Overview
ISO 23431:2021 - Measurement of road tunnel air quality - specifies methods for measuring air speed and flow direction, carbon monoxide (CO), nitric oxide (NO) and nitrogen dioxide (NO2) concentrations, and visibility in road tunnels using direct‑reading instruments. The standard focuses on measurement procedures, instrument checks, calibration routines, maintenance, data expression and uncertainty estimation. It explicitly excludes requirements for instrument conformance testing.
Key topics and technical requirements
- Measured parameters: air speed, flow direction, CO, NO, NO2, and visibility (transmissometry and scattered‑light techniques).
- Instrument types covered: open‑path and single‑point gas monitors, transmissometers, scattered‑light visibility instruments and related flow sensors.
- Procedures and checks: initial checks, zero and span checks/calibrations, multipoint precision checks, cross‑section calibration (for flow), and system component checks.
- Reference devices: use of reference path length devices, reference barometer and thermometer for accurate concentration correction.
- Maintenance and care: optical interface cleaning, light source/cell replacement, optical alignment and on‑site maintenance checks.
- Data handling: calculation and expression of results, measurement uncertainty estimation, instrument logs, data acquisition, validation and test reporting.
- Quality assurance: requirements for ongoing QA/QC to ensure reliable tunnel air quality monitoring.
Practical applications and users
ISO 23431:2021 is designed for organizations and professionals involved in tunnel air quality management and monitoring, including:
- Tunnel operators and road authorities - to guide operational monitoring and ventilation control.
- Environmental and public‑health agencies - for exposure assessment and regulatory reporting.
- Consultants and testing laboratories - conducting field measurements and performance checks.
- Instrument manufacturers and integrators - to understand field use expectations (note: the standard does not set conformance specifications).
- Researchers and designers - for ventilation system commissioning and modeling validation.
Typical applications:
- Real‑time ventilation control and optimization in road tunnels.
- Incident response (e.g., fire, heavy traffic) where pollutant levels and visibility must be rapidly assessed.
- Long‑term exposure assessment and compliance monitoring for tunnel environments.
- Commissioning and acceptance testing of tunnel monitoring systems.
Related standards
ISO 23431:2021 was prepared by ISO/TC 146 (Air quality). For instrument performance criteria, calibration standards and conformity assessment, consult other ISO and national standards on air quality instrumentation and calibration produced by ISO/TC 146 and relevant national bodies. Note that ISO 23431 does not include instrument conformance testing requirements.