Overview - EN ISO 7243:2017 (WBGT heat stress screening)
EN ISO 7243:2017 (Ergonomics of the thermal environment - Assessment of heat stress using the WBGT index) provides a practical, screening method to evaluate occupational heat stress using the WBGT (wet bulb globe temperature) index. The standard applies to total working-day exposures (up to 8 hours), for adult workers fit for duty, and to both indoor and outdoor environments. It is intended to establish the presence or absence of heat stress; it is not designed for very short heat exposures.
Key topics and technical requirements
- WBGT index definition - combines natural wet-bulb temperature and globe (radiant) temperature (with air temperature weighting when direct solar radiation is present).
- Measurement and instruments - specifications and methods for determining WBGT and its component temperatures (Annex B describes measurement requirements and acceptable sensor types).
- Metabolic rate estimation - guidance on assessing internal heat production from work activity (Clause 6; Annex E provides estimation approaches).
- Clothing effects - procedures to adjust WBGT for clothing that differs from standard work clothing, using Clothing Adjustment Values (CAVs) and the concept of effective WBGT (Clauses 7 and Annex F).
- Timing, duration and variability - rules for timing and averaging measurements over the work period, addressing spatial and temporal heterogeneity in the workplace (Clause 8–9).
- Reference (exposure) values and interpretation - WBGT exposure limits for screening and next steps if measured WBGT exceeds reference values (Annex A).
- Supplementary methods - alternative globe thermometers and methods to predict natural wet-bulb temperature (Annex C and D).
Practical applications - who uses it and why
EN ISO 7243 is widely used for:
- Occupational health & safety professionals, ergonomists, and industrial hygienists conducting workplace heat risk screening.
- Safety managers and employers in industries with thermal hazards - construction, mining, manufacturing, agriculture, sports event organizers, and emergency response planning.
- Facility and HVAC engineers assessing cooling needs and control strategies.
Use cases:
- Quick screening to decide whether heat stress controls or detailed analysis (e.g., ISO 7933 predicted heat strain) are required.
- Designing work–rest schedules, hydration programs, PPE selection, and administrative controls based on WBGT and metabolic load.
Related standards
- ISO 7933 - analytical prediction of heat strain (detailed assessment when WBGT exceeds limits)
- ISO 13731 - vocabulary and symbols for thermal ergonomics
- ISO 7726 / ISO 9920 - instruments and clothing thermal properties (referenced for measurements and clothing equivalents)
Keywords: EN ISO 7243:2017, WBGT, wet bulb globe temperature, heat stress assessment, occupational heat exposure, ergonomics of the thermal environment, clothing adjustment value, metabolic rate.
