All of the following factors are considered as safety measures in X-ray production except:
The optimal operating potential of dental X-ray units is between 60 and 70 kVp (ADA 2012). Although image diagnosis may be improved slightly with increased image contrast (low kVp) images, the patient dose is reduced with higher kVp exposures.
White and Pharoah's Oral  Radiology Principles and Interpretation 8th edition
Use of low kVp is recommended
Use of lead foil is mandatory
Use of high kVp is recommended
None of the above