Worst-case test condition

Safety is known. Most DOD standard designs have been proof-tested" by exposure of a test structure to the explosive effects of a nearby detonation. The worst-case test condition is depicted in Figure 2. 

At the Biyan site the main line flow constrictor was installed flush against an isolation valve and a 90° elbow. This was done to establish worst case test conditions. It was expected on theoretical grounds that the operation of the flow separator would be insensitive to upstream flow conditioning of the gas. Test data taken to date has proven this to be the case. 

Experimental methods coming from laboratory-based studies of worst-case testing of simulated workplace conditions. 

For reaction systems without solvents, the time at the test temperature is important. In these cases, the elected period of time and temperature should be based on the worst case operating conditions. 

The system is not only tested under typical operating conditions but also at the limits under which it will be required to operate - an approach known variously as worst case testing, gray box testing or testing of boundary conditions. Testing boundary conditions is important because most software errors occur around its boundary limits. Combinations of several worst cases are also tested. For example, if a system is specified to acquire data from multiple instruments and the data acquisition rate can be varied, test cases include acquisition from the maximum number of instruments at the highest data rate. 

FIGURE 37.2 Frequency distribution of the test statistic for the primary analysis resulting from 500 completed simulated randomized concentration-controlled trials (RCCTs) with mycophenolate mofetil under worst case trial conditions, completed before real study initiation. The actual study outcome is shown, falling in the central portion of the distribution in the interval centered at 18.3 (From Ref. 18.)... 

To illustrate the use of designed experiments in this process, a case study is presented involving a packaging sealer (3). Designed experiments in conjunction with other tools are used to create a control plan that is then validated. The DOE results are also used to identify worst-case conditions for worst-case testing, and to help select sample sizes for worst-case and final PQ testing. 

The stability tests were performed over 52 weeks storage at +4°C and +20°C. A short-term stability study was also carried out at -i-40°C to test worst-case transport conditions. No instability could be detected at any of the conditions tested [15]. 

The stability of the total mercury contents was tested at +20°C over a period of 18 months. In addition, a short-term stability experiment was performed at -(-40°C to simulate worst-case transport conditions. No instability could be demonstrated and the material was considered suitable for certification. Transport at elevated temperature (40°C or below) for a short-term period (4 weeks or below) would not affect the stability of the material [29,30]. 

Filters were kept at respectively +5°C and +20°C over a period of 12 months, and the Cr(VI) and total soluble Cr contents were determined at regular intervals during the storage period. An additional stability test was performed after 29 months, consisting in the determination of Cr(VI) at +20°C followed by a short term stability test at +40 C to simulate worst-case transport conditions. Tests were made after 1 week, 1, 6 and 12 months. Samples were analysed using the same procedure as for the homogeneity study. Cr(VI) and total soluble Cr were each determined in three fold (one replicate analysis in each of 3 filters stored at different temperatures) at each occasion of analysis. No instability could be found at any of the temperatures tested even storage at +40°C for 14 days does not likely affect the samples. 

Challenge Tests/Worst Case A condition or set of conditions encompassing upper and lower processing limits and circumstances, within standard operating procedures, that pose the greatest chance of process or product failure when compared with ideal conditions. 

Objective data for exemption from requirement for initiai monitoring, (i) For purposes of this section, objective data are information demonstrating that a particular product or material containing cadmium or a specific process, operation, or activity involving cadmium cannot release dust or fumes in concentrations at or above the action level even under the worst-case release conditions. Objective data can be obtained from an industry-wide study or from laboratory product test results from manufacturers of cadmium-containing products or materials. The data the employer uses from an industry-wide survey must be obtained under workplace conditions closely resembling the processes, types of material, control methods, work practices and environmental conditions in the employer s current operations. 

Endurance Burn Under certain cou(itious, a successfully arrested flame may stabilize on the unprotected side of an arrester element. Should this condition not be corrected, the flame will eventually penetrate the arrester as the channels become hot. An endurance burn time can be determined by testing, which specifies that the arrester has withstood a stabilized flame without penetration for a given period. The test should address either the actual or worst-case geometry, since heat transfer to the element will depend on whether the flame stabilizes on the top, bottom, or horizontal face. In general, the endurance burn time identified by test should not be regarded as an accurate measure of the time available to take remedial action, since test conditions will not necessarily approximate the worst possible practical case. Temperature sensors may be incorporated at the arrester to indicate a stabilized flame condition and either alarm or initiate appropriate action, such as valve closure. 

Operational qualification involves performing a series of tests to check that all elements of the system are functional across the specified operating range. This usually involves performing challenges at the worst case extreme operating conditions. The process should allow confirmation of final operation, maintenance and calibration procedures. 

Soil properties A Soil texture (sand, silt, clay), organic matter/carbon content, and pH Stones, roots, and hardpans must be largely absent to allow representative sampling of soil profile Soil properties should appear uniform over test site Soil texture data should be available at time of site selection. Soil properties must match study purpose. This can be realistic use conditions, realistic worst-case or worst-case in terms of agrochemical mobility and persistence Must ensure that the majority of samples can be taken from the deepest sampling horizon. Information about sub-soils can be obtained from soil maps, test coring and on-site interviews... 

It is assumed that the moisture content of the soil has been determined to be approximately 50% under worst-case conditions. Using this information and the results from vendor tests, it has been determined that a minimum dose of one part solidification reagent to two parts soil is required for the migration control of lead. Testing has shown that the optimum solidification reagent mixture would comprise ca. 50% fly ash and ca. 50% kiln dust. Thus, ca. 7000 t (6364 T) each of fly ash and cement kiln dust would be required. The reagents would be added in situ with a backhoe. As one area of the soil is fixed, the equipment could be moved onto the fixed soil to blend the next section. It may be anticipated that the soil volume would expand by ca. 20% as a result of the fixation process. This additional volume would be used to achieve the required slope for the cap. An RCRA soil/clay cap placed over the solidified material is necessary to prevent infiltration and additional hydraulic stress on the fixed soil. It is estimated that the fixation would reduce lead migration by 40% and that the fixed soil may pass the U.S. EPA levels for lead. 

Worst-case analysis based on the DSC data, namely, the test with the lowest onset temperature, resulted in a graph showing the relationship between initial temperature and time-to-maximum rate under adiabatic conditions. For an initial temperature of 170°C, it would take 2 hours to reach the maximum rate. Venting simulation tests were undertaken on a larger scale to detect safe venting requirements for the separator and for the MNB hold tank. Several vent sizes were tested. It was found that a 10-cm rupture disc with a burst pressure 1 bar above the operating pressure was adequate. 

Simple illustrations of the variety of service conditions are the difference in climates of Moscow, London and Phoenix, or the different chemicals that might come in contact with an engineering component. The implications are that uncertainty may mean designing for the worst case (or being unexpectedly caught out) and the variation potentially calls for testing (or making extrapolations) under many conditions. 

When extrapolating accelerated test results it is generally necessary to refer to typical, average or worst case conditions, unless the intended application is very specific. 

The committee notes that the analysis of the cell membrane failure that occurred in the 500-hour DMMP (discussed in the next section) suggests that the cell membrane tests did not represent worst-case conditions for membrane life under actual operating conditions and that limited credence can be given to the conclusions from this test (AEA, 2001k). It also notes that in the absence of organics, parasitic oxidation of water may offset the Ag2+ attacks that were anticipated in this test. 

As an alternative, SST limits can be determined from the results of a robustness as recommended by the ICH. It can be done using the worst-case results for the response, derived from the experimental design results. This allows defining SST limits for responses such as resolution or peak asymmetry. The main idea behind the approach is that the most extreme results are considered, obtained under experimental conditions resulting in acceptable quantitative determinations. SST limits can thus only be meaningfully derived when the tested method is considered robust concerning its quantitative aspect. Then, nowhere in the domain, described by the experimental design, a problematic quantitation occurs, even not at the conditions where the SST responses are worst. 

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