🌿 Radon measurement in buildings

Environmental PN-EN ISO 11665

Overview

STATUS (as of 02.11.2026). ISO 11665-4 has NOT been adopted as a Polish Standard: the PKN search for “11665” returns 12 items — PN-EN ISO 11665 parts 1, 2, 3, 5, 6, 7 and 11 — and parts 4 and 8 are not among them; the queries “ISO 11665-4” and “ISO 11665-8” return nothing (read on 02.11.2026). The Polish title of the standard is a working translation. The description is based on ISO 11665-4:2021, the third edition (March 2021) — a minor revision of the second edition, ISO 11665-4:2020 (January 2020), in which the introduction and the bibliography were updated.

SCOPE (clause 1). Integrated measurement techniques for radon-222 with passive sampling: indications for determining the average activity concentration of radon-222 in air from easy-to-use and low-cost passive measurements, and the conditions of use for the sensors. Samples are taken without interruption over periods from a few days to one year; the method applies to activity concentrations greater than 5 Bq/m³.

RADON INDOORS (introduction). The radon isotopes 222, 219 and 220 (thoron) are produced by the disintegration of radium isotopes from the uranium-238, uranium-235 and thorium-232 series present in the earth’s crust. The health effects are caused by the solid, radioactive decay products (polonium, bismuth, lead), which are inhaled and deposited in the bronchopulmonary tree. According to UNSCEAR radon accounts for around 52 % of the average exposure to natural radiation (radon-222 — 48 %, radon-220 — 4 %), which is why the standard deals only with radon-222. In buildings the main source is soil gas, which enters by diffusion and convection; the concentration depends on the underlying soil, the building structure, its equipment (chimneys, ventilation), environmental parameters and the occupants’ lifestyle. According to WHO, radon is one of the leading causes of lung cancer — in many countries the second after smoking — and accounts for 3–14 % of all lung cancers in a country, depending on the national average radon level and smoking prevalence (WHO: news release of 21.09.2009, fact sheet “Radon and health” of 25.01.2023). WHO recommends a national reference level of 100 Bq/m³ and, where this is not possible, not more than 300 Bq/m³; in the EU the reference levels for the annual average concentration may not exceed 300 Bq/m³.

PRINCIPLE AND SENSORS (clauses 4–5, 7). Air reaches the sensor without interruption — by free convection and diffusion (open configuration) or through a filter into an accumulation chamber (closed configuration). The sensor accumulates a physical quantity: “latent tracks” in the polymer of a solid-state nuclear track detector (Annex A), charges in a silicon detector, discharge of an electret (Annex B), or radon atoms adsorbed on activated charcoal, measured by gamma spectrometry of the decay products ²¹⁴Pb and ²¹⁴Bi (Annex C). In the closed configuration the sensor records the alpha particles of radon; in the open one also those of decay products near its surface and of other alpha emitters in the atmosphere. The result of an integrated measurement is the exposure of the sensor to radon over the sampling duration; the average concentration is the exposure divided by the duration, and the analysis may require laboratory operations.

SAMPLING (clause 6). Indoors the sensor is placed in a normally occupied zone, 1–2 m above the floor (the “breathing zone”), with at least 20 cm of clear space around it (influence of thoron from the walls), away from heat sources, areas of traffic, doors, windows, walls and ventilation, and secured against disturbance. The date and hour of installation and removal are recorded. Example durations (Table 1): track detector — one week to several months, electret — a few days to several months, activated charcoal — a few days. A whole week includes the variation between days; to approach the annual average and not under-estimate it, measurements of at least two months are advisable (ISO 11665-8). Saturation of the sensor must be avoided.

CALIBRATION AND RESULT (clause 8). The measuring system is calibrated at least annually according to ISO 11665-1, in a radon-222 reference atmosphere whose concentration is traceable to a primary radon-222 gas standard; internal blind tests and proficiency tests or interlaboratory comparisons are also recommended. Average activity concentration C = (µ − µ₀) · ω, where µ₀ is the background and ω a correction factor linked to the calibration factor and the sampling duration; uncertainty according to the GUM, decision threshold and detection limit according to ISO 11929.

REGULATIONS. Atomic Law (consolidated text: Dz.U. 2026 item 1): reference level for the annual average radon concentration in indoor workplaces and in rooms intended for human occupancy — 300 Bq/m³ (Art. 23b); the annual average is estimated from measurements lasting at least one month (Art. 3 point 47a). Measurement is ensured by the head of the organization in workplaces on the ground floor or in basements in areas designated by a regulation of the minister of health, underground, and in groundwater treatment in such areas (Art. 23c). The seller or lessor of a building, dwelling or room provides on request information on the annual average radon concentration; the measurements for it are carried out by laboratories accredited for this, which inform the provincial sanitary inspector of exceedances (Art. 23d).

WHAT WE DO NOT GIVE HERE. Annexes A–C with the procedure of each method (processing of track detectors, measuring the electret voltage, spectrometry of activated charcoal), the influence quantities for the individual methods and the way of determining the factor ω are outside the available text — we give no temperatures, processing times or detection limits, and the etching solution for track detectors in the list of reagents is given according to the IAEA review (2013), not the standard. ISO 11665-8 is used only to the extent that part 4 refers to it.

Method principle

The sensor — e.g. a solid-state nuclear track detector, an electret or activated charcoal — is exposed without interruption in the atmosphere under investigation: air reaches it by free convection and diffusion (open configuration) or through a filter into an accumulation chamber (closed configuration). During exposure the sensor accumulates a physical quantity — tracks, a drop in electret potential or radon atoms — which is measured afterwards, usually in a laboratory.

The average activity concentration of radon-222 is the exposure of the sensor divided by the sampling duration, converted with the calibration factor determined in a reference atmosphere (clauses 4, 8).

Applications

• Average activity concentration of radon-222 in indoor and outdoor air — sampling from a few days to one year, concentrations above 5 Bq/m³ (clause 1, Table 1)
• Estimating the annual average radon concentration in buildings — measurement of at least two months (6.3.3, ISO 11665-8)
• Measurements in workplaces covered by the obligation of Art. 23c of the Atomic Law: ground floors and basements in designated areas, underground work, groundwater treatment
• Information on the annual average radon concentration when a building, dwelling or room is sold or let — measurements by an accredited laboratory (Atomic Law, Art. 23d)

Key parameters

Standard

Standard number

ISO 11665-4:2021

Title (PL)

Pomiary promieniotwórczości w środowisku — Powietrze: radon-222 — Część 4: Metoda pomiaru całkującego do wyznaczania średniego stężenia promieniotwórczego z próbkowaniem pasywnym i analizą odroczoną (tłumaczenie robocze — normy nie wprowadzono do PN)

Title (EN)

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

Step-by-step procedure

1. Choice of method and duration

   Sensor and duration are chosen to suit the purpose, the expected activity and the sensor characteristics (Table 1): track detector — one week to several months, electret — a few days to several months, activated charcoal — a few days; for the annual average at least two months (6.3.3).

2. Placement

   In a normally occupied zone, 1–2 m above the floor, with at least 20 cm of clear space around it, away from heat sources, areas of traffic, doors, windows, walls and ventilation; sensor secured against disturbance (6.3.2).

3. Exposure

   Without interruption; recording of the date and hour of installation and removal of the sensor; attention to sensor saturation (6.3.3).

4. Analysis

   Measurement of the accumulated quantity according to the annex for the method (A, B or C), taking the influence quantities and the sensor manufacturer’s recommendations into account (8.1–8.2).

5. Calculation

   C = (µ − µ₀) · ω: measured quantity minus background, times the factor linked to the calibration factor and the sampling duration; uncertainty according to the GUM, decision threshold and detection limit according to ISO 11929 (8.4–8.6).

6. Calibration and control

   At least annually in a reference atmosphere traceable to a primary radon-222 standard; internal blind tests and proficiency tests or interlaboratory comparisons (8.3).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• In the available text the standard gives no safety warnings
• The sodium hydroxide etching solution is corrosive — causes severe skin burns and eye damage (H314, harmonised classification under Regulation (EC) No 1272/2008)

Frequently asked questions