In today’s market, there are several different types of cooling technologies that are available for portable body cooling. The most sophisticated of these are essentially portable, tethered air conditioners that have been developed for military explosive ordinance disposal. As you would expect these systems are not only heavy, but are also extremely expensive. Furthermore, as with any system, there is the tradeoff between cooling effect and burden on the individual by adding weight. Other systems relying on fluid flow include recirculating vests. These too suffer from severe weight penalties and are generally not user friendly.
Probably the most common cooling vests are those that rely on ice packs that are inserted into pockets in the vest. These systems tend to be heavier and also offer limited cooling effect when compared to the CoolTek™ products. The ice packs are bulky and the fact that they are placed at specific body areas means that cooling is only provided to those locations where the pockets are located. This type of design also makes it more difficult to configure this clothing for full body applications. In addition, non-uniform body cooling can present false impressions to the wearer about their true physiological state (e.g., core temperature is rising even though they feel cool). There is still a weight penalty for CoolTek product, but because it does not rely on bulky, localized cooling areas, the weight penalty is spread out and still works out to be less than a similarly design ice pack vest. Of course, both type of vests have specific logistics requirements. CoolTek products must be wetted before use, while the icepacks must be kept in a freezer before use. Typically, it is much easier to wet the garments than it is to have handy access to a freezer.
It is best to examine the CoolTek product line (made with Hydroweave™ fabric) from two different perspectives related to its performance.
The first perspective applies to its ability to provide heat stress relief. This is the foremost quality of the product and certainly should be one of the product features with which safety personnel will be most interested.
The effectiveness of the vests is based on its ability to absorb heat from the body and release that heat to the outside environment. The water that is absorbed by the batting material provides a heat transfer medium for this effect. As the heat accumulates in the material, the heat causes water to evaporate from the vest. The direction of this heat is to the outside because the moisture differential is less to the outside (the environment next the body is generally at a high relative humid). Thus the vests are capable of provide both evaporative cooling and conduction, the two principal means for body cooling.
The length and magnitude of this cooling effect will depend on several factors. These include the activity level of the wearer, the temperature and relative humidity of the working environment, and the type and configuration of other clothing being worn. As might be expected, higher activity levels will reduce the effective cooling time. Similar effects will be experienced with relatively high temperatures and relative humidity. In addition, the greater the surface area of the body covered and in contact with Hydroweave fabric, the more cooling effect that can be provided.
However, because both conductive heat transfer (based on a temperature differential) and evaporative cooling (based on a humidity differential) occur, usually one of the heat transfer modes will work to provide cooling. Cooling effects may also be diminished if insulated underclothing is worn to limit contact of the vest with the wearer's skin, or if barrier clothing is worn over the vest, creating a high humidity microenvironment immediately outside the vest.
Certainly, use of the vests is limited to warm-to-hot conditions, or where activity is high during moderate temperature environments. Use of the vests is not advisable during cool weather operations because heat will be transferred from the body to vest making the wearer feel uncomfortably cool.
Some concerns have arisen that Hydroweave can act as a heat sink under certain environmental conditions, i.e., once it has absorbed heat from the body in a warm environment, then continued wearing could result in heat transfer back to body as the vest's cooling ability is depleted. This phenomena should not be a concern because as explained above, the driving force is away from the body because of the microenvironment between the body and vest is generally at high humidity, therefore the evaporative heat is released away from the body as water evaporates from the CoolTek product. In addition, any system (including ice pack technology) will have its effectiveness diminished over time where the transfer of heat away from the body is lessened as the material reaches its heat storage capacity. For example, as the icepacks absorb heat they obviously reach ambient temperature. The same is true for CoolTek products, but the key difference between the technologies is that while ice pack vests rely on conductive cooling only, while the Hydroweave based vests use the two forms of heat transfer for achieving their cooling effect.
The second perspective involves the flame and heat resistance characteristics of the vests. In this case, the vests are constructed of materials and components which meet the minimum requirements for flame resistance (based on an aggressive vertical flame resistance test) and heat resistance (using the exposure of 500 degrees Fahrenheit for five minutes to determine if the material melts, drips, or separates).
For example, the interior batt is a 100% Nomex batting, while the shell is a DuPont Nomex™ brand fabric and the innermost layer is flame-resistant (FR) polyurethane or similar breathable film product. The material has further been subjected to insulative tests including a manikin test. In the small scale tests, the material, when activated, provides three times the insulation provided by similar thickness materials. In the manikin testing (under simulated flash fire conditions) using the material in a coverall design, no burns are indicated for 10 second exposures (the equivalent exposure experienced during a severe flash fire for firefighters).
There has been concern that, because the material contains water, that "steam" or "scald" burns can occur during an extended high heat exposure. A number of tests conducted where materials are exposed to temperatures of approximately 400 degrees Fahrenheit for 60+ seconds. Under these conditions, the material provides superior heat transfer resistance compared with similar thickness, FR materials, but more importantly remains wet during the process (some researchers have postulated that the rapid elevation of water temperatures in material as it dries out creates scalding).
Despite the high heat to the exterior of the clothing material, the driving force for moisture is still towards the outside. This fact, combined with the batt’s tendency for holding water, prevents formation of steam or scalding water in the CoolTek clothing.
Further, it must be remembered that a person who is sweating will already be generating water that is absorbed into conventional clothing or stays on the surface of skin. Since the CoolTek product is already providing cooling, it is preventing much of the body sweating that normally occurs and uses the material instead to transfer heat via evaporation of the water in the material.
The makers of Hydroweave material are currently engaged in further sophisticated testing to further address this issue. However, there are no foreseeable conditions presented by the CoolTek product that create any special or unusual hazards for the wearer.
DISCLAIMER
"The use of CoolTekTM products should be based on a risk assessment of the work place as required by OSHA in 29 CFR 1910.132. This risk assessment must not only account for the potential for heat stress, but any other hazards that may be present in the work environment. The effectiveness of CoolTek products will depend on factors including but not limited to, the physical condition of the wearer, the wearer's activity, the environmental conditions, the amount of product coverage on the wearer's body, and the degree of intimate contact of the product with the wearer's body. Use of the CoolTek products does not relieve any responsibility for appropriate monitoring workers during heat stress or other hazardous conditions. No protective product can provide protection under all conditions. Read the product instructions before using CoolTek products."