Heat Stress One-On-One

May 4, 2001
Targeting the needs of individuals rather than the entire crew is the key to preventing heat-related illness.

Add high temperatures and relative humidity to radiant heat, minimal air circulation and physical labor. What you have, by many standards, is the perfect equation for workplace accidents.

Research conducted by the National Institute for Occupational Safety and Health (NIOSH) shows that work in hot environments is linked with lower mental alertness and physical performance, and subsequently, more injuries. Factor in elevated body temperature and physical discomfort and it's easy to see how workers can divert their attention from hazardous tasks and overlook common safety procedures.

If a heightened risk of workplace accidents isn't bad enough, heat also can prompt the development of potentially life-threatening illnesses, ranging from rashes and dizziness to more serious complications including fainting and loss of consciousness.

Because heat production is difficult to control, particularly when furnaces or sources of steam or water are present in the work area, or when the workplace is outdoors and exposed to varying conditions, employers have to realize that just checking the thermometer isn't the most accurate way to measure the potential for heat-related dangers.

In fact, experts agree that some of the most critical factors to consider when it comes to preventing heat stress have more to do with individual workers than they do with the environment.

An individual's ability to withstand heat can be reduced by his or her health and physical conditioning, the equipment used, changes in the work environment and even day-to-day variables, such as caloric, fat and water intake, said Kris Bancroft, safety, health and environmental analyst and former safety consultant for the Florida Division of Safety.

Bancroft said workers are particularly at risk for heat-related disorders when they:

  • Take certain medications,
  • Are obese,
  • Use alcohol or drugs,
  • Have certain medical conditions,
  • Had a heat-induced illness in the past, or
  • Wear personal protective equipment.

Acclimatization Process

Heat disorders occur most often among workers who have not been given enough time to adjust to working in heat or in those who have been away from hot environments for an extended period of time. By teaching workers to recognize the symptoms of heat stress and exposing them to hot environments in gradual increments, employers can ensure that employees will acclimate to higher temperatures.

Under normal circumstances, this process can take from five days to two weeks. On the first day of work in a hot environment, a person's body temperature, pulse rate and overall discomfort level is high. With each succeeding day of exposure, response to heat gradually decreases, while perspiration increases. As this happens, the worker finds it possible to perform work with less strain and distress.

It's important to note, however, that the rate of acclimatization is a function of the individual's level of physical fitness. Unfit workers take 50 percent longer to acclimate than those who are in good physical condition.

At Bethlehem Steel, the nation's second-largest steel producer, new employees are allocated seven to 14 days to adjust to the heat, humidity and having to wear protective clothing before they are able to work at full pace. Employees returning from vacations or extended illnesses are also required to reacclimate, said Tom Civic, manager of safety and industrial hygiene at the company's Bethlehem, Pa., headquarters.

"Even when you're away from the heat for a week, your body has readjusted to cooler temperatures. So if a person does not rebuild [his or her] tolerance, the potential for heat-related illness is extremely high," Civic said.

Employee Monitoring

Because a worker's tolerance varies from day to day, employees working in extraordinarily hot conditions should be closely monitored.

"One extra caution to employers -- remember that no two employees are the same," he said. "When it comes to heat stress, workers should be dealt with as individuals, not as groups."

Even employees who are conditioned to working in hot environments can have an occasional battle with heat-stress symptoms, Civic explains. For that reason, any Bethlehem Steel worker who experiences symptoms of heat stress is instructed, as part of ongoing heat stress prevention education, to notify his or her supervisors or co-workers as soon as possible.

"It's difficult to predict just who will be affected and when because individual susceptibility varies so drastically," Civic said. "It's also not uncommon for an employee who's been working in the same capacity for years to have days when the heat can get the best of him."

Because certain medical conditions predispose people to having trouble dealing with the heat, OSHA recommends that employers monitor changes in employee health to ensure they are continually capable of performing their assigned tasks. This means that when any major health events occur, ranging from sickness to being prescribed new medication, a clearance from a physician should be obtained prior to the employee's return to work.

Work-Rest Cycles

Rather than expose employees to intense heat for extended periods of time during the course of a job, another option is to distribute the workload evenly over the day and incorporate what's referred to as "work-rest cycles" into the work day.

During unusually warm-weather periods of two days or more, the number of heat-related illnesses usually increases due to progressive body-fluid deficit, loss of appetite, salt deficit and buildup of heat in work or living areas.

When this happens, many employers, like those at Bethlehem Steel, instruct their workers to strategically schedule their work patterns so that the most strenuous jobs are conducted at the coolest times of day. Employees are also encouraged to take frequent breaks in an attempt to eliminate excess heat, slow the production of internal body heat and provide greater blood flow to the skin.

Just allowing individuals to get out of the heat and, more importantly, out of the humidity, even if only for a few minutes to take in fluids and get their heart rates back to normal, has proven extremely beneficial, Civic said. In keeping with this philosophy, Bethlehem Steel has created several "cool rooms" throughout its facilities. Employees can use the cool rooms throughout the day whenever they feel they need a relief from the heat, Civic said.

Bancroft also suggests that employers factor in extra rest periods whenever employees have to wear extra protective equipment. Likewise, they should be certain to select the coolest equipment legally permitted, he said.

At the Arizona division of the Burlington Northern Santa Fe Railroad (BNSF), for example, the majority of workers are instructed to wear loose-fitting, lightweight clothing that permits airflow. A few also have to wear protective body suits and coveralls.

"The white suits we use reflect the sun and help our workers manage the Arizona heat," said Greg Kreie, safety assistant for the division's right-of-way maintenance operation. "The long sleeves protect the skin against sun and ultraviolet rays, and because humidity isn't a problem, there's no problem with moisture buildup inside the suits."

Other workers, including many chemical and steel-mill workers, aren't as fortunate. Although the suits they have to wear protect workers and ultimately reduce the heat load, the moisture buildup can be rather uncomfortable. In these circumstances, Civic said, Bethlehem Steel employs the following strategies to manage heat stress:

  • Reschedule labor-intensive jobs to cooler parts of the day and, in some cases, to cooler parts of the year;
  • Postpone nonessential tasks;
  • Permit only those workers acclimatized to heat to perform the most strenuous tasks;
  • Provide additional workers; and
  • Rotate workers who work in strenuous jobs.

Fluid and Dietary Recommendations

BNSF machine operators and track laborers can face desert temperatures as high as 126 degrees in the shade during the summer months, so managers make sure to schedule the majority of the heavy work for the early morning hours so that the most labor-intensive jobs are completed by noon.

Because of the dry heat, Kreie said, the most critical aspect of his heat-stress prevention program is fluid intake. In the course of a day, a worker may produce up to two to three gallons of sweat. Because so many heat disorders involve excessive dehydration of the body, it is essential that water intake during the workday be about equal to the amount of sweat produced.

Most workers exposed to hot conditions drink less fluids than needed because of an insufficient thirst drive. Workers, therefore, should be instructed not to depend on thirst to signal when and how much to drink. Instead, NIOSH recommends workers drink 5 to 7 ounces of fluids every 15 to 20 minutes.

Cool water and electrolyte replacement beverages that replace sugar and sodium depleted through perspiration are best. Caffeinated and alcoholic beverages should be avoided because they cause the body to lose water.

Likewise, a special emphasis should be placed on what employees eat. Consuming large or heavy meals during or before work can increase an employee's susceptibility to heat-stress injury. For that reason, employees should be advised to eat lighter meals more frequently, on and off the clock. They should also avoid high-protein foods, which have been shown to increase metabolic heat.

"The success of any heat-stress prevention program is based strictly on the awareness of its workers," Civic said. "The more information and tools workers have in terms of prevention, the more effective they will be at dealing with the heat."

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