The proton peak flux (in pfu) of the SEP events in the SEP part of the database for E > 10 MeV (A) and E > 100 MeV (B), as a function of the SXR rise time (in minutes). The vertical dashed black line, in both (A) and (B), indicates a rise time of 18 min. The horizontal black line highlights a threshold of 10 and 1 pfu for E > 10 MeV and E > 100 MeV, respectively. (C), (D) SEP occurrence probabilities and their respective errors as a function of the NOAA radiation storm scales. Different symbols are used for each quadrant in (A) and (B), (see text for details).