Sailors aboard the aircraft carrier USS Nimitz (CVN 68) are participating in a research study to beat the heat with science!

A team from the Naval Health Research Center in San Diego is aboard Nimitz conducting research to determine the current metabolic work rates of shipboard personnel performing routine shipboard work.

Jay H. Heaney, an environmental physiologist and principal investigator of the research project, along with his team (Doug Jones, Kat Wilson, and Eric Duckworth) will be conducting a pilot study to reassess the physiological heat exposure limits (PHEL) that were established in the 1960s. The purpose of this study is to examine Sailors who work in heat stress producing workspaces, with modern technology that wasn't available approximately 60 years ago. They will also be testing the accuracy of the PHEL curves for certain shipboard watchstanders that have decreased in manual labor with the help of automated technology.

The team is on pace to recruit and consent 37 Sailors who volunteered to participate in the research study, said Heaney. These Sailors will come from different work spaces and departments on the ship to include reactor, galley, scullery, laundry, bow catapults, fuels, and Helicopter Maritime Strike Squadron (HSM) 75.

Heaney and his team will be the first to conduct a heat stress study examining the potential PHEL guidance for hangar bay and flight deck personnel.

"We're collecting the first metabolic work data on hangar bay and flight deck personnel," said Heaney. "That's never been done in the Navy."

The research team will be using various devices to measure metabolic work rate, oxygen consumption, core temperature, and skin temperature, as well as heart rates. They will also use a thermal environment monitor that measures both the wet and dry temperatures of a workspace.

One of the devices being used to measure a Sailor's metabolic work rate is the Viasys Oxycon Mobile Metabolic System. This system is comparable to the equipment an Olympic athlete or an astronaut would use to train, just portable and small enough to wear in work spaces.

"The face mask allows you to breathe in and out freely with no restriction," said Heaney. "In the mouthpiece, there's a turbine that allows us to measure the volume of air that a Sailor is breathing with each breath. We then measure the number of breaths and then we sample that air into the devices on the vest. The devices on the vest that the air travels through are an air volume sensor, an oxygen sensor and a carbon dioxide sensor. From that we get a Sailor's true metabolic work rate."

A participant in the study, Aviation Boatswain's Mate (Equipment) 2nd Class Brandon Fulton, from Lake Tahoe, California, was one of the Sailors who donned the equipment out on the flight deck and in the bow catapults.

"The device was hot," said Fulton. "It was hard for people to hear me through the mask on the sound powered telephones. I didn't want to jeopardize the study or the mission so we made it work, I just had to talk a little louder."

Although the equipment may be a bit uncomfortable, the research team aboard Nimitz believes the data being collected will be extremely valuable.

But before participants can don the equipment and begin their work routines, there are a few steps they must take first.

First, a participant must ingest an activated thermistor capsule four hours before beginning their work duties. About three hours later they will then be equipped with a polar heart rate monitor to measure heart rate. Then, they will have three VitalSense skin thermistor patches taped to their body on their chest, shoulder and thigh. Lastly, they will don the Viasys Oxycon Mobile Metabolic System. Once the research team has established resting values for heart rate, oxygen consumption, core temperature and skin temperature, the Sailors can begin their work routine. Participants will do this twice in their respective work spaces.

Heaney and his team will then gather the information from the participants, as well as the environmental conditions recorded by the thermal environment monitor and establish PHEL curves. PHEL curves will enable personnel to identify maximum, safe heat exposure limits.

The current six PHEL curves, established about 60 years ago, are assigned PHEL 1 through PHEL 6 with PHEL 1 being lighter work, such as monitoring gauges, and PHEL 6 being extremely heavy work, said Heaney. Their goal is to assess how accurate current PHEL curves actually are. They hypothesize that with the advances in technology to reduce manual labor over the past 60 years and the use of their new equipment to gather data, will give a more accurate representation of heat-stress on Sailors in their respective workspaces.

"What we're doing is evaluating the metabolic work rate, to perhaps reset what PHEL 1 means, what PHEL 2 means and what PHEL 3 means and so on," said Heaney. "For example, a PHEL 2 watch stander might be downgraded to a PHEL 1 watch stander. However, a watch stander like a messenger or rover, the person going in and out spaces and up and down ladderwells delivering samples, would likely remain a PHEL 3. The scullery in particular, with a current PHEL 5 rating, is being evaluated because in the 1960s a lot of the work was manual labor. Now they have a lot of automated dishwashers and high pressure rinse nozzles, thus their PHEL could most likely be reduced to a PHEL 3."

The research team's modern day equipment allows them to obtain real-time metabolic data of Sailors working; a vast improvement compared to the studies done by Capt. Adolf Dassler in the 1960s, where a lot of the results were estimated. This provides the opportunity to revise shipboard work and rest cycles, as well as heat exposure guidance.

"The research team said the issue with heat stress hasn't been looked at for a while, so I'm hoping that for future Sailors, they will be able to find a way to manage heat stress a little better," said Fulton. "We still have a job to do, so no matter what we as motivators are going to push our bodies past what is expected. The fact that people are looking into the situation gives me warm and fuzzy feelings that heat stress is recognized and they're trying to make the working conditions better for Sailors and Marines aboard."

While there was no collection of data on flight deck and hangar bay personnel in the development of the PHEL curves in the 60s, Heaney and his research team intend to use the information they gather to evaluate a potentially better way to approach guidance to prevent heat injuries for such personnel. This research is relevant to shipboard operations, particularly in the Gulf, where there have been 12 reportable heat casualties so far this deployment.

"We want to be able to beat the heat by preventing injuries and reducing fatigue from continuous exposure to heat stress conditions," said Heaney.

Nimitz is deployed in the U.S. 5th Fleet area of operations in support of Operation Inherent Resolve. While in this region, the ship and strike group are conducting maritime security operations to reassure allies and partners, preserve freedom of navigation, and maintain the free flow of commerce.

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