Wind screens

The wind fences/screens method uses screens, which take up or deflect a sufficient amount of wind so that the wind velocity is lowered below the threshold required for initiation of soil movement. The maximum reduction of wind velocity is expected for a distance of one to five fence heights downstream. Tests have shown that wind screens can achieve up to 60% efficiency in controlling inhalable particulates and 75% of total suspended particulates at wind speeds of about 10 to 13 mi/h. 

Each method has both strengths and weaknesses the best strategy will usually involve a combination of the two. Many miniature tape recorders require wind screens for use out of doors. 

Toughening of glass is most frequently used with sheet glass intended for vehicle wind screens, building items (e.g. all-glass doors) etc. Toughening is also employed in the manufacture of domestic glass-ware, spectacle lenses, instrument parts, etc. 

Drying rates are varied by controlled changes of conditions in the drying chamber. The wind velocity has been varied between 3.25 m/s to 0.5 m/s (wind screens present). The last value corresponds with a mild drying regime and is used unless stated otherwise. 

The solid sorbent diffusional dosimeter usually consists of a small badge-like container which can be attached to a worker or placed in an area for sampling. It is basically composed of a diffusion space or a group of spaces with a defined length to cross sectional area ratio. A porous wind screen may be used to define the opening and the solid sorbent, usually bound in a pad, is placed at the opposite end of the space. 

Working from scaffolds is prohibited diuing storms or high winds unless a competent person has determined that it is safe to do so. The employees must be protected by personal fall arrest equipment or a wind screen. 

Working on scaffolds is prohibited during storms or high winds unless your competent person says it is safe to do so and you are protected by a personal fall arrest system or wind screen. 

Reduction of wind velocity at the fill surface and protection of facilities by strategic placement of wind screens. Given the fact that the majority of the soil movement as a result of wind erosion occurs within one metre of the ground, artificial screens, rows of natural willow twigs and/or other natural materials of limited height may be particularly useful to mitigate the saltation and creep types of soil transport. 

Lenses, wind screens, attractive signboards, TV-screen guards. 

Plant layout and noise suppression material are two general noise abatement methods. Plant layout does not affect noise levels at any given point however, noise can be abated by screening off a section of the plant. An example of this is to orient cooling towers with their closed faces toward the critical location. This method must also consider wind direction to balance air draft. Tankage can be located to act as a noise screen. 

After the waterwaH tubes deHver the saturated steam back into the top of the boHer dmm, moisture is separated out by a series ofbaffl.es, steam separators, and cormgated screens. The water removed drops down into the hot water contained in the steam dmm. The steam travels out through either a dry pipe, which leads to a superheater header, or a series of superheater tubes that connect directiy into the top of the steam dmm. The superheater tubes wind back into the top of the furnace and/or a hot flue-gas backpass section, next to the economizer, where heat from the combustion gases exiting the furnace superheats the steam traveling through the tubes. 

Thus, the user can input the minimum site boundary distance as the minimum distance for calculation and obtain a concentration estimate at the site boundary and beyond, while ignoring distances less than the site boundary. If the automated distance array is used, then the SCREEN model will use an iteration routine to determine the maximum value and associated distance to the nearest meter. If the minimum and maximum distances entered do not encompass the true maximum concentration, then the maximum value calculated by SCREEN may not be the true maximum. Therefore, it is recommended that the maximum distance be set sufficiently large initially to ensure that the maximum concentration is found. This distance will depend on the source, and some trial and error may be necessary however, the user can input a distance of 50,000 m to examine the entire array. The iteration routine stops after 50 iterations and prints out a message if the maximum is not found. Also, since there may be several local maxima in the concentration distribution associated with different wind speeds, it is possible that SCREEN will not identify the overall maximum in its iteration. This is not likely to be a frequent occurrence, but will be more likely for stability classes C and D due to the larger number of wind speeds examined. 

The discrete distance option of SCREEN allows the user to input specific distances. Any number of distances (s 1 meter) can be input by the user and the maximum concentration for each distance will be calculated. The user will always be given this option whether or not the automated distance array option is used. The option is terminated by entering a distance of zero. SCREEN will accept distances out to 100 km for long-range transport estimates with the discrete distance option. However, for distances greater than 50 km, SCREEN sets the minimum 10 meter wind speed at 2 m/s to avoid unrealistic transport times. 

Since the concentration at a particular distance downwind from a rectangular area is dependent on the orientation of the area relative to the wind direction, the SCREEN model provides the user with two options for treating wind direction. The first option, which should be used for most applications of SCREEN and is the regulatory default, is for the model to search through a range of wind directions to find the maximum concentration. 

The range of directions used in the search is determined from a set of look-up tables based on the aspect ratio of the area source, the stability category, and the downwind distance. The SCREEN model also provides the user an option to specify a wind direction orientation relative to the long axis of the rectangular area. The second option may be used to estimate the concentration at a particular receptor location relative to the area. The output table for area sources includes the wind direction associated with the maximum concentration at each distance. 

Table 4. SCREEN S Wind Speed and Stability Class Combinations.

The area source is assumed to be a rectangular shape, and the model can be used to estimate concentrations within the area. SCREEN examines a range of stability classes and wind speeds to identify the "worst case ... 

Shoreline Fumigation - For rural sources within 3000 m of a large body of water, maximum shoreline fumigation concentrations can be estimated by SCREEN. A stable onshore flow is assumed with stability class F (A0/AZ = 0.035 K/m) and stack height wind speed of 2.5 m/s. Similar to the inversion break-up fumigation case, the maximum ground-level shoreline fumigation concentration is assumed to occur where the top of the stable... 

Flexible metallic media are especially suitable for handling corrosive liquors and for high-temperature filtration. They have good durability and are inert to physical changes. Metallic media are fabricated in the form of screens, wire windings, or woven fabrics of steel, copper, bronze, nickel and different alloys. Perforated sheets and screens are used for coarse separation, as supports for filter cloths or as... 

Another method is a series of exhaust dilution equations based on Wilson and Lamb " and a series of earlier papers summarized in ASHRAE. This method is based on wind tunnel tests on simplified buildings and is intended to provide conservative (low dilution) results. Wilson and Lamb compared the model to actual field data collected at a university campus and found that the model did indeed predict dilutions similar to measured worst-case dilutions suitable for a screening model. However, many cases resulted in conservative Linderpredictions of dilutions. ... 

T/ e effect of altering major assumptions on the downwind distance (radius) of the estimated vulnerable zone. Calculations made using (1) credible worst case assumptions for initial screening zone. (2) reevaluation and adjustment of quantity released and/or rate rf release cf chemical, (3) reevaluation and adjustment of wind speed (increase) and air stability (decrease), (4) selection of a higher level of concern. Note that adjustment oftwo or more variables can have an additive effect on reducing the size cf the estimated vulnerable zone. 

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