It's probably gas...
A few too many refried bean burritos, a couple of tequila shots, and suddenly the ISS is full of lethal levels of methane. Far safer to wait until everyone stops pretending to be a booster rocket out their exhaust nozzles and _then_ send them up for the intended mission.
Nobody enjoys sharing an enclosed space (station) with a bunch of windy-arsed gits asking others to pull their finger...
