PubMed · 15052895
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Paul Littlefair. 2004. Controlling solar overheating.. https://pubmed.ncbi.nlm.nih.gov/15052895/
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Engineers usually do an excellent job of documenting WHAT they build--the plant drawings and specifications record in excruciating detail the materials of construction, temperature and pressure ratings, size of pipes and equipment, equipment layout, piping and equipment interconnections, and all other information required to construct and operate a plant. However, the design basis--the WHY of the plant design--often is not nearly so well documented. Understanding the design basis of the plant, particularly with regard to the safety features, devices, and procedures, is as important, or perhaps more important, than understanding the exact specifications of the equipment for the long term safe operation of the plant. Sometimes the reason for critical safety features, particularly inherently safer design features, may not be apparent to people who were not involved in the original design. These features may be vulnerable to compromise or elimination in future modifications of the plant. The people running the plant at the time the modifications are made no longer remember the original design basis. This can also work in the opposite sense-a plant may continue to accept and manage certain hazards long after the original reason for designing the plant to operate in that way has been eliminated, because it has "always been done that way". This important information about the safety design basis of a plant must be preserved by implementation of a process safety information management system. Several case studies and examples illustrating these points will be discussed.
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Pervious concrete is an alternative paving surface that can be used to reduce the nonpoint source pollution effects of stormwater runoff from paved surfaces such as roadways and parking lots by allowing some of the rainfall to permeate into the ground below. This infiltration rate may be adversely affected by clogging of the system, particularly clogging or covering by sand in coastal areas. A theoretical relation was developed between the effective permeability of a sand-clogged pervious concrete block, the permeability of sand, and the porosity of the unclogged block. Permeabilities were then measured for Portland cement pervious concrete systems fully covered with extra fine sand in a flume using simulated rainfalls. The experimental results correlated well with the theoretical calculated permeability of the pervious concrete system for pervious concrete systems fully covered on the surface with sand. Two different slopes (2% and 10%) were used. Rainfall rates were simulated for the combination of direct rainfall (passive runoff) and for additional stormwater runoff from adjacent areas (active runoff). A typical pervious concrete block will allow water to pass through at flow rates greater than 0.2 cm/s and a typical extra fine sand will have a permeability of approximately 0.02 cm/s. The limit of the system with complete sand coverage resulted in an effective system permeability of approximately 0.004 cm/s which is similar to the rainfall intensity of a 30 min duration, 100-year frequency event in the southeastern United States. The results obtained are important in designing and evaluating pervious concrete as a paving surface within watershed management systems for controlling the quantity of runoff.