Building barriers

Layered security—A physical security approach that requires a criminal to penetrate or overcome a series of security layers before reaching the target. The layers might be perimeter barriers building or area protection with locks, CCTV, and guards and point and trap protection using safes, vaults, and sensors. 

In the boundary layer theory of chemisorption on semiconductors it is assumed that when a molecule of gas is adsorbed on a solid, charge transfer occurs resulting in the formation of a potential barrier at the surface. As adsorption proceeds, the potential barrier builds up, the chemical potential of the surface changes until at equilibrium the chemical potential at the surface of the solid is the same as the chemical potential of the adsorbate gas. 

The principal use of LDPE and LLDPE in building products is as a film water barrier under below-grade doors as a wall vapor barrier, though PVC is typically preferred and as temporary enclosure film during constmction. The film is made either by extmding a thin-waHed tube, which may be sHt or wound up direcdy, or by extmsion through a slot die and cast direcdy on to a cold roU, cooled, then wound up. The former method is more widely used. A much smaller use for low density polyethylene is in piping. 

Wherever the rising mains crosses through a floor of the building, fireproof barriers are provided as shown in Figure 28.3(b) to contain the spread of fire to other floors. 

Profiling - Sheet steel may be pressed into the correct shape for crash barriers or the cladding of buildings (known as profiling). 

Certain polymers have come to be considered standard building blocks of the polyblends. For example, impact strength may be improved by using polycarbonate, ABS and polyurethanes. Heat resistance is improved by using polyphenylene oxide, polysulphone, PVC, polyester (PET and PBT) and acrylic. Barrier properties are improved by using plastics such as ethylene vinyl alchol (EVA). Some modem plastic alloys and their main characteristics are given in Table 1.2. 

Air barrier A device that provides a jet barrier between two zones in a building. See Air curtain. 

Air curtain A high-velocity air jet that provides an air barrier between two different building or work zones. 

Windbreak A natural or artificial barrier that protects a building from the prevailing winds. 

Regardless of the implementation strategy you select, try to build in at least some degree of local involvement in planning and implementation. Local involvement can give facility personnel "ownership" of the process, meaning that they will be more likely to work to overcome any problems or false starts. In addition, local participation means that you will be able to identify any local barriers to implementation—sooner rather than later. 

Lovins, A. (1992). Energy-Efficient Buildings Institutional Barriers and Opportunities. Boulder, CO E-Sourcc, Inc. 

Like wave and OTEC power plants, one of the main barriers to the increased use of tidal energy is the initial cost of building tidal-generating stations. It has been estimated that the construction of the proposed facility on the Severn River in England would have a construction cost of 15 billion. 

The security system can be considered as layers of protection. Physical barriers and deterrents constitute not only the building stmcture itself, made up of walls, doors, windows, floor and a roof, but the yard around the building and probably a perimeter fence or wall. 

For an adequate barrier against moisture, sufficient thickness of paint must be applied. The modern trend is to apply high-build coatings based on media having high intrinsic water resistance. Such paints may be pigmented with corrosion inhibitors or minerals which impede the flow of moisture through the film. 

Traditional cold store construction was to build an insulated lining within a masonry shell. The outer skin would be erected in brick and concrete, and rendered as smooth as possible inside with cement plaster, to take the insulation. When the surface was dry, it would have several coats of bitumen applied as a vapour barrier and slabs of insulation material stuck to this with hot bitumen. This was normally carried out in two or more layers so that joints did not pass right through the insulant, but were staggered. The inner skin would be finished with cement plaster, reinforced with wire mesh. The usual insulant was slab cork. 

The effectiveness of a vapor barrier can be rated in a term such as perms. An effective vapor barrier in buildings should have a rating no greater than, say, 0.2 perm. A rating of one perm means that one ft2 of the barrier is penetrated by one gram of water vapor per hour under a pressure differential of one in. of mercury. One in. of mercury equals virtually 0.5 psi one gram is one seven-thousandth of a pound. 

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