Department of Health Seal

TGM for the Implementation of the Hawai'i State Contingency Plan
Section 7.11


This section provides a general overview of recommended indoor and outdoor air sample collection procedures and is not intended to be comprehensive. More detailed guidance, including the references noted, should be reviewed prior to the preparation of an indoor air sampling work plan (see HDOH 2016). Example guidance includes:

  • Massachusetts: Indoor Air Sampling And Evaluation Guide (MADEP 2002b);
  • DoD: Tri-Services Handbook for the Assessment of the Vapor Intrusion Pathway (DoD 2008);
  • Massachusetts: Vapor Intrusion Guidance (MADEP 2010); and
  • California: Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air (CalEPA 2011).

Due to potential complications from indoor and outdoor sources of VOCs, the collection of indoor air samples as part of a vapor intrusion study will rarely be practical or recommended (see Sections 7.2 and 7.3). The collection of indoor air samples is only recommended if concentrations in subslab soil vapor exceed 1,000 times (residential) to 2,000-times (commercial/industrial) anticipated background in indoor air, due to potential indoor sources of the same VOCs (see Section 7.7). When needed, however, active sampling of indoor air can be carried out in order to assess the risk posed by contaminants present within a building. Multiple lines of evidence in addition to indoor air data will be required to demonstrate a link between apparent impacts to indoor air and the intrusion of subsurface vapors (refer to Section 7.1 and HEER Office EHE guidance, HDOH 2016). This includes the magnitude and nature of subsurface contamination (e.g., free product on shallow groundwater), concentrations of targeted VOCs in source area and subslab soil vapor samples, presence or absence of apparent pathways for vapor intrusion, building ventilation design and operation (e.g., likelihood to be over- or under-pressured) and the anticipated concentrations of targeted VOCs in indoor air due to known or suspected indoor and/or outdoor sources.

Discrete sampling approaches are still relied on for the collection of air samples, with six-liter Summa canisters or sorbent tubes most commonly used (see Section 7.8 and following sections). Alternative sampling approaches that provide better coverage of targeted, indoor areas and volume of air (i.e., “Decision Units (DU)”) are currently being reviewed (see TGM Sections 2 and 3). Although guidance has not yet been fully developed, this could include the placement of multiple, passive samplers in individual, targeted areas of a building (i.e., “DUs”) and combination of the samplers from individual areas for testing as a single sample. This could allow an improved coverage and resolution VOCs in indoor air, especially in areas of poor circulation or where distinct layering of VOCs in air might be possible (e.g., higher concentration of HVOCs near the floor).

Indoor air samples are typically collected under operational conditions representative of the use of the structure (i.e., doors open or closed depending on their typical condition and the type and operating status of the air conditioning/ventilating system in use in the building). From a risk perspective the objective is to determine the average, long-term concentration of targeted VOCs in the space or spaces occupied by an individual within the structure. As discussed in the following sections, samples collected from multiple locations within a building during different times of the year are usually required to establish a baseline health risk. Although not necessarily representative of long-term exposure conditions or risk, it may be also useful to collect a sample(s) directly from a point of suspected vapor entry, including bathrooms, utility rooms or other areas where utilities protrude through the building floor. As discussed in Sections 7.2 and 7.3, temporal changes due to differences in ventilation and other factors that could influence indoor concentrations of VOCs throughout the year should be evaluated and taken into consideration. For example, buildings may be more prone to vapor intrusion during periods of the year when air conditioning is not routinely used and the potential for the building to be under-pressured due to wind effects is increased. Buildings could also be more susceptible to vapor intrusion during dry periods of the year due to the exposure of subsurface smear zones as the water table falls.

If collecting a combination of indoor air samples, outdoor air samples, and sub-slab soil vapor samples for one project, the indoor and outdoor air samples should be collected concurrently, immediately followed by collection of the sub-slab soil vapor samples. The collection of sub-slab samples simultaneously with the indoor air samples it not recommended because the installation and purging of the probes could introduce site VOCs into the indoor air.

Concurrent outdoor, ambient air samples should be collected when conducting indoor air sampling as part of a vapor intrusion study. Ambient air samples are important for evaluation of potential outdoor sources of targeted VOCs. Like indoor air, ambient air can contain a number of VOCs typically targeted for vapor intrusion studies. Examples include TPH, BTEX and other petroleum-related chemicals associated with auto exhaust as well as chlorinated solvents from nearby industrial activities. Concentrations of these VOCs in heavily populated or industrialized urban areas often exceed purely risk-based, indoor air action levels (HDOH 2016, USEPA 2011e, USEPA 2012, USEPA 2012b).

For residential structures, outdoor air samples should be ideally collected from a representative upwind location, away from wind obstructions such as trees and buildings. The intake should be at five feet off the ground and five to 15 feet away from the building. For commercial structures, outdoor air samples should be collected in representative locations for the intakes of the building HVAC systems.

Outdoor background samples should be collected at locations to minimize bias toward obvious sources of volatile chemicals (e.g., automobiles, lawn mowers, oil storage tanks, gasoline stations, industrial facilities). Outdoor air samples should be collected and analyzed by the same method as indoor air samples and generally for the same time periods as the indoor air samples.

7.11.1 Initial Building Survey

The indoor environment in any building is a result of the interaction between the site, climate, building heating, ventilation and air conditioning (HVAC) systems, construction design, indoor VOC sources (building materials and furnishings, cleaning fluids, carpet glues, activities within the building, and outdoor sources) and building occupants (smoking, dry cleaning, etc.). An initial building survey is therefore an important part of the indoor air sampling event. This should include interviews with building occupants to assess exposure areas and duration, an evaluation of the building ventilation system and typical operating conditions, an inspection of the building to identify appropriate sampling locations, and an inventory of products or wastes in the building that could release VOCs into the indoor air (i.e., indoor sources). It is recommended that a checklist be used as a guide when conducting building surveys. Vapor intrusion assessment guidance manuals from the USEPA (USEPA 2004e), the Interstate Technology and Regulatory Council (ITRC 2007) and the California EPA (CalEPA 2011) contain example building survey checklists, as do several other state guidance documents (see also vapor intrusion discussion in HEER EHE guidance; HDOH 2016).

As part of the building survey, potential preferential vapor intrusion pathways should also be evaluated. Utility corridors can act as contaminant migration pathways allowing VOCs to travel long distances. Primary entry points for subsurface vapors include bathrooms, kitchens and utility rooms where water, sewer, gas, electric and telecommunication lines penetrate the floor. Wall outlets for electrical fixtures can also serve as a vapor intrusion pathway.

Depending on the COPC, screening for VOCs using direct reading instruments, such as a high sensitivity PID (e.g. ppbRAE), field portable GC/MS (e.g. Hapsite by Inficon), or combustible gas meter (sometimes known as an explosivity meter) can be useful. These instruments have detection limits in the parts per billion (ppb) range, and are best used for screening at points of potential vapor entry, locating indoor VOC sources, or identifying acute exposure or potentially explosive situations. Note that petroleum vapors are dominated by aliphatic compounds. PIDs primarily target aromatic compounds and are not good indicators of total TPH levels in soil vapors without inclusion of a correction factor (ASTM 2006f; refer also to HDOH 2012). This is especially important to remember for aromatic-poor vapors from diesel fuel of other middle distillate fuels.

7.11.2 Indoor Air Sample Locations

The concentrations of contaminants in various locations within a building can vary substantially. Indoor air samples should be collected in a manner which represents this variability (see Section 7.7). The number of indoor air samples collected is dependent upon the size, layout, and use of the building. A typical single family residential dwelling (approximately 1,500 ft2) should have at least one indoor air sample collected from each floor and one from the basement or crawl space (if present). Initial samples should target rooms where utilities penetrate the floor or large cracks are obvious, including basements, bathrooms, kitchens, laundry rooms and utility rooms. Although these rooms are unlikely to be continuously occupied, they represent high-risk areas for initial screening of potential problems. Follow-up samples could include bedrooms and living rooms where occupants spend the majority of time in order to provide a better estimate of potential health risk. Larger dwellings in particular may require multiple samples per floor to adequately represent the targeted room or area, especially in areas of poor air circulation. Multi-family residential units and commercial or retail buildings will require a more careful review of the building features and typically warrant multiple sample locations. The sampling plan should take into account the different exposure scenarios (e.g., day care, medical facilities) that exist within the building and any sensitive populations that may be exposed to the contaminated vapors. In structures with basements, both the occupied living areas and basement areas should be sampled from a risk management perspective. Note that ambient concentrations of VOCs from indoor sources will typically be much higher in poorly ventilated rooms such basements and utility closets. For multi-storied residential buildings, consideration should be given to the collection of individual samples or sets of samples on each floor.

Samples are typically collected in the breathing zone of the primary living or working area, approximately three to five feet from the floor (Figure 7-32). If convenient, samples should be collected from the center of the room. The canister or sorbent tube inlet should be placed so that the airflow is unrestricted and the sampling location allows free airflow that is typical of normal conditions. At a minimum, the inlet should have at least one to two meters of free space in an arc of at least 270 degrees around the inlet.


Figure 7-32: Typical Summa Canister Indoor Air Sampling Apparatus.

7.11.3 Indoor Air Sample Duration

The duration of indoor air sampling is typically matched to the type of building (see ITRC 2007, CalEPA 2011). In general, sampling duration is typically 24 hours for residential building samples and eight to ten hours for commercial/industrial building samples. Longer duration samples may be appropriate if significant variability in VOC concentrations is suspected. Summa canister flow controllers calibrated to seven-day collection periods are also available. Sorbent tubes can be used for longer duration or larger volume samples.

7.11.4 Indoor Air Sample Frequency

Sampling frequency is determined by the CSM, objectives of the study and the nature of the contaminants and should be discussed with the HEER Office on a site-specific basis (see ITRC 2007, CalEPA 2011). A single sampling event is unlikely to yield data that are representative of exposure concentrations over a chronic period of time (i.e., many years). If the contaminant source is non-constant, more frequent sampling should be considered in comparison to constant contaminant sources.

7.11.5 Indoor Air Sample Containers and Analytical Methods

The most common methods for collecting indoor air samples are:

  1. Use of Summa canisters equipped with a calibrated flow controller for VOCs (Section 7.8.1).
  2. Use of sorbent tubes connected to a calibrated flow pump for VOCs and SVOCs (Section 7.8.2).

Currently available flow controllers and flow pumps enable collection periods ranging from less than 1 hour to 7 days.

Samples collected in Summa canisters should be analyzed for VOCs in the laboratory using USEPA method TO-14 or TO-15 (Section 7.13.1). Methods TO-14 and TO-15 are similar. Method TO-15 offers additional target analytes over TO-14, however, and has largely replaced the latter. Both methods use gas chromatography-mass spectrometry (GC/MS) instruments and can be operated in full-scan or SIM mode. Full scan mode offers a broader range of target analytes and is typically less costly than SIM mode, but has higher detection levels. SIM mode provides extremely low detection levels. Consultation with the analytical laboratory can assist in determining the most appropriate analytical method for a given air sample. Samples collected on sorbent tubes or passive samplers are typically analyzed using USEPA methods TO-1, TO-2, or TO-17, with the latter most commonly selected (see Section 7.13).

For vapor intrusion studies, the suite of VOCs targeted for Indoor and outdoor air samples should be identical to the suite targeted for soil vapor and identified in subslab soil vapor samples. Inclusion of additional VOCs can complicate the evaluation of impacts associated purely with vapor intrusion.

7.11.6 Indoor-Outdoor Air Sample Logs

A sample log should be maintained during indoor and outdoor air sampling. Information to be recorded can include:

  • Sample identification;
  • Names of sampling personnel;
  • Date and time of sample collection;
  • Weather conditions;
  • Building conditions (e.g., HVAC on/off, windows/doors opened or closed);
  • Sampling location;
  • Sampling height;
  • Sampling methods and devices;
  • Depending upon the method used, volume of air sampled;
  • If canisters are used, vacuum of canisters before and after sample collection;
  • Chain of custody protocols and records used to track samples from the sampling points to the laboratory.

General information for field notes and logs presented in Section 7.10.7 are also applicable for indoor and outdoor air sampling.