Examples of class 1 cooking are burger joints, breakfast places, french fry shops, etc. Essentially this is the typical kitchen that you see across North America.

Any time you cook raw meat or fry vegetables, eggs, etc you are class 1 cooking.  For a more detailed explanation: https://vancouver.ca/files/cov/2007-005-kitchen-ventilation-systems-commercial-type-cooking-operations.pdf

This installation requires a CLASS 1 Hood with wet chemical fire suppression, welded black iron duct that is liquid tight, kitchen exhaust fan and make-up air unit.