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Chemical Screening Of Residences Using Real Time Instruments

by Michael Ridosh, CIH

There are several methods for testing for volatile organic chemicals (VOC) in a home. The term “volatile organic chemicals” includes hundreds of organic chemicals. These chemicals are characterized by being volatile, that is they are liquids that may be present in a vapor form at ambient temperatures, and by being organic, that is, they are based on the element carbon. (Non-organic (inorganic) chemical vapors encountered in daily life are chlorine, ammonia, hydrogen sulfide, carbon monoxide, sulfur dioxide, and hydrogen chloride.)

VOC chemicals include solvents found in paints and adhesives such as toluene, acetone, methyl ethyl ketone, and pentane; industrial solvents such as perchloroethylene and chloroform; chemicals found in household cleaning products such as ethyl alcohol, isopropyl alcohol, d-limonene, and alpha pinene; chemicals found in building materials such as formaldehyde, acrolein, vinyl chloride; refrigerants such as dichlorodifluoromethane (Freon); chemicals related to gasoline and diesel powered engines such as benzene, xylene, ethylbenzene, hexane, and octane. And don’t forget the “natural gas” (methane), with the odorant added to the gas for easy detection, methyl mercaptan. Don't forget PCBs.

VOC may also enter a home from environmental sources, such as nearby traffic, factories, businesses such as gas stations and dry cleaners, and landfills.

There are different approaches to testing for VOC that produce different types of results. For example, a test may give an instantaneous “snapshot” of VOC levels in a specific location in a home. Or it may give an average value of VOC over a long time period, such as eight hours. A test may be designed to measure levels of VOC in a home’s breathing air, or in the soil beneath the slab of a home. There are test methods designed to test a worker in a workplace to evaluate the amount of VOC a worker may breath during an 8 hour shift, for comparison to OSHA established exposure levels.

Three fundamental types of tests are: 1. using a pump to collect VOC from the air by passing the air through an absorbent which absorbs the VOC, 2. collecting the air in the home directly in a container, or 3. measuring the VOC in the air in the home directly.

1. Pumps may be used to pull a measured amount of air through an absorbent for a measured amount of time. The absorbent, usually powdered activated carbon, absorbs the VOC. Pumps are placed in a particular area, are battery operated, and run at a calibrated flow rate for a measured time. At the end of the test period, a known amount of air has passed through the sorbent, and the sorbent is sent to a laboratory for analysis. This analysis usually takes about two weeks and costs about $200 to $300 each. This is also the most commonly used method for workplace testing, where the pump may be attached to the belt of a worker, as well as placed in the working area.

2. Air from a home may be collected in a container. There are two ways of accomplishing this. One is to use a pump to blow the air into a specialized container, called a Tedlar bag. Another is to obtain an evacuated container, called a Summa canister, from a laboratory. The Summa canister contains a pure vacuum. The canister is opened in the home, and the air is sucked into the canister. A regulator may be attached to the inlet of the canister, allowing the air to flow slowly into the canister, averaging the sample over 4 or 8 hours. Tubing may be attached to the canister, allowing air to be drawn from a specific location, like a hole in the concreter slab floor of a home, thereby sampling the gases in the soil beneath the home. The container is then sent to the laboratory for analysis. This analysis usually takes about two weeks and costs about $300 to $400 each.

3. Portable battery powered electronic instruments are available which can measure low levels of various toxic gases. These instruments can measure toxic gases at “parts per billion” (ppb) levels in a matter of minutes. Instruments are available for such gases as benzene and formaldehyde. Each instrument tests for one or more target chemicals.

These instruments allow the testing of several locations in a home within an hour, at a cost of a few hundred dollars. A trained inspector can sample several rooms of a house, allowing a search for the most impacted area, in a short time and at low cost. This “screening” approach enables one to test tens or hundreds of homes at a reasonable cost to find those that are affected by contamination. Although only offering a “snapshot” of a specific location at a specific time, test locations may be selected to test areas of a home where the air has remained stagnant for several hours. If gases are slowly seeping into a home from the external environment, they may accumulate in such stagnant areas. Such areas may be in a closet, pantry, the cabinet under a sink, in a corner of a room near the floor or behind furniture.

The alternative approach, using a Summa canister, takes hours to perform, days or weeks to get results, and costs hundreds of dollars for each reading. And only one location can be done per house without prohibitive cost. The Summa canister test identifies hundreds of compounds in a shotgun approach.

Screening with an instrument can be used to segregate many homes into groups, such as “of no further interest”/”further screening recommended”/“elevated”. Due to being more precise, and more legally defensible, Summa canister tests can be performed subsequent to the screening with an instrument. The screening provides target homes and locations to test with the canister, increases the potential for finding positive results, and reduces testing of unaffected homes with the more expensive methodology.

Environmental Assessment Association

Better Business Bureau

Indoor Air Quality Association, Inc.