This project takes about 90 minutes (or two 45 minute class periods); I used to assess the students understanding of a specific lab safety symbol. I had the students start the project in class after I was done explaining it; I then had them finish it up the next day in class. Since I usually assign this project the first week of school, I usually let them take it home and have it due the day after. I also love this project, because it lets the student be a kid again; the first week of middle school is scary, so why not relief some stress by coloring!
At my school we had a specific set of symbols we had to use; the best part of this project is that you can gear it towards whichever lab worksheet you must use.