• Question: What would the pressure per square inch have to be for a water jet to rip through a human

    Asked by Harry to Anna, James, Joe, Leonie, Olivia on 10 Mar 2015.
    • Photo: Joe Spencer

      Joe Spencer answered on 10 Mar 2015:

      Harry,
      There are water jets that are used to cut metal, so i imagine water cutting people is pretty easy. As for exact numbers, not sure.
      But let’s think it through, so you want PSI, or pounds per square inch, so let’s assume you want a jet of water 1 inch in diamter to cut a hole of 1 inch through your enemy (i’m assuming you’re not doing this to your friend.
      According to wiki the UTS (ultimate tensile strength) of skin is 20MPa (Mega pascals) This is a unit of pressure (which we can convert to PSI) where 1MPa is 145Psi (roughly). So in total you’d need about 2900psi (about 100 times the pressure in a tyre)
      UTS is not simply a measure of cutting power you need force to keep the jet going, depth is also important, now obviously you don’t want a little dent in your enemy, but want to ‘rip through them’ so let’s assume from chest to back that distance is about 25cm (0.2m or 10inches)
      so 10 inches * 1 inch * 2900psi = 29,000 pounds of pressure

      That’s probably enough to think about now

    • Photo: James Pope

      James Pope answered on 11 Mar 2015:

      That’s a great answer Joe, all I can add is that if you take a pressure washer you can buy in B&Q or Homebase and use at home, and put the nozzle right against a Welllington Boot it cuts through it as a small hole in the ankle, right through in about 10-20 seconds, but you have to keen pressing it against the skin of the wellington boot for it to cut through.

      This was an “experiment” I did when I was 15, which resulted in my mum tearing me a new one and lots of wet ankles when I wore my wellies in future.

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