Photo By Lawrence Crespo | This graphic shows the flag condition at various wet bulb globe temperatures and the...... read more read more
ARNOLD AIR FORCE BASE, Tenn. – The heat isn’t ready to wave the white flag just yet.
Plenty of hot days still lie ahead as the conclusion of the 101 Critical Days of Summer remains a month away. Defined as the time between Memorial Day weekend through Labor Day weekend, people across the nation more frequently take part in outdoor activities during this period. It is also the time of year when the mercury climbs to its highest levels.
More time spent outside during the hottest days on the calendar inevitably leads to increased occurrences of potentially fatal heat-related illnesses throughout the country each year.
Those at Arnold Air Force Base tasked with notifying the rest of the workforce of hazardous outdoor weather maintain a high level of vigilance during this annual stretch. Safety and Industrial Hygiene personnel at Arnold monitor outside conditions, such as temperature and humidity, at least bihourly.
If the situation warrants, these team members reach out to the base Operations Center which disseminates heat-related notifications and updates to the workforce that include the current Wet Bulb Globe Temperature and flag condition.
“While I was a Facility Support Services contractor, I worked with Air Force Bioenvironmental and the Operations Center to formulate a process to get these thermal stress notifications to the base populace,” said Amber Wolfe, occupational safety specialist at Arnold AFB. “During the process formulation, the biggest pushback I got was, ‘It’s summer in Tennessee. Of course it’s hot. Why do we need to publish these alerts?’ And this was an important question.
“We wanted these alerts published because it is the duty of the employer to provide a workplace as free from hazards as possible, and while the hazards from thermal stress cannot be removed completely, they can be mitigated using the appropriate work/rest cycles.”
In recent weeks, team members across the installation have regularly received such alerts via both email and through the AtHoc message system.
“At Arnold Air Force Base, we use four websites to gather and calculate weather information,” said Richard Fleming, ground safety specialist with the Facility Support Services contractor at Arnold. “We look at temperatures, both projected and current; humidity; barometric pressure; wind speed; and solar irradiance. We put the results in the computer, and it gives us what heat category we have reached. We notify the Ops Center, and they send out the notice.”
According to the National Weather Service, Wet Bulb Globe Temperature, or WBGT, index is a measure of heat stress in direct sunlight taking into account temperature, humidity, wind speed, the angle of the sun and solar radiation. The NWS website states this differs from the more commonly known heat index, which takes into consideration temperature and humidity and is calculated for shady areas.
Military agencies, the Occupational Safety and Health Administration, athletic associations and other organizations use the WBGT as a guide to managing workload or activity level, according to the NWS.
WBGT differs from the standard temperature in that the latter provides only the air temperature without the additional data that is included in the heat stress calculations.
Air Force Instructions stipulate that WBGT must be used for heat stress monitoring.
The WBGT determines the flag condition used to guide activity restrictions at different levels.
“Heat is an especially major concern because, if an individual begins to experience the extreme stages of heat illness, such as heat stroke, it can be fatal,” Wolfe said. “Even though I am no longer a contractor, I still help with the monitoring because our goal in Safety is to make sure everyone returns home in the same condition that they came to work, and that can be done by ensuring the appropriate rest cycles are in place.”
Along with the current flag condition and WBGT, the notifications sent to the Arnold AFB workforce during hot outdoor conditions contain the current heat category. The heat category at a given point is assigned a number from 1 to 5, with 1 indicating conditions at which heat-related illnesses are least likely to occur and 5 representing severe conditions at which the risks for heat-related illnesses are highest.
Each heat category number corresponds to a flag condition:
• Heat category 1 is represented by a white flag.
• Heat category 2 is represented by a green flag.
• Heat category 3 is represented by a yellow flag.
• Heat category 4 is represented by a red flag.
• Heat category 5 is represented by a black flag.
Guidance on work/rest cycles at each flag condition for various outdoor work classifications is provided in Air Force Instruction 48-151, which covers the prevention and management of thermal illness. The classifications include easy work such as weapon maintenance and marksmanship training, moderate work such as patrolling with a 30-pound load, heavy work such as jogging 4 miles per hour and patrolling with a 45-pound load, and very heavy work which includes two-person litter carry of at least 150 pounds and obstacle courses.
Rest is defined by the AFI as minimal physical activity, such as sitting or standing, in a shaded area if possible. The guidance is to help employers and base leadership ensure that team members are taking necessary breaks to cool down in order to lower the risk of heat illness.
A black flag condition indicates a WBGT index of 90 degrees Fahrenheit or greater. The AFI does not provide work/rest guidance for easy work for any of the flag conditions, however, for moderate work, 40 minutes of rest per hour is recommended at the black flag level. The rate for heavy work is 45 minutes of rest per hour if working in direct sunlight, and the guidance suggests 50 minutes of rest per hour if very heavy work is being performed.
The AFI states that physical training should not occur during black flag conditions.
At red flag conditions, 10 minutes of rest per hour is recommended for moderate work, 40 minutes of rest per hour for heavy work and 50 minutes of rest per hour for very heavy work.
Thirty minutes of rest per hour is suggested for heavy work at yellow flag conditions and, again, 50 minutes of rest per hour is recommended for very heavy work at this level.
At green flag conditions, 30 minutes of rest per hour is again recommended for heavy work, and 45 minutes per hour is suggested for very heavy work.
For white flag conditions, 20 minutes of rest is recommended per hour for heavy work, and 40 minutes per hour for heavy work.
Because outdoor conditions are monitored throughout the day at Arnold, heat categories and flag conditions are subject to change as the day gets hotter. Whenever these indicators increase or decrease, notifications are sent to base personnel.
AFI 48-151 also provides hourly fluid intake guidance at each flag condition and work classification.
At least 1 quart per hour is recommended across workload classifications at black flag conditions.
The same hourly water intake is recommended at red flag and yellow flag conditions for heavy and very heavy work. Three-quarters of a quart per hour is recommended for easy and moderate work at these conditions.
At both green flag and white flag conditions, one-half quart per hour is recommended for easy work and three-quarters of a quart per hour for moderate work. The latter amount is also recommended for heavy work at white flag conditions, while 1 quarter is recommended heavy work at green flag conditions and very heavy work at both white and green flag levels.
The instruction states hourly fluid intake should not exceed 1.25 quarts and daily intake should not exceed 12 quarts. Drinking too much water is a concern as the kidneys may be unable to get rid of the excess water, leading to the sodium content of the blood becoming diluted, according to the Mayo Clinic. This can lead to a potentially life-threatening condition called hyponatremia.
“Staying hydrated is not hard, but it is a choice,” Fleming said. “The Red Cross suggests ways to stay hydrated include plenty of water, you can augment with sports drinks, coconut water or milk. Avoid sugary, caffeinated and alcoholic drinks which can dehydrate you. In my 40-plus years in safety, I have had to deal with more emergency events involving heat illness than all other reasons combined.”
Precautions to mitigate the risk of heat-related illnesses at high flag conditions include limiting time outdoors, if possible. If this is not possible, breaks in shaded areas are recommended. Another step is to schedule outside work as early or late in the day as possible, as these are generally the coolest times of the day.
Clothing may also help lessen risks. Some clothing, such as UPF clothing, is designed to be more breathable and cooler while still protecting the skin from sun exposure. Wearing lighter colors, which reflect sunlight, is also suggested as opposed to wearing dark colors.
“If you suspect someone has a heat-related illness, move the person to an air-conditioned building or shaded area,” said Arnold AFB Fire and Emergency Services Deputy Chief Jim Evans. “Lay the person down and raise the legs and feet slightly. Remove or loosen tight-fitting or heavy clothing. Have the person sip chilled water, a sports drink with electrolytes or other nonalcoholic beverage without caffeine. Cool the person with a cool wet towel and fanning. If symptoms worsen or do not improve after taking first aid measures, dial 911.”
AFI 48-151 also provides cold stress guidance, though the “flag conditions” are based upon frostbite risk rather than heat stress concerns. When temperatures begin to plummet this winter, the process for teams at Arnold will be much the same as they are during the summer. Safety and Industrial Hygiene personnel will monitor outdoor conditions and appropriate workforce notifications will be sent via the Operations Center.
| Date Taken: | 07.31.2025 |
| Date Posted: | 08.01.2025 15:39 |
| Story ID: | 544423 |
| Location: | ARNOLD AIR FORCE BASE, TENNESSEE, US |
| Web Views: | 9 |
| Downloads: | 0 |
This work, Alerts help combat heat-related illnesses at Arnold AFB, by Bradley Hicks, identified by DVIDS, must comply with the restrictions shown on https://www.dvidshub.net/about/copyright.
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