Past experience

Project planning techniques are employed to prepare realistic schedules within manpower, materials and funding constraints. Realistic schedules are those that include a time allocation for delays where past experience has shown they may be likely, and... 

Fertilizer Use. The worldwide use of fertilizers has an important, positive effect on the environment. Conservative estimates (112) iadicate that about 30% of world food production is direcdy attributable to fertilizer use. Without fertilizer, therefore, at least 30% mote virgin land would have to be devoted to agriculture, and 30% more labor and other resources would have to be expended. Even more serious would be the effects of land tillage and cropping without nutrient replenishment. Past experience has shown that, under such a condition, crop yields progressively decrease, the land eventually becomes barren, and forces of wiad and water erosion prevail. 

To determine in the laboratory if a component survives in use, a test bogey is frequentiy estabUshed based on past experience. The test bogey is with the particular test used to dupUcate (or simulate) field conditions. The bogey can be stated in cycles, hours, revolutions, stress reversals, etc. of components are placed on test and each component either survives or faUs. The reUabiUty for this situation is estimated. 

Consumers expectations depend on several factors including cultural background, past experiences, desire for color coordination, esthetic appeal, local customs, fads, etc. Thus, eg, a Texas red hot sold ia the South is often colored quite differently than one sold ia the North, Midwesterners prefer butter with a deep yellow color, and on birthdays the decoration on a boy s cake are often blue and those on a gid s are often pink. 

The past experience of the dyestuff industry in its use of dye intermediates such as ( -naphthyl amine and benzidine (4), known human bladder carcinogens (334—343), have led to studies as to whether or not handlers of dyes are exposed to medical ha2ards such as cancer, dermatitis, and other disorders (344-360). 

Data available from past experience can be used to generate frequency distribution cuiwes. It is essential for a company to have an efficient commercial-intelhgence system to assess market conditions. 

Past experience has shown that cryogenic fluids can be used safelv in industrial environments as well as in typical laboratories provided all facihties are properly designed and maintained, and personnel handling these fluids are adequately trained and supeiwised. There are many hazards associated with ciyogenic fluids. However, the principal... 

The type of evaporator to be used and the materials of construc tion are generally selected on the basis of past experience with the material to be concentrated. The method of feeding can usually be decided on the basis of known feed temperature and the properties of feed and produc t. However, few of the listed variables are completely independent. For instance, if a large number of effects is to be used, with a consequent low temperature drop per effect, it is impractical to use a natural-circiilation evaporator. It expensive materials of construction are desirable, it may be found that the forced-circulation evaporator is the cheapest and that only a few effec ts are justifiable. 

Example 1 Calculation of FUG Method A large hutane-pentane splitter is to he shut down for repairs. Some of its feed will he diverted temporarily to an avadahle smaller column, which has only 11 trays plus a partial rehoiler. The feed enters on the middle tray. Past experience on similar feeds indicates that the 11 trays plus the rehoiler are roughly equivalent to 10 equilih-rium stages and that the column has a maximum top-vapor capacity of 1.75 times the feed rate on a mole basis. The column will operate at a condenser pressure of 827.4 kPa (120 psia). The feed will he at its huhhle point (q = 1.0) at the feed-tray conditions and has the following composition on the basis of... 

In certain cases, it is necessary to choose materials for equipment to be used in a process developed in the laboratory and not yet in operation on a plant scale. Under such circumstances, it is obviously impossible to make plant tests. A good procedure in such cases is to construct a pilot plant, using either the cheapest materials available or some other materials selected on the basis of past experience or of laboratory tests. While the pilot plant is being operated to check on the process itself, specimens can be exposed in the operating equipment as a guide to the choice of materials for the large-scale plant or as a means of confirming the suitability of the materials chosen for the pilot plant. 

If repetitive tolls are the norm for a client, a good way to screen candidate tollers is to make use of past experience. A satisfying business relationship between a toller and a client is a prelude to the continued use of a toller and the toller s continued desire to meet a good customer s needs. 

What level of formal education is required for each position Is there a requirement for past experience for employment or advancement ... 

The assessor should establish whether for various types of jobs or job-levels criteria are formalized is there a job profile What formal education is required Is there an age limit Past experience Language ability Medical examinations Interview system ... 

The severity of the transient conditions can be established on the basis of past experience or data collected from similar installations. However, for large and more critical installations, such as a generating station or a large switchyard, it is advisable to carry out transient network analysis (TNA) or electromagnetic transient programme analysis (EMTP) with the aid of computers. For more details refer Gibbs et al. (1989) in Chapter 17. Where this is not necessary, the system may be analysed... 

This is too low. But it is possible to make it up by selecting the arrester at the primary with a lower switching if possible, or provide an arrester at the secondary. Moreover, the response factor, q, is considered very high, which may not be true in actual service and an arrester at the secondary may not be necessary in all probability. The design engineer can use a more realistic factor based on his past experience and the data available from similar installations. 

Based on past experience, it has been found that the protection current density for buried storage tanks coated with bitumen is over 100 /xA m. With coatings in very good condition, it can amount to a few tens of jiA but for coatings in a very poor state, it can rise to a level of mA The protection current demand can... 

In all static surge-detection devices, the actual plienonemon of flow reversal (surge) is not directly monitored. What is monitored are other conditions related to surge. Control limits are set from past experience and a study of compressor characteristics. 

The L-foot fm covers the tube more or less completely to protect the base tube against corrosive attack, but still leaves a potential corrosive site at the base of the fin adjacent to the preceding fin. The double L-foot is intended to provide complete coverage of the tube, where corrosion would otherwise be a problem. Where corrosion is troublesome, soldered or galvanized tubes may offer a solution. The dimensions of fmned tubes are results of past experience in the design of air cooled heat exchangers. Tube diameters range from about 1.905 cm (0.75 in.) to 5.08 cm (2.0 in,). 

Typical events that are considered are fire, explosion, ship collision, and the failure of pressurized storage vessels for which historical data established the failure frequencies. Assessment of consequences was based partly on conservative treatment of past experience. For example ilic assessment of the number of casualties from the release of a toxic material was based on past histoiy conditioned by knowledge of the toxicology and the prevailing weather conditions. An altemati. e used fault trees to estimate probabilities and identify the consequences. Credit is taken in this process for preventative measures in design, operation, and maintenance procedures. Historical data provide reliability expected from plant components and humans. 

The question is often asked. How often should calibration be carried out Is it sufficient to do it once, or should it be repeated The answer to this question depends on the instrument type. A very simple instrument that is robust and stable may require calibrating only once during its lifetime. Some fundamental meters do not need calibration at all. A Pitot-static tube or a liquid U-tube manometer are examples of such simple instruments. On the other hand, complicated instruments with many components or sensitive components may need calibration at short intervals. Also fouling and wearing are reasons not only for maintenance but also calibration. Thus the proper calibration interval depends on the instrument itself and its use. The manufacturers recommendations as well as past experience are often the only guidelines. 

A key advantage of the business process redesign approach is that while it draws on past experience (in the form of the team s collective expertise) it is not bound by it. This helps minimize the risk that inadequate practices may become institutionalized through habit or neglect, and forces the team to take a fresh look at the critical processes under review. At the same time, this approach requires more concentrated effort than either TQM or model programs and may not be necessary in cases where incremental improvement is all that s required to address PSM gaps. 

Decision making may involve calculations, reference to procedures and past experience, and other demands on long-term memory. This contributes further to the overall mental workload. From the HF/E perspective, many errors are likely to arise from information processing overload, essentially from the mismatch between demands and capabilities. Information-processing demands can be reduced by the provision of information in the form of job aids such as flow charts or decision trees. 

Stereotype takeover Reversion to an habitual or preprogrammed mode of behaviour derived from past experience with a similar, yet in some respects different, situation. 

Historical data Data receded from actual past experience. 

Past experience indicates tliat tlie wear-out time of tliis electronic device, like tliat of a large variety of products in many different industries, tends to be... 

An existing lO-in. I.D. packed tower using 1-inch Berl saddles is to absorb a vent gas in water at 85°F. Laboratory data show the Henry s Law expression for solubility to be y = 1.5x, where y is the equilibrium mol fraction of the gas over water at compositions of x mol fraction of gas dissolved in the liquid phase. Past experience indicates that the Hog for air-water system will be acceptable. The conditions are (refer to Figure 9-68). 

Short, W.B. Learning from Past Experience—45 Years With Boilers. Waterline Industrial Water Society (now Water Management Society), U.K., June 1991. 

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