Civil Engineering Reference
In-Depth Information
teaching “hours” (each of 50 min) each week; typically they teach for 32 weeks
yr. U.S. high school stu-
/
dents typically have six to seven periods
day; each period is 60 min, which includes a 5 min break. Often
one period is physical education; lunch is an additional break. Typically they go to school
/
190 days
yr.
,
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vigilance) are process control monitoring, hospital monitor-
ing, and industrial inspection. The Accreditation Council for Graduate Medical Education, in an
effort to reduce medical errors, set new standards for doctors-in-training. They are now limited to
80 h workweeks and they must get at least 10 h of rest between shifts. They are not be to be on duty
for more than 24 h continuously. Craig (1985) summarized some vigilance studies. Changes that
reduced boredom were beneficial; one example was loading
Example underload tasks (monitoring
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unloading (10 min) as well as inspecting
coins (14 min). Another example was 30 min of inspection followed by 60 min of other tasks.
Driving
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piloting at night is an underload problem. Buck and Lamonde (1993) reported locomotive
drivers had sleep problems — especially close to 0300 and 1500 h. Fatigue may be more of a problem
when the driver is “externally scheduled” — for example, when tired, a bus driver or a pilot cannot
stop and take a break, whereas a car or truck driver, being self-paced, can stop. Japanese taxi drivers typi-
cally work a 16 h day and then have the following 1 or 2 days off.
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38.7.4 Sleep
Biological Clock
Three divisions are sleep, biological clock (circadian rhythm), and countermeasures.
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38.7.4.1 Sleep
Sleep restores the functions of the brain. Only sleep allows some form of cerebral shutdown. Females and
people over 50 yr are more prone to night-sleep problems. Sleep deprivation of 24 to 48 h primarily
affects motivation to perform rather than ability to perform; thus uninteresting, undemanding,
simple tasks are the most affected.
38.7.4.2 Circadian Rhythm
Various physiological functions vary in a circadian (24 h) rhythm. Both internal temperature and pot-
assium peak during the day and bottom at night. Cortisol (the “wake-up” hormone) peaks around
9 a.m.; melatonin (the “go-to-sleep” hormone) peaks around 2 p.m. Alertness peaks in the late afternoon
and bottoms during 2300 to 0600 h.
38.7.4.3 Countermeasures
Three sleep-deprivation countermeasures are rest, drugs
food, and environmental stimulation.
Naps are a potential supplement to sleep at night. However, people tend to think of naps as inadequate
opportunity to sleep rather than an opportunity for partial recuperation. A nap problem is sleep
inertia — poor performance for about 15 to 30 min after being awakened.
The most common drug to decrease sleepiness
/
increase alertness is caffeine. Amphetamines also work
well. Caffeine has a metabolic half-life of 3 to 7 h. Pregnancy increases half-life (to as much as 18 h) while
smoking decreases caffeine's half-life. A pharmacologically active dose, depending on the individual, is
about 3 mg
/
kg of body weight. Truck drivers often recommend eating — possibly while still driving.
Eat a moderate intake of carbohydrates rather than fats or proteins. Another possibility is having a
drink with caffeine.
Environmental stimulation can be exposure to bright light such as daylight. (Normal indoor lighting is
too dim to stimulate.) In a vehicle, modify the ventilation or decrease isolation by listening to a radio
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CD
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or talking on a cell phone. Physical activity (say walking 100 m) can be useful.
38.8 Fatigue Guidelines
The seven guidelines are divided into fatigue prevention (guidelines 1 to 3) and fatigue reduction (guide-
lines 4 to 7).
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