SpaceflightMemes

I don't remember NASA mentioning anything like that - either at the briefing I've just come across, or any other time they've talked about it.

So my guess is that they didn't bother. Just hoping that whatever could cause the crew to have to return to Earth in a hurry wouldn't also cause any problems with the cabin air in Dragon. (Problems like ... there not being any! Or it being filled with smoke, or ammonia.)

Perhaps they would've gone with your plan if they'd had all the necessary equipment.