Ghouls may or may not breathe at all, I'd say it depends on how they SURGE, what new modifications they end up with. However, any other test subjects should breathe just like any normal person. I will stick with the inhalation vector just to make things easier, and to give you guys the option of the gas grenades.
As to your successes, Gilga, your architecture knowledge will remind you that hospitals do have robust ventilation, and possibly more importantly, either filtration or ejection systems to keep disease from spreading. It's likely the gas will never reach the rest of the hospital as it is either scrubbed through filtration, our ends up getting jettisoned out an upper floor to become inert. Chemical side, you will know about neuro sun VIII, and will be able to caution everyone about the time it takes to go inert, also the possibility of it lingering slightly longer if in a small room with poor ventilation. And finally, for security, you don't think up anything new security wise.