Quantcast Decay patterns

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TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
wet and dry is commonly subject to rapid decay, a
possible occurrence in warm regions with frequent
rainfall.
(2) Temperature. The temperature range of
rapid fungus growth is 75 to 95 degrees F (24 to 35
degrees C). As temperature decreases below 75 de-
grees F (24 degrees C), the rate of growth decreases,
and at about 40 degrees F (5 degrees C) fungi be-
come dormant but resume growth when the tem-
perature increases.
(3) Type of soil. A porous soil, and one slightly
acid (hydrogen ion concentration or pH of 4 to 6)
and containing certain mineral requirements, pro-
motes most rapid decay. The growth of fungi usually
Decay has r e d u c e d
(300
pole
(250
pole
only
of cross
stops about 5 feet (1.5 meters) below the surface of
end 57X
slrenglh
to bendrng)
the ground due to lack of air, and in compact soil
decay usually extends no deeper than 2 feet (0.6
Figure C-l. Twelve-inch (300-millimeter)  pole with l-inch (25-
meters).
millimeter) surface decay
(4) Optimum time element. Since temperature
and moisture are the most important consider-
ations, the time element, or number of days in the
1(
year when optimum decay conditions prevail, be-
comes an important factor. In southeastern states,
for example, fungi are generally more active
throughout a greater part of the year than in other
parts of the country, but local topography can affect
the situation in small areas.
C-6. Decay patterns.
The pattern of decay varies dependent upon the
influence of each of the preceding pole failure fac-
1
tors and results in the following types of damage.
a. Surface damage. Surface damage from exter-
hes r e d u c e d
(300
pole to
nal decay above the ground line is more or less
pole
only 45X of cross
(load
end
of bendrng)
visible, but digging is required to reveal damage
below the ground line.
Figure C-2. Twelve-inch (300-millimeter)  pole with 2-inch (50-
External decay. In any species of timber,
(1)
millimeter) surface decay
external decay results from a poor preservative
treatment or too low an absorption of preservative.
b. Interior damage. Interior damage from inter-
In older poles, it is a consequence of gradual loss of
nal decay that occurs in the interior of the pole is
most of the preservative in the sapwood through
known as "heart rot" or "hollow heart" and requires
leaching, evaporation, and chemical change. In
sound testing or probing to reveal its existence and
most cases, the first occurrence of decay will be just
extent.
below the ground line. This is where the conditions
of moisture, temperature, air, and the absence of
(1) Internal decay. When the preservative in
direct sunlight are most favorable to the growth of
the sapwood is shallow in depth, fungi may gain
fungi. Unfortunately, this is a portion of the pole
access through a check or injury to attack the un-
usually hidden from view and most affected by a
treated inner sapwood and the heartwood. Pine
reduction in strength.
poles are particularly susceptible to internal decay
(2) Loss of strength. Loss of strength at the
if not thoroughly treated. Deep separations
ground line is critical because this part of the pole is
(checks), occurring after treatment, or woodpecker
stressed the most in bending. Figures C-l and C-2
holes expose untreated wood to internal decay. Oc-
show the results of surface decay on a 12-inch (300-
casionally deep-seated infection in seasoned poles is
millimeter) diameter pole. Any pole with extensive
not killed during the treating process and continues
decay, as shown in these figures, is dangerous and
to grow, resulting in premature reduction of
should be replaced immediately.
strength.
C-3





 


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