Civil Engineering Reference
In-Depth Information
Oxygen debt; (B) repayment of oxygen
debt during rest. A=B.
12.5
MEASUREMENT OF PHYSICAL WORKLOAD
As we have previously noted, it is mostly impractical to use oxygen uptake to assess
workload in a manufacturing situation. Heart rate (pulse rate) is a far easier measure.
However, heart rate is a good predictor only of workloads of intermediate intensity (about
100-140 beats/min). Simple measurements of heart rate can be useful to estimate if there
are any problems with the current level of physical workload. This is illustrated by the
following example.
The author once visited an automobile assembly plant. There was a female assembly
worker who seemed physically exhausted. She was about 45 years of age and of small
stature (about 150 cm [5 ft]). The type of work did not seem to put overly great demands
on any of her coworkers. However, I stepped up and asked if I could take her pulse rate.
It was running at about 130 beats/min, clearly excessive for an 8-hour work day. She was
moved to another less physically demanding task.
12.6
HEAT STRESS
Heat stress is often a serious problem in hot climates, especially in industrially
developing countries, where work is conducted outdoors, or where manufacturing
facilities lack insulation and/or cooling. Surprisingly, it is also a problem in southern
Europe and the U.S. In this section I will also briefly review some of the many standards
on heat stress that have been issued by the International Standards Organization.
THERMOREGULATION
There are several physiological mechanisms for regulating body temperature. These are
under involuntary control by nerve cells in the hypothalamus (a structure in the lower
brain), and they maintain the body temperature within a narrow range (about 37 ± 0.5°C).
This process is known as thermoregulation. As illustrated in Chapter 16, the body
temperature exhibits daily variations. It peaks in the late afternoon and reaches its lowest
level in the early morning. In order to keep the body temperature within a narrow
regulated range, the amount of heat gained and lost by the body over the short span of
time must be equivalent. If the body gains an excessive amount of heat, there could be
excessive sweating, dehydration, and heat stroke; finally, death may occur.
There are two major ways of adapting to a hot environment: through
acclimation
and
through
acclimatization
(Parsons, 2003). Acclimation refers to physiological changes,
such as sweating, in response to temperature. Acclimatization refers to more enduring,
long-term changes in physiological mechanisms that enable an individual to work in
extremely hot environments. Repeated exposure to hot environments leads to an
improved tolerance to the heat load. During acclimatization there are progressive
increases in body temperature, working heart rate, and sweat rate. These processes can be
