TM 5-852-9/AFR 88-19, Vol. IX
in the 35 to 50 percent range reduces susceptibility to colds and other respiratory disorders. Hospital studies
have shown that bacteria carried by personnel, including certain resistant strains, thrive in dry air with less
than 35 percent relative humidity and in moist air with greater than 65 percent relative humidity. These same
bacteria languish and die in the middle zone. In addition, moisture evaporation from the body causes the
blood to thicken and reduces effective circulation. These problems can be eliminated by adding moisture to
the air to maintain a relative humidity between 30 and 40 percent. Hospitals, computer rooms and other
facilities that require or generate higher relative humidities should have moisture resistant designs.
(2) Static electricity. Although static electricity is being generated constantly, it does not become
a problem unless it has a chance to accumulate. When relative humidity is sufficiently high, an invisible film
of moisture forms on room surfaces. In the presence of normal impurities, this moisture film becomes a
conductor and carries static electricity harmlessly away before it can become a hazard. With low relative
humidities, however, static electricity can pose fire and explosion hazards. Control of humidity and finish
materials should be designed to reduce static electricity.
(3) Deterioration of materials and equipment. Dryness causes brittleness and cracking of many
materials including rugs, paper, and wood, which increases the combustion rate of building materials and the
deterioration rate of furnishings. Dryness causes dust particles to break loose and enter the air stream.
c. High humidity. Although higher relative humidities are extremely desirable in cold climates, excessive
amounts of humidity can cause serious damage. The maximum humidity to which areas should be maintained
depends upon the dew point of the coldest room surface. In turn, the coldest surface depends upon the
outside temperature and the type of construction. For instance, higher humidities can be maintained by using
triple-glazed windows rather than double glass windows.
(1) Condensation. Condensation can cause structural damage when excessive humidities are
maintained within the building, or within the building walls or ceilings. Condensation will occur on a cold
surface whenever the temperature falls below the dew point of the air and will appear first on windows, since
they will be first to reach the dew point temperature. Condensation within building walls can be effectively
reduced or eliminated by a vapor retarder.
(2) Control of relative humidity. To maintain a reasonably controlled atmosphere, the maximum
relative humidity should not exceed the amount which causes condensation. Table 2-1 shows relative
humidities at which condensation will appear on different types of windows at a room temperature of 70EF.
The table was developed from basic data in the ASHRAE Handbook of Fundamentals. Higher limits are
possible if constant circulation forced air induction units are used underneath windows.
4-6. Plumbing.
a. General. Plumbing design, unless stated differently herein, shall be in accordance with TM 5-810-
5/AFM 88-8, chapter 4, and the National Standard Plumbing Code.
b. Special considerations for arctic areas. Where adequate water supplies are available and normal
sewage systems can be installed, interior plumbing facilities vary little from those used in temperate climates.
Water, however, is not always readily available in arctic areas, and sewage treatment and disposal is difficult
in permafrost areas. For remote buildings and those infrequently occupied, tank type toilets with marine
handpumps, floor mounted chemical toilets, incinerator type toilets, composting toilets, and recirculation type
toilets should be considered. Electrical incinerating toilets installed in conjunction with gray water-black
water systems have been particularly successful at some remote sites on Alaska's North Slope. In this type
of system, the black water (human waste) is separated from the gray water (laundry, shower, etc.). Each type
of waste water is separately collected, conveyed, and treated. Under "combined" systems, all wastes can be
piped into a sewage storage tank for ultimate conveyance to treatment and/or disposal facilities. Figure 4-4
shows an isometric piping diagram of a typical sewage system. Figure 4-5 is a typical fresh water flow
diagram. Collecting small waste flows and discharging them in slugs, rather than allowing the sewage to
trickle by gravity and glaciate the lines, should be considered. A water storage tank can also be installed to
supply water for the domestic plumbing and fire protection systems. The water storage tank should be heated
to prevent freezing. Figure 4-6 is a fire protection schematic. Figure 4-7 is a water tank heating and
circulation system schematic. Water should be piped to individual buildings by the most economical method.
A utilidor system may be used to distribute water along with heating and sewer lines. Utilidor design shall
be in accordance with TM 5-852-5/AFR 88-19, chapter 5. An analysis of site operating capabilities, reliability
of the water supply system, and fire protection requirements should be used to determine the size and type
of storage tanks used for water systems. One method used to eliminate long exterior water supply lines is to
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