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Kool Suit NEDU Testing

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United States Navy Experimental Diving Unit Testing

Please Note: All suggestions for improvement found within this memo have been implemented in the latest version of the Kool Suit.

TECHNICAL LETTER NO. NEDU TL 03-01
From: Commanding Officer, Navy Experimental Diving Unit
To: Program Manager - Personnel Protection Subgroup
Subj: FINAL REPORT FOR QUICK LOOK EVALUATION OF A COOLING VEST

FOR USE UNDER BODY ARMOR OR WITH MOPP GEAR, PMS NSW TASK 01-13 Ref: (a) E-mail from TSWG to NEDU of 18 March 2003 (b) NEDU Protocol 03-15/32127 Encl: (1) Graph - Rectal temperature (2) Graph - Weighted skin temperature (3) Graph - Mean heart rate

1. Under reference (a) the Technical Support Working Group (TSWG) tasked the Navy Experimental Diving Unit to evaluate a cooling vest for use under body armor or with Mission-Oriented Protective Posture (MOPP) gear. A comparative analysis was designed to assess the effectiveness of the cooling vest during cooled versus non-cooled trials. Results will be used to provide guidance for further development and/or design changes and improvements.

2. The primary objective of the testing was to evaluate the cooling system during environmentally stressful conditions while exercising at light to moderate workloads, and to assess the capability of the cooling system to reduce thermal strain and extend exposure duration under those conditions. The results will determine whether this cooling vest provides a method to extend endurance for operational personnel wearing body armor and MOPP gear in hot environments.

3. Testing was conducted in an environmental chamber at NEDU, Panama City, FL, from 12-16 May 2003. Four subjects tested the cooling unit while wearing one of two garment ensembles: (1) battle dress uniform (BDU) with body armor (NIJ Level IIIA), and (2) Level III MOPP gear without hood and mask and no body armor. The cooling unit was worn during all tests. Each subject was tested twice in the body armor configuration: once with the unit operating, and once with the unit not operating. Due to time constraints, each subject was tested only once in the MOPP configuration - two subjects with the cooling unit operating and two without the unit operating. Environmental chamber conditions were 100 ± 0.5 °F (37.8 °C), 40 ± 5% relative humidity (RH). Exercise consisted of a repeated cycle of 8 minutes walking and 2 minutes jogging on a treadmill until voluntary termination by the subject or termination by supervising personnel following predetermined abort criteria. Target oxygen consumption was 1.2 L/min walking, 2.2 L/minute jogging. A prehydration regimen (0.5 L/hr for 4 hours before each test) was established. Hydration during the tests was limited to 2 liters of water consumed during the walking phase of exercise. Variables measured included pre- and postexposure weights, five skin temperatures at preselected sites (used to calculate a weighted mean skin temperature), rectal temperature, heart rate, and oxygen consumption. Alcohol, caffeine, and nicotine intake were not allowed during the 24 hours before each test.

4. During the evaluation, several issues were raised regarding improvements in the cooling system to improve fit and function. Proposed improvements included these:

a. The fabric to which the cooling coils are attached should be made of a material that is more form-fitting to improve contact with the operator. Wearing body armor over the cooling vest improved contact of the vest with the torso, as subjects commented about a noticeable difference in cooling between the body armor condition and the MOPP condition, in which the loose-fitting MOPP gear reduced skin contact with the cooling coils by allowing the cooling vest to drape away from the body. In one instance the lack of body contact impaired the circulation of cold fluid for approximately 20 minutes, with circulation resuming after the subject pressed the vest against his body.

NOTE: Garment used for testing was one size only and made of 100% cotton. Current garment is now optimized in six form-fitting sizes made of a 91% cotton and 9% Lycra blend.

b. Several subjects demonstrated evidence of skin abrasion and chafing from the lower portions of the cooling vest. Design of the vest in this area must be improved to prevent such injury.

NOTE: Current garment has redesigned channel patterns and connectors that provide comfort to the wearer.

c. Several subjects reported pinching in the areas of the backpack and shoulder straps. Design of a system to more equally distribute the weight of the pumping unit may alleviate this problem.

NOTE: Backpack used for testing was an off-the-shelf model and not optimized for housing the Kool Suit components. Current backpack has been designed and manufactured specifically to house the Kool Suit components. Its H-harness design is now comfortable to the wearer.

5. Average exposure durations for the four conditions included:

a. MOPP/uncooled = 56 minutes,

b. MOPP/cooled = 86.5 minutes,

c. body armor/uncooled = 98.3 minutes,and

d. body armor/cooled = 138.5 minutes.

Therefore, the cooling system increased exposure duration in the MOPP condition by 54% and in the body armor condition by 41%. The rate of increase and the absolute increase in rectal temperature were reduced significantly (p<0.05) for both cooled conditions when compared to the uncooled conditions (Enclosure 1). Weighted mean skin temperatures for the four conditions document the effects of the cooling system on the body surface (Enclosure 2). Heart rate responses also provide evidence of the effects of the cooling system vs. the uncooled conditions (Enclosure 3). Oxygen consumption was not significantly different when subjects were compared cooled versus uncooled for both MOPP and body armor conditions, but was approximately 10% higher in the MOPP conditions than in the body armor (a result from setting the workload during the body armor conditions and maintaining that workload during the MOPP conditions). This difference could have resulted from the increased bulk and more restrictive nature of the MOPP gear. No differences in fluid loss between the four conditions were apparent: subjects fluid loss averaged 1-1.3 L, or 2.3-2.5 lb. (Because the fluid loss was measured over time, fluid loss was 50% less when wearing the Kool Suit)

6. This evaluation demonstrated that the cooling system significantly extended exposure duration and reduced the thermal strain imposed by the combination of exercise and hot environment for both the MOPP and body armor conditions.

NEDU Testing Results- rectal temperature

NEDU Testing Results- weighted skin temperature