We recommend using the NFPA 70E Tables if you have no study. This should be a "preliminary" plan until a study could be completed. If there are table parameters which are known to be unmet (fault current, clearing time, equipment condition) you may wish to use a higher level of PPE.
Our IEEE paper indicated that out of 40 incidents the Tables worked every time unless there was an "oil filled" equipment explosion or part of the PPE was removed.
D. R. Doan, E. Hoagland and T. Neal, "Update of field analysis of arc flash incidents, PPE protective performance and related worker injuries," 2010 IEEE IAS Electrical Safety Workshop, Memphis, TN, 2010, pp. 80-87.