A more thorough explanation:

An unavoidable accident is an event that cannot be prevented due to an irresistible physical cause that cannot be foreseen or prevented by human skill or reasonable 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.

Examples of unavoidable accidents include accidents resulting from lightning or storms, perils of the sea, inundations or earthquakes, or sudden illness or death. These events are beyond human control and cannot be prevented by any reasonable precautions.

For instance, if a driver is driving on the road and suddenly a tree falls on the car due to a storm, it is an unavoidable accident. The driver could not have foreseen or prevented the accident, and it was caused by an irresistible physical cause beyond human control.

Unavoidable accidents are different from culpable accidents, which are accidents due to negligence. A culpable accident is no defense except in those few cases in which wrongful intent is the exclusive and necessary basis for liability.