NRPP RMS cheat sheet

Radon is a colorless, odorless, radioactive noble gas; the primary health concern is inhalation of its short-lived decay products (polonium-218 and polonium-214), which emit alpha particles in the lung.

The U.S. action level and EPA-recommended mitigation trigger is 4 pCi/L; the WHO reference level is 100 Bq/m3 (about 2.7 pCi/L).

Unit conversions: 1 pCi/L = 37 Bq/m3; 1 WL (working level) = 100 pCi/L at equilibrium, and equilibrium ratio (ER) = actual WL divided by potential WL.

Short-term tests are typically 2-90 days; closed-building conditions require 12 hours before the test begins and must be maintained for the full exposure period (doors and windows closed, no fans or dryers venting air).

Device types: passive (charcoal, alpha track, electret ion chamber, liquid scintillation) versus active/continuous monitors; CRM tests need a minimum 48-hour exposure and hourly data.

Test placement: lowest livable level, 20 inches (50 cm) above the floor, at least 12 inches (30 cm) from exterior walls, and at least 4 inches (10 cm) from other objects.

Duplicate measurements (simultaneous side-by-side devices) and blank/spike controls assess precision and bias; a duplicate pair should be within 25 percent of their mean or 0.3 pCi/L, whichever is larger.

The CRM and electret measurement standards are ANSI/AARST MS-PC (continuous monitors) and MS-IM (electret ion chambers); MS-PC requires annual calibration and a control chart with a known-source spike every 30 days.

Long-term tests run more than 90 days and better represent the annual average; if a short-term test is 4 pCi/L or higher, a follow-up test (short- or long-term) is recommended before mitigation is decided.

The most common mitigation method is active soil depressurization (ASD): a suction point through the slab (sub-slab) or through a sump, a sealed piping run, and a continuously operating fan venting above the roof.

The vent stack must discharge above the roofline, at least 10 feet above grade and 10 feet from any window, door, or air intake, and must be labeled as a radon vent.

The post-mitigation retest is performed within 30 days of system activation (no sooner than 24 hours after start-up) under closed-building conditions; a passing result is below 4 pCi/L, with a goal of 2 pCi/L or less.

A system failure indicator (u-tube manometer or a system monitor/alarm) must be visible and labeled; the manometer reading should be recorded at installation to serve as the baseline for future checks.

Sub-slab communication is verified with a pressure-field extension test (PFE): a pressure differential of at least 50 Pa (0.2 inches water column) is the usual target at the farthest test hole from the suction point.

A depressurization field test (DFT) can be used on a diagnostic hole to confirm pressure field extension; diagnostic work should precede installation to size the fan and number of suction points.

The maximum radon concentration in the vent stack is typically several thousand pCi/L; the fan should be rated for continuous duty and the system must be sized so that the stack velocity is adequate, generally 20-30 feet per second at the fan.

For schools and large buildings, ANSI/AARST MA-MFLB (large building) and MAH (multifamily) standards govern design; HVAC pressure differentials and combustion appliance backdrafting must be evaluated before and after ASD installation.

Mitigation by sealing alone is not an approved stand-alone method; sealing is a supplemental measure used with ASD, and the system must not create a health or safety hazard (e.g., backdrafting of combustion appliances).