Your best source for complete information on the NFPA 70E Standard is via the actual standard, available for purchase at www.nfpa.org. In 2000, the NFPA 70E Standard first addressed electric arc flash hazard and required flame resistant arc flash clothing to protect workers. The current edition of the NFPA 70E standard was released in 2012, and further details personal protective equipment.
Fluoride ions exist predominantly as hydrofluoric acid in acidic environments with a pH below 5.2. Fluoride ions corrode the glass. Therefore, the pH measurement with the glass electrode for a solution which includes fluoride ions is basically impossible. Although the useful life of the electrode may be shortened, however, the measurement with immersing the electrode in the sample for a given short time is possible.
Private water sources that have a pH level of less than 5.5 may corrode plumbing and appliances. The EPA mandates the pH of tap water to be a pH of at least 6.5 to prevent corrosion. Like the Richter scale for measuring earthquake intensity, the pH scale is logarithmic. A solution with a pH of 8.0 is ten times more alkaline than a solution with a pH of 7.0. A solution with a pH of 9.0 is 100 times more alkaline than a solution with a pH of 7.0.