ANSI/AARST MA-MFLB-2023: Conducting Measurements Of Radon

Conducting radon measurements across homes adhering to ANSI/AARST MA-MFLB-2023.

Radon is a naturally-occurring radioactive gas, and exposure to it can cause lung cancer (radon is the second leading cause of lung cancer in the United States). It comes from the natural decay of uranium found in nearly all rock and soils; it typically moves up through the ground to the air above and into an occupancy through cracks and other holes in the foundation. ANSI/AARST MA-MFLB-2023: Protocol For Conducting Measurements Of Radon And Radon Decay Products In Multifamily, School, Commercial And Multi-Use Buildings details protocols when measuring radon concentrations in residential and non-residential occupancies.


ANSI/AARST MA-MFLB-2023 specifies procedures and minimum requirements when measuring radon concentrations in shared structures, or portions of shared structures, used for residential, non-residential, or mixed-use purposes. These procedures and requirements are used to determine if radon mitigation is necessary to protect current and future occupants. These protocols in ANSI/AARST MA-MFLB-2023 address low-rise and high-rise structures and procedures for testing whole buildings but also for testing only one or several individual rooms or dwellings within a shared building.

What Is Included in the Scope of ANSI/AARST MA-MFLB-2023?

Any building on any parcel of land can have a radon problem. Any home, school or building can have high-levels of radon, including new and old homes, well-sealed and drafty homes, and homes with or without basements. Testing is the only way to know if an occupancy has elevated radon levels. The requirements and testing protocols in ANSI/AARST MA-MFLB-2023 address both residential occupancies and non-residential occupancies.

Multifamily and Other Residential Occupancies

  • Buildings having more than one attached dwelling or other occupied unit under the same ownership or designated maintenance or management authority
  • Buildings or structures that are used, for example, as apartment houses, dormitories, military congregate residences, fraternities and sororities, non-transient boarding, houses, hotels, convents, monasteries, motels, and live/work unit
  • Multifamily structures that can include those with shared ownership or maintenance such as co-op units, townhouses, condominiums or vacation timeshare properties

Schools, Commercial Buildings, and Other Non-Residential Occupancies

  • Educational occupancies including for religious and educational purposes through the 12th grade and day care facilities
  • Business occupancies including for offices, training, and educational facilities to include universities
  • Professional services or service-type transactions
  • Assembly occupancies including for civic, social, or religious functions
  • Factory occupancies including for fabrication or manufacturing, repair or processing
  • High-hazard occupancies
  • Institutional occupancies including those where people are cared for or live in a supervised environment such as under restraint or security, detained in a penal institution, or for medical, surgical, psychiatric, nursing, and custodial care or for childcare facility purposes
  • Mercantile occupancies including for the display and sale of merchandise, goods, wares, or merchandise incidental to such purposes and accessible to the public


ANSI/AARST MA-MFLB-2023 consolidates ANSI/AARST MAMF (rev. 1/21) and ANSI/AARST MALB (rev. 1/21) into a single publication. In superseding and revising both documents, it contains one notable update: revised latitude in Section 6.2 (Quality Control for Number of Valid Tests). To learn more about these editions of this standard, please see our past posts:

Radon Measurements in Multifamily Buildings

Radon Measurements in Schools (ANSI/AARST MALB)

How Are People Exposed to Radon?

For most people, exposure to radon comes from being indoors in homes, offices, schools, and other buildings. The EPA estimates that nearly 1 out of every 15 homes in the United States has elevated radon levels. The levels of radon in buildings depend on the characteristics of the rock and soil in the area. Radon levels therefore vary greatly in different parts of the United States, sometimes even within neighborhoods, but radon has been found in parts of every state.

Radon gas given off by soil or rock can enter buildings through cracks in floors or walls, construction joints, or gaps in foundations around pipes, wires, or pumps. Since radon comes from rocks and soils, it usually collects in rooms that are in the closest contact with the ground, like basements. Therefore, people who spend much of their time in basement rooms at home or at work have a greater risk for being exposed.

Further, small amounts of radon can also be released from the water supply (ground water) into the air. Water that comes from deep, underground wells in rock may have higher levels of radon, whereas surface water (from lakes or rivers) usually has very low radon levels and is not a concern. To clarify, radon is only a concern if drinking water comes from underground, such as a well that pumps water from an aquifer, though not all water from underground sources contains radon When water that contains radon is used in the home for showering, washing dishes, and cooking, radon gas escapes from the water and goes into the air. So, as the radon moves from the water to air, it can be inhaled and breathing radon increases the risk of lung cancer over the course of one’s lifetime. For most people, water does not contribute much to overall exposure to radon as only about 1 to 2% of radon in the air comes from drinking water.

People can also be exposed to radon from some building materials that are made from radon-containing substances, such as sandstone, concrete, brick, natural stone, gypsum, and granite. Almost any building material made from natural substances, including concrete and wallboard, might give off some level of radon as they contain naturally-occurring radioactive elements like radium, uranium, and thorium. In most cases, these levels are very low and it is rare these materials may contribute significantly to a person’s radon exposure.

Radon Measurement Systems Quality Assurance dives deeper in the dangers of radon gas, and it explains the standard for radon quality assurance: ANSI/AARST MS-QA-2019.

ANSI/AARST MA-MFLB-2023: Protocol For Conducting Measurements Of Radon And Radon Decay Products In Multifamily, School, Commercial And Multi-Use Buildings is available on the ANSI Webstore.

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