SANTA FE, N.M. (AP) — Federal officials are investigating the Los Alamos National Laboratory after an employee was involved in an incident described as a "near-miss to a fatality."

A worker entered a lab room that had insufficient oxygen despite an alarm sounding. The September incident was characterized as potentially deadly and a violation of building requirements and emergency response protocol, according to a letter sent last week to the outgoing lab director by the Department of Energy's Office of Enforcement.

No workers were injured during the incident, lab spokesman Matt Nerzig said in...