reduce or control contaminant releases for purposeful reasons, such as pesticides, need to be spelled out and should be part of training procedures. Maintenance practices (many of which cut across other control procedures listed here) are vital, especially in the automated control and HVAC areas.

8. Replacement-insulation, carpeting, wall coverings, etc., which when wet can serve as breeding grounds for microorganisms, need to be checked regularly and replaced immediately when damaged.

9. Education, training, labeling and warning procedures-some training, labeling and warning procedures are required by law.

Whether required or not, workers and management must be educated as to the nature of hazardous materials and ways to minimize risk in their use. In some instances, educating building occupants, guests or public may be necessary.

Owners may need to force some education on professionals, through specification or professional qualifications. The owner carries the ultimate responsibility to see that architects and engineers use appropriate designs and select safe building materials.

10. Sanitary procedures and personal protective devices-the use of hygienic principles to reduce or eliminate hazardous materials from a person may be critical under certain conditions. In a hospital setting, protective procedures are accomplished through clothing changes, showering, chlorination, etc. Protective devices are usually used where other control devices are not technically or economically feasible; e.g., respiratory protective devices when O&M people are working with microbial contamination.

11. Storage and disposal-laws prescribe the storage and disposal of some contaminants. Care should always be taken to use and store materials as indicated on the label. When in the slightest doubt as to proper use, storage or disposal, good control practices dictate contacting manufacturers, state and /or federal agencies first.

12. Filtering and air cleaning-the use of adequate and properly selected filters and purification devices in the air distribution system, with outdoor air and mechanically recirculated air, is an essential control factor. Filters and purification devices appropriate to the need should be used and maintained/replaced on a regularly scheduled basis. Generally, the conventional 1-2 inch disposable throw-away furnace filter does not provide adequate cleanliness protection for either the system or the occupants. In new construction, Standard 62 currently requires a minimum filtration efficiency level of MERV 6 on any system having a wet coil. Recommendations are pending to increase this minimum to MERV 8 because field research by Burroughs has indicated that the MERV 6 filter does not assure distribution system cleanliness. Design guidance for more advanced IAQ attainment is recommending MERV 13 minimums along with more elaborate filter seal and by-pass avoidance.

13. Ventilation-through increased outside air or exhaust with con trolled make-up air. Dilution is a preferred control when the contaminant/source is unknown, source treatment is too costly, or when the source is not localized. Ventilation control means much more than the amount of outside air brought into a facility. It includes the quality of outside air; the effectiveness with which it reaches occupants; and its efficiency in reducing contaminant levels. The opportunities and limitations of ventilation as a control are treated in greater depth later in the guide.

Management may also wish to seek the advice and counsel of medical experts as a control support through medical surveillance or treatment. Medical surveillance may include occupant preplacement screening that will restrict high risk persons or provide medical exclusion; e.g., reassignment by location or task of chemically sensitive individuals. Building related illnesses (BRI) by definition depend on medical verification, which in turn usually suggests the cause and the control measures to be taken.

Overriding all of these control procedures are some administrative and management considerations as well as judgment calls. Personnel rotation or scheduled relief breaks may be necessary to reduce the time of exposure to an essential process. As an example, equipment requiring relatively high power charges, such as computers, put positive and negative charges on tiny airborne dust particles; thus, attracting some while pushing others in the face of the operator. That's why computer and TV screens get dusty even on the lower side of convex surfaces. Unfortunately, the same amount of dust that is forced into the air, computer operators must breathe. These concerns and others related to the use of monitor screens may require task rotation and consideration of female workers who are pregnant. To assure control procedures are planned and executed properly, formal organizational steps to delegate authority and responsibility must be made. These management considerations are discussed in the management section.


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