ATP-3-09-30 Observed Fires Download
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Chapter 6 6-24 ATP 3-09.30 28 September 2017 Table 6-16. HC and WP smoke effectiveness based on relative humidity Relative Humidity HC WP % Effectiveness (percentage) Effectiveness (percentage) 0 100 100 10 146 353 20 152 372 30 159 391 40 173 411 50 189 434 60 211 465 70 240 510 80 325 588 90 572 785 Legend. HC—hexachloroethane WP—white phosphorous Wind Speed 6-103. The movement of smoke depends on the speed and direction of the wind. Wind speeds ranging from 4 to 14 knots are best for the production of smoke screens. Optimum speeds vary with the type of smoke used (see figure 6-13). Figure 6-13. Optimum wind speed chart 6-104. To determine an approximate wind speed, the observer can use either the equivalent wind scale table (see table 6-17) or the grass drop (expedient) method. With the grass drop method, extend your arm downward and drop grass from your hand. Point your extended arm at the dropped grass on the ground. Divide the angle (in degrees) between your arm and your body by 4 to determine the approximate wind velocity in knots.