A more thorough explanation:

An inevitable accident is an occurrence that could not have been avoided by any reasonable precautions or foresight. It is an unintended and unforeseen injurious occurrence that does not occur in the usual course of events or that could not be reasonably anticipated.

For example, accidents resulting from lightning or storms, perils of the sea, inundations or earthquakes, or sudden illness or death are considered inevitable accidents. These accidents cannot be prevented by human skill or reasonable foresight, and they are produced by an irresistible physical cause.

Another example of an inevitable accident is when, in the act that precedes an injury, something unforeseen or unusual occurs that produces the injury. The injury results through accident, and it is not attributable to mistake, negligence, neglect, or misconduct.

It is important to note that an inevitable accident is different from a culpable accident. A culpable accident is an accident due to negligence, and it is not a defense except in those few cases in which wrongful intent is the exclusive and necessary basis for liability.