The pump affinity laws provide a useful way to estimate the effect of changes in either the revolutions per minute (rpm) or the diameter of the impeller on a pump’s performance. In this article, Roy C. E. Ahlgren, discusses why these laws can be better used to predict performance in some cases as opposed to others. Using an example, he demonstrates how the pump affinity laws predict actual performance with better accuracy at variable rpms than after trimming the impeller. In addition to better predictions when efficiency changes are smaller, the affinity laws assume geometric similarity and noncavitating pump operation with cold water. Finally, the affinity laws cannot take into account system curve, which also affects pump efficiency. The article includes figures showing several curves and tables of curve estimates.
Water and water treatment are the very heart of a dialysis system. Plumbing engineers must understand system design, installation, and maintenance. Dialysis fluid, or dialysate, is composed of water and a concentrated solution that contains the same electrolytes as normal extracellular fluid. Extracellular fluid is the body fluid outside of cells that includes blood plasma, lymph, and the interstitial fluid between cells. Water is added to the concentrate to produce a solution at a similar dilution. In the two types of dialysis systems, water is fed via a loop, which allows high flow rates, water velocity being an important factor. Changes in pipe direction should be done with a 45-degree angle, and connections to dialysis stations should be as short as possible. Those connections should be of types to facilitate removal or change without dismantling the piping system. Valves should be PVC or CPVC, with further technical details listed. Water should be sampled and analyzed periodically to measure both microbe numbers and disinfectant level. The system should be disinfected on a regular basis. Details are included. An illustrated sidebar explains types of dialysis treatments.
Most codes and standards that apply to the design of site and roof drainage systems are governed at the local level, and these can vary greatly from region to region across the country. As a result, it is incumbent upon plumbing designers to be familiar with the actual code used by the jurisdiction in which they are working. The designer should also be in contact with the authority having jurisdiction, AHJ, early in the process, because the AHJ must approve the methods for draining building sites before the permit is issued. Considerations that apply to site drainage include oil/water separators and pollutant-removal devices, and retention basins and detention ponds. There is an abbreviated discussion of combined storm/sanitary systems; these are rarely used because they place additional loads on municipal sewage disposal plants. Materials for aboveground and underground piping and bedding materials are discussed. A large portion of the article is devoted to interior storm drainage system considerations. The designer must research local weather conditions and details of the building to be constructed (type of roof, vertical wall and parapet height, etc.). The steps necessary to determine the primary system?s pipe size and slope are presented and discussion is complemented by tables and figures. Secondary overflow system requirements, pipe expansion and anchoring, backflow prevention, and leaders are all discussed within the context of the interior storm drainage system. Drainage control from the roof into the storm drainage system is covered next. This is often accomplished by means of either a controlled-flow drainage system or a siphonic roof drainage system, although neither system can be employed when the roof is to be used for functions that preclude some level of water storage. The roof drain placement section includes a list of acceptable rule-of-thumb minimum dimensions. Secondary roof drainages systems are often mandated by the AHJ, and sizing, types, and disposal points are discussed. The design method for exterior storm drain systems, those used to drain parking lots and other areas, is different than that used for interior drainage systems. A formula and table of runoff coefficients for different surface types is provided.
Cancer risk was studied in 10,552 Swedish hyperthyroid patients treated with 131I between 1950 and 1975. Patients were followed for an average of 15 years (range 1-35 years) and were matched with the Swedish Cancer Register (SCR) and the Swedish Cause of Death Register (SCDR). The overall standardized incidence ratio (SIR) was 1.06 [95% confidence interval (CI) = 1.01-1.11], and the overall standardized mortality ratio (SMR) was 1.09 (95% CI = 1.03-1.16). The stomach was the only site for which cancer risk increased over time (p < 0.05) and with increasing activity of 131I administered (p = not significant). No increased incidence of leukemia was found, which adds further support to the view that a radiation dose delivered gradually over time is less carcinogenic than the same total dose received over a short time. A possible excess owing to radiation was suggested only for stomach cancer.
ASPE’s second design standard, written in conjunction with the American Rainwater Catchment Systems Association, will help plumbing engineers design code-approved rainwater harvesting systems to encourage water reuse and conservation in commercial buildings.
Health agencies throughout the world have evaluated the safety of irradiated foods by considering the likelihood that irradiation would induce radioactivity, produce toxic radiolytic products, destroy nutrients, or change the microbiological profile of organisms in the food. After years of study, researchers have concluded that foods irradiated under the proper conditions will not produce adverse health effects when consumed.
Plumbing engineers, designers, contractors, maintenance, and operating personnel are often involved in litigation concerning liability for injuries sustained by the users of hot water systems. For example, scald injuries and legionella danger occur when hot water is not maintained at an optimal temperature. These dangers are greatest for the old and the young. These age groups will grow in absolute and relative numbers in the United States for some time to come. Thus, litigation regarding hot water injuries is anticipated to increase. Hot water injuries are preventable. Implementation of best practices for hot water systems is a prudent step. Based on existing industry standards and guidelines, these best practices apply to the design, build, operate, and maintenance aspects of hot water systems. Practices to directly control hot water systems include: 1. Minimize hot water temperature. Methods to bring water to taps within a variety of systems at a temperature of approximately 122 degrees are presented, along with reasons behind this temperature choice. Legionella-contaminated systems are also discussed. 2. Point-of-use, pressure-regulated thermostatic mixing valves are required on new bathing installations. Install on kitchen taps, where not required, to prevent scalds. Retrofit existing showers and baths with cutoff devices. 3. Install redundant protection to ensure that water too hot for safety does not reach taps. Redundancy for small and large systems is discussed. 4. Verify and document hot water system performance by testing under a variety of conditions prior to placing into service. Ongoing testing and periodic monitoring for legionella bacteria are recommended. 5. Recirculate water continuously. Use of energy management systems on recirculating hot water systems can result in pockets of water that rise above or fall below safety levels. 6. Properly size pipes to ensure that a system does not experience surges of hot water as a result of instantaneous demand at another fixture. 7. Maintain the domestic hot water system or ensure that building owners understand the need to do so. 8. Adjust mixing valves on central boilers to accommodate fluctuations in ambient temperature and demand. 9. Prevent mineral deposit buildup that can decrease pipe diameters and provide conditions that allow legionella bacteria to grow. 10. Periodically assess the hot water system to help identify when design conditions have changed and adjustments are necessary. 11. Do not increase water temperatures in an attempt to meet the needs of an inadequate or aging hot water system. 12. Replace damaged parts, particularly mixing valves.
Epidemiologic data from underground miners confirm that radon decay products are carcinogenic, but evidence for the quantitative risks of these exposures, especially for indoor air, is less conclusive. Experimental animal studies, in conjunction with dosimetric modeling and molecular-cellular level studies, are particularly valuable for understanding the carcinogenicity of human radon exposures and the modifying effects of exposure rate, the physical characteristics of the inhaled decay products, and associated exposures to such agents as cigarette smoke. Similarities in animal and human data, including comparable lung cancer risk coefficients, tumor-related dosimetry, and tumor pathology, presently outweigh their differences. The animal models, therefore, appear to be reasonable substitutes for studying the health effects of human radon exposures.
Although a far cry from their counterparts of the 1970s, solar heating systems still present a significant up-front expense and can be less than aesthetically pleasing. Both cost and design improve as owners move toward green building and as architects incorporate solar components into more projects. This article presents the basics of solar-powered hot water heaters, which differ from traditional water heaters primarily in their power source. Major components include solar collector(s), circulation systems, storage tanks, a backup heating system, and control system. Direct systems (open loop) circulate domestic water between collectors and storage tanks. Direct systems can be downdrain or recirculating. Indirect systems (closed loop) circulate liquid (water, glycol) as a heating medium. Depending on their components, indirect systems can be more expensive and require more maintenance, but also have a number of advantages. Web-based resources are presented, along with a checklist including design criteria, types of systems, installation considerations, and mounting systems.
A Test of the Linear-No-Threshold Model of Radiation Carcinogenesis
Bernard L. Cohen and , Graham A. Colditz Radiation and Public Perception
Chapter 6, pp 67–77
Pub Date : May, 1995
American Chemical Society
The linear-no-threshold theory used to estimate the cancer risk of low level radiation from the known risks of high-level radiation is tested by studying the variation of lung cancer mortality rates (m) with average exposure to radon (r) in various U.S. states and counties. The data indicate a strong tendency form to decrease with increasing r, in sharp contrast to the theory prediction of a strong increase of m with increasing r. To explain this discrepancy by a strong tendency for areas of high radon to have low smoking prevalence, and vice versa, would require almost 100% negative correlation between radon and smoking, whereas current information indicates a correction of only a few percent. Several other possible explanations for the discrepancy are explored, but none seem to be effective in substantially reducing it.