UNITED STATES MILITARY USE OF THERMAL MANIKINS IN PROTECTIVE CLOTHING RESEARCH

Thomas L. Endrusick, B.Sc.
Leander A. Stroschein, B.Sc.
Richard R. Gonzalez, Ph.D.

U.S. Army Research Institute of Environmental Medicine
Biophysics and Biomedical Modeling Division
Kansas Street
Natick, MA 01760-5007

Today, sophisticated thermal manikins are used worldwide in a vast array of government, industrial, and academic research settings to evaluate the environmental and occupational protective capabilities of clothing, footwear and handwear.

However, prior to 1941, there was no method available for U.S. military clothing developers to accurately assess thermal heat transfer through protective clothing ensembles.

During the 1930's, 1 dimensional guarded-ring flat plates and 3 dimensional heated cylinders were commonly used to measure thermal resistance of single or multiple textile layers.

The development of the clo unit in 1941 by Gagge, Burton, and Bazett was an important advancement in clothing science as it provided for a standard measure of the thermal insulation of clothing. At that time, 1 clo equaled the insulation provided by a typical business suit. 2 clo could be said to provide twice the protection of a business suit, etc.. This concept of insulation was intentionally developed to be understood by non-scientists and was the first to establish a relationship between man, his clothing and the environment.

Early Thermal Manikin History
The building of the first working thermal manikin for the U.S. military is attributed to Dr. Harwood Belding in 1941, who was working as a civilian contractor for the military at the Harvard Fatigue Laboratory testing protective clothing and equipment using human volunteers. Belding was inspired by a store window fashion manikin to build a crude, headless and armless manikin from stovepipe and various sheet metals. The manikin had a simple internal heater and fan to distribute the heat.

In 1942, Belding collaborated with engineers at the General Electric Co., in Bridgeport Connecticut to build a thermal manikin similar to the one GE had been using since 1939 in their research program to develop an electrically heated blanket for the consumer market. This manikin was formed from molds cast from an exquisite clay form done by the Connecticut sculptor, Leopold Schmidt. It was composed of an electroplated copper shell from 3 to 6 mm in thickness and had a single electrical circuit that uniformly heated the copper shell with a provision to vary the temperature of the hands and feet without affecting the surface temperature of the rest of the manikin's body. (This thermal manikin, later refurbished in 1971 and completely rebuilt in 1995 for better temperature control, is still used to evaluate protective clothing at the U.S. Army Research Institute).

As World War II drew to a close, many members of the Harvard Fatigue Laboratory, including Belding and his thermal manikin, joined the U.S. Army Quartermaster General's new Climatic Research Laboratory in Lawrence, Massachusetts to continue work on improving environmental protection for military personnel. In September 1945, General Electric was asked to build the next generation thermal manikin for the Climatic Research Laboratory. General Electric combined its previous manikin expertise along with detailed data from an anthropometric study of nearly 3000 Army Air Force cadets to construct another electroplated copper shell manikin with a total of six separate electrical circuits and based on the average physical dimensions of a young U.S. military recruit.

WW II Thermal Manikin Research
From 1940-47, the Harvard Fatigue Laboratory under the direction of Belding conducted both basic and applied U.S. Army clothing research. During the war, they investigated reports of inadequacies in protective clothing capabilities coming in from various battlefronts, and suggested possible improvements to the Quartermaster's clothing specialists. In the process, Belding, along with fellow scientists using thermal manikins in Canadian and British clothing research efforts, developed the fundamental basis for today's scientific study of protective clothing.

From 1941-1950, the Aero Medical Research Laboratory at Wright Air Field in Dayton, Ohio, conducted similar research for the U.S. Army Air Corps. They also obtained a General Electric thermal manikin in 1945, where Gagge and his associates used it to completely redesign most Army Air Force aviators clothing away from the use of natural to newly-developed artificial materials.

From 1942-54, the Climatic Research Laboratory in Lawrence, Massachusetts also conducted military clothing research. After WWII, this laboratory absorbed many scientists from the Harvard Fatigue Laboratory and grew into the lead military facility for conducting pioneering work on improving environmental protection for U.S. military personnel.

Thermal Manikin Research: 1950's
By the early 1950's, clothing researchers had successfully used thermal manikins to measure the resistance to sensible, dry, heat transfer of a wide range of protective clothing from all the military services. In the process, military footwear, handwear, sleeping bags, and combat clothing ensembles were further improved for comfort, durability, and environmental protection.

Thermal manikin research during this decade also revealed that the highly curved surfaces of the human body created a complex and dynamic microclimate between the clothing and skin surface. Unlike the heat transfer characteristics of textiles established from earlier guarded ring flat plate work, thermal manikins showed that actual clothing, when draped over the human figure, can have localized variations in thermal conductivity as well as in the ensemble's convective and radiative properties.

Thermal Manikin Research: 1960's
In 1961, most military thermal manikin work was centered at the new U.S. Army Research Institute of Environmental Medicine (also known as "USARIEM") located at Natick, Massachusetts. One area of new research was focused on the resistance by protective clothing to the transport of water vapor and its impact on soldier performance. This work was possible due to the introduction of the moisture permeability index (im) by Woodcock in 1962 who was then working at USARIEM. This value is the ratio of the maximum evaporative cooling, at a given ambient vapor pressure, from a 100% wetted surface through a fabric, to the maximum evaporative cooling of a psychrometric wet bulb thermometer at the same vapor pressure. This parameter characterized the permeability of clothing materials to the transfer of water vapor.

Woodcock used a sweating, heated cylinder to conduct his permeability evaluations of both the bare cylinder surface and various protective clothing textiles. Goldman and Breckenridge, interested in utilizing this index for practical clothing applications, outfitted thermal manikins with tight fitting cotton skins that could be saturated with water to simulate a sweat wetted skin surface. These "sweating" manikins could now measure the maximum evaporative heat transfer allowed to an individual wearing a given protective ensemble. This work made it possible to begin a concerted effort to increase the "breathability" of chemical and biological protective clothing.

Thermal Manikin Research: 1970's
Comparisons made between thermal manikin data and controlled human volunteer studies indicated that the movement of air within and immediately adjacent to a multilayered clothing system could have a dramatic impact on the evaporative cooling potential of the protective ensemble. Consequently, Givoni and Goldman developed a pumping coefficient ('p') that described the effects of wearer-generated air motion on the thermal and water vapor resistances of clothing.

Givoni and Goldman then used clothing thermal and water vapor resistances from thermal manikins along with the derived pumping coefficient to develop a series of equations that predicted rectal temperature when wearing military clothing in a range of cool to very hot environments. These early equations were further modified by Givoni and Goldman to predict heart rate while wearing protective clothing and working in stressful environments.

In the mid-1970's, thermal manikin data continued to be critical coefficient input as these equations were developed into more sophisticated predictive models. Pandolf and associates made modifications to assess the impact of the level of dehydration, and Givoni and Goldman further enhanced the models to include the effects of acclimatization on wearers of protective clothing.

Thermal Manikin Research: 1980's To Present
In the early 1980's, the U.S. Army began a complete redesign of major clothing systems for air, ground, and vehicle based personnel utilizing a variety of novel technologies and materials. On an increasing basis, the military has evaluated and then adopted numerous commercial textile developments (i.e., Gore-Tex, Thinsulate, Primaloft) for use in these new combat clothing, footwear, handwear, and sleeping systems. In fact, several U.S. textile manufacturers created specialized, in-house groups interfacing directly with military clothing developers to provide ready access to novel developments and test results.

In 1984, USARIEM began using a new articulated, thermal manikin employing 19 separate heating zones, which has the ability to simulate the bodily movements involved in walking and running. The manikin is housed in a climatic chamber with precise control over the air velocity directed at the manikin. A minimum of three different air velocities are usually necessary to accurately determine the effect of air movement on the thermal and moisture transfer properties of protective clothing ensembles.

Thermal manikins have evolved within the U.S. military as a direct result of the need to provide better personal protective clothing and equipment in an increasing variety of environmental zones of operation. Thermal manikin data have been instrumental in improving both the comfort and functional performance of a multitude of military clothing and equipment as well as providing input to develop tactical clothing issue doctrine and practical human performance predictive models.