BELLE, W.Va. (AP) — An aging hose, corrosion and a pressure buildup are responsible for a phosgene leak at a DuPont chemical plant in West Virginia that resulted in the death of one worker in January, the company said Thursday.

The leak was the latest in a weeklong series of leaks to hit the sprawling Belle plant in late January. The phosgene unit has remained off line since the leak, and a second unit involved in a separate leak has been permanently closed as part of a business decision, DuPont said.

All other units at the plant, located east of Charleston, have resumed production.

Fifty-eight-year-old Carl Fish died in a Charleston hospital a day after being exposed to phosgene. The 32-year DuPont employee had entered the phosgene building to take a reading when the line failed.

Phosgene is used to make plastics and pesticides, and can damage the respiratory system. The chemical was used as a weapon during World War I and caused the large majority of deaths from gas warfare in that conflict, the Centers for Disease Control said on its Web site.

"Our investigation concluded that several factors combined to cause the hose to fail, including the length of time the hose was in service, physical corrosion concealed by the manufacturer's label, and pressure buildup in the line," the company said in a prepared statement.

DuPont's findings were submitted to the U.S. Environmental Protection Agency. The U.S. Chemical Safety Board and the federal Occupational Safety and Health Administration are also investigating.

The company also said it had submitted reports on the release of 2,000 pounds of methyl chloride and 22 pounds of a sulfuric acid solution.

Officials earlier reported that the hazardous methyl chloride leaked for five days before the leak was discovered. DuPont said the leak was caused by a ruptured disk. A ruptured line was cited as the cause of the sulfuric acid solution leak.

DuPont said it has taken steps to improve its emergency actions, including a dedicated telephone line to Kanawha County emergency officials.