Garment Comfort

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Garment Comfort: Inside the Micro-Environment

A new method for measuring garment comfort can help ensure that workers wear their protective clothing correctly.

Protection and comfort. When selecting protective garments, these are the two key garment characteristics purchasers consider to determine the best suit for the job. The majority of apparel purchasers are most concerned with protection. Because if the garment doesn't protect the wearer from hazards in the work environment, it won't matter how comfortable the garment is...it will be dangerous.

With all protection characteristics being equal, however, the garment's comfort becomes a key factor in gaining wearer compliance and in guarding against heat stress injuries. Because, again, a garment that is modified to be more comfortable, or a garment that is not worn because it is uncomfortable, creates a dangerous situation.

There are numerous methods for measuring the protection a garment offers, but the issue of comfort has been more difficult to measure quantitatively. Some researchers are now using a new method for measuring garment comfort. This method measures the micro-environment inside the protective suit, assessing the humidity and temperature of the thin layer of air that closely surrounds the body. The micro-environment is a more useful indicator of how a user perceives comfort when wearing a suit than other analytical methods traditionally used to study the material's breathability.

While many material tests provide useful data for garment purchasers, they are conducted on fabric swatches in controlled laboratory settings, which is quite different from mobile workers in work situations wearing a complete, functioning garment.

However, some tests involving human subjects do exist to help bridge the gap between material testing measurements and human measurements. Traditionally, testing garment performance properties on human subjects requires measuring core temperature (the definitive measure of the body's response to heat stress) and heart rate (which indicates the amount of overall body strain). These measurements indicate how long workers can remain safe and productive in their protective garment, but don't necessarily indicate how the wearers feel while they work.

Better Indicator of Comfort

The micro-environment (conditions inside the suit) can be substantially different from the ambient or work environment. In fact, conditions inside the suit can be 10o C WBGT above the ambient work environment if the wearer is working hard and producing high metabolic heat. Essentially, the micro-environment inside the suit is the only environment the body experiences, regardless of the environmental surroundings. It is therefore a more accurate indicator of comfort than other environmental measurements.

The study of the micro-environment focuses on two things: the water vapor pressure between the suit and the skin (micro-humidity), and the mean skin temperature. Under semi-permeable or impermeable suits, macro-environmental (outside the suit) air movement makes only a small impact on the micro-environmental conditions affecting heat stress. Humidity in the macro-environment (outside the suit) also does not contribute a great deal to heat stress.

The micro-environment is dynamic, yet reaches a near plateau by 30-40 minutes. It is important to note that the heat stress that workers experience does change over time when wearing a protective garment. Therefore, it is important for apparel purchasers to review the comfort-related performance of garments at various points during the work shift. Testing on human subjects should show performance throughout a minimum 1.5-hour work bout.

Other tips to help purchasers make a fair comparison among different garments include:

* Full garment testing should supplement material bench testing to obtain a true evaluation of comfort. Tests of the micro-environment are a very good way to characterize comfort in addition to traditional tests.

* Full garment testing should be conducted in realistic work conditions (hot temperatures, high humidity as indicated by high WBGT measurements) comparable to field conditions. Since heat stress is not a major issue in cool environments, testing should occur in warm to hot conditions.

* Physiological monitoring must be conducted to measure the heat strain experienced, regardless of self-reported comfort.

* Fit is also a key comfort factor. Look for designs that fit the great variety of body shapes seen in the workforce.

In conclusion, when choosing safety apparel based on comfort and safety, micro-environmental test results can help you bridge the gap between material characteristics and human comfort characteristics. A garment with superior micro-environmental characteristics will minimize the potential for heat stress and result in higher productivity.

Kimberly Dennis is a research scientist with Kimberly-Clark Safety Division, Alpharetta, Ga. Dr. Phillip Bishop is a professor and director of the Human Performance Laboratory at the University of Alabama.