Heat Index Reference Card

The NWS bands (shade)

Caution

80-90°F - fatigue possible

Extreme Caution

90-103°F - cramps, exhaustion possible

Danger

103-124°F - exhaustion LIKELY

Extreme Danger

125°F+ - heat stroke highly likely

⚠ Every band says

"prolonged exposure and/or activity"

⚠ FULL SUN adds

up to 15°F - not included above

Measured in

shade, light wind

Below 80°F

a simpler formula is used

Dry air

can feel COOLER than the thermometer

Today

Date

Time

Air temperature

Relative humidity

HEAT INDEX (shade)

In full sun

NWS band

Working outside?

Water on hand?

Shade available?

Working or exercising in the heat

• Heat index checked for the hottest part of the day, not now
• Full-sun figure used if the work is in direct sun
• Water available and actually being drunk, not just present
• Shade or air conditioning reachable within a few minutes
• Heaviest work moved to early morning
• Breaks scheduled rather than taken when someone feels bad
• Nobody working alone in Danger conditions
• New or unacclimatised people watched closely for the first week
• Medications that affect sweating or fluids considered
• Everyone knows confusion or stopped sweating is an EMERGENCY

The shade caveat is the whole thing

Heat index values were devised for shady, light-wind conditions. The National Weather Service says full sunshine can add up to 15°F. A shade reading of 95°F is Extreme Caution; the same afternoon in direct sun can be Danger. If the work is outdoors and uncovered, read the full-sun figure and plan from that one.

Stopped sweating is not "coping well"

Heat exhaustion looks like heavy sweating, weakness, nausea and clammy skin - move to cool, sip water, and it usually turns around. Heat STROKE looks different: hot dry skin, a body that has stopped sweating, confusion, slurred speech or collapse. That is a medical emergency and the person needs cooling and an ambulance, not a rest and a drink. The change from one to the other can be quick.