Temperature Wind Chill

For outdoor work there may be a risk of frostbite in the wintertime. The report uses the wind chill temperature, WCI, calculated as... 

TABLE 6.12 Wind Chill Index, WCI, Chilling Temperature, and Effect on Exposed Flesh... 

Wind chill index An empirical scale that correlates well with the sensation of bare dry skin due to the chilling effect of the outdoor air temperature and wind speed. 

WORST 1 No written procedures, or standard way of performing tasks Not integrated with training High levels of noise Poor lighting High or very low temperatures and high humidity or wind chill factors... 

Wind Chill Equivalent Temperatures on Exposed Flesh at Varying Velocity... 

Cold injury (frostbite and hypothermia) and impaired ability to work are dangers at low temperatures and when the wind-chill factor is low. To guard against them, the personnel at an industrial site should (a) wear appropriate clothing, (b) have warm shelter readily available, and (c) carefully schedule work and rest periods, and monitor workers physical conditions. 

The temperature at the surface of the droplet is determined by the evaporation rate obtained from simultaneous mass and heat transfer equation (8.10). (This temperature is the same as the wind chill factor discussed in weather forecasts, which can be calculated with equation (8.10) assuming the form of a moist sphere the size of the average human head.) Under some drying conditions, the heat transfer is the slow step, limiting evaporation, and in others the mass transfer is the slow step. In either case the evaporation rate, dRJdt, can be written as... 

Figure 5.75. Hourly time variation of low-temperature heat (space heating and hot water) calculated for the 2050 scenario with use of actual temperature and wind chill data for Denmark during the year 1999 (Sorensen et al, 2001).

Fur heal transfer purposes, a standing man can be modeled as a 30 Cm diameier, 170 cm-loag vertical cylinder with both the top and botiom surfaces insulared and with the side surface at an average temperature of 34"C. For a convection heat transfer coefficient of 15 W/m "C, deiemiine the rale of heat loss from ihis man by convection in still air al 20°C. What would your answer be if the convection heal transfer coefficient is Increased to 50 W/m °C as a result of winds What is the wind-chill factor in this case Ansuers 336 W, 11 0 W, 3 .7 C... 

See also Air masses and fronts Atmosphere observation Atmosphere, composition and structure Atmospheric circulation Atmospheric temperature Dew point Fog Greenhouse effect Hydrologic cycle Weather forecasting Weather mapping Weather modification Wind chill Wind shear. 

Elence W decreases only very slowly at wind speeds above 50 mi / h, at least assuming that if not Eq. (14) in its entirety then at least this aspect of Eq. (14) retains at least approximate validity at Neptune-like temperatures. The singularity in (dW/dV)T at V = Omi/h is sufficiently weak that it has no effect on values of W itself.] Since standard atmospheric pressure at sea level on Earth is approximately lbar, for illustrative purposes and for argument s sake let us assume that the standard wind chill formula [Eq. (14)] retains at least approximate validity at the 1 bar level on Neptune, especially since the atmospheric density of 0.45 kg / m3 at the 1 bar level on Neptune is at least comparable to that at the 1 bar level on Earth. (We will appraise this assumption later in this Sect. 4.2, especially in the second-to-last paragraph thereof.) The temperature in Neptune s atmosphere at the 0.1 bar level is T = 55 K = — 218 °C = — 361 °F [65], Since Eq. (14) was derived for standard conditions (lbar atmospheric pressure on Earth), its accuracy may be reduced if it is applied at the 0.1 bar level on Neptune. If we nevertheless apply it at the 0.1 bar level on Neptune, we obtain, even with a slow (by Neptune standards) V = 50 mi / h wind, W = -544 °F = -320 °C = -47 K. 

The standard wind-chill formula [Eq. (14)] should not be confused with the standard wind-chill table [66], The standard wind-chill table is based on a standard of calm of 3 mi / h (typical walking speed), rather than on the true standard of calm V = 0 mi / h in true accordance with the standard wind-chill formula [Eq. (14)] that we adopt in this Sect. 4.2. Also, the recommended ranges of applicability of the standard wind-chill table are —50°F < T < 50°F and 3mi/h < V < 110mi /h [66], But we base our calculations of W on the standard wind-chill formula [Eq. (14)], for which no limits on the range of applicability are stated for either T or V [66]. If there is a sufficiently strong wind on Neptune, then Eq. (14) yields a cold negative Kelvin effective wind-chill temperature VV. 

Re Entries [66] and [67], Refs. [66] and [67]) An online brochure accessible at Ref. [66] provides more information. Reference [67] augments Ref. [66] with still more information, including references and a few alternative formulas for wind-chill temperature W. (In Australia the wind-chill temperature >V is dubbed as the apparent temperature AT.) In this Sect. 4.2. we always calculate W based on the formula employed by the U. S. A. National Weather Service [Eq. (14)]. 

It has been argued [83], that Eq. (14) for wind-chill temperature W is only an approximation [83], that even as an approximation it is valid only at Earth-like or "human"... 

We are familiar with the cooling effect of wind and rain on our own exposed skin weather forecasters refer to the wind chill factor . The data in Table 5.1 shows the effectiveness of water sprays in removing heat from the surface of extruded plastic pipes. Consequently, the pipe cooling rate is limited by the transient conduction within the plastic the melt surface can be treated as if kept at the water temperature, and the analysis of the last section be used. 

Whereas the Humidex accounts for the effect of humidity on how the body perceives temperatures above 20 °C, the wind chill factor accounts for the enhanced cooling effect caused by wind. The sensation of temperature depends... 

The combination of ambient temperature and wind speed is called windchill. Wind-chill may be used to predict the risk of freezing of the exposed skin and to predict the amount of manual dexterity decrease (Daanen, 2009). The windchill index, as an estimator of cold injury risk, is part of an ISO standard (11079, 2007). In the heat, wind has a cooling effect by enhancing convective and evaporative heat loss. 

Daanen, H.A.M., 2009. Manual performance deterioration in the cold estimated using the wind chill equivalent temperature. Ind. Health 47 (3), 262-270. 

In cold air, the body loses heat principally by radiation from exposed skin surfaces and a small amount of convection or conduction. The rate of heat loss increases with movement of air across the exposed skin, which produces a cooling effect. The heat lost from skin exposed to a 10-mile-per-hour wind when the ambient temperature is 10°F will be the same as that from skin in still air at -9°F. The wind chill factor is an indication of relative heat loss only. Freezing of tissue will not occur unless the temperature is 32°F or lower. For example, the wind chill factor for a 15-mile-per-hour wind at an ambient temperature of 40°F is 22°. Tissue and blood will not freeze, but the body will compensate for the added heat loss. 

Wind-Chill Factor—Wind or air movement causes the body to sense coldness beyond what a thermometer actually registers as the temperature. 

The effects of the low air temperatures in the Transantarctic Mountains are magnified by wind which accelerates the loss of heat from the human body. This phenomenon is expressed quantitatively by the wind-chill scale (Rees 1993) that converts the measured temperature into an equivalent wind-chill temperature. For example, the arrow in Fig. 2.5a indicates that the measured air temperature of -10°C at a wind speed of 8 m/s corresponds to a wind-chill temperature of-20 C. In addition, a wind speed of 8 m/s in Fig. 2.5b is equivalent to a speed of 28.8 km/h. The wind-chill temperature also permits the definition of the discomfort index in Table 2.1. Accordingly, a wind-chill temperature of -20°C is perceived as being bitterly cold. Such conditions are not unusual during the austral sununer on the polar plateau and in the Transantarctic Mountains, except along the coast. 

Fig. 2.5 (a) Conversion of the measured air temperature in degrees Celsius and the wind speed in meters per second into the wind-chill temperature which includes the effect of accelerated heat loss of the human body with increasing wind speed. The arrow indicates that a measured temperature of -10°C at a... 

Table 2.1 Discomfort scale based on the wind-chill temperature derived in Fig. 2.5a from the measured temperature and the wind speed (Stonehouse 2002, p. 293)...

Discomfort level Range of wind-chill temperatures (°C)... 

Former residents of McMurdo Station will also recall the windstorms that suddenly reduce visibility to less than 100 ft (30.48 m), with wind speeds in excess of 55 knots (101.9 km/h), and wind-chill temperatures that drop below -100°F (-73.3°C). Under these conditions, all personnel in McMurdo are required to remain in-doors (Condition 1) and all travel is suspended for the duration of the storm that may last several days. The classification of weather conditions detailed in Table 2.3 is the responsibility of the McMurdo Weather Office (Mac Weather). Condition 1 storms can occur anywhere within the Transantarctic Mountains during the austral spring and fall especially on major outlet glaciers, such as the Reedy Glacier in Fig. 2.11, that channel the katabatic winds from the polar plateau to the Ross Ice Shelf or to the Ross Sea. Field parties that experience such storms learn first-hand that weather still rules in Antarctica. 

Wind speed between 48 and 55 knots, wind chill temperature between -75 and -100°F, and visibility between 1(X) and 1,320 ft (0.25 miles). Only pedestriem travel between buildings in McMurdo is permitted. Travel outside of McMurdo is restricted to marked tiails and roads in radio-equipped vehicles. 

Wind speed in excess of 55 knots, wind chill temperatures less than -100°F, and visibUity less than 100 ft. These parameters indicate extreme weather conditions. All personnel must remain inside buildings or in the nearest available shelter. 

Prolonged exposure to freezing temperatures can result in health problems as serious as trench foot, frostbite, and hypothermia. When body temperature drops even a few degrees below its normal temperature of 98.6°F, the blood vessels constrict, decreasing peripheral blood flow to reduce heat loss from the surface of the skin. The four environmental factors that contribute to cold-related stress include low temperatures, high/cool winds, dampness, and cold water. Wind chill, a combination... 

Frostbite occurs when the skin tissue actually freezes, causing ice crystals to form between cells and draw water from them, which leads to cellular dehydration. Although this typically occurs at temperatures below 30°F, wind chill effects can cause frostbite at abovefreezing temperatures. 

Initial Wind Chill This index originally resulted from measurements of the rate of cooling of a container of water. Antarctic explorers measured the cooling power of wind at some temperature in comparison to the equivalent cooling power of still air at another temperature. The resulting equation derived from the study underestimated the time to freezing and overestimated the chilling effect of the wind. 

Revised Wind Chill Temperature Index In 2001, the U.S. National Weather Service issued a new wind chill index. The study, conducted jointly by the U.S. and Canada,... 

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