Sampling Indoor Air Quality

How to ensure meaningful results for baseline, vapor intrusion, and LEED purposes

Spore trap samplers can capture a majority of spores and particulate matter in the air.
Today, indoor air quality (IAQ) assessments may be performed to find out more than just if a building's air is contributing to or causing adverse health effects in occupants. They also are conducted to establish baseline conditions, evaluate vapor intrusion, and determine if air quality meets requirements for Leadership in Energy and Environmental Design (LEED®) accreditation. These assessments often involve a variety of sampling methods to accomplish the intended purpose.

In order to develop a sampling plan that will generate meaningful results, an investigator should consider how the results will be interpreted and used. The investigator gains a thorough understanding of the nature of the building through building walkthroughs. Responses to complaints, conversations with building management and affected individuals, and an understanding of types of physiological responses that might occur as the result of some exposure are important factors in preparing a sampling plan. Finally, the investigator should understand the nature of the suspect pollutants, which may include biological agents, chemicals, and particulates or aerosols from various sources inside or outside the building.

An investigator performs general indoor air quality indicator sampling.

Once the investigator has identified substances for sampling, appropriate sampling methods can be selected. The following are brief descriptions of sampling methods for common IAQ contaminants.

General IAQ Indicators
General IAQ indicators include carbon dioxide (CO2), carbon monoxide (CO), temperature, and relative humidity (RH). These are easily sampled using direct-reading instruments. Many of the available instruments can store spot checks and datalog over extended periods. It is important to use instruments that are properly maintained and calibrated.

Testing for CO may be done as part of achieving LEED accreditation.

Volatile Organic Compounds
Volatile organic compounds (VOCs) are emitted from building materials, finishes (floor and wallcoverings), and furnishings. VOC testing may be conducted in response to IAQ complaints, to achieve LEED accreditation, or to evaluate vapor intrusion from underground contamination.

Testing methods include calibrated sampling pumps, sorbent tubes, and evacuated canisters. The purpose of the testing may dictate the methods to some extent. For example, LEED® for New Construction Version 2.2 specifies testing protocols consistent with the U.S. Environmental Protection Agency Compendium of Methods for the Determination of Air Pollutants in Indoor Air. These methods were published in the 1990s, and it can be difficult to find a laboratory that uses them. Equivalent methods have been developed and analytical laboratories will work with investigators to identify the appropriate methods for the purpose. Results may be reported as total VOC (TVOC) or as individual VOC concentrations.

Formaldehyde, a common indoor air pollutant, is a VOC. It is found in glues and adhesives, pressed wood products, fabrics such as draperies and upholstery, paints and coatings, paper, and even personal care products such as cosmetics. Indoor concentrations tend to be very low, and the sampling method must take this into account. Sampling may be conducted using calibrated sampling pumps and sorbent tubes or passive sampling badges. If extended sampling times are necessary, passive badges are a good choice. Consult with the analytical laboratory to determine the best sampling method for the purpose.

Other VOCs can be emitted after the installation of new carpet. The “new carpet” smell is usually the liberation of 4-phenylcyclohexene (4-PCH), an odorous contaminant constituent in carpets with styrene-butadiene-latex rubber (SBR) backing but can also be a combination of caprolactam, a component of Nylon-6, and other VOCs.

To measure for these compounds, an investigator can use charcoal media found in sampling tubes that require a pump to pull air through the tube or passive badges that contain a charcoal bed but no pump. Another method that is general screen tool for VOCs is to obtain a sample of the air using an evacuated canister that is opened in the suspect area, filled with a sample of air, and analyzed at a laboratory following either a U.S. Environmental Protection Agency VOC or Occupational Safety and Health Administration analytical method. This method is not specific for carpet VOCs but provides an indication of off-gassing compounds used in the production of many synthetic carpets.

Please note that 4-PCH is a LEED-evaluated indoor air contaminant.

Particulates and Fibers
Usually invisible, indoor airborne particles are comprised from many sources, such as clothing fibers, animal dander, organic particles (plants, molds, wood), insect parts, minerals, smoke, and soot and a host of other combination of materials. Some of these airborne particles and fibers can act as allergens to sensitized people or cause indirect and direct health effects. Sampling can be conducted to determine the quantity of particles, evaluate their physical properties, or identify the composition of the particulate. Equipment is available that provides real-time particle counting and sizing but cannot differentiate the composition of the materials. To determine the structure, composition, and help identify the source, samples collected on the proper filter media can be submitted to a laboratory for determination by polarized light microscopy and scanning electron microscopy.

Testing for particulates may also be done as part of achieving LEED accreditation.

Sampling for molds in indoor environments is typically conducted using three methods:

  • The first is a tape lift using clear, single-sided tape that is touched to a visibly contaminated surface. This sample is analyzed under a microscope to identify the types of molds present.
  • The second is an air sample that pulls a measured volume of air and impacts mold spores and other particles onto a sticky surface. This tape surface is analyzed by a microscopist to identify and count the genus of the mold in the air, hyphae, skin cells, pollen, and other debris.
  • The third type of sample is to obtain a culturable air sample. Culturable testing is often used when it is necessary to identify mold species, usually in health care settings. This method uses a high-volume pump, pulling up to 28 liters of air per minute, connected to an impactor such as the Anderson impactor. The impactor is equipped with a culture plate containing a specific type of agar as media for the mold to grow. The impactor is connected to the pump, air is pulled through small holes in the cover plate that increase the air velocity, and mold spores are impacted into the agar and then cultured for a few days to grow the mold. The number of colony forming units (CFU) are calculated by the laboratory and reported in CFUs per cubic meter of air (CFU/m3).

Mold spore sampling is performed for many reasons and the investigator should determine why they are sampling and what level is acceptable. Interpretation of the results continues to receive considerable debate, and there is some ambiguity on interpretation of mold sampling results. The results from air and tape lift sampling must be evaluated properly by someone with knowledge of mold contamination.

As with any evaluation of a potential health hazard, knowledge of the behavior of indoor air pollutants and other air quality variables will help guide the investigator in selecting the correct sampling methods and equipment. Once the investigator has identified the intent and scope of the IAQ investigation, either by visual assessment, questionnaire or interview, the method selection, equipment calibration, documentation, and interpretation of the results comprise the IAQ assessment. For the health and safety professional, knowledge and skills in conducting quantitative and qualitative investigations helps guide the reliable investigation into known and recognized indoor air quality concerns with the intent of finding a suitable resolution.

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