In North Carolina, authorities asked more than 6,500 residents of Winston-Salem to remain away from their homes for a second straight night as fire crews battled a blaze at a fertilizer plant that threatened to ignite a massive explosion. Fire officials said the plant had about 600 tons of highly explosive ammonium nitrate fertilizer stored on site. That’s nearly triple the amount that exploded at a West, Texas, plant in 2013, killing 15 people and damaging 200 homes. This is Winston-Salem Fire Chief Trey Mayo.

Trey Mayo: “Somebody who has spent many decades in the fire service texted me earlier and said this is potentially the largest explosion in U.S. history.”

Fire officials said the fertilizer plant did not have a sprinkler system or alarm in the building where the fire broke out. North Carolina building codes allowed the 80-year-old plant to operate without the safety systems in place because the plant was built before 1953, when sprinklers were first required.