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Facilities Tech Tip
March 2006
5100 Fire
0651-2312-MTDC
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The Effect of Color on Temperatures Inside Hardhats

John Smith Equipment Specialist
Wes Throop Mechanical Engineer

The Missoula Technology and Development Center was asked to determine the effect of a hardhat's color on the wearer's comfort. Wildland firefighters may select a hardhat's color based on their personal preferences, on the color of hardhats worn by their crew, or on their position in the Incident Command System.

MTDC conducted an informal test to evaluate the temperatures inside hardhats of various colors. The hardhats used were all new, cap-style Bullard FH911 Wildfire series hardhats. White, black, red, blue, yellow and orange hardhats were tested.

A simple test rack was set up that allowed full exposure of the hardhats to solar heating. Air circulated freely, providing some ventilation to the hardhat. The temperature inside each hardhat and the ambient air temperature at the test site were measured and recorded using type K thermocouples wired to a Campbell Scientific CR10X Datalogger (figure 1).

The thermocouples were in the center of each hardhat, 4 inches from the bottom rim, at about the same depth as the top of a wearer's head. Data were collected at 5-minute increments, over a 6- to 7-hour period, for three consecutive days.

Photo of six hardhats, each a different color, placed on a test rack and wired to a datalogger.
Figure 1—The six hardhats on the test rack were wired to a
datalogger that recorded the temperature inside the
hardhat every 5 minutes.

Test Results

The data show a consistent pattern of differential heat absorption by hardhats of different colors. For the three test days, ambient air temperatures ranged from 61.3 degrees Fahrenheit to 98.1 degrees Fahrenheit. The weather was mostly sunny with very little wind. During the test period each day, the temperatures inside all six hardhats generally rose above the ambient air temperature.

The temperature inside the white hardhat increased the least, with a 3-day average recorded increase of 1.3 degrees Fahrenheit above the ambient air temperature and a maximum increase of 4.5 degrees Fahrenheit. The temperature inside the black hardhat increased the most, an average of 9.1 degrees Fahrenheit with a maximum increase of 23 degrees Fahrenheit. The red and blue hardhats had the next highest temperature increases, averaging 6.9 and 6.7 degrees Fahrenheit, respectively. The yellow and orange hardhats were relatively cooler, increasing an average of 3.2 and 4.2 degrees Fahrenheit, respectively (figure 2).

Bar graph illustrating the temperature differences of a hardhat based on color.
Figure 2—Hardhats with lighter colors were cooler— sometimes
dramatically so—than hardhats with darker colors. The
temperature increases are the average difference of the
temperature inside the hardhat and the ambient air
temperature over 3 days of testing.

The mean ambient air temperature during the warmest hour of the test was 95.8 degrees Fahrenheit. The average temperature in the white hardhat then was half a degree Fahrenheit cooler than the ambient temperature. During the coolest hour of the test, the mean ambient air temperature was 63.8 degrees Fahrenheit. The temperature in the black hardhat then averaged 10.2 degrees Fahrenheit warmer than the ambient air temperature.

During the warmest hour, the difference in temperature between the coolest and warmest hardhats was just 3.2 degrees Fahrenheit (white compared to black). During the coldest hour, the difference between the coolest and warmest hardhats was 8.9 degrees Fahrenheit (white compared to black). Figure 3 illustrates the average increase in temperatures inside hardhats during the warmest and coldest hours.

3-D bar graph showing the changes in temperature for the six different colors of hardhats. One set of bars shows the temperature change during the warmest hour of the day and the other shows the temperature change during the coldest hour of the day.
Figure 3—During the warmest hour of the 3-day test, the
difference between the temperature of the ambient air and
the temperatures inside hardhats of different colors was
less than during the coolest hour of the test.
For a long description click here.

Conclusions

This test shows measurable differences in the amount of heat absorbed by hardhats of different colors. The data support the basic principle that lighter colors absorb less solar radiation, generating less heat inside a hardhat than darker colors. While the heating effect is less pronounced when temperatures are warmest, firefighters wearing lighter colored hardhats generally will be subjected to less heat gain throughout the day.

About the Authors

John Smith joined MTDC in 2005 as an equipment specialist. He graduated from the University of Montana with a bachelor's degree in education and taught elementary school in Ovando, MT. He began his Forest Service career in 1974 as a wildland firefighter on the Superior District of the Lolo National Forest. A Missoula smokejumper for more than 2 decades, John's experience as assistant loadmaster foreman, master parachute rigger, and safety program manager will be applied to fire equipment development.

Wes Throop is a project engineer at MTDC. He received his bachelor's degree in mechanical engineering from the University of Idaho in 1983. Wes has worked as a smokechaser, hot-shot, and engine foreman for the Forest Service, and as a civilian mechanical engineer for the U.S. Department of the Navy. Before coming to MTDC in 1999, he worked as a mechanical engineer at the test reactor area of the Idaho National Engineering and Environmental Laboratory near Idaho Falls, ID.

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E-mail: jrsmith01@fs.fed.us

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