Semi-detailed estimating procedure

The semi-detailed estimating system and related procedures presented in this book will allow project managers to prepare reasonably accurate estimates very quickly and confirm the validity of estimates prepared by others even quicker. 

The proposed semi-detailed estimating system is consistent with the guidelines presented in Section 10.4 and includes simple procedures and tools that will allow project managers to quickly and accurately ... 

These procedures are more suitable for detailed or semi-detailed estimates where the various commodities (civil, piping, electrical, etc.) are estimated individually or related to equipment count rather than to equipment cost. These procedures should not be used in factored estimates where an error in the equipment account would be greatly amplified by the time it reaches the bottom line. 

Semi-Detailed Estimate Example-Case Study (Appendix L illustrates the application of all the estimating procedures presented in Chapter 19.)... 

A semi-detailed cost estimate prepared with the procedures and guidelines included in Chapter 19 could easily be dissected into a multitude of comprehensible construction activities that could be integrated, at the Project Manager s option, into a manageable number of discretely sized units. Every single activity could be assigned consistent relative values based on field hours... 

Note For a preliminary estimate, the cost can be calculated in a few minutes with the aid of the charts provided. For definitive estimates intended for appropriation and/or progress monitoring, the cost should be developed with the semi-detailed procedure. Both approaches should result in approximately the same cost. 

The Phase 1 design package is the basis for a very good quality semi-detailed preliminary cost estimate that can be prepared quickly using the procedures in Chapter 19. Appendix L illustrates the preparation of the estimate for the case study... 

The equipment account and all civil accounts, as well as the Electrical Account and the Contract Engineering man-hours can be estimated with the respective semi-detailed procedures in Chapter 19. 

Another popular method to estimate overpressures is the Baker-Strehlow method. This method is based on a flame speed, which is selected based on three factors (1) the reactivity of the released material, (2) the flame expansion characteristics of the process unit (which relates to confinement and spatial configuration), and (3) the obstacle density within the process unit. A set of semi-empirical curves is used to determine the overpressure. A complete description of the procedure is provided by Baker et al.18 The TNO multi-energy and Baker-Strehlow methods are essentially equivalent, although the TNO method tends to predict a higher pressure in the near field and the Baker-Strehlow method tends to predict a higher pressure in the far field. Both methods require more information and detailed calculations than the TNT equivalency method. 

Uncertainties in semi-quantitative applications are generally around 30-50% for non-interfered analytes. For carefully developed semi-quantitative procedures, lower uncertainties can be reached, but only for certain elements. Strongly interfered or blank dominated elements (e.g. Cl, Si, S) result in higher uncertainties, sometimes of the order of several hundred per cent. Semi-quantitative calibration therefore is suited for sample screening and preliminary tests, when only a rough estimate of the sample composition is required. More details on the applications of semi-quantitative calibration can be found in the literature. 

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