I work for an electric utility that has open air substations with voltages of 12kV to 345kV. We are currently re-evaluating our PPE requirements for arc flash hazards. The NFPA 70E requires a face shield at 1.2 cal/cm2 but the NESC does not require a face shield until 9 cal/cm2. What incident energy do you recommend a face shield be worn and why? Any thoughts on why the requirements are so different between NFPA 70E and NESC?