I’d play it in the safe side, however, I have heard in the game I play “Trench Warfare” that they didn’t install gas because of war crimes in World War 1 pertaining to gas but this may also fall to real-life tragedy according to the Terms of Use. As for that, in full honesty, I have never seen a game in Roblox which actually “gases” someone, and depicting as the character perishing in-game. As for your case, however, it still depicts some sort of violence and may fall unto this according to my interpretation of the Terms of Use even when the person does not perish and only goes unconscious.
Violent Content and Gore
17+ experiences on Roblox may include graphic and realistic-looking depictions of violence and heavy bloodshed, but we do not allow content that contains extreme violence or serious physical or psychological abuse, including:
Animal abuse and torture
Real-world depictions of extreme gore, graphic violence, or death
The depiction, support, or glorification of war crimes or human rights violations, including torture
The depiction, support, or glorification of real-world mass shootings and/or terrorism
I believe however, you should take this seriously and preferably make the game 17+, just to be safe. However, your game may fall under the violation of “The depiction, support, or glorification of war crimes or human rights violations including torture”. In my opinion, they may moderate your game under the excuse of “torture” at least. Gassing in Roblox, as far as I’ve played in many games in its platform, have never seen such game even when its intention is to make someone unconscious. Not to also offend your work, but the room also looks like a gas chamber, which isn’t looking too good.
If you want kids to be able to play your game, try to make it less disturbing and less scary, if you want to be 100% certain that it won’t get taken down.
But if your game is meant to be scary and disturbing, set it to 13+