Not a chance of there ever being safe standing in SS3, its too steep, and H&S would never allow it. SS2 will also go corporate when the NS is extended, so that won't be happening either.
@Prophet of Doom - An observation about acoustics, I normally sit in 315 (where the amazing Burnley and Bristol C fans have been located), and whilst the atmosphere varies, when its good, its good, and the proximity of the roof is the reason why, and from there we rarely hear the SS1 singers.
Against Burnley I was moved down into SS1, in the SW corner, and whilst I could hear the singing section, and see they were singing, even that close, the noise generated by them is not loud (no roof above), and they were completely drowned out by the away fans above.