ISO 11665-5:2020

Overview

ISO 11665-5:2020 specifies continuous measurement methods for radon-222 (radon) activity concentration in air. It provides guidance for in situ, continuous sampling and detection to assess temporal variations of radon activity concentration in open or confined atmospheres. The standard is applicable to air samples with radon activity concentration greater than 5 Bq/m3 and supports environmental monitoring, indoor air assessment, and occupational exposure evaluations.

Key topics and technical requirements

• Principle: Continuous sampling of representative air (filtered) with ongoing detection of radiations from radon and its short‑lived decay products. Results are available instantly and can be integrated over user-defined intervals.
• Detection technologies: Examples include ionization current (vented and current ionization chambers - Annex A) and solid‑state detectors (semiconductor/silicon) that detect alpha particles.
• Sampling and installation: Requirements cover sampling objective, device siting, sampling duration, integration interval and sample volume to ensure representative, time‑resolved measurements.
• Temporal resolution: Integration intervals shall be compatible with the phenomenon studied and in all cases less than or equal to one hour. The document notes that detecting daily variations may require measurement periods of the order of one week.
• Performance metrics: Guidance on calibration, standard uncertainty, decision threshold, detection limit, and confidence interval limits. Instruments and procedures should follow recognized uncertainty and calibration practices (e.g., GUM and ISO/IEC 17025 principles).
• Influence quantities: Addresses the effect of ventilation, meteorological conditions and other environmental factors on radon temporal variations.
• Reporting: Defines required elements for the test report, including the measured radon activity concentration and associated uncertainty.

Practical applications and users

ISO 11665-5:2020 is intended for:

• Environmental and public‑health laboratories conducting continuous radon monitoring.
• Building assessors and radon service providers evaluating indoor radon dynamics and mitigation effectiveness.
• Occupational safety and hygiene professionals monitoring workplace radon exposure.
• Researchers studying radon variability linked to ventilation, weather or building use.
• Instrument manufacturers developing and validating radon monitoring devices.

Typical uses:

• Time‑resolved radon surveys to identify daily/seasonal patterns.
• Verification of mitigation measures and ventilation strategies.
• Long‑term indoor and outdoor environmental monitoring and compliance checks.

Related standards

Relevant documents referenced by ISO 11665-5:2020 include:

• ISO 11665-1 (origins and measurement methods for radon)
• ISO 11929 (characteristic limits for ionizing radiation measurements)
• ISO/IEC Guide 98-3 (GUM: uncertainty of measurement)
• ISO/IEC 17025 (laboratory competence)
• IEC 61577-1 and IEC 61577-2 (radon measuring instrument requirements)

Keywords: ISO 11665-5:2020, radon-222, continuous measurement, radon activity concentration, indoor radon monitoring, environmental monitoring, ionization chamber, calibration, measurement uncertainty.