It was dusk when the chain of explosions began, feeding a towering fireball that would force the evacuation of 30,000 locals and send 1,200 firefighters scrambling to the arms depot situated outside the central Ukrainian town of Kalynivka.
Miraculously, when the dust settled the next day it was revealed that only two people had been injured, and the facility that stored more than 200,000 tons of munitions no longer posed an immediate threat to the community.
But concerns about Ukraine's aging Soviet-era ammunition depots didn't go away after residents returned. Blasts have been reported at four ammo dumps in Ukraine in the past two years, raising fears about the stability of munitions, security, and sabotage as Kyiv continues to wage war with Russia-backed separatists in the east of the country.
More than a week after the dramatic events of September 26-27, Ukraine is still coming to grips with the scale of the Kalynivka explosion.
According to Ukrainian media reports, some 32,000 metric tons of artillery shells worth $800 million were destroyed in the chain of fires and explosions at the site.
By comparison, Ukrainian forces are estimated to have used some 24,000 metric tons of munitions during the fighting in eastern Ukraine.
Kyiv classified the incident as sabotage.
A presidential adviser, Yuriy Biriukov, suggested on Facebook that a drone could have been used to touch off the explosions, noting: "We are at war."
It was eerily similar to a blast and blaze in March at another ammo dump in the town of Balaklia, near the city of Kharkiv.
Oleksandr Turchynov, the secretary of Ukraine's Security and Defense Council, said on September 28 that the two incidents together had dealt the deadliest blow to Ukraine's combat capability since the conflict with separatists in the east erupted in early 2014.
Over that time, Kyiv has blamed "saboteurs" for most of the incidents involving arms depots, suggesting Russia-backed separatists or Moscow itself.
Russia has longed denied playing any role in the conflict in eastern Ukraine, despite strong evidence to the contrary. Kyiv has provided no conclusive proof that any of the mishaps were directly caused by drones or other outside forces.
With skies overhead unguarded, the depots are seen as tantalizing targets for drones.
"On a number of occasions, starting in October 2015, incendiary drone attacks have been identified as taking place against Ukrainian arms depots as a component of Russian linked antimateriel operations," says Dr. Robert J. Bunker of the U.S. Army War College.
Ukraine's domestic intelligence service, the SBU, believes that a drone carrying a Russian thermite hand grenade caused the explosions at the Balaklia arms depot in March.
Some 70,000 metric tons of munitions were destroyed in the incident, with one person killed amid damage estimated at some $1 billion.
Balaklia, reported to be one of the world's largest ammunition dumps, had also been targeted in December 2015, when small drones were reported to have dropped 14 grenades on the site. The fire was put out by Ukrainian soldiers, and one grenade, a Russian ZMG-1, was recovered.
"This type of grenade would easily burn through such a facility roof with the hot molten, still-burning thermite mixture then igniting whatever cases of munitions that it came in contact with, setting off explosions throughout an arms depot," explains Bunker.
Situation 'Far From Ideal'
It wasn't the first suspected drone strike on an ammo dump in Ukraine. In October 2015, an attack on such a site near the town of Svatovo destroyed some 3,500 metric tons of explosives and damaged 1,700 nearby homes.
Biryukov has noted that explosions have not taken place where ammunition was stored in warehouses or bunkers.
Despite the heightened risk, Kyiv has been slow to react to upgrade security at the sites, many still stockpiled with obsolete weapons dating back to the Soviet era.
"The situation in Ukraine is far from ideal. The country had over a million tons of ammunition left over from the Cold War and Ukraine's military still doesn't understand it is not an asset, but a liability," said a senior UN weapons inspector who requested anonymity out of concern that revealing his identity could compromise his work.
Accidents at Ukraine's arms depots predate the current conflict.
Between 2003 and 2011, there were 10 "incidents" in Ukraine that left 22 dead and 111 injured, according to the Small Arms Survey.
Propellant used in projectiles is the main risk, according to the UN arms expert.
"It is inherently unstable. It reacts quickly. What they do to make it safe to store is that they add in stabilizers. But stabilizer over time is used up as it interacts with propellant. Once gone, it is a 'scientific inevitability' the propellant will eventually ignite. That sets off a chain reaction, leading to shells being set off, very rapidly, sending shells out, some as far as 20 kilometers out," the UN expert explains.
Mishaps Common Across Ex-U.S.S.R.
With Ukraine lacking proper storage facilities in some cases, some crates of ammunition are simply left out in the open, ratcheting up the risk of an accident.
"For many years, ammunition has been stored outdoors. This just doesn't make sense," says military expert Mikhail Zhirokhov.
Outside of some fencing, Kalynivka lacks other security systems, a problem common at Ukrainian ammo depots.
"Barbed wire, electrified fencing, camera surveillance, motion cameras, motion sensors; all these systems should be used," said Vadym Kodachigov, the president of the Association of Arms Manufacturers and Military Equipment of Ukraine.
Mishaps at ammunition sites across the former Soviet space are unfortunately all too common, according to the UN expert.
"You see 20 or 30 a year. Eventually it will stop when there are no shells left to react. In that time, how many lives will be lost?"
In June 2009, an arms depot on the outskirts of the Kazakh city of Almaty witnessed a series of late night explosions. One soldier was killed and dozens of civilians had to be evacuated.
In July 2008, an explosion at a military depot in Kogon, Uzbekistan, killed at least three people and injured 21.
In Samara, Russia, in 2013 more than 6,000 people were evacuated after a series of massive explosions at an arms depot. Since then, few similar disasters have been reported in the official Russian media. And that's not necessarily because Russia has cleaned up its arms depots.
"The [Russian] Ministry of Defense has tried to stop any inconvenient reports from getting out," explains Ruslan Leviev from the military think tank Conflict Intelligence Team.https://citeam.org/"Moreover, what has been written off in Russia [obsolete arms] now go to the Donbas [in eastern Ukraine] and Syria."
With material from RFE/RL's Ukrainian Service