DOI: 10.5683/sp2/wb8jko
title: TNT Free-Field Blast Wave Properties Interface

description: A set of Excel© spreadsheets, TNTFFI 1.1c.xlsx, has been developed to display the physical properties of blast waves produced by explosions for which the waves have not interacted with the ground or other structures, sometimes called free-field or free-air blast. The spreadsheets have been developed using an extensive database of experimentally derived measurements of the hydrostatic pressure, density and particle velocity from a large number of TNT explosions ranging in size from 4 kg to 500 kg, as described by Dewey and McMillin (1987, 1989). The results of these analyses were made available via an interface known as AirBlast (Dewey and McMillin, 1990). The AirBlast interface was licensed to more than 30 international agencies, but is no longer compatible with modern operating systems. However, the original databases of experimental measurements remain accessible and are being incorporated into a series of Excel© files, the first of which is TNTFFI 1.1c. It is anticipated that files providing the blast wave properties for surface burst and height-of-burst explosions, TNTSBI and TNTHOBI respectively, will also be developed. Excel© has been chosen as the interface platform because it is a component of most computer systems and has proved to be compatible with all operating systems as they have been upgraded over several decades. Some of the functions used in the interface may not be included with all versions of Excel©, but if missing, they can be downloaded from Microsoft. TNTFFI 1.1c consists of four spreadsheets. The first, Input Values, allows the user to input: the charge mass in kilograms; the TNT equivalence as a fraction, e.g. 0.8, if an explosive other than TNT is being used; the ambient atmospheric pressure in kiloPascals, and the ambient temperature in Celsius. The input values are used to calculate the Hopkinson (1915) and Sachs (1944), (Dewey 2000, 2016) scaling factors for radius and time. These scaling factors are used in the subsequent spreadsheets to determine the physical properties of the blast wave as functions of radial distance and time without further application by the user. The second spreadsheet, Peak Values, displays the physical properties immediately behind the primary shock at a series of radial distances from the centre of the blast wave defined by the input values. The range of distances covers those for which reliable experimental measurements of the physical properties are available. The third spreadsheet, Time Histories, displays the physical properties of the blast wave at a series of times after the arrival of the primary shock at the radial distance input by the user. The integrals of the physical properties during their positive phases are also displayed. The fourth and final spreadsheet, Wave Profiles, displays the physical properties of the blast wave at a series of radial distances behind the primary shock at the time after detonation input by the user. The integrals of the physical properties during their positive phases are also displayed. The spreadsheets can be downloaded as TNTFFI 1.1c.xlsx and a Users’ Guide that describes the spreadsheets in more detail and how they may be used can be downloaded as TNTFFI Users’ Guide.pdf.