(Fakeedit: Slightly ninjaed, it seems. So I'll add that 'sleeping gas' is a crapshoot. Remember the Dubrovka Theater siege?)
Completely different situation. Theater full of innocent bystanders vs small appartment with no innocents left unevacuated.
Also, the agent used in the Dubrovka theater isn't the only gas in existance. There's all kinds of gas that will incapacitate yet have less death risk.
Well, apartment with who-knows-what ventilation issues, including shared ducts all over the complex, necessitating even more evacuation than they likely did already. Not sure what degree of evacuation they used, but if any, it was probably as minimal as possible (bearing in mind the likelihood of explosives, but at the same time not wanting to give substantial forewarning to those in the flat). Probably the immediate neighbours (inc. above and below) would get a quiet knock before first-contact, but if they did more before they alerted the group concerned I'd be surprised.
And ask an anaesthetist about their job. It's a preciously fine line between not-sedated-enough and sedated-to-death, that they have to ride. And that's one individual, fully monitored, directly connected to the mixed-gas line that they control. There's probably better gasses, but not one that is a guaranteed 'phaser on stun setting' whilst being harmless in all
1 effects.
Noting that IANASiegeSpecialist, and IANAnaesthetist neither, but I'm going by what I know as gained from reliable sources that are, thus my confidence. New(er) information could change my opinions.
1 Non-physical, i.e. discounting falling badly.