There are two types of Transportation of Dangerous Goods (TDG) certificate. One TDG certificate is for transportation by air, and the other TDG certificate is for all other forms of transportation. When students take the online TDG course, they will be asked to select whether they need the certificate for air transportation or other forms of transportation.
The TDG certificate for air transportation expires after 2 years. The TDG certificate for the other forms of transportation expires after 3 years. The certificate needs to be signed by the employer in order for it to be valid.
If a student changes employer, the certificate signed by the former employer will become invalid (even though the expiration date has not been reached). The student will then have to complete a new TDG course and get a new certificate.