The collection of both physical and chemical evidence from the scene of a large bomb can be useful in determining the type of explosive charge used and its approximate size. Six charges of calcium carbonate (limestone) ammonium nitrate/sugar (LAN/S) improvised explosive devices were fired (three at 454 kg and three at 2,268 kg) together with one charge of 2,4,6-trinitrotoluene (TNT, 454 kg) and one charge of ammonium nitrate fuel oil (ANFO, 2,268 kg). The charges were surrounded by vehicles, roadsigns, and lampposts that acted as witness material to provide both physical and chemical evidence. Ammonium, higher levels of nitrate, and some sugars were recovered from the LAN/S firings; low levels of nitrate from the ANFO firing; and significant levels of TNT from the TNT firing. Levels of recovery generally decreased with increasing distance from the charge. The pattern of physical damage to the witness pieces at given distances from the charge was recorded. The velocities of detonations were measured and the corresponding TNT equivalence calculated. All firings were performed at the High Performance Magazine Site, New Mexico Institute of Mining and Technology, Socorro, New Mexico. Figures, tables, references