Beirut Blast Was Among History’s Largest Accidental Explosions

The explosion, fueled by 2,750 tons of ammonium nitrate abandoned in Beirut’s port, wounded 6,000 people and killed about 200

A map of Beirut before the explosion shows the locations of videos analyzed in the new study
To qualify for use in the study, videos of the explosion needed to have known locations and include a line of site to the warehouse. Courtesy of Shock Waves

On August 4, about 2,750 tons of ammonium nitrate exploded in the port of Lebanon’s capital, Beirut. Now, new research gives a clearer picture of the size of the blast, George Dvorsky reports for Gizmodo.

The explosion’s force makes it the sixth-largest accidental, non-nuclear explosion in history, reports Gizmodo. The largest ever accidental explosion occurred in 1917, when two ships—one carrying TNT and other explosives—collided near Halifax, Nova Scotia. The blast killed about 1,800 people and shattered windows 50 miles away. The largest non-nuclear, human-caused intentional explosion was a mock-up test of future nuclear blasts. Dubbed “Minor Scale,” the test blast had the power of about 3,500 tons of TNT, per BBC News' Jonathan Amos and Paul Rincon.

The blast shattered windows around the capital, destroyed three neighborhoods, killed about 200 people and injured thousands more. Engineering researchers at the University of Sheffield estimate that the explosion had a force equivalent to between 550 and 1,200 tons of TNT, according to research published in the journal Shock Waves. The researchers carefully selected 16 videos of the disaster and analyzed them using known rules about how explosions and shock waves move.

"When we know what the yield is from these sorts of events, we can then work out the loading that comes from that,” University of Sheffield engineer Sam Rigby, who works with the Blast and Impact Engineering Research Group, tells BBC News. “And that tells us how to construct buildings that are more resilient.”

Thousands of tons of ammonium nitrate had been sitting in Beirut’s port for six years, Prime Minister Hassan Diab said after the explosion, reported Austin Ramzy and Elian Peltier for the New York Times. The cargo was first abandoned on a ship that sat in the city’s port, but it was later moved to a warehouse nearby, which was the site of the August explosion.

Ammonium nitrate is used in fertilizers, and it's also used in quarrying and mining operations as an explosive, Reuters reported in August. It can be stored safely, but when contaminated, mixed with fuel, or exposed to intense heat, ammonium nitrate can explode. Ammonium nitrate fumes created the white smoke seen in videos of the explosion’s aftermath, toxic nitrous oxide formed the red and brown smoke, as chemist Stewart Walker of Flinders University in South Australia, told Reuters.

The new research uses videos of the explosion to visualize a timeline of how the shockwave moved across the city. To qualify for the study, videos needed to meet certain criteria. They needed to show a clear line of sight to the warehouse; begin before the explosion and continue filming until after the shockwave passed; include recognizable landmarks as well as the exact location that the video was filmed from; and have synchronized audio and video, per Gizmodo.

The researchers used Google Earth to map the distance from the site of the explosion to the locations where each video was recorded. Then, by using known laws of how explosions and shockwaves move through the environment, the team worked backwards to figure out how powerful the blast was. They found that in just milliseconds, the explosion released about one gigawatt-hour of energy—enough to power around 100 homes for a year, according to a statement.

The explosion was also as powerful as between 550 and 1,200 tons of TNT, which is lower than the team originally estimated.

"The Beirut explosion is interesting because it sits almost directly in a sort of no-man's land between the largest conventional weapons and nuclear weapons," Rigby tells BBC News. "It was about 10 times bigger than the biggest conventional weapon, and 10 to 20 times smaller than the early nuclear weapons.”

Gizmodo reports that in the future, the new study could be used by first responders to anticipate injuries or structural damage that may result from similar disasters.

"Beirut's certainly the most powerful non-nuclear explosion of the 21st century,” Rigby tells BBC News.

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