body {
font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
background-color: #f8f9fa;
color: #333;
line-height: 1.6;
margin: 0;
padding: 20px;
}
.wbgt-calc-container {
max-width: 800px;
margin: 30px auto;
background-color: #ffffff;
padding: 30px;
border-radius: 8px;
box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
}
h1, h2 {
color: #004a99;
text-align: center;
margin-bottom: 20px;
}
.input-group {
margin-bottom: 20px;
padding: 15px;
border: 1px solid #e0e0e0;
border-radius: 5px;
background-color: #fdfdfd;
}
.input-group label {
display: block;
margin-bottom: 8px;
font-weight: 600;
color: #004a99;
}
.input-group input[type="number"] {
width: calc(100% – 22px);
padding: 12px;
border: 1px solid #cccccc;
border-radius: 4px;
font-size: 1rem;
box-sizing: border-box; /* Include padding and border in the element's total width and height */
}
.input-group input[type="number"]:focus {
outline: none;
border-color: #004a99;
box-shadow: 0 0 0 2px rgba(0, 74, 153, 0.2);
}
button {
display: block;
width: 100%;
padding: 12px 20px;
background-color: #28a745;
color: white;
border: none;
border-radius: 5px;
font-size: 1.1rem;
cursor: pointer;
transition: background-color 0.3s ease;
margin-top: 20px;
}
button:hover {
background-color: #218838;
}
#result {
margin-top: 30px;
padding: 20px;
background-color: #e0f2f7; /* Light blue for emphasis */
border: 1px solid #b3e5fc;
border-radius: 5px;
text-align: center;
}
#result h3 {
margin-top: 0;
color: #004a99;
font-size: 1.4rem;
}
#result-value {
font-size: 2.5rem;
font-weight: bold;
color: #0056b3;
}
#result-description {
margin-top: 10px;
font-size: 1.1rem;
color: #555;
}
.article-content {
margin-top: 40px;
padding-top: 30px;
border-top: 1px solid #e0e0e0;
background-color: #ffffff;
padding: 30px;
border-radius: 8px;
box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
}
.article-content h2 {
text-align: left;
margin-bottom: 15px;
}
.article-content p, .article-content ul, .article-content li {
margin-bottom: 15px;
}
.article-content li {
list-style-type: disc;
margin-left: 20px;
}
.article-content code {
background-color: #e0e0e0;
padding: 2px 5px;
border-radius: 3px;
font-family: Consolas, Monaco, 'Andale Mono', 'Ubuntu Mono', monospace;
}
/* Responsive Adjustments */
@media (max-width: 600px) {
.wbgt-calc-container {
padding: 20px;
}
h1 {
font-size: 1.8rem;
}
button {
font-size: 1rem;
}
#result-value {
font-size: 2rem;
}
}
Understanding Wet Bulb Globe Temperature (WBGT)
The Wet Bulb Globe Temperature (WBGT) is a measure used to estimate the heat stress in direct sunlight. It takes into account temperature, humidity, wind speed, and solar radiation. Unlike the heat index, which measures heat stress in the shade, WBGT is specifically designed to assess the risk of heat-related illnesses during outdoor activities and work.
The WBGT index is particularly important for sports, military training, and occupational safety in hot environments. It helps organizations implement appropriate heat safety guidelines, such as scheduling breaks, providing fluids, and modifying work or activity intensity to prevent heat exhaustion and heatstroke.
How WBGT is Calculated
There isn't a single, universally agreed-upon formula for WBGT, as it depends on the availability of measurements and the specific application. However, a common formula used by the U.S. military and others is:
WBGT = 0.7 * Tw + 0.2 * Tg + 0.1 * Td
Where:
Tw is the wet-bulb temperature.Tg is the black globe temperature.Td is the dry-bulb temperature (air temperature).
Calculating Tw (wet-bulb temperature) and Tg (black globe temperature) requires specific sensors and complex psychrometric calculations or empirical formulas. For practical purposes, simpler formulas exist that use readily available weather data. A widely used approximation formula, especially when direct wet-bulb and globe thermometers are not available, is:
WBGT = 0.567*Ta + 0.443*Tr + 1.80*Ws - 3.16 (for shaded, natural ventilation conditions)
However, a more common and general approach considering direct sunlight is:
WBGT = 0.7 * Tw + 0.1 * Td + 0.2 * Tg
Since measuring Tw and Tg directly requires specialized equipment (a wet-bulb thermometer and a black globe thermometer), many calculators use empirical formulas to estimate WBGT from standard meteorological measurements like air temperature, humidity, wind speed, and solar radiation. One common empirical formula for WBGT in direct sunlight is:
WBGT = (0.567 * Ta) + (0.443 * Tr) + (1.80 * Ws) - 3.16
Where:
Ta is the air temperature (°C)Tr is the radiant temperature (often approximated using the dew point or assumed based on solar radiation)Ws is the wind speed (m/s)
Another simplified approximation that incorporates solar radiation directly is:
WBGT = 0.7 Tw + 0.1 Td + 0.2 Tg
A more practical empirical formula, often used when you have air temperature, humidity, and wind speed, and an estimate for solar radiation, is:
WBGT = 0.7 Tw + 0.2 Tg + 0.1 Td
Where Tw (wet-bulb temperature) can be approximated based on air temperature and humidity. The direct solar radiation component is often implicitly included in the measurement of the black globe temperature (Tg).
This calculator uses an approximate formula that combines air temperature, humidity, wind speed, and solar radiation to estimate the WBGT index. It's important to note that this is an estimation, and actual conditions can vary.
Interpreting WBGT Values
WBGT values are categorized to indicate the level of heat stress risk:
- Below 25°C (77°F): Low risk. Use normal precautions.
- 25°C – 28°C (77°F – 82°F): Moderate risk. Use discretion for strenuous activities.
- 28°C – 31°C (82°F – 88°F): High risk. Strenuous activities should be limited.
- 31°C – 34°C (88°F – 93°F): Very high risk. Limit activities to 50% of the usual time.
- Above 34°C (93°F): Extreme risk. All activities should be curtailed.
These thresholds can be adjusted based on acclimatization, age, and health of individuals.
Example Calculation
Let's consider a scenario with the following conditions:
- Air Temperature (
Ta): 32°C
- Relative Humidity: 60%
- Wind Speed: 1.5 m/s
- Solar Radiation: 800 W/m²
Using a sophisticated model or a more detailed approximation, these values would be processed. For this calculator's approximation, we input these values.
Suppose the calculation yields a WBGT of approximately 29.5°C. This falls into the 'High Risk' category, suggesting that strenuous physical activity should be limited, and ample rest and hydration breaks are necessary.
function calculateWBGT() {
var temperature = parseFloat(document.getElementById("temperature").value);
var humidity = parseFloat(document.getElementById("humidity").value);
var windSpeed = parseFloat(document.getElementById("windSpeed").value);
var solarRadiation = parseFloat(document.getElementById("solarRadiation").value);
var resultDiv = document.getElementById("result");
var resultValueDiv = document.getElementById("result-value");
var resultLabelDiv = document.getElementById("result-label");
var resultDescriptionDiv = document.getElementById("result-description");
// Basic validation
if (isNaN(temperature) || isNaN(humidity) || isNaN(windSpeed) || isNaN(solarRadiation)) {
alert("Please enter valid numbers for all fields.");
return;
}
if (humidity 100) {
alert("Humidity must be between 0 and 100.");
return;
}
if (windSpeed < 0) {
alert("Wind speed cannot be negative.");
return;
}
if (solarRadiation < 0) {
alert("Solar radiation cannot be negative.");
return;
}
// — WBGT Calculation Approximation —
// This is a simplified empirical formula. More complex models exist.
// The formula used here attempts to approximate WBGT based on commonly available data.
// It's crucial to understand this is an estimation.
// First, approximate the wet-bulb temperature (Tw) from dry-bulb temperature and humidity.
// This is a complex psychrometric calculation. Here we use a common approximation.
// Using the August-Roche-Magnus formula for saturation vapor pressure, then deriving Tw.
var a = 17.27;
var b = 237.7;
var gamma = (a * temperature) / (b + temperature) + Math.log(humidity / 100.0);
var Tw = b * gamma / (17.27 – gamma); // Approximate wet-bulb temperature in °C
// Then, estimate black globe temperature (Tg) based on solar radiation and wind speed.
// This is highly dependent on the globe properties and solar intensity.
// A simplified approach:
var Tg_base = temperature; // Assume it starts close to air temp
var solar_effect = 0.0002 * solarRadiation; // Solar radiation contributes significantly
var wind_cooling_effect = 0.005 * windSpeed; // Wind reduces temperature
var Tg = Tg_base + solar_effect – wind_cooling_effect; // Simplified Tg estimation
// Weighted average for WBGT (this is a common approximation structure)
// The weights can vary based on the specific model (e.g., 0.7*Tw + 0.2*Tg + 0.1*Td is common)
// Here, we use a commonly cited empirical formula that directly incorporates inputs:
// WBGT = 0.7 T_w + 0.1 T_d + 0.2 T_g is the most standard definition.
// Let's use that structure with our estimated Tw and Tg.
var wbgt = (0.7 * Tw) + (0.1 * temperature) + (0.2 * Tg);
// Alternative simplified formula sometimes used:
// var wbgt = 0.567 * temperature + 0.443 * Tw + 1.80 * windSpeed – 3.16; // This formula structure requires different inputs/assumptions
// Ensure calculated WBGT is not unrealistically low (e.g., below Tw)
if (wbgt temperature + 15) { // Arbitrary cap to prevent extreme values
wbgt = temperature + 15;
}
var wbgtRounded = wbgt.toFixed(1);
var description = "";
if (wbgt = 25 && wbgt = 28 && wbgt = 31 && wbgt < 34) {
description = "Very high risk. Limit activities to 50% of usual time.";
} else {
description = "Extreme risk. All activities should be curtailed.";
}
resultLabelDiv.innerText = "Estimated WBGT:";
resultValueDiv.innerText = wbgtRounded + "°C";
resultDescriptionDiv.innerText = description;
resultDiv.style.display = "block";
}