Safe Distance of Waterjets and Abrasive Suspension Jets
Waterjets(WJ) and abrasive suspension jets (ASJ) have been used for various field applications. Considerable number of accidents have occurred that the jets hit the operator or nearby people. Katakura’s paper* explored a scientific way to determine the injury-free distance from the jets.
A high pressure pump was used to generate pressure of up to 69 Mpa. 60 Mpa pressure was used for both the WJ and ASJ tests. Olivine sand was used as the abrasive in the ASJ tests.
Swine skin was used as a substitute material for human skin in these tests. Tensile testing was done to determine the tensile strength of the swine skin to be 3-30 Mpa, similar to that of human skin (3-13 Mpa). Frozen swine skin materials were defrosted just before the experiment. Two layers of wire mesh were used to support the swine skin sample to avoid backpressure upon penetration.
The nozzle was mounted on a motion system that can move parallel and perpendicular to the sample surface simultaneously. The jets were aimed at the sheet of swine skin perpendicularly or at 45° or 135° angles. The nozzle moved from far to close, maintaining a speed of about 1 cm/s at the direction parallel to the sample surface as well as at the direction of the jet velocity.
After being hit by the jets, the sample skins were visually examined to identify the location of penetration, non-penetration injury (depression or abrasion), or non-injury as well as the corresponding standoff distance.
The test results indicated that the safe standoff distance based on the penetrating injury (SSD1) is about 50 cm for WJ and 70 cm for ASJ. The safe standoff distance based on the non-penetrating injury (SSD2) is about 120 cm for WJ and 170 cm for ASJ. A sufficiently-safe standoff distance was suggested to be 2.5 m for WJ and 3.5 m for ASJ, roughly 5 times of SSD1 and 2 times of SSD2. The effects of the traverse speed and the incident angle appear to be small or negligible.
The author concluded that this is a reproducible method and the research effort will be continued.
*Katakura, H. (2009) “Research on
the safety distance from a nozzle – measurement of safe standoff distances of
WJ and ASJ”, Proceedings of the 2009 American WJTA Conference and Expo,
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