Hydrogen gas is explosive within the given range of 4% - 75% v/v. Assuming that each student in your class produces 6L of H2 and that the lab is not ventilated, is there a danger of an explosion?

I think the answer is Yes, because the Gas could goes to their respiratory system and the explosion could cause a fire. You have to take precaution next time the students will have a laboratory and should wear proper attire or uniform for safety