NNSA spokesman Steven Wyatt confirmed that the accidental discharge of a firearm at the Y-12 nuclear weapons plant occurred shortly after midnight, around 12:15 a.m. That means that the mishap occurred on the anniversary of the plant’s worst-ever security breach, adding another stinger to the ongoing saga.

The National Nuclear Security Administration has not revealed how the incident occurred or how two security police officers were injured. The guards were treated at the site with first-aid and later at the local hospital, where the guards were treated and released. The injuries were described as minor.

Wyatt would not confirm what type of weapon was accidentally discharged. Here is a list of the weapons used by Y-12 security officers, according to information released in a procurement document last year.