For any scenario, proceed in order: (1) Which fast was being kept? (2) What exactly happened? (3) What was the intent and circumstance—forgetfulness, involuntary event, or deliberate action? (4) What consequence does the source prescribe—validity, qaḍāʾ, or both qaḍāʾ and kaffārah?
For example, “the person vomited” is insufficient information. Was it involuntary or induced, and was it a mouthful? The qualifications change the case.