Katakura and Guo* presented a research study in this subject, aiming to provide data necessary for establishing industrial safety standards.

A waterjet with a diameter of 0.2 mm and up to 200 MPa pressure was used in this study. Commonly used industrial safety helmets were cut in halves and then impacted with the jet at different angles, different stand-off distances, and different pressures. The helmet is made from fiber-reinforced plastics (FRP). Its thickness varies between 1.4 mm and 2.8 mm. The face shield was simulated with 2 mm thick acrylic resin plates. The time from the jet exiting the nozzle till penetration was recorded with a hand-operated stop watch. Jetting was stopped after 30 seconds if no penetration occurred.

The results are summarized as follows:

• No penetration occurred on the helmet within 30 seconds of impact if the jet is 200 mm away, shotting at the front of the helmet, and the pressure is below 40 MPa.
• Penetration occurred 100% on the helmet within 30 seconds of impact if the jet is only 100 mm away, shotting at the front of the helmet, and the pressure is above 100 MPa.
• When the pressure reached 200 MPa, the helmet was penetrated at the weakest spot within 30 seconds when the jet was at 350 mm or within 10 seconds when the jet was at 320 mm.  The helmet was not penetrated within 30 seconds when the jet was 410 mm or further away.
• The chance of penetration is higher if the jet hits the side (instead of front) of the helmet.

• The jet aiming at an angle (instead of perpendicular to the target surface) has a lower chance of penetration.
• The simulated face shield (2 mm thick acrylic resin plate) was not penetrated within 30 seconds under 200 MPa if the jet was 0.5 meter or further away. The plot to the right shows the safe distance at different pressures
  
  
  

Their conclusion was that the commercially available helmets and face shields are useful protective devices if the jet is kept at a suitable distance away.

* Katakura, H. and Guo, C. (2006) Research on personal protective devices for water jetting operation --- performance of head and face protectors, Proceedings of the 8^th Pacific Rim International Conference on Water Jet Technology, Oct. 10-12, Qingdao, China, Paper 42.