At BMA (DC-9 15 series) at LHR we could disembark, and board if the jetty was on the front door when fuel was going on. (fuel was going on as soon as the aircraft arrived on stand sometimes)
Cannot recall what we did if front air-stairs only were down as the -15 had no ventral stairs, but the -32 series did have them so fuelling whilst boarding was OK.
Viscount and 707 was OK if we had 2 sets of steps put on (On the front and rear doors)
Ground Oily was always around dealing with the Shell chaps, Despatcher/Traffic guy/girl was aware, and FD crew were on board or doing a walk around. CC were on board too.
Pax PA's were made - no smoking allowed - of course!
Bit of nostalgia for you....