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The temperature-humidity index (THI) is a measure that combines temperature and humidity to estimate the overall effect of these factors on humans or animals. It is particularly relevant in assessing heat stress or discomfort. There are variations in the calculation of THI, but here are two common methods:
- Temperature and Humidity Combination: THI is calculated by combining dry-bulb temperature (the usual air temperature) and wet-bulb temperature (a measure of humidity). The specific formula may vary, but a common approach is to multiply the sum of dry-bulb and wet-bulb temperatures by a factor (such as 0.4) and then adding a constant (such as 15). This results in a single index value that represents the combined effect of temperature and humidity.
- Comparison to Standard Conditions: THI can also be calculated by comparing the actual temperature and humidity of a given air sample to standard conditions. These standard conditions typically represent a comfortable or neutral environment for humans. By comparing the actual conditions to these standards, the THI provides an indication of how comfortable or stressful the environment is likely to be.
In both cases, a higher THI indicates a greater potential for heat stress or discomfort, while a lower THI suggests a more comfortable environment. THI values can be used to make decisions about heat management, such as adjusting ventilation, providing cooling measures, or modifying activities to reduce the risk of heat-related illnesses.
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