Fragment distribution as an aid to forensic failure investigations at the scene of explosions

Abstract

Twelve pipe bombs were exploded, and the fragments were collected and weighed. The distribution of fragment masses was shown to follow a Weibull-type form M (n)=M₀ [1 − exp (−Bn^λ)] when RDX-based military explosives were used and a bimodal distribution when commercial explosives were used. The constant, B, was a function of the mass of fragments recovered, making its use inappropriate in a forensic context where complete collection of the fragments would not be possible. For RDX-based explosives with added Mg or Al powder, the value of the constant, λ, was reduced compared to that of the RDX-based explosive without metal powder additions. An alternative fragment distribution formula, log [(100 M (N))/M₀]=FWDM [m(N)/ M₀], can also be used to distinguish between explosives, although the correlation coefficient is inevitably somewhat lower and the scatter between the results of nominally identical tests can be greater. The coefficient, FWDM, has a dependence on the mass of fragments collected, restricting its utility in forensic contexts.