What designation is given to a fire when the cause cannot be determined?

When a fire's cause cannot be determined, it is designated as an "undetermined fire." This classification is critical in fire investigation, as it indicates that investigators were unable to find sufficient evidence to ascertain how or why the fire started. Such a designation is often a result of a lack of physical evidence, completely destroyed materials, or conflicting findings that do not lead to a clear cause.

In contrast, a natural fire usually refers to fires caused by natural events, such as lightning strikes or wildfires. An intentional fire is one that is deliberately set, often associated with criminal activity, while an explosion represents a sudden release of energy that often leads to a fire but is a different phenomenon entirely. Understanding these classifications helps in accurately reporting and analyzing fire incidents within the framework of fire science and investigation.