Customizing Heat-Related Work/Rest Schedules
By Nicole Moyen, Contributor
The hot working days of summer are upon us, bringing the added risk of heat injuries and fatalities for workers with them. Summer 2020 is forecasted to be the hottest one on record. One of the most important ways to prevent heat stress among the workforce this year—and every year—is to implement an appropriate, effective work/rest schedule on site.
Sounds easy enough. But there’s no standard work/rest schedule that fits all people. Implementing the same cadence of work then rest for all won’t prevent heat injury or illness for every person.
Standard work/rest schedules for people working in hot conditions were developed based on studies in young, healthy men. This means other populations of workers were not taken into consideration when standard schedules were designed and recommended by various organizations and governing bodies that advise on occupational health and safety. There are many groups for which these work/rest schedules might not work, including older individuals, women and workers who have certain health conditions. The standard work/rest schedules aren’t flexible enough to accommodate the individual needs of multiple employees, “thereby leaving a large segment of the population under-protected.” (1)
There are standard work/rest schedules from OSHA, NIOSH and the U.S. Army, which are fairly similar across worker population groups. And, there are agreed-upon work/rest schedules from the International Organization for Standardization (ISO).
It’s important to understand the differences in standards, so you can pick the best one for your team, and know how to adapt it for the individuals on your team— based on their needs.
HOW TO CHOOSE WISELY
You should pick a work/rest schedule based on what you have available at your site and which environmental conditions are most important. For example, some work/rest schedules are based on WBGT, which is an index that combines the stress from radiative heat (black globe), ambient temperature (dry bulb) and humidity (wet globe) to assess overall risk of the environment. However, you need a black globe monitor to assess radiative heat, and some sites do not have this measurement tool. If you do not have a black globe monitor as a part of your weather station, then you should select a work/rest schedule that does not use radiative heat (or WBGT), but factors in whether the workers are in partial or full sun, or working in the shade.
Some work/rest schedules include how many clothing layers workers wear, while others do not. That being said, if your workers are wearing two-three layers of clothing (or PPE), make sure you are using a work/rest schedule that accounts for extra clothing layers. The work/rest schedule you select should always include the worksite temperature and humidity, along with the workers work rate or intensity.
Additional factors to consider are the sun (black globe) and the clothing level. If your workers are indoors, you do not need to consider the sun, and the WBGT would be an inappropriate index. Consider which factors are most important to your workers at their specific work location, and use a work/rest table that accounts for those variables.
CUSTOMIZE FOR INDIVIDUAL WORKERS’ NEEDS
After you’ve selected a work/rest schedule that makes sense for your site, you will need to consider individual characteristics that might modify that schedule. Every worker on your team comes to the job with unique physiological characteristics that should be taken into consideration when it’s time for them to work and time for them to rest. Natural factors make each person susceptible to heat-related injuries and illnesses in different ways.
- Age After age 35, the body’s ability to dissipate heat, primarily through sweating, declines. As a result, older adults tend to have higher core body temperatures than younger adults, when working at the same rate in the heat. This difference between older and younger individuals can be minimized with heat acclimatization (gradually building up your tolerance to the heat over one-two weeks). Endurance training—undertaking healthy exercise, like running or biking, in hot conditions—will also prepare someone to better withstand working in the heat. Make sure older adults are heat-acclimatized before spending long periods of time in the heat, and note that they might need to stop working before the younger individuals on the team.
- Genetics Some people are able to acclimatize faster and tolerate the heat better than others; some of this appears to be attributable to genetic makeup. Heat acclimatization for an entire team can help level the playing field. If an entire team has not been working lately, or it’s the first hot day of the season, the team will benefit from a work/rest schedule that allows for more rest during the first few days of the job, to allow for acclimatization.
- Diseases Various skin disorders (e.g., psoriasis), cardiovascular diseases (hypertension), sweat gland disorders (Type I and Type II diabetes), and metabolic disorders can impair the body’s ability to effectively thermoregulate. This means core body temperature will be higher for individuals who have these conditions, when working at the same intensity as someone without these diseases. This person might need more frequent breaks or an altered work/rest schedule to successfully manage long days of work in the heat.
- Gender Men generally have a higher sweat rate than women, as men are usually larger than women. This is important to consider, because sweating is the best way to get rid of body heat to keep the core body temperature in a safe range. In hot-dry (low humidity) climates, men will likely be able to work for a longer period of time with a lower core temperature than women, because they are better able to get rid of body heat through increased sweating. In hot-humid climates, women will likely be able to work for a longer period of time in the heat (with a lower core temperature), because their lower sweat rate will keep them from losing body water (through sweating) that isn’t evaporating and cooling. Men, on the other hand, due to their higher sweat rate, will be losing a lot of body water through sweating, because it won’t be evaporating in the high humidity. So men will become dehydrated more quickly than women and, therefore, experience a faster increase in core temperature.
With this knowledge, you can better alter the work/rest schedules for your team. Remember that during a rest period, the worker needs to actually rest and rehydrate in order for these work/rest schedules to be effective.
Other factors that may require the alteration of work/rest schedules:
- Drugs that affect the nervous system, such as antidepressants, sympathomimetics, anticholinergics and antipsychotics. These drugs have been shown to impair sweat gland function and increase heat production. Employees regularly taking these drugs will likely have a higher core body temperature for the same work rate than someone who is not taking these medications, so they might need shorter work periods and/or more rest each hour.
- Antihistamines (e.g., allergy medications). These drugs can impair sweat gland function, making it harder for an employee to get rid of heat as readily, which can lead to an increased core body temperature. Again, those on antihistamines may need more rest each hour to stay productive and safe.
- Drugs that affect the cardiovascular system, such as beta blockers and calcium channel blockers). These drugs work to lower the heart rate. This is a problem when working in the heat, because the body needs a higher heart rate to be able to pump blood to the skin (to get rid of heat) and the working muscles (for energy). As a result of the lower heart rate induced by these drugs, an employee’s body might heat up faster and have a harder time maintaining a high work rate in the heat. More rest might be required for these individuals, and it is advised to monitor their heart rate throughout the workday.
- Diuretics. These drugs make it difficult for a person to stay hydrated, which means that in the heat, the body will be working extra hard to keep cool. Remember, dehydration exacerbates the effects of heat stress, so allow these individuals to carry water with them and take more frequent water breaks.
- Fitness. Employees who are more fit can better handle the heat. Endurance exercise leads to similar adaptations as those gained with heat acclimatization. This means that individuals who are more fit will better tolerate the heat. Therefore, these individuals might be able to work longer (and take less rest) than the prescribed work/rest schedule.
- Nutritional intake. Poor nutrition and excessive caffeine, alcohol and nicotine, can reduce the body’s ability to work effectively in the heat. Be sure to stress to your employees the importance of eating healthy foods and minimizing drug and alcohol use, especially on hot days.
While both natural and external factors affecting a person’s ability to work in the heat are out of your control, you do have control in adapting the work/rest schedule of your team and each individual to ensure they are staying safe and productive on the job. Vigilantly observe and monitor the individuals on your team and adapt their work/rest schedule as needed. Encourage the team to monitor each other through buddy systems. Consider using smart PPE or physiological monitoring devices that can detect unsafe core body temperatures, and then relay that information back to the manager.
Individualized monitoring is the way of the future: It will allow you to intervene before it’s too late, so you can prevent heat injuries and illnesses on the worksite—while keeping productivity high. Remember: one size does not fit all when it comes to work/rest schedules. Be knowledgeable and accommodating to keep workers healthy and productive at work, especially under hot conditions. WMHS
- Kenny, G.P., Notley, S.R., Flouris, A.D. and Grundstein, A., 2020. Climate Change and Heat Exposure: Impact on Health in Occupational and General Populations. In Exertional Heat Illness(pp. 225-261). Springer, Cham.
About the Author
Nicole Moyen, Vice President of R&D at Kenzen, and heat stress blogger, leads R&D at Kenzen, the smart PPE innovator focused on physiological monitoring and the prevention of heat injury and death among workers. Kenzen’s real-time heat monitoring system is used by companies to keep workers safe from heat. Moyen has a decade of research experience in industry and academia related to human physiology and wearable devices, and advises companies on heat stress physiology and dehydration.
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