Do you have this awesome tool to help prevent heat injuries? March 20th marks the official change from winter to spring. Many parts of the nation are still reeling from the effects of the late winter storms. However, spring signals that warmer temperatures and the summer months will soon be here. The warmer temperatures of spring and summer bring with them their own unique weather-related injuries. Heat injuries are just as life-threatening as cold weather injuries. The three common heat injuries are heat cramps, heat exhaustion, and heat stroke. A valuable tool to keep in your kit is the Work-Rest and Water Consumption Table published by the U.S. Army Public Health Command (USAPHC).
1. The Work to Rest Definition Section
The work to rest section of this card helps people understand how much work a person can do within a range of temperatures. There are three categories of work annotated on this instrument: Easy Work, Moderate Work, and Hard Work. Each section gives examples of the type of work that a person can do. The critical part of this section for outdoorsman are the walking distances and weights for carrying loads. The reason that this is critical for outdoorsman is that these annotations directly address their particular concerns. Hikers, backpackers, hunters, anglers, and others, who spend time outdoors in the spring and summer, will find that information crucial for their activities. The information annotated in this section comes as a result of decades of research to help soldiers stay healthy, as well as, function safely and effectively in hot weather conditions.
2. Heat Category Section
The Heat Category Section is a unique numerical and color code system that the U.S. Army developed to alert supervisors of the potential for heat casualties based on the current temperatures. These heat categories are in use throughout the year. However, their relevance increases during the spring and summer months. The types are numbered one through five. Heat Categories 3, 4, and 5 are heat conditions with a higher risk for heat injuries. Heat Categories 1 and 2 have temperature conditions with the lowest risk for heat injuries. Nevertheless, remember that there is always a risk for a heat injury even at Heat Category 1.
3. Wet Bulb Globe Temperature Index (WBGT) Section
The next section on the card is the Wet Bulb Globe Temperature (WBGT) Index correlated to the levels of heat categories. The WBGT index offers a more comprehensive assessment of heat conditions than air temperature alone or the Heat Index. The definition of the WBGT Index is that it is a measure of the heat stress in direct sunlight, which takes into account: temperature, humidity, wind speed, sun angle and cloud cover (solar radiation) (https://www.weather.gov/tsa/wbgt). The critical point is heat stress attributable to exposure to direct sunlight.
Thus, the WBGT Index is an indicator of the accumulated effects of weather and heat conditions upon a person working in direct sunlight. Therefore, in Heat Category 4, people working in direct sunlight when WBGT conditions are between 88° and 88.9° are at a dangerous risk of having a heat injury (heat cramps, heat exhaustion, or heat stroke). One way to determine the WBGT for your area is to call your local weather station. Another way to learn the WBGT for your area is to purchase a WBGT Heat Stress Meter.
4. Work-Rest Time Section
The third section is the Work-Rest Time section. The division is a guide to inform people on the recommended level of work versus rest within the various heat categories. It is based on any given sixty minutes of outdoor activity. This section is one of the more controversial parts of the card. For example, if a unit is provided a training mission to conduct a dismounted movement in the desert in the summer, how is this work/rest cycle implemented without jeopardizing the mission or the health of the soldiers? The answer to that question goes into the required risk assessment of which commanders must sign.
However, outdoorsman, hikers, and backpackers are outside of the constraints of the military application of this chart. Therefore, it is best to follow the work-rest recommendations to increase avoidance of experiencing a heat injury. For example, under the Easy Work column, there are no limitations on easy work until Heat Category 5. Whereas, on the Hard Work column, the work-rest recommendation for Heat Category 1 is 40 minutes of work with 20 minutes of rest. Thus, hiking a trail rated as difficult would fall under the Hard Work column of the chart. Therefore, heed the work-rest cycle in hot weather conditions appropriate for the level of difficulty of your outdoor activity.
5. Water Intake Section
Another relevant section of this chart is the Water Intake section. The measurements on the Water Intake section are in quarts per hour. A cautionary note on the margin of this chart warns, “Hourly fluid intake should not exceed 1 ½ quarts. Daily fluid intake should not exceed 12 quarts.” These warnings are given for the prevention of the onset of overhydration or water intoxication which can lead to hyponatremia.
Hyponatremia is a dangerous heat-related injury caused by diluting the electrolytes in the bloodstream through too much water intake. In other words, too much water intake will cause your electrolytes to be depleted. Consequently, your body shuts down because the electricity needed to run your body cannot get from your brain to your organs. As a result, your internal organs begin to shut down. Therefore, watch your fluid intake in hot weather and do not over do it.
Final Thoughts
The prevention of heat injuries in hot weather conditions is crucial to enjoying the outdoors in the warmer months of the year. The Work-Rest Water Consumption Table is a valuable tool to employ in your outdoor planning activities during the spring and summer. Additionally, it is essential to read the marginal notes of this card as they help in defining terms and explaining annotations on the card. There is a more comprehensive document that contains this table. It is the Heat Illness Prevention (HIP) Pocket Guide (2018). The document also includes The Work-Rest Water Consumption Table, as well as, other useful information and tips to enable the prevention of heat injuries. Therefore, as you get ready for more outdoor activities in the coming months, remember to consult The Work-Rest Water Consumption Table before leaving on your next outdoor adventure.
Major Hykr 