I think there's a lot of AT&T spin in this article, but it's interesting to see the issues they faced. In spite of the damage caused by the explosion, AT&T's systems continued to operate. It was several hours later, after the batteries were drained, that the system went down.
AT&T provides initial insights about FirstNet performance, recovery efforts after Nashville explosion – Urgent Comms
Some FirstNet subscribers experienced service outages after the massive Dec. 25 explosion at AT&T’s Nashville network hub, but backup battery power at the facility and the use of deployable cell sites meant that many FirstNet users were able to communicate “within hours,” according to AT&a...