GENERAL INSTRUCTIONS
WET BULB-GLOBE
TEMPERATURE KIT
NSN
6665-00-159-2218: Kit without Tripod (Sigma# 601301)
NSN
6665-01-381-3023: Kit with Tripod (Sigma# 601301/T)
Complete WBGT Kit:
Includes 6665-01-381-3023, Carry Case, Signal Flag Kit (Sigma# 601301/TSF)
A.
The wet bulb-globe temperature kit is an instrument
for providing information on hot weather risks to the health of troops
undergoing training. The information is displayed on a scale in the form of an
index, computed from the weighted readings obtained from three different
thermometers.
1.
A stationary wet bulb (WB) thermometer exposed to the
sun and prevailing wind.
2.
A similarly exposed “black globe” (BG) thermometer
with a black sheath over the bulb. The sheath and bulb are inside a transparent
perforated plastic shield.
3.
A dry bulb (DB) thermometer with its bulb shielded
from the direct rays of the sun by a shield painted white.
B.
The wet bulb-globe temperature index (WBGT Index) is
equal to 70% of the wet bulb (WB) temperature reading plus 20% of the black
globe (BG) temperature reading plus 10% of the dry bulb (DB) temperature
reading and can be computed as follows:
WBGT Index
= 0.7 WB + 0.2 BG + 0.1 DB
Use of the
attached slide rule calculator provides the correct WBGT Index automatically.
C.
To use the WBGT Index as a control of physical
activity, the following guidelines from TB-MED-175 are provided.
1.
When the WBGT Index reaches 82, discretion should be
used in planning exercise for unseasoned personnel.
2.
When the WBGT Index reaches 85, strenuous exercises
such as marching at standard cadence should be suspended for unseasoned
personnel during their first three weeks of training. At this WBGT Index,
training activities may be continued on a reduced scale after the second week
of training.
3.
Outdoor classes in the sun should be avoided when the
WBGT Index exceeds 85.
4. When the
WBGT Index reaches 88, strenuous exercise should be curtailed for all recruits
and other trainees with less than 12 weeks training in hot weather. Hardened
personnel after having been acclimatized each season, can carry on Limited
activity at WBGT indices of 88 to 90 for periods not exceeding six hours a day.
D.
The WBGT Kit is enclosed in an aluminum case. The
case is kept closed with a miniature stainless steel catch. The threaded hole
in the bottom of the case is used to attach the case to a standard lightweight
photographers tripod.
1.
The wet globe kit is opened by disengaging the catch
and lifting the cover.
2.
Lift the thermometer assembly up and out using the
sun shield (see figure 1).
NOTE: Examine the column of each
thermometer. If the liquid has separated, heat the bulb slowly and carefully
until the liquid reunites in the expansion chamber at the top of the
thermometer. Keep the thermometer upright as it cools until the column has
fully retracted into the bore of the thermometer. CAUTION: Never use a match or
any kind of open flame to heat a thermometer bulb. Use a warm liquid only.
(1)
3.
Wet the wet bulb wick thoroughly. NOTE: The wick is
cotton and is 5-inches long with a knot 1-inch from one end. The end nearer the
knot is pushed into the reservoir and the other end is slipped on the
thermometer bulb (See Figure 1). The water reservoir should be filled with
clear, preferably de-ionized or distilled water and utilized as indicated. The
water should be changed daily and the wick washed with soap and rinsed
thoroughly. To avoid error in the measurement of the wet bulb temperature, the
water in the reservoir must be free of salt and soap.
4.
5.
Review the instructions on the right side of the
slide rule (WET BULB-GLOBE TEMPERATURE INDEX CALCULATOR). Assume for purposes
of instruction that the Black Globe (BG) temperature reading is 120, the Wet
Bulb (WB) temperature reading is 80, and the Dry Bulb (DB) temperature is 100.
a.
Move 80 on the Wet Bulb Temperature (WB TEMP) scale
so that it is directly under 100 on the Dry Bulb Temperature (DB TEMP) scale.
b.
Find 120 on the Black Globe Temperature (BG TEMP)
scale.
c.
Read Wet Bulb Globe Temperature Index (WBGT INDEX)
scale at the point directly above the Black Globe Temperature (BG TEMP)
reading.
d.
If you performed the slide rule movement correctly,
the Index should read 90.
E.
CAUTION: After use, empty the water
reservoir to prevent wetting or rusting of parts.
F.
The kit contains, in addition to the parts shown in
Figure 1, the following spare components:
1.
1 each transparent perforated airflow reducer.
2.
1 each water reservoir
3. 18 inches of extra wicking
Sigma Products & Mfg. Co., Inc.
(800) 215-0440 –
Fax: (803) 547-8880 www.wetglobe.com (2) rev. 4/12/04