7. Players Temporarily Suspended 7.1 When a Player is Temporarily Suspended, subject to clause 7.3, below, that Player must remain in the ‘sin bin’ area (as designated pursuant to clause 4.8.2 of the Championship Rules) for the duration of the Temporary Suspension. 7.2 A Temporarily Suspended Player may be given water and warm clothing while in the ‘sin bin’ area. If half-time occurs during the Temporary Suspension period, the Player may go to his Club’s dressing room but must return directly to the designated ‘sin bin’ area for the remaining period of his Temporary Suspension when the second half begins. 7.3 A one-minute warm-up period is permitted prior to the Temporarily Suspended Player returning to the Playing Area, in which the Player may leave the ‘sin bin’ area.
Found it eventually. its in the regulations of the relevant competition organisers in this case the URC