When a 'ferocious lunge' is not a 'slight prick'

January 20, 1995

Courts look set to benefit from research at University of Wales, College of Cardiff, which aims to help bring hard science to bear on the often difficult task of assessing the force used on victims of stabbings.

Len Nokes of the university's medical systems engineering research unit says that such assessments can be of vital importance in passing judgement on the accused. He says, "it is a question that is extremely difficult to answer objectively.

One person's "ferocious lunge" might approximate to another's "slight prick". Even more important for relating the type of force used to the injury caused, is the type of weapon, its sharpness and tip it possesses, he says.

Dr Nokes's research team has been studying ways of quantifying the force used during knife attacks using an instrument called a load cell. The device converts forces into electrical signals which can be fed into a computer for analysis. The instrument is specially designed so that it can fit into the handles of knife blades with which stabbing actions are performed by researchers.

Dr Nokes says that early studies used foam and polyethylene to simulate human tissue. But this was unsuccessful and the team is now using pig tissue to provide a more realistic model to work on.

Results so far confirm that the most important factor in determining the depth of a wound from a knife blow of given force is the sharpness of the knife point which enables it to penetrate the skin. After puncturing the skin, another major instance of resistance, apart from bone or cartilage, occurs when the knife meets different layers of muscle.

The team is now examining the effect of different speeds of approach of the knife before it make contact with the skin.

Capturing the stabbing action on high-speed film is one method being explored for making these measurements.

It is planned that a group of people will be shown the films as well. This will allow studies to be carried out on how viewers' subjective judgements on the film compares against data extracted from the images by researchers.

Dr Nokes says that eventually it should be possible to build up a bank of data to help answer questions arising in court cases involving stab wounds.

The researchers work on linking depth of wounds to force and speed of impact may also be of help in accident investigations where victims suffer wounds from sharply pointed objects in falls or collisions, he says.

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