🌿 Radon measurement in buildings

Environmental PN-EN ISO 11665

Overview

Radon-222 is a natural radioactive noble gas, a decay product of radium-226 in the Earth's crust. Radon penetrates buildings through foundation cracks, pipes, and fractures, accumulating in basements and ground floors. It is the second (after smoking) cause of lung cancer — WHO estimates 3–14% of lung cancer deaths are due to radon.

EURATOM Directive 2013/59 establishes a reference level of 300 Bq/m³ for existing buildings. In Poland, radon measurements are regulated by Atomic Law and regulations of the President of PAA. Measurement is performed with passive CR-39 type detectors (alpha track detectors) exposed for 2–12 months to obtain reliable average concentration.

TWO DESIGNATIONS IN ONE KEY, BUT ZERO REMAINS ZERO (23.09.2026). The key field had the form "PN-EN ISO 11665-4/-8" — the same defect as with noise: two part numbers glued together with a slash in a string compared character by character. It was corrected to the common prefix "PN-EN ISO 11665", BUT THE NUMBER DID NOT CHANGE AND COULD NOT HAVE CHANGED: the measurement (23.09, copy of the scopes) gives 0 entries for "PN-EN ISO 11665", 0 for "PN-ISO 11665" and 0 for "ISO 11665" alone, and THE STRING "11665" DOES NOT OCCUR IN THE WHOLE SET EVEN ONCE — checked by searching the whole value, not its beginning. SO THE ZERO IS TRUE AND COMES FROM THE SET, NOT FROM THE KEY: none of the 1281 Polish testing laboratories has measurement of radon-222 according to this standard in its accreditation scope. The correction was nevertheless needed, because until now the zero had two causes at once — a defective key and the absence of the method from the scopes — and the second could not be seen before the first was removed.

Method principle

A passive detector (CR-39 film in diffusion housing) is exposed in a room for 2–12 months. Alpha particles emitted by radon and its progeny (²¹⁸Po, ²¹⁴Po) leave microscopic tracks in the CR-39 film. After exposure, the film is etched in NaOH (6 mol/L, 90°C, 6 h), which enlarges the tracks to sizes visible under microscope. The number of tracks per cm² is proportional to radon concentration × exposure time. Concentration is calculated from calibration (detector calibration factor).

Applications

• Radon measurement in residential and public buildings
• Testing buildings in radon zones (Sudetes, Kraków-Częstochowa Jura)
• Radon control in workplaces (mines, caves, basements)
• Assessment of anti-radon remediation effectiveness
• Testing for real estate transactions

Key parameters

Standard

Standard number

PN-EN ISO 11665-4:2020, PN-EN ISO 11665-8:2020

Title (PL)

Pomiary promieniotwórczości w środowisku — Powietrze: radon-222 — Część 4: Zintegrowana metoda pomiaru średniego stężenia aktywności z użyciem pasywnych próbników

Title (EN)

Measurement of radioactivity in the environment — Air: radon-222 — Part 4: Integrated measurement method for determining average activity concentration using passive sampling

Step-by-step procedure

1. Detector placement

   Place 2 detectors on lowest occupied floor (bedroom, living room). Height 0.5–2 m, away from windows and ventilation.

   ⏱ Time: 15 min

2. Exposure

   Leave detectors for 3–12 months. Record start and end dates with 1-day accuracy.

   ⏱ Time: 3–12 months

3. Detector retrieval

   Close detectors in housing and send to analytical laboratory.

   ⏱ Time: 10 min

4. Chemical etching

   CR-39 film etched in 6 mol/L NaOH, 90°C, 6 h. After etching rinse in distilled water and dry.

   ⏱ Time: 7 h • 🌡 Temperature: 90°C

5. Track counting

   Count alpha tracks under microscope (automatically or manually). Typically 3–10 fields of view per detector.

   ⏱ Time: 15 min/detector

6. Concentration calculation

   C [Bq/m³] = (track density − background) / (calibration factor × exposure time). Result as annual average concentration.

   ⏱ Time: 10 min

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• NaOH 6 mol/L — highly corrosive. Acid-resistant gloves, goggles, apron.
• 90°C bath — burn risk. Thermal gloves.
• Radon — radioactive, but detectors pose no hazard
• NaOH waste — neutralize before disposal

Frequently asked questions