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)
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.
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.
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