Hypothermia occurs when the deep body temperature drops from the normal 37 degrees C (98 degrees F) to approximately 32 degrees C (89.6 degree F). Primary heat loss occurs at the head, neck, chest and groin.
This anti exposure flotation suit system is an innovative product that my team and I at Protexion Products developed, in accordance with the national standards CAN/CGSB-65.11M88, CAN/CGSB-65.21M89 and US/Ul-1123. It was designed in a manner that would permit the user the most possible comfort, maintain its water integrity and to delay the onset of hypothermia.
It was an excellent project that demanded a great deal of research and testing. My personal responsibilities consisted of; setting the design parameters, pattern development, developing necessary software, prototype construction and supervising laboratory testing.
The function of a flotation suit is to provide a high level of protection to individuals performing various tasks on or near a body of water where immersion in cold water is a possibility.
The suit system should be light and allow all of the activity the situation demands without hampering your mobility. It must be designed to keep one dry and contend with water coming from any direction, and in the event of immersion, it must provide flotation and guard against the onset and the eventual death caused by hypothermia.
Hypothermia occurs when the deep body temperature drops from the normal 37 degrees C (98 degrees F) to approximately 32 degrees C (89.6 degree F). Primary heat loss occurs at the head, neck, chest and groin.
The cause of death is usually cardiac arrest and occurs when the core temperature falls below 30 degree C (86 degree F). Even a small increase in survival time can mean the difference between being alive or dead when rescuers arrive.
Objectives of the project
Design Parameters
As the water in the suit exchanges, there is little chance for it's temperature to increase. By trapping and restricting the flow of water between a layer of insulative and buoyant foam, the waters temperature will increases as a result of body heat. This extends the survival time by as much as 2.5 times longer than can be expected from a normal (vest type) personal flotation device.
The following table shows how the predicted survival time of an average adult in water at 10 degrees C (50 degrees F) varies in different situations.
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Situation |
Predicted Survival Time (hours) |
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With no flotation |
Drown-proofing |
1.5 |
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Treading water |
2.0 |
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With Flotation (PFD) |
Swimming slowly |
2.0 |
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Holding still |
2.7 |
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HELP (Heat Escape Lessening Position) |
4.0 |
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 |
Huddle |
4.0 |
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With Flotation Suit |
Holding still |
7.0 |
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Items 2 and 3, above were addressed by constructing a waterproof and insulated foam liner that would provide flotation as well as hypothermia protection to the wearer. The insulative value of the suit must provide a minimum of .25 CLO when measured in turbulent water conditions after one hour. The liner was constructed from various guages of foam. Careful placement of these foam panels contributed to the in water performance of the suit system as a flotation device and its ability to minimize the risk of drowning. Note: A CLO value of 1 is the insulative value of clothing required to keep a resting subject comfortable at a room temperature of 21 degrees C (70 degree F).
The buoyancy of the suit system was tested so that the total buoyancy (Bt) of the suit was not less than 69 N (15.5 lb), or the value determined according to the following equation, whichever is greater.
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where: | |
| Bt | Total design buoyancy required for the suit, in newtons. | |
| F | Regulatory minimum buoyancy for the suit (F = 69 N) | |
| Qi | Fraction of buoyancy provided by the ith material to the applicable regulatory minimum buoyancy of the suit. | |
| Ri | Foams having V factors of 94 or more Ri = 0.94 Foams having V factors of less than 94 Ri = Vfactor/100 (V factor is a value that expresses the foams ability to retain buoyancy). | |
| n | Number of materials used in the suit. |
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Item 4, above was addressed by drafting the suits patterns to provide the best possible fit and buoyancy for the wearer within the size range. The suit needed ample room to aid in mobility; however, the internal cavity could not be so large that it would contain volumes of water that could not be heated by the body and consequently affect the hypothermic qualities of the suit.
Problems encountered
In an effort to construct the prototype to allow optimum comfort it was necessary to make many pattern modifications. As patterns were modified the buoyancies of the foam inserts were constantly changed. After each change a timely, manual and inaccurate recording of the new buoyancy configuration had to be determined by dipping each insert and processing the dip results by use of the buoyancy formula above, this procedure took several hours.
I addressed this problem by developing the
PFD software that would allow me to simulate a buoyancy test and determine the exact buoyancy configuration of the garment. What if scenarios with a higher degree of accuracy, could then be obtained instantly.
Conclusion
The focus of work on the suit system was a project that required several
years. It concluded with a successful testing session conducted by the Underwriter's Laboratories and the granting of approval certificates from the Coast Guard.
