Selected tier

Given that identified uncertainties have been characterized qualitatively, this is considered a Tier 1 characterization. At this point, none of the sources has been treated deterministically or probabilistically (i.e. Tier 2 or Tier 3). 

Although this case-study does not reflect a Tier 0 level, it does include many of the elements of Tier 0 (i.e. characterization of level of uncertainty without analysis of each source), but then moves on to Tier 1 (additionally characterizing individual sources). 

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The Tier 2 testing assays are intended to confirm, characterize, and quantify effects for estrogen, androgen, and thyroid active substances. The EDSTAC selected Tier 2 to include the most sensitive developmental Ufestage, to identify the specific hazard caused by the chemical and establish a dose-response relationship, and to include a range of taxa. The Tier 2 screening assays under consideration by the US-EPA are summarized in Table 4.22. 

Consult Recycle heuristics and Rules for Selecting Operations (tiers 1 and 2) and do one of the foUowing with the current stream ... 

Separation method selection is governed by a two-tier set of rules for selecting among potential operations. The first tier involves the selection between strategic and opportunistic operations. Strategic separations are favored, as these are known to be required in the flow sheet at some point, as are separations which directly reach a desired product composition. The rules in the first tier state that once all the potential opportunistic and strategic operations have been identified for the current stream, the next step is to determine the order in which these operations should be tried. The foUowing... 

In addition, the source of sponsorship may differ, reflecting centralized vs. decentralized corporate structures. In either case, effective sponsorship requires two tiers prime mover and key advocate, as shown in Figure 2-1. The prime mover, or primary sponsor, is the one who authorizes the initiative, while the key advocate is the individual without whose explicit support the initiative cannot go forward. To select the right sponsor for your company s PSM initiative, start by identifying the appropriate prime mover and key advocate. 

Working with an established Tier 1 supplier Houghton International, Ford selected a two-phase metalworking lubricant/coolant based on vegetable oil. In trials at the Dagenham Engine Plant Ford foimd many benefits ... 

Boilers and most industrial furnaces must follow a tiered system for the regulation of both hydrogen chloride and chlorine gas. The owner and operator determine the allowable feed or emission rate of total chlorine by selecting one of three approaches, called tiers. Each tier differs in the amount of monitoring, and in some cases, air dispersion modeling (i.e., modeling the air pathways through which pollutants may travel) that the owner and operator are required to conduct. 

The final performance standard is for toxic metals. For RCRA combustion units, both carcinogenic and noncarcinogenic metals are regulated under the same type of tiered system as chlorine. The facility determines an appropriate tier for each regulated metal and assures that the facility meets these feed rate and emission standards. A different tier may be selected for each metal pollutant. 

Factors that may be considered in selecting a tier include the physical characteristics of the facility and surrounding terrain, the anticipated waste compositions and feed rates, and the level of resources available for conducting the analysis. The main distinction between the tiers is the focal... 

Combinatorial approach to unsymmetrically tiered macromolecules [214] is a brand new area of research which would allow dendrimerization of materials (e. g., glass, classical polymers, fibers) and thus enable fine tuning of macromole-cular properties. For example, treatment of an amine terminated dendrimer with a mixture of complementary, isocyanate-based monomers [215, 216] affords a heterogeneous surfaced dendrimer. Selective transformation of the surface nitrile moieties via metal-catalyzed reduction to obtain a new polyamine dendrimer allows further combinatorial-based elaboration as illustrated in Fig. 42. 

Data used to describe variation are ideally representative of some population of risk assessment interest. Representativeness was a focus of an earlier workshop on selection of distributions (USEPA 1998). The role of problem formulation is emphasized. In case of representativeness issues, some adjustment of the data may be possible, perhaps based on a mechanistic or statistical model. Statistical random-effects models may be useful in situations where the model includes distributions among as well as within populations. However, simple approaches may be adequate, depending on the assessment tier, such as an attempt to characterize quantitatively the consequences of assuming the data to be representative. 

Another characteristic example of analytical strategy is that followed in the United Kingdom for the analysis of tranquilizers and -blockers (78). A total of 180 samples distributed over a whole year (15 samples per month) should be analyzed within a turnaround time of 28 days from receipt of sample. In that case, the expense of developing a two-tier analytical strategy was not justified by the sample throughput. Thus, the selection was direct application of a multiresidue LC/PDA confirmatory method (80). 

For example, the Threshold of Toxicological Concern concept has been proposed, which reduces the amount of toxicological data necessary and therefore reduces the number of animals used in the assessment of hazard. This uses a tiered approach and excludes certain kinds of chemicals such as dioxins and organophosphates. It also makes use of structural alerts and chemical classes to select out chemicals, which are likely to be of little toxicological concern (13). 

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