Sisko told O'Brien to maintain light duty and specifically told him he didn't want him crawling about any Jefferies tubes. The crew was on a Cardassian built space station though and wouldn't have any Jefferies tubes.
"Jefferies tube" is a Starfleet term for maintenance conduits that run throughout a starship, DS9 has plenty of maintenance conduits so technically the station does have Jefferies tubes.
Miles O'Brien is shown wearing 1 dark pip on his collar, pips are for commission officers and he's a senior enlisted member.