Security setbacks

The derrick or mast must also be designed to withstand wind loads. Wind loads are imposed by the wind acting on the outer and inner surfaces of the open structure. When designing for wind loads, the designer must consider that the drill pipe or other tubulars may be out of the hole and stacked in the structure. This means that there will be loads imposed on the structure by the pipe weight (i.e., setback load) in addition to the additional loads imposed by the wind. The horizontal forces due to wind are counteracted by the lattice structure that is firmly secured to the structure s foundation. Additional support to the structure can be accomplished by the guy lines attached to the structure and to a dead man anchor some distance away from it. The dead man anchor is buried in the ground to firmly support the tension loads in the guy line. The guy lines are pretensioned when attached to the dead man anchor. 

In the discussion above, conditions described referred to perfect world conditions—that is, to those conditions that we would want (i.e., the security manager s proverbial wish list) to be incorporated into the design and installation of new chemical industry infrastructure. Post-9/11, in a not-so-perfect world, however, many of the peripheral (fence line) measures described above are more difficult to incorporate into chemical industry site infrastructure. This is not to say that industrial chemical facilities do not have fence lines or fences most of them do. These fences are designed to keep vandals, thieves, and trespassers out. The problem is that many of these facilities were constructed several years ago, before urban encroachment literally encircled the sites—allowing, at present, little room for security stand-backs or setbacks to be incorporated into plants or critical equipment locations. Based on personal observation, many of these fences face busy city streets or closely abut structures outside the fence line. The point is that when one sits down to plan a security upgrade, these factors must be taken into account. 

In contrast, a-methoxy glycolate silyl ketene acetal 54f enjoys a wider substrate scope. Here, the steric bulk that biases selectivity resides farther from the reactive a-carbon. Despite an initial setback with 54f, excellent results with aliphatic aldehydes could be secured by modulating the size of the ester substituent (entry 4). In fact, with silyl ketene acetal 54h, a broad range of aliphatic aldehydes react with good yield and moderate to excellent selectivities. 

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