A 2019 pipeline explosion that resulted in one death and the destruction of five homes in Kentucky happened when the pipeline ruptured and released natural gas caught fire, the National Transportation Safety Board said Wednesday.

Fourteen other homes were damaged as the fire burned about 30 acres (12 hectares) in Lincoln County, the NTSB said.

The 30-inch pipeline, owned and operated by Enbridge Inc., had a preexisting manufacturing defect known as a hard spot, the agency said. That combined with a degraded pipeline coating and ineffective cathodic protection led to cracking induced by hydrogen at the outer surface, the NTSB said.

Cathodic protection prevents corrosion where the coating has been damaged, according to the agency.

The NTSB said Enbridge’s integrity management program did not accurately assess the pipeline condition or estimate risk, contributing to the accident.

The NTSB issued safety recommendations to the Pipeline and Hazardous Materials Safety Administration and Enbridge Inc. The safety recommendations address topics including incomplete evaluation of risks, incomplete assessment of threats and missed training opportunities.

Enbridge pipelines carry about one-quarter of the crude oil produced in North America and one-fifth of the natural gas used in the U.S. Several of its pipelines have been the subjects of lengthy legal and political fights and two of the largest inland oil spills in U.S. history.