First responders to chemical, biological, radiological, or nuclear (CBRN) events face decisions having significant human consequences. Some operational decisions are supported by standard operating procedures, yet these may not suffice for ethical decisions. Responders will be forced to weigh their options, factoring-in contextual peculiarities; they will require guidance on how they can approach novel (indeed unique) ethical problems: they need strategies for “on the spot” ethical decision making. The primary aim of this paper is to examine how first responders should (...) approach on the spot ethical decision-making amid the stress and uncertainty of a CBRN event. Drawing on the long-term professional CBRN experience of one of the authors, this paper sets out a series of practical ethical dilemmas potentially arising in the context of a large-scale chemical incident. We propose a broadly consequentialist approach to on the spot ethical decision-making, but one which incorporates ethical values and rights as “side-constraints”. (shrink)