Here is an official statement regarding the fact that Britney stopped the 'Circus Tour' for 30 mins... as there was Marijuana Smoke around the stage :
Britney's Camp : "We want to apologize to all the fans who attended our Vancouver show tonight for the brief pause in Britney’s set. Crew members above the stage became ill due to a ventilation issue."
PerezHilton.com : "Sources told Perez it really was a safety issue. “We were concerned for the lighting guys and everyone else working on the show.” If one of those guys up above got dizzy or sick from all that marijuana smoke….it wouldn’t have been pretty."