What is an Indoor Air Sample?

fresh air at sunsetIn addition to asking for soil gas samples, many state and county environmental health agencies in California ask for indoor air samples. Let’s take a look at the "five Ws and a H” of an indoor air sample - or the what, why, who, when, where, and how of an indoor air sample.

What is an Indoor Air Sample?

An indoor air sample is what you get when you remove a small portion of the air inside an indoor space and isolate it for testing. Air inside a building can contain suspended particles, chemicals from inside the building, chemicals from outside the building, and chemicals from soil and water beneath the building. At some level, these airborne particulates and chemicals become harmful to human health. One strategy used to protect human health is to take a look at the chemical makeup of indoor air by collecting and analyzing indoor air samples. By the way, a volume of air is approximately 21% oxygen, 78% nitrogen, 1% argon, and 0.04 percent carbon dioxide.

Where underground chemical contamination is a concern, a sample of indoor air can be used to find out if contaminated soil gas has entered the buildings above it. Contaminated soil gas entering an indoor space can contain chemicals such as gasoline and cleaning solvents (tetrachloroethylene or PCE). Contaminated soil gas may also have by-products of chemical spills like the vinyl chloride that comes from the breakdown of PCE.

Why get an Indoor Air Sample?

Indoor air is sampled to look for the presence of particulates and/or harmful gasses that are either naturally occurring or the result of a spill. The samples are analyzed to find out what particulates or chemicals are in the air, what the levels are, and what the risk to human health is. Particulate or chemical levels detected at the lab are typically assessed by comparison against levels judged to be safe by the regulatory community. These levels, sometimes called environmental screening levels (ESLs), are considered safe becuase they were shown not to pose a risk to public health and the environment.

Who is the Indoor Air Sample For and Who Collects the Sample?

In most cases an environmental consultant or environmental oversight agency proposes collection of indoor air samples. Sometimes building owners hire an environmental consultant to collect indoor air samples as a precautionary matter. Indoor air samples are tyoically collected by personnel trained in indoor air sampling and related health and safety concerns. Sampling objectives and methods are typically spelled out in a work plan that is approved by the regulatory oversight agency prior to samping.

Where are Indoor Samples Collected and Where do They go?

Indoor air samples are collected in indoor spaces away from walls, windows and doors. In the case of soil gas contamination, bathrooms or utility rooms are targeted because pipes and utilities that go through the building floor are places where contaminated soil gas can enter a building. An indoor air sample is collected in mid-air, about 4 to 5 feet above the floor. Once the air samples are collected, they are taken to a laboratory for chemical testing.

Indoor air samples go to a state-certified laboratory for analysis. Sample containers are labeled with the sampling location, time sampling started and stopped, the initial and final canister pressure, and the sample identification. After labeling, the samples are placed in a sealed container and transported to a lab for analyses.

A chain of custody is prepared at the point of sample collection and travels with the samples to the laboratory. The chain of custody contains contact information, a list of the samples collected, and instructions on analysis. Each person that handles the samples during the trip from the sample location to the laboratory signs and dates the chain of custody, so that if anything happens to the samples, there is a clear line of responsibility from the sample location to the laboratory.

When are Indoor Air Samples Collected and When do the Results Arrive?

Indoor air samples can be collected at any time. For contaminated soil gas, it is suggested that indoor air samples be taken twice per year to show levels during rainy and dry seasons. Indoor air samples are collected over a time period that usually spans 8 hours, but sometimes extends to 24 hours. One specific method of indoor air sampling allows sampling periods of up to a month. Once at the lab, it usually takes about two weeks to get the results. Of course, if you are willing to pay more, sample testing can be “rushed”.ambient air sample

How are Indoor Air Samples Collected?

Indoor samples are collected using a vacated stainless steel canister, a passive sampler (container of adsorption material), or a combination or pump and adsorption material, any of which are supplied by a laboratory.

The canister is delivered sealed and under a vacuum. The canister is equipped with a valve that controls the air flow into the canister. The laboratory sets the flow rate according to the sample period. For example, the valve for an 8-hour sample is set to limit the air flow so that it takes about 8 hours to fill the canister. During sampling, the canister is mounted about 4 to 5 feet above the floor. Sample collection stops after sample period or when the canister pressure gauge shows the canister is nearly filled.

Passive air samplers work by allowing natural air currents to bring air into contact with a material that certain airborne chemicals stick to (adsorb). Chemicals that stick to the adsorbent material are later removed at the lab and tested to find out what chemicals are in the air and at what levels. Passive samplers are placed just like canister samplers and sampling periods can extend up to a month. Some passive air samplers come in the form of a badge that is worn by someone who could be exposed to particulates or chemicals in the workplace. If a certain particulate or chemical level is reached, the badge turns color or emits a sound.

Indoor air is also sampled using an air pump combined with an absorption material as used in passive air samplers. In this case, instead of relying on the natural air movement inside a building, a specific amount of air is collected at a set air flow using a pump. As with the passive method, chemicals that stick to the adsorbent material are later removed at the lab for analysis.


Here we answered the five Ws and a H for an indoor air sample. If you have any other questions about indoor air sampling, or need help with another environmental question, please call us or click the button below for a free consultation.