How it works

Three public sources and one published formula. Nothing hidden.

1. Find the site

Your address is matched with the U.S. Census Bureau geocoder, with OpenStreetMap (Photon) as a fallback. The location is only used to look up the forecast.

2. Load the forecast

We ask the National Weather Service API for the forecast grid cell (about 2.5 km) that covers the site, then read its hourly wet-bulb globe temperature, air temperature, humidity, heat index, wind and HeatRisk values for the next 7 days. Where NWS doesn't publish WBGT for a grid, we estimate it from temperature and humidity using the Australian Bureau of Meteorology shade approximation, cap it at the air temperature (shade WBGT can't exceed it), and label those hours as estimates. That estimate reads low in direct sun.

3. Apply the NIOSH limit

NIOSH publication 2016-106 sets a Recommended Exposure Limit for acclimatized workers, REL = 56.7 − 11.5·log₁₀(M), and a Recommended Alert Limit for unacclimatized workers, RAL = 59.9 − 14.1·log₁₀(M). M is the metabolic rate in watts, averaged over the hour. We use the ISO 7243 classes: light 180 W, moderate 300 W, heavy 415 W, very heavy 520 W, rest 115 W.

For each hour, we find the most work minutes (in 5-minute steps) for which the time-weighted metabolic rate keeps the forecast WBGT at or below the limit. If the WBGT is above the limit even at rest, the hour shows Stop non-essential work.

4. Water and the best shift

When an hour is near or over the limit, the plan shows NIOSH's advice of 1 cup (8 oz) of water every 15–20 minutes. The best shift start is the window that allows the most total work minutes.

What it is not

Aeonis Heat is planning guidance. It isn't a medical device, a heat illness prevention program or a legal compliance determination. Forecasts can be wrong, and on-site conditions (radiant heat from roofs, PPE, enclosed spaces) can be hotter. Measure on site when you can, and stop work for anyone with symptoms of heat illness.