Mcdonalds Gas Leak

Carbon Dioxide used to carbonate pop at a mcdonalds in va was leaked in to the womens resstroom. 10 people were sickened from it and 1 woman died the next day. I dont understand why they do not have detectors in there store. I also dont get how no one noticed it had been leaking for 2 days i would think someone would have complained about their pop being flat.