Fashion Forward
Written by Terry Rice
MMT 2009 Volume: 13 Issue: 8 (December)
U.S. Army Research Institute of Environmental
Medicine uses thermal manikins to test
clothing and individual eqiupment.
The U.S. Army’s interest in the physiological health and cognitive performance of warfighters can be traced back to research done at the U.S. Army Quartermaster Research Command in Lawrence, Mass., from 1944-1952. Those pioneering scientists made important advances in the areas of protective textile development, clothing design, climate mapping and human tolerance to adverse combat environments.
Today’s warfighters work in a variety of environmental conditions with stressors such as heat, cold and altitude. They carry heavy loads of equipment, ammunition and food, exert huge amounts of energy and stretch the physiological and physical limits of their bodies on a regular basis. Like highly trained athletes, they need the best available clothing and equipment to meet the demands of their work.
Researchers at the U.S. Army Research Institute of Environmental Medicine, a unit with the Medical Research and Materiel Command, located on the Soldier Systems Center in Natick, Mass., are particularly interested in how warfighter physiology, clothing and individual equipment (CIE) and job performance interact.
Understanding the insulating and breathability qualities of protective clothing is where the research begins—on thermal manikins. Through biophysical testing and mathematical modeling, manikin data is used as input to a series of mathematical models developed to predict various human thermophysiological responses when operating in a wide range of environmental and occupational scenarios. Modeling results are routinely used for selecting CIE for human wear-trial testing, procuring new CIE, writing operational doctrine and conducting health hazard assessments. This test/model approach has proved to be a cost-effective method to develop improved CIE for the warfighter.
To assess the potential for thermal stress to the warfighter, CIE is evaluated in three steps. First, biophysical measurements of the thermal insulation and moisture permeability of the CIE are made with specialized manikins. Second, biomedical modeling is conducted to predict the physiological (body temperatures, sweating rate and heart rate) strain expected of warfighters wearing particular CIE under conditions of environmental (temperature, humidity, air motion, radiant load) and metabolic (work, rest) stressors. Third, actual human volunteer testing of CIE is conducted while exposed to a variety of controlled environmental and metabolic stressors.
Military clothing, footwear, handwear and headgear are first tested for thermal and water vapor resistances using appropriately shaped manikins. Tom Endrusick, a research physical scientist at the institute, explained that “once CIE has been evaluated by the manikins, then the information is provided to the thermal research group to develop a specific protocol for human testing.”
The life-size full body thermal manikin, thermal head and thermal foot are designed to simulate the heating and sweating of the human skin body surface. Manikin test procedures are under the purview of the American Society for Testing and Materials and in-house test procedures.
“Using the various manikins provides a cost-effective evaluation of new CIE, while also providing data for prediction modeling and human wear-trial efforts,” said Endrusick.
RECENT EVALUATIONS
Recent efforts have included evaluating systems to mitigate heat stress when wearing body armor; assessing the heat stress potential of new flame resistant combat uniforms; determining the cooling requirement of a modular helmet; and predicting the thermal performance of new modular boot systems during cold exposure.
Evaluations on active and passive garments used to mitigate heat stress under interceptor body armor (IBA) have been conducted by thermal manikins. The IBA system consists of a front/rear torso fragmentation vest; front/ rear ballistic plates; and optional attachments for throat, groin, upper arm, and side torso protection. When fully configured, the IBA can weigh 15 kilograms and cover upwards of 30 percent of the body surface area with multiple layers of low-permeability materials. Use of the IBA can contribute to heat stress and limit wearer performance by insulating the body and limiting heat loss.
Two different garments designed to increase air ventilation and subsequent evaporative cooling under the IBA were evaluated: a passive, interceptor ventilation vest (IVV) and an active, battery-powered body ventilation system (BVS).
Thermal manikin testing showed that whole body thermal and water vapor resistances were lower (10 percent and 25 percent) when the IVV was worn under IBA. Biomedical modeling using the manikin data indicated that use of the IVV could also result in reduced skin wettedness, sweat rates, core temperature and heart rate. With the BVS blower unit on, thermal and water vapor resistances were also lower (17 percent and 20 percent), compared to values with the blower off. Flame-resistant (FR) combat clothing was tested on the thermal manikin to see if the new material posed a risk of increased thermal heat stress. Manikin data showed no significant difference in thermal and water vapor resistances between the FR material and current Army combat uniform material.
In a temperature profile test of Army combat helmet (ACH) suspension system materials, the thermal head was used to provide a heat source to evaluate the performance of memory foam suspension pads in the ACH. The thermal head surface was controlled at 35 degrees Celsius while the testing was done in a range of moderate to cold ambient temperatures. Testing results indicated detrimental changes in the foam material at lower ambient temperatures.
The U.S. Army is considering a new Modular Boot System (MBS) to replace several separate footwear systems with one system that will allow for donning and doffing various components depending on the environmental conditions. Thermal foot testing showed the MBS can provide protection in all environmental conditions that may be encountered by today’s warfighters, but might prove impractical due to the weight and bulk of the entire system.
OTHER APPLICATIONS
Also using thermal manikins, researchers studied chemicalbiological (CB) protective shelters for military working dogs. Military working dogs (MWDs) are valuable assets used in security, rescue and explosive detection missions. A heated, sweating thermal head was used to mimic a panting MWD placed inside a closed CB kennel shelter. A dog-specific prediction model was developed in order to define safe tolerance times for kennel occupation based on ambient environmental conditions.
In addition, research also looked at CB protective patient wraps (PPWs). Warfighters injured on a CB-contaminated battlefield are placed inside a CB PPW for movement to a medical treatment facility. A thermal manikin was placed inside a series of new PPWs to assess the potential for heat stress and injury. A prediction model indicated that injured warfighters could safely tolerate a six-hour PPW occupation in temperate weather when placed in the shade. Tolerance times were greatly reduced when the PPW was placed in direct sunlight.
Through the use of manikin testing, CIE is evaluated for thermal performance characteristics. Manikin data can then be used as input to mathematical models that will predict user physiological performance. Past efforts have been instrumental in improving numerous CIE including clothing systems, footwear, handwear, headgear, body armor and microclimate cooling systems. Customized testing and modeling to accommodate unique CIE can also be done.
Successful material test performance by the thermal manikins could result in recommendations to the developers to pursue a particular CIE item for prototype study of human performance. Thermal manikin testing and evaluation ensures that U.S. warfighters are wearing and using the most up-to-date materials that provide them the ability to work in varying environments while minimizing the physiological stress on their health and performance. ♦
Terry Rice is the public affairs officer for the U.S. Army Research Institute of Environmental Medicine.