Unit 4 – Safety MarksBy Admin / December 8, 2014 You must first complete Unit 1 – Introduction to TDG before viewing this LessonPlease sign up for the course before starting the lesson. This unit examines the safety marks used with dangerous goods. Unit 3 - Classification of Dangerous Goods Unit 5 - Means of Containment Back to: Transportation of Dangerous Goods (TDG)