Air Force says Osan munitions residue was corrosion, not white phosphorus

The Air Force has reversed its initial assessment of residue discovered in a munitions storage area at Osan Air Base, saying laboratory testing found no white phosphorus and determined the material was nonhazardous corrosion.

“Following thorough inspection and testing, we can confirm that the crystallization and residue identified during a routine munitions inspection on July 28, 2026, was not white phosphorus nor contained traces of white phosphorus,” the 51st Fighter Wing said in a news release Thursday.

“After follow-on analysis, we are confident that the residue was non-hazardous surface corrosion resulting from environmental exposure over time,” the wing said.

The residue was discovered during a routine inspection and was initially described by the wing as white phosphorus, a hazardous substance used in some munitions that can ignite when exposed to air.

The area was cordoned off and explosive ordnance disposal personnel responded to evaluate the material, wing spokesman Master Sgt. Eric Flores said at the time. The amount discovered was not disclosed.

The initial response also triggered emergency notifications on and off the installation.

The base alert sent at 5:08 p.m. through the AtHoc emergency notification system was “incorrect,” Flores said previously.

Pyeongtaek city issued its own emergency message at 5:37 p.m., advising those near the base to evacuate and others to take precautions. The city withdrew the alert 37 minutes later.

Flores said at the time that the public was not in danger and that no base-wide or off-base evacuation was required.

Emergency responders acted immediately “using layered protection protocols to ensure full containment of the munitions,” according to Thursday’s release.

No injuries were reported, and base operations continued normally, the wing said.

“Safety is paramount, and we care deeply about the well-being of our service members, their families, and our Pyeongtaek neighbors,” wing commander Col. Ryan Ley said in the release.

“We appreciate the city’s close partnership in keeping our community safe, and we thank everyone for their patience as our team worked to resolve this situation,” he said.