The International Standard: ISO 7243
Published by the International Organization for Standardization and adopted by standards bodies across Europe, North America, Asia-Pacific, and beyond, ISO 7243 is the foundational international framework for measuring environmental heat stress using the Wet Bulb Globe Temperature (WBGT) index.
The standard defines WBGT as a screening method to establish the presence or absence of heat stress, applicable to indoor and outdoor environments for adults exposed to occupational and activity-based heat.
iso.org/standard/67188.html ↗What WBGT Measures
Unlike simple air temperature, WBGT accounts for four simultaneous factors that determine how well the human body can actually cool itself under real-world conditions:
This is what makes WBGT the metric of choice for heat stress assessment worldwide. A 95°F day in dry desert air and a 95°F day in humid coastal air are physiologically very different environments. WBGT captures that difference. Simple temperature does not.
Regional Implementations of ISO 7243
ISO 7243 provides the scientific framework. Individual countries and organizations have adopted it, published it as a national standard, or referenced it directly in their occupational health and safety guidance:
Recommends WBGT in heat illness prevention guidance and the OSHA Technical Manual (Section III, Chapter 4).
osha.gov/heat-exposure ↗Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments uses WBGT thresholds throughout.
cdc.gov/niosh/docs/2016-106/ ↗All branches of the U.S. military use WBGT to govern training and operational activity in heat.
WBGT is required for all NCAA athletic programs under mandatory heat acclimatization guidelines.
NCAA Training & Performance ↗ISO 7243 is adopted as a European Standard (EN ISO 7243:2017) and is referenced in occupational safety frameworks across EU member states.
Work health and safety guidance references WBGT for heat stress assessment in outdoor and high-heat occupational environments.
safeworkaustralia.gov.au/heat ↗WBGT-based Threshold Limit Values (TLVs) used by industrial hygienists globally.
acgih.org TLV Guidelines ↗For our broader philosophy on proactive heat intelligence, see Know Before You Go.
Hydration Science
Foundational Research
The hydration recommendations in the Suayves app are informed by the following peer-reviewed literature:
Important Note
Suayves is an environmental awareness tool, not a medical device. WBGT measures the thermal environment, not an individual's physiological condition. See our Disclaimer for full details.