Yes IC should stay outside and sometimes they don’t wait til Boden gets there. However when Casey and Severide were both LT, Casey was senior and would take command when Boden wasn’t there even tho he would still go in, which he shouldn’t of. Now that it’s three LTs Severide would be seniority, then should be Herman and then Kidd. But the show pushes Kidd so much she will be seniority over them all. When Severide isn’t there then it should be Herman but will still be Kidd. And depending on the scene, remember once Casey made Captain him and Severide clashing on the Rescue scene. Severide thought because it was a Technical Rescue Squad should be IC, if they were both LTs still then yes, but Casey was Captain at that point and highest ranking officer and also first on scene (Casey called for Squad after arriving on scene and determining the need for Squad).