The members of Firehouse 51 are almost always in danger that "Chicago Fire" fans heartily welcome any quiet, happy moments. Unfortunately, those moments are short on the ground next episode as 51 try to save one of their own.

The previous episode saw Casey (Jesse Spencer) telling off Susan Weller (Lauren Stamile) when he realized that she was the one who caused trouble for him and Dawson (Monica Raymund). Brett (Kara Killmer) also put her foot down and convinced "Chicago P.D.'s" Det. Antonio Dawson (Jon Seda) to give their burgeoning attraction a chance.

Casey might have been able to keep Louis safe with him and Dawson, but it's the Alderman himself who'll be in need of saving next episode. It would seem that in episode 4, the lieutenant will find himself in a bad situation when a forklift accidentally pierces a tank filled with acid, trapping Casey and several others in the warehouse he was inspecting as part of his Alderman duties. With the fumes threatening to overcome them, Casey has to use extreme measures to survive. On a lighter note, Mouch (Christian Stolte) and Brett continue to work on their secret project, while Otis (Yuri Sardarov) receives exciting news as he prepares for an unusual expedition.

The trailer for the upcoming episode, "Nobody Else Is Dying Today," gives viewers a look into Casey's dire situation. The clip begins with a shot of acid pouring out from the tank and Casey instructing the others that they have to get away from the fumes. The Alderman and several people later barricade themselves in a room. But despite their efforts to keep the area sealed, the fumes are still coming in. The clip ends with Casey trying to smash through the wall using a fire extinguisher.

Episode 4's title is comforting enough for fans, as it hints that no one is dying and photos from the episode suggests that 51 will be doing everything they can to save Casey. However, it doesn't mean that he will come out of the incident unscathed.

Episode 4 of "Chicago Fire" season 5 is set to be aired on Nov. 1 at 10 p.m.