During the first week of school, I welcome my students to the What Not To Do Lab. The PDF is available for free at the Laboratory Safety Institute website. I use the cartoon activity to review their Safety Contract handout from the night before (I use the one from FLINN Scientific). With more than 30 safety violations shown, the cartoon serves as a great ice breaker as I have each student introduce themselves and then list a safety infraction being shown on the cartoon.
This can be completed easily within a 50 min class period.