Barrett et al. (2013) distinguish between accidental/unauthorised, inadvertent, and deliberate nuclear launches or detonations:
"In an accidental or unauthorized launch or detonation, system safeguards or procedures to maintain control over nuclear weapons fail in such a way that a nuclear weapon or missile launches or explodes without direction from leaders."
"In an inadvertent detonation, the attacking nation mistakenly concludes that it is under nuclear attack and launches one or more nuclear weapons in what it believes is a counterattack."
In a deliberate detonation, the attacking nation decides to launch one or more nuclear weapons either in response to a genuine nuclear attack or without believing that it is under nuclear attack.
The only non-test nuclear weapons to date, by the US in 1945, were both deliberate. But a future nuclear conflict could in theory begin with any of those three types of detonations, which could then be followed by detonations from the same or other types.
Will there be at least one fatality due to inadvertent nuclear detonation by 2024?
This question will resolve positively if, before January 1, 2024, an inadvertent detonation by a state, as defined above, results in at least one fatality. Detonations by non-state actors will not count towards positive resolution of this question.
The fatality must be caused by the immediate effects of the detonation, so a fatality caused by things like fallout, rioting, or climate effects will not count towards a positive resolution.
Resolution criteria will be gathered from reliable news sources or from direct government or multi-national reports such as from the UN. If information is unclear, then resolution will be left up to the resolution council or Metaculus admins.