DG 1110-3-106
135 decibels. At 150 decibels even short-term exposure
airborne particles such as dust, pollen, and bacteria,
may cause damage. These facts have important
which make up the room air. The composition of the
implications for the design of shop areas, where high
air greatly affects the comfort and safety of building
intensity noise is frequently a problem. The designer
occupants and hence must be controlled.
must provide some means of attenuating shop noises
to protect the hearing of students and shop personnel.
d. Air motion is an important thermal consideration
because it influences the rate of body heat transfer.
The higher the air velocity, the greater the rate of
(3) Acoustic Considerations.
The key to providing an acoustic environment
body heat loss.
conducive to learning consists of controlling
(2) Human Performance and the Thermal
background noise while at the same time reinforcing
Environment.
the projection of the instructor's voice.
Investigations in the area of human performance show
that when temperature and humidity become high,
a. Background Noise.
working efficiency decreases, errors increase, and under
Background noise other than the white noise discussed
extreme conditions health is adversely affected. In
in paragraph 3-3a above is distracting. As the
areas such as shops, in which students are working
background noise level rises, the difficulty of hearing
with equipment and machinery, temperature control
increases. This masking effect is greatest when the
devices should be provided for safety purposes.
frequency range of the desired audio stimuli and the
background noise are similar. For example, voice noise
of 35 db is more disruptive than mechanical ventilation
a. Temperature Control.
Whenever the daytime outside temperature is above 55
noise of 35 db.
degrees F., heat gains will usually outweigh losses.
Therefore the fundamental problem in controlling the
b. Reflective and Absorptive Surfaces.
thermal environment in a service school is cooling,
In order to reinforce the instructor's voice and help
rather than heating, the facility. The desirable
eliminate distracting reverberations in the classroom,
temperature for a building depends on the activity of
the ceiling, the wall behind the instructor, and the
its occupants. Acceptable temperature limits vary from
upper half of the side walls should be provided with
60-70 degrees for vigorous activity to 68-78 degrees for
sound reflective surfaces. The remaining surfaces of
sedentary activity. In a service school, where learning
the room should be sound absorptive so that noise
activities range from sedentary to vigorous, separate
generated close to the floor (e.g., dropping objects,
temperature zoning should be provided. For example,
scuffling of shoes, or the moving of chairs) is reduced.
shop areas should be zoned for a lower temperature
(Figure 3-8).
than classrooms or administrative areas.
D. Design of Thermal Environment.
b. Humidity Control.
This generally is not necessary. Relative humidity has
(1) Thermal Considerations.
little influence on comfort, provided that it is in the
A controlled thermal environment is another important
intermediate range (30% to 70%). Humidity levels
factor in designing comfortable, safe, and effective
above 70% can impair human performance and levels
instructional spaces. Control of the thermal
below 30% can cause respiratory discomfort and create
environment includes the following considerations. (For
undesirable levels of static electricity in activity spaces.
specific requirements related to control for the thermal
environment, see Chapter 4, Individual Space Criteria.
c. Air Composition.
This should be carefully controlled. In a closed,
a. Temperature is the most important element of the
occupied space, the amount of oxygen in the air
thermal environment. In designing for temperature
decreases and the amount of carbon dioxide increases.
control, the temperature of surrounding surfaces, as
Normally, ventilation sufficient for the removal or
well as that of the air, must be taken into account.
dissipation of odors is also adequate for maintaining
the proper balance between oxygen and carbon
b. Humidity determines the evaporation rate at a given
dioxide. Dust, pollen, and bacteria should be eliminated
air temperature and thus affects human body
by air filtration.
temperature by limiting the amount of natural
evaporative cooling that can take place. The higher the
humidity, the less heat the body can dissipate through
d. Air Motion.
This is another factor requiring control. Air
perspiration.
distribution systems should provide uniform air
c. Air Composition refers to the relative amounts of
oxygen, carbon dioxide, and other gases, as well as
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