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Concepts in Human Factors Engineering (Part 10 of 11)

Concepts in Human Factors Engineering (10): The Rhythm of Working

by Dennis R Andrews PhD, PSP, CECD

By Dennis R Andrews PhD, PSP, CECD (ExpertPages member profile page)

The body changes during the day much as the tide of the ocean. At some times of the day the body is more alert than others and consequently can be the cause of injuries. These different alert periods are also known as circadian rhythms. These physiological rhythms change the heart rate, body temperature, blood pressure and hormonal fluctuations. These changes are at their apex between Noon and 6 PM. Their Low point is usually between 3 AM and 6 AM, which is usually when most people are sleeping. Given this information it is obvious that a person performing shift work may become less productive in the beginning of their shift change until their body catches up with their work routine. It is best not to have short shift work periods such as one week for one eight hour shift and after one week shift to the second eight hours, etc. This period of time is much too short for the body to become accustomed to the various three shifts of a 24-hour period. If one shift lasts for one week the workers body may take until Thursday or Friday to become accustomed by that time the hours of the shift will change i.e. Monday through Friday 8 AM to 4 PM then the next week 4 PM to midnight and the third shift midnight to 8 AM. Each of these shifts requires acclimation of the worker. Females have another cycle that they must contend with on a monthly basis. The menstrual cycle of the female worker usually plays an important part even if not formally acknowledged. This period typically has a cycle of 28 days that is divided into five phases the premenstrual and menstrual phase is probably the most important when relating to strenuous or hazardous working conditions.

Concepts in Human Factors Engineering is a series containing eleven articles:
  1. An Overview of Anthropomorphic Data Gathering
  2. The Fragile Skeletal System
  3. The Energy Force of Our Frame
  4. The Message Delivery System
  5. The Body as a Machine
  6. The Oxygen Machine
  7. The Body’s Transportation System
  8. Human Body Energy
  9. A Hot Workplace
  10. The Rhythm of Working
  11. The Bionic Worker of the Future
While determining and considering these various circadian phases one must also allow for adjustments if justified. Individuals are not all the same and consequently will not be affected the same by short or long work shifts. As previously mentioned short shifts are not as stabilizing as longer shifts, for example the shift of 8 AM to 4 PM lasts for three weeks or one month. Longer shifts may produce better productivity and fewer accidents with the possible exception of the first few days of the week of a shift change. Some companies decided that shift work might not be the best way to keep productivity up and injuries down. Some companies have gone with permanent shift work i.e. the workers remain on a specific eight-hour work schedule or at minimum the shifts change once a year. This seems to work better in reducing accidents simply because it may take only one week out of that year for the body to become acclimated to the new shift. Although all workers may not adjust so fast it is far better than changing shifts once a week or even once per month. One problem with the permanent or yearly shift change is the hiring of individuals who are willing to work the second or third shift on a permanent basis or even work on a three rotating shift once a year.

Moral values are very important to productivity and safety. When deciding whether to have permanent shift work or rotating shift work it is crucial to consider the type of person and how it will affect their home life. A person with children may find the third shift better than the second shift since they will have time with their children and spouse in the late afternoon and early evening. Personal lives and shift work cannot work against each other for moral, productivity and safety will no longer be at their best levels. Obviously sleep is a crucial part to any working person whether a person performs physical tasks or sits at a desk. Sleep is the only time the body has to replenish itself such as tired muscles, physical fatigue as well as mental fatigue. Psychologically it would be unhealthy for someone to only work and sleep during the week as opposed to having time each day to relax and enjoy a hobby or their family. Workers need diversity off the job to make their working times more productive and safe.

Sleep periods are usually associative with REM (rapid eye movement) and non-REM. The deep sleep or "true" sleep is in one of the non-REM stages, which account for approximately 45 percent of the total sleeping time. Another large portion of the total sleeping time, 30 percent, is during the REM stage. Sleep deprivation has the effect of raising the body temperature, which is incompatible with safe and productive work. Normal sleeping time is a term which at best fits no one, just as normal anthropomorphic measurements actually fits no one since there are no person which would fit into the term "normal". Sleep, just as circadian rhythms of individuals, can vary widely. Some persons can survive on as little as four hours a night while others may need more than eight hours. Obviously the type of sleep is important as well as the ability to compartmentalize, in other words leave your work problems at work.

Longer periods of concentration are more affected by lack of sleep then shorter periods. It would be best to complete longer tasks during the first shift that it would be to perform the same tasks during the third shift, if this can be accommodated. Napping or short sleeps may help in the short term but for heavy work and long tasks more than one or two hours would be required on a regular basis. Delicate tasks requiring concentration should normally be performed during the beginning of any shifts so that the high degree of probability of safety and productivity can be accomplished. In recent years with the increase of rush hour traffic both in the morning and afternoon companies have developed what's called flextime. Depending upon the job requirements workers can decide whether to come to work after the morning rush hour and leave after the evening rush hour. This method would work only with the cooperation of management and the workers. Another form of flextime is working 40 hours within Monday through Thursday leaving Friday to comprise a longer weekend. Insurance carriers have pioneered this method and it appears to be relatively successful for the summer months. Most workers feel they could maintain productivity and alertness for a 10 hour day knowing they will have three days to spend with their family or simply relaxing. It should be acknowledged that not all companies or workers might take advantage of flextime schedules. In a production process flextime may not work since everyone on the production line must be there or the line will backup at the vacant station.

One very important element in second and third shift work other than the temperature of the environment is the lighting. Sufficient lighting without glare is necessary when working in a confined space such as a desk or assembly line. Florescent illumination is by far easier for the eyes and leaves no shadows. The proper illumination or lux rating must be chosen so the workers eyes will not be strained or become tired.

In summary the human body is a delicate organism and as such all possible considerations must be reviewed. Reasons for the increase or decrease of body temperature, heart rate, blood pressure, hormonal excretions and alertness must be investigated and determined. Shift work can be a benefit or a hazard to both the worker and the company. When setting up shift work there are many aspects that must be considered not the least of which is the effects upon the workers themselves. The paramount importance for management is productivity and safety of the workers. Either one can negatively effect the bottom-line and consequently investors attitudes. Pre-existing health problems or mental problems need to be identified and if necessary be compatible with any task a worker is required to perform. A worker having to work at two jobs may have incompatible circadian rhythms and may pose a serious injury problem to themselves or to others depending upon the job itself. If three shifts are required by the nature of the product of the Company the workers of the shifts must be totally compatible. High concentration and detailed work should be performed at the beginning of the shift and regular breaks must be encouraged.

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