Witness plate for assessment of human injury
Publish date: 2021-12-03
Report number: FOI-R--5169--SE
Pages: 26
Written in: Swedish
Keywords:
- witness plate
- skin perforation
- lethality analysis
- vulnerability analysis
- risk analysis
- fragments
Abstract
There has been a vast increase of incidence involving improvised explosive devices (IEDs) and hand grenades in Sweden in recent time. The attacks are often directed towards apartment complexes or vehicles, but there have also been attacks against police stations and other governmental facilities. In the forensic investigations, both civil and military, it is of importance to be able to determine and describe the threats and risks posed by an IED. Exploding devices pose a threat to people and property, and it is central to assess if there were, or could have been, people exposed to the risk of obtaining mild, severe or deadly injury due to the explosion. In case of a non-exploded device, there is a need to understand what the exposure would have been if it detonated. A description of the hazards and risks can provide a basis during trials for these kind of crimes. Due to the variety in how the IEDs are constructed and how they are used, it is difficult to compile a general description of hazards connected to them. Thus, there is sometimes a need to conduct characterisation of an IED by experimental testing. From the experiments, it is desirable to obtain simple and distinct results that display the hazards, even for complex scenarios such as explosive devices in vehicles or in confined spaces, where it is sometimes both difficult and costly to include advanced instruments. One relatively inexpensive and easy-to-use method are witness plates. Witness plates are often included in experimental testing for various reasons, but in this context, it can supply information on the characteristics of the fragmentation impacts at different positions and distances. If these characteristics are compared with human injury criteria, this can offer a simple and distinct result that could be used in court to provide information of the hazardous nature of an IED. In this work, a number of models for skin perforation by fragments are described and compared to a witness plate of aluminium. The analysis show that aluminium plates of SS4007-14 quality and 1.0 mm thickness has a good agreement with models for skin perforation for steel spheres with sectional density exceeding 6 g/cm2 . With sectional density below 6 g/cm2 the aluminium plate becomes more resilient than skin (as described by the models). A number of potential errors and possible uncertainties were identified in the described skin perforation models and their underlying data. It is recommended that the model presented by Tausch should be used until further notice.