ISO 7708:1995

Overview

ISO 7708:1995 - "Air quality - Particle size fraction definitions for health-related sampling" defines internationally accepted sampling conventions for airborne particle size fractions used when assessing health effects in occupational and ambient environments. The standard specifies target collection curves for the inhalable, thoracic and respirable fractions (with extrathoracic and tracheobronchial fractions derived from those conventions). Conventions are expressed in terms of particle aerodynamic diameter and mass fractions and are intended to improve the relationship between measured concentration and potential health risk.

Key topics and technical requirements

• Sampling conventions and definitions: Clear definitions for inhalable, thoracic, tracheobronchial, extrathoracic and respirable fractions and corresponding target specifications for sampling instruments.
• Inhalable convention: Target collection curve averaged over wind directions for typical breathing rates (equation form provided for windspeeds u < 4 m/s); tentative adjustment exists for higher wind speeds within experimental limits.
• Thoracic and respirable conventions: Thoracic convention approximates particles penetrating beyond the larynx (median ~11.64 µm, geometric SD 1.5). Respirable conventions include a “healthy adult” and a “high-risk” (children, sick, infirm) target (medians ~4.25 µm and 2.5 µm respectively; geometric SD 1.5).
• Derived fractions: Extrathoracic = inhalable − thoracic; tracheobronchial = thoracic − respirable.
• Assumptions & limitations: Conventions approximate average behavior; results vary with breathing route (nose vs mouth), breathing rate, wind speed/direction and individual variability. Not suitable for limit values defined by other metrics (e.g., fibre length/diameter).
• Instrument performance: Instruments should conform to the selected convention; ISO provides guidance and a separate publication for instrument verification and performance testing. Informative annexes cover nomenclature and numerical approximations.

Applications and users

ISO 7708:1995 is used by:

• Occupational hygienists and safety professionals for workplace exposure assessment
• Environmental and air quality monitoring agencies for ambient particle measurement
• Manufacturers and testers of size-selective samplers and aerosol instruments
• Industrial hygienists and researchers designing exposure and epidemiological studies

Practical uses include sampler design and selection, performance verification, converting measured mass concentrations into health-relevant fractions, and harmonizing exposure data for regulatory or research purposes.

Related standards (if applicable)

• Prepared by ISO/TC 146 (Air quality). ISO 7708:1995 replaces earlier ISO/TR 7708:1983.
• Instrument verification and performance criteria are addressed in related ISO publications and technical reports covering sampler testing and calibration.

Keywords: ISO 7708:1995, particle size fraction, inhalable, thoracic, respirable, air quality, health-related sampling, aerodynamic diameter, occupational exposure, ambient air monitoring.