Managers responsible for the safety and well-being of workers must be concerned with minimizing the risk of heat related problems, such as heat stress, especially when they’re wearing personal protective equipment.

While protective garments do not necessarily cause heat-related disorders, they can contribute to the problem. Nonbreathable garments restrict air circulation, which can lessen the body’s ability to cool down through evaporation.

The human body has a natural heat protection system built in, but heat stress is a potentially dangerous condition that occurs when the body is unable to regulate its temperature. Normal body temperature is about 98.6º F. To maintain that normal temperature, the body continuously reduces the heat it produces through increased flow of blood and perspiration. Blood vessels near the surface of the skin expand, allowing more blood to come to the skin’s surface. This allows heat generated within the body to be released into the air.

When increased blood flow is not sufficient for cooling the body, perspiration begins. The brain signals the sweat glands to release fluids. As sweat evaporates, the body is cooled.

Vigorous activity in hot areas can cause the body’s temperature to rise dangerously. As the body tries to cool itself, other body functions may be neglected, and heat stress disorders may begin. For example, when more blood flows to the skin for cooling, less blood is available for the brain, internal organs and working muscles.

Excessive perspiration can cause the body to lose large quantities of fluid and salt. And when high heat is accompanied by high humidity, perspiration doesn’t evaporate, and the body isn’t cooled. In extreme circumstances, the temperature regulating system can fail and sweating stops completely.

Results of heat stress can range from tiredness, irritability, loss of concentration and coordination, headache, muscle cramps, and prickly heat, to nausea, dizziness, fainting or even death (under certain circumstances).

Preventing Heat Stress

One of the best ways to reduce heat stress is to minimize heat in the workplace. However, there are some work environments where heat production is difficult to control, such as when furnaces or sources of steam or hot water are present in the work area or when the workplace itself is outdoors and exposed to varying warm weather conditions.

To avoid heat stress, it’s important to allow the body to adjust to heat naturally and gradually. Most people acclimate to warmer temperatures in four to seven days. On the first day of work in a hot environment, the body temperature, pulse rate, and general discomfort will be higher. With each succeeding daily exposure, all of these responses will gradually decrease, while the sweat rate will increase.

When the body becomes acclimated to the heat, the worker will find it possible to perform work with less strain and distress. When workers are away from their hot environment for a week or more, they need to start the acclimation process again. In hot environments, the body loses up to 3 gallons of fluid a day. Drinking cool water every 15 to 20 minutes helps to combat the effects of heat stress, even when workers don’t feel thirsty. Moving around and stretching when working in hot temperatures can improve circulation and decrease the risk of fainting. And short, frequent rest breaks in an air-conditioned or well-ventilated room are more effective than longer infrequent rest breaks.

Protective Clothing

Protective clothing can limit the length of time that work can be performed in moderate to warm environments because of restriction of normal heat dissipation resulting in heat storage in the body. Strength, alertness and accuracy can be affected. One way to increase worker productivity when wearing protective clothing is to reduce heat stress by improving protective clothing design and using fabrics which decrease heat storage by permitting sweat evaporation, or reducing insulation.

In choosing the most appropriate protective apparel, safety professionals need to consider both protection and comfort. Begin by identifying the particulates, liquids and other hazardous substances that will be present in the worksite and the hazards associated with those substances.

In general, the nature of the hazard will steer you to the appropriate garment material. Be sure to consider the breathability and comfort quality of the fabric, which are both critical factors when trying to prevent heat stress. You don’t want workers ripping or cutting their garments to improve air circulation to keep cooler.

Common sense says that when workers are more comfortable, they’re more productive. Today, technological advances in fabric development mean that safety professionals no longer need to choose between comfort and protection.

Nonwoven fabric constructions featuring outer layers made with spun bond polypropylene provide extra strength and cloth-like comfort. Melt blown middle layers composed of an intricate matrix of microfibers that act like a filter keep out many fine particulates and water-based liquids.

Since these melt blown middle layers are breathable, both air and sweat vapor can pass through the garment to keep the skin cool, thus reducing the risk of heat stress in hot environments.

As an alternative, a microporous film middle layer provides repellency to many non-hazardous liquids, even when under pressure, such as when kneeling or flexing. This microporous film layer also provides resistance to many dry particulates, while allowing moisture and vapor to pass through for added comfort.