Protective clothing

Responding is Mark Saner, technical manager, Workrite Uniform Co., Oxnard, CA.

The answer is no. Heat stress occurs due to the body’s inability to adequately dissipate body heat. The body is continuously generating heat, which must be released to maintain the proper core temperature of 98.6° F. During overheating conditions, the body pumps more blood to the skin’s surface to both release heat and create sweat, causing blood loss to the organs, dehydration and eventually some form of heat stress (heat rash, heat cramps, heat exhaustion or heat stroke).

When working in hot, humid environments, two of the body’s basic cooling mechanisms (radiation and evaporative cooling) often do not function properly. For example, in temperatures of 95° F or higher, heat radiation off the body does not function because the surrounding air is no longer cooler than the skin. And in high-humidity situations, the surrounding air is saturated with moisture, leaving no chance for sweat evaporation (evaporative cooling) to take place.

When working in these conditions, many factors play a role in whether or not a worker experiences some form of heat stress, including:

• Age and gender
• Body mass index
• Use of alcohol, caffeine or medications
• Diet and fitness level
• Hydration level
• Breathability of clothing

There are a number of ways to reduce the chance that workers will experience heat stress, including:

• Taking regular rest breaks
• Staying hydrated by drinking plenty of water
• Taking advantage of shade when possible
• Performing physical activities when the temperature is cooler, if possible
• Acclimating employees to working conditions
• Wearing garments made from breathable woven or knit fabrics that promote moisture wicking and do not trap heat

Although the type of garment/fabric is a contributing factor, research indicates that garments play a relatively minor role in reducing heat stress – especially when compared to work practices regarding proper hydration and rest breaks. As long as the garment is made from a fabric of a reasonable weight (typically 4.5 to 7 oz/yd²), a breathable woven or knit fabric that allows heat to radiate off the body, and one that helps move sweat off the skin and onto the surface of the fabric to evaporate (wicking), the actual weight of the fabric will have little impact on heat stress.

The bottom line is, protective clothing is worn to protect workers against extremely dangerous hazards, such as flash fire or electric arc flash, and is therefore necessary for worker protection. The weight of the fabric can play a role in its ability to protect from these hazards, so choosing a lighter-weight fabric may not be an option. If heat stress is also a hazard, choose the lightest-weight, most breathable fabric to meet your electric arc flash or flash fire protection needs, and then follow the basic heat stress reduction work practices to minimize or prevent heat stress:

• Take regular rest breaks.
• Drink plenty of water.
• Occasionally get out of the sun.
• Minimize worker use of alcohol and caffeine.
• Recognize heat stress signs, including headache, lightheadedness, fatigue, confusion, nausea and cramping, and take appropriate action when necessary.

Editor's note: This article represents the independent views of the author and should not be construed as a National Safety Council endorsement.