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Cpl. Shane Piazza, scheduling noncommissioned officer at Range Management Branch, checks the branch’s wet bulb globe thermometer in the late morning of June 17, 2013. The device, which determines heat stress flag conditions, is checked every 30 to 60 minutes during the day, every day from May 1 to Sept. 30.

Photo by Mike DiCicco

Contraption invented at Parris Island determines heat flag conditions

24 Jun 2013 | Mike DiCicco Marine Corps Base Quantico

With summer officially begun and daytime highs around 90 degrees, those in charge of training are taking cues from color-coded flags placed throughout Marine Corps Base Quantico.  These “heat stress flags” indicate the level of intensity that is advisable for outdoor training in given weather conditions with a simple, four-tier system.

The system that determines flag conditions, however, is a little more complicated.

The wet bulb globe thermometer dates back to Marine Corps Recruit Depot Parris Island of the 1950s, when a particularly stifling summer resulted in a high number of heat casualties, said Anna Smith, safety manager at The Basic School.

“The elements were knocking them out left and right,” she said.

A joint effort between Army doctors and the Navy, carried out at the Marine Corps recruit depot, resulted in an early version of the contraption that is now the standard for gauging heat stress not just in the military services but also for the federal Occupational Safety and Health Administration and others.

 “The WBGT takes into account the effects of temperature, humidity, wind speed, sun angle and cloud cover on an individual,” Smith said. “This method takes into account the whole environment Marines are exposed as they train in all weather.”

The wet bulb globe thermometer is actually three thermometers, explained Gunnery Sgt. Clifton McChesney, scheduling chief at Range Management Branch, which sets the official flag conditions for the west side of Quantico. A regular, shaded thermometer gives the standard temperature, while another one inside a black bulb measures the effect of direct sunlight, and a third, whose bulb is wrapped in a cloth soaked with distilled water, takes into account humidity and wind.

In days of old, he said, Marines had to take the reading from each thermometer and plug the numbers into an equation to determine the wet bulb globe index.

“But we don’t have to do that, seeing how we have a nice, high-speed machine to do it for us,” he added.

In the late morning of June 17, 2013, when Cpl. Shane Piazza, scheduling noncommissioned officer at RMB, went out to check the machine held precisely four feet off the ground on a tripod in an open field near the branch’s two buildings, the standard temperature, according to the digital readout, was 81.7 degrees Fahrenheit. The wet thermometer read 75.3 degrees, and the one in the black bulb was roasting at 105.6 degrees.

Piazza didn’t need to know any of this, though. The gizmo’s computer, constantly running the three readings through the same equation, showed a wet bulb globe index of an even 82 degrees.

“We’re actually going to have to put up a green flag,” he said.

Until the WBGT reads 80 degrees, no flag is flown. From there up to a reading of 89.9 degrees, the flags progress from green to yellow to red. Anything 90 degrees and higher is a black-flag condition, meaning all strenuous outdoor activity that is not considered essential should be halted.

“When it’s a black flag, if it’s not absolutely necessary for you to be outdoors training, you shouldn’t be doing it,” McChesney said.

However, he said, the flag is not an order, and individuals are free to accept the risk of exercising in dangerously hot conditions, just as commanders can take the responsibility for continuing their units’ training under a black flag.

To make sure everyone is aware of the risks, though, RMB notifies all units stationed on the west side of the base, as well as all who are training on the ranges that day, every time flag conditions change. Marine Corps Air Facility also has a WBGT and is responsible for keeping organizations on the main side of base posted about conditions, via the base Operations Division. A backup WBGT is located at the Officer Candidates School.

Actual flags are hoisted at about 10 locations around the base.

But Smith noted that conditions can vary widely from one location to the next, and units with TBS often train miles from the RMB building. This is why she’s secured five handheld WBGT units that commanders can check out when they train on a hot day.

“If you’re training in the shade, you need to take your reading in the shade,” Smith said.

That’s how location-specific the readings are, and they fluctuate constantly. A cloud drifting under the sun can drop the black globe’s temperature considerably, and a passing breeze can momentarily bring down the wet bulb’s reading.

But this constant flux is a result of the instrument’s accuracy, and Smith said flag conditions are not to be taken lightly. “Heat mishaps are a major deterrent to training effectiveness and training quality,” she said, adding that heatstroke can lead to brain damage if not treated promptly and properly.

McChesney said flag conditions are monitored from May 1 to Sept. 30, and any other day the temperature could hit 80 degrees. The WBGT is checked every 30 to 60 minutes, depending on conditions, from 7 a.m. until 7 p.m., and will be monitored until 10 p.m. if conditions don’t drop as low as green-flag levels.

He noted that there is one flag condition that’s determined by commanders, rather than the WBGT — “admin black.”

“That’s when a command’s had too many heat casualties, and they can’t take any more,” he explained.

— Writer:

Marine Corps Base Quantico