What are the legal duties of a First Aider in Ontario?

According to the Good Samaritan Act in Ontario, Canada, if you are qualified in First Aid you do not have the legal obligation to assist an injured person. For example, you pass by a car accident on the highway, this is when you would not be obligated. However if you are a teacher in a school, you would be required to provide help. In addition, even if you injury a person while giving first aid, for example, breaking the ribs when doing CPR, you are free from any liable damages and can not be sued.