Toxic fumes and smoke from a fire involving up to 100 tons of lithium-ion batteries prompted emergency services to set up an evacuation order for up to 4,000 people from the area.
Firefighters in Illinois, US, battled for more than three days to bring the fire involving around 180,000 to 200,000 pounds of lithium batteries under control.
The lithium-ion batteries, ranging from mobile phone to SLI sized, were reportedly around three feet deep, covering an area of about 30 feet by 40 feet.
Exploding lithium batteries inside the building prompted fire officials to let the blaze burn out because they feared that trying to extinguish it could trigger more explosions, reported the Star Tribune newspaper.
Crews initially used water on the blaze before realising the batteries were inside the building. They then used more than 1,000 pounds of dry chemical Purple-K cement powder, and pumped 28 tons of dry Portland cement to cover a "trouble spot" of burning batteries.
Two federal agencies were involved: the US Environmental Protection Agency and FEMA headquarters in Washington DC.
Speaking at the time, fire chief Tracey Steffes from the Morris Fire Protection & Ambulance District, said: “We were advised that we're dealing with between 80 and 100 tons of lithium batteries- so around 180,000 pounds to 200,000 pounds of lithium batteries.
"These batteries range in size from your cell phone to a little bigger than a car battery and as these batteries get wet, they short out and they ignite and explode. And that's the problem we're having. So we started our initial attack with water, and then we learned very quickly that that was not going to be a good avenue for extinguishment for this fire."
"The biggest hazard we have is the smoke and fumes as well as the gas from the fire. Highly poisonous and very deadly."