Calculating Contained Firing Facility (CFF) explosive firing zone

The University of California awarded LLNL contract No. B345381 for the design of the facility to Parsons Infrastructure & Technology, Inc., of Pasadena, California. The Laboratory specified that the firing chamber be able to withstand repeated fxings of 60 Kg of explosive located in the center of the chamber, 4 feet above the floor, and repeated firings of 35 Kg of explosive at the same height and located anywhere within 2 feet of the edge of a region on the floor called the anvil. Other requirements were that the chamber be able to accommodate the penetrations of the existing bullnose of the Bunker 801 flash X-ray machine and the roof of the underground camera room. These requirements and provisions for blast-resistant doors formed the essential basis for the design. The design efforts resulted in a steel-reinforced concrete snucture measuring (on the inside) 55 x 5 1 feet by 30 feet high. The walls and ceiling are to be approximately 6 feet thick. Because the 60-Kg charge is not located in the geometric center of the volume and a 35-K:: charge could be located anywhere in a prescribed area, there will be different dynamic pressures and impulses on the various walls? floor, and ceiling, depending upon the weights and locations of the charges. The detailed calculations and specifications to achieve the design criteria were performed by Parsons and are included in Reference 1. Reference 2, Structures to Resist the E@xts of Accidental L%plosions (TMS- 1300>, is the primary design manual for structures of this type. It includes an analysis technique for the calculation of blast loadings within a cubicle or containment-type structure. Parsons used the TM5- 1300 methods to calculate the loadings on the various fling chamber surfaces for the design criteria explosive weights and locations. At LLNL the same methods were then used to determine the firing zones for other weights and elevations that would give the same or lesser loadings. Although very laborious, a hand calculation of the different variables is possible, and an example is given in Appendix C. Fortunately, a code called �SHOCK� is available to perform these calculations rapidly, and the code runs on a personal computer. The original code was developed by the fii Amman and Whitney, which they called �Paimpres�; this was modified to its present form by the U.S. Naval Civil Engineering Laboratory. Parsons used the SHOCK code extensively, as well as several single- and multiple-degree-of-freedom codes, which were provided by the U.S. Corps of Engineers. In addition, Parsons based their analysis/design on procedures stipulated in the publication DOE/TIC- 11268, A Manual for the Prediction ofBlast and Fragment Load&s on SlrzuAwes. Loadings on structures in Reference 2 and in calculations performed with the SHOCK code are based on weights of explosives in pounds of TNT equivalent. The equivalency of an explosive (for its blast effects on structures) is calculated by the ratio of its heat to detonation to that of TNT. We intend to use the explosive C-4 for testing the response of the firing chamber. Various values of the ratio for C-4 are available: Reference 2 lists numbers leading to a ratio of 1.15, while I. 13 is the ratio calculated from numbers given in the LLNL, Explosives Handbook (Reference 3). Parsons used a ratio value of 1.3 for generic high explosive-to-TNT equivalency. For design purposes, Reference 2 recommends a 20 percent increase in explosive weight. Parsons adopted this recommendation. Therefore, for calculational purposes, 60 Kg of generic high explosive was taken to be equivalent to 206.3 pounds of TNT. That is, 60 Kg x 2.204 lb/Kg x 1.3 x 1.2 = 206.3 lb (TNT).