Overview
ISO/TS 18222:2025 - Natural gas: Correlation between odorant concentration in air and odour intensity describes a standardized procedure to establish the relationship between odorant concentration in air and perceived odour intensity, typically presented as odour intensity curves. The Technical Specification defines the odour intensity scale, training and selection of an olfactory panel, apparatus and sampling requirements, safety and environmental controls, and methods for reporting results. It does not set required odour levels for natural gas - those are determined by local or national regulation.
Key topics and technical requirements
- Odour intensity scale: Uses the olfactory degree scale (0 = no odour; 1 = detection threshold; 3 = certainty threshold; 10 = terminal threshold) for panel judgements (Clause 5).
- Panel requirements: Minimum panel size and selection follow EN 13725:2022; panel members are trained, examined and re-assessed at least annually (Clauses 7, 11).
- Training standard odorant: Panel training uses Tetrahydrothiophene (THT), purity ≥ 98 %, with specified nominal concentrations for olfactory degrees (e.g., 0, 5.5, 16.6, 50, 150, 454, 1 370 µg/m3 for degrees 0–6) (Clause 11, Table 2).
- Apparatus & test environment: Guidance for test rooms, dynamic olfactometers (must meet EN 13725), and sample bags made of non-adsorbing materials; environmental controls to avoid background odour (Clause 6).
- Measurement principle: Panel members judge odour intensity at several concentrations and results are plotted versus concentration on a logarithmic diagram to generate odour intensity curves (Clause 4).
- Data quality: Methods for expression of results, precision, and uncertainty calculations are included (Clauses 14–16).
- Safety: Toxicological considerations to avoid hazardous concentrations for smellers (Clause 9).
Applications and users
ISO/TS 18222:2025 is applicable to organizations involved in natural gas odorization and odour testing, including:
- Natural gas distribution and transmission operators
- Odorization laboratories and testing facilities
- Gas safety and compliance officers
- Regulatory bodies and standards developers
- Manufacturers of odorants and olfactometry equipment
Practical uses include establishing calibrated odour intensity curves for odorants, validating odorant dosing, training and qualifying olfactory panels, and supporting risk assessments and compliance verification related to gas leak detection and public safety.
Related standards
- EN 13725:2022 - dynamic olfactometry and odour concentration measurement (referenced for panel selection and olfactometer requirements)
- ISO 5492:2008 - sensory analysis vocabulary
- ISO 14532:2014 - natural gas vocabulary
Keywords: natural gas, odorant concentration, odour intensity curves, dynamic olfactometry, olfactory panel, THT, gas odorization, ISO/TS 18222:2025.