You will have to have the definition of "harmless" in terms of your country's juridiction (the ethics law), if any. Since the publisher requires an ethics clearance, you should inform from the publisher their acceptable ethics authority, who will access your "harmless" data.
Your university's ethical board is obliged to give you permission for your research. You need to state that your participants gave their informed consent to take part in the research, that they knew that they could discontinue their participation at any point without consequences and that their completed questionnaires were anonymously and confidentially handled and used only for the research purpose in question. ---If you do not have an ethical board ask permission from the leading person.
If your university does not have an institutional review board / research ethics board, you need to find out what your national body is and ask them for guidance. Presumably someone who has published in similar journals would be able to help you.
Oftentimes, the author of the paper is not the best person to view what a "simple" data collection is "harmless". This needs to be evaluated by an institutional review board (IRB) or similar body in your university to determine whether or not it is "minimal risk" study. The determination of whether a study is "minimal risk" or not is a decision made by the institutional review board (IRB).
Dennis Mazur is largely correct, although there is often an intermediary administrative officer who can make a preliminary decision as to whether a proposed survey or similar data collection actually warrants an evaluation by the review board or whether the proposal has been adequately described for evaluation. This intermediary may either deem that (1) no action is necessary and let the survey proceed, (2) request more information or clarification, or (3) pass the proposal on to the review board.