Although educational researchers will acknowledge that they have a moral imperative to avoid harming their participants whilst carrying out research, it does not necessarily mean that they can describe the nature of what this harm might be or how it can be recognised and so avoided. This is particularly important for those working with vulnerable participants, yet there is limited specificity within the educational literature as to what constitutes harm in such a setting. The article addresses this by de-constructing ethical dilemmas that arose during a research study that was carried out among adult students who had mental health problems, in England. The article outlines how these dilemmas were resolved safely due to preparation before the interviews; the 'ethical triage' employed in the interviews; and the reflexivity practised after the interviews. The article proposes that the issue of defining harm and how to recognise and avoid it, needs to be discussed more among educational researchers and those writing ethical guidelines, especially in relation to interviewing vulnerable participants. Not only will this help to better prepare researchers for when ethical dilemmas arise, but will also promote equity and access to participating in research, for those considered to be vulnerable.