The blast, which Lebanese officials say was caused by 2,750 tons of ammonium nitrate in storage near the port, registered as a magnitude 3.3 earthquake, according to the U.S. Geological Survey.
Ammonium nitrate, also called AN, is a compound of ammonium and nitrogen that is used in agricultural fertilizer and explosives. Generally, AN can be relatively stable and is used in U.S. farming regularly, according to the Environmental Protection Agency. But contaminants and other trace material can make AN unstable. The volatile nature of the compound had led some governments to create strict policies when it comes to storing the material.
An undated photo verified by NBC News’ Social Newsgathering team, which has been circulating online following the blast, appears to show bags of ammonium nitrate stored inside a warehouse reportedly at the port. NBC News has reached out to port officials for confirmation but has not received a response.
Port of Beirut is a major port in the eastern Mediterranean and is considered a main gateway to the country. The port, which is owned by the Lebanese government, is managed by the head of the port, Hassan Koraytem, who is now under house arrest, according to local media reports.
Matthew Mulligan is a reporter for NBC News’ Social Newsgathering team based in London.