Not sure what the purpose of going outside would be, though, other than for maintenance, given you'd be 50km up in the clouds.
Plus makes emergency procedures for leaks MUCH cheaper - light emergency ponchos and masks, and just walk over to the next sealed building.
I'm assuming you mean sealed buildings inside the blimps here, because you'd have nowhere to walk to on the outside on account of being 50km above ground. In which case you probably wouldn't need anything in the case of a leak.