Heat Index

Overview

Engineering reference data for Heat Index in miscellaneous.

Key Formulas

Unit Conversion

$y = x \cdot k$

Multiply by conversion factor.

Linear Interpolation

$y = y_1 + \frac{(x - x_1)(y_2 - y_1)}{x_2 - x_1}$

Estimate between two known points.

Percentage

$p = \frac{\text{part}}{\text{whole}} \times 100\%$

Part as fraction of whole.

Variables

Symbol	Description	Unit
$x$	Input value	—
$y$	Output value	—
$k$	Conversion factor	—

Heat Index in Celsius

The heat index formula in degrees Celsius is commonly approximated as:

$t_{HI} = -8.7847 + 1.6114 T + 2.3385 \phi - 0.1461 T \phi - 0.0123 T^2 - 0.0164 \phi^2 + 0.0022 T^2 \phi + 0.0007 T \phi^2 - 0.0000036 T^2 \phi^2$

where:

• $t_{HI}$ = heat index (°C)
• $T$ = air temperature (°C)
• $\phi$ = relative humidity (%)

Heat Stress Categories

The numerical values in the table correspond to the following general risk categories:

• Caution: Fatigue is possible with prolonged exposure and/or physical activity.
• Extreme Caution: Sunstroke, heat cramps, and heat exhaustion are possible with prolonged exposure and/or physical activity.
• Danger: Sunstroke, heat cramps, and heat exhaustion are likely. Heat stroke is possible with prolonged exposure and/or physical activity.
• Extreme Danger: Heatstroke/sunstroke is highly likely with continued exposure.

Interactive Charts

References

• Original Source