Joe Kennedy, commander's representative at HAAP, said explosives were detonated after coming in contact with a fire in the manufacturing area.
"The building that caught fire was constructed from wood framing," Kennedy noted. "It was a standard ranch home ... the sprinkler system was automatically engaged at the start of the fire. The building itself did not burn. The roof system caught fire and burned."
A trailer with about 2,500 pounds explosives in it caught fire from the roof, according to Kennedy. The detonation destroyed the trailer and burned some nearby wood barriers, he added.
But the area was safely evacuated, said Kennedy, and everything "operated as it was supposed to."
Production for those explosives resumed the following June, and the plant as a whole restarted by the end of January.
"(The explosion) is in the past and we are moving forward," said Col. Luis Ortiz, commander, Pine Bluff Arsenal. "We're as safe as we can be. Safety is our number one priority."
Spanning more than 6,000 acres in Kingsport, the HAAP is the major supplier of explosive materials (primarily RDX- and HMX-based products) to the U.S. Department of Defense.
BAE Systems, the plant's contractor, is in the process of modernizing the facility. Four new boilers will be central to a new gas-fired steam facility that will replace the existing coal-fired power supply. This modernization effort is one of many the Army and BAE Systems are undertaking that will reduce emissions associated with coal and significantly increase energy efficiency.
BAE Systems has been the operating contractor for HAAP since 1999.
What's the latest on open burning at the site?
As for open burning at the plant site, Kennedy announced the Army in the interim will divert waste from burning grounds to an onsite landfill. The long-term plan is to have a flashing furnace in place by the end of 2024.
Holston stretches more than 6,020 acres across two counties in Tennessee. There are over 450 buildings and storage magazines onsite. The plant has 107 miles of roads and 30 miles of railroads.