Is the frequency a factor in the spl?I would think so, Stfoth, to some degree. That would seem likely based on the fact that (as you can see in the figure at the upper right of the Wikipedia page on "Equal Loudness Contour") our hearing mechanisms are most sensitive in the area of 3 to 4 kHz or so, while being considerably less sensitive at deep bass frequencies.
So it wouldn’t surprise me if an organization such as OSHA has developed standards for maximum SPL exposure which take frequency into account, but if so I have no specific knowledge of them.
Best regards,
-- Al