We know this about the substance that is said to be behind the explosion

• For a few years now, the highly explosive material in the form of the substance ammonium nitrate has been stored in Beirut's port area, according to Lebanon's security chief Abbas Ibrahim.

• The substance is most often used in mineral fertilizers, also called artificial fertilizers. It is used in large quantities in Sweden to fertilize forests or fields as it quickly dissolves in moisture, which means that nitrogen is released. In addition, it is used as an explosive in, for example, mining.

According to the Swedish Civil Contingencies Agency, ammonium nitrate should never be stored so that it can be exposed to fire or mixed with combustible substances, as it would then become an explosive.

• The substance has caused several explosion accidents, especially if it has been exposed to a large external fire, the authority writes. At the same time, according to explosives expert Henric Östmark at the Swedish Defense Research Agency FOI, it is not flammable at all, but on the contrary "very difficult to speed up".

The decomposition formed by ammonium nitrate is, according to Henric Östmark, gases that are brownish red in color - which indicates that the substance may have been involved in the explosion in Beirut. At the same time, white smoke appears later in the pictures, which may indicate other subjects.

• According to Henric Östmark, the rapid course of events indicates that something triggered the large explosion - as other explosions with ammonium nitrate have taken a longer course. According to him, this could be due to the fact that it was not pure ammonium nitrate that was present at the site, that other chemicals were stored there or that the ammonium nitrate was mixed.

Ammonium nitrate has been used in the manufacture of bombs. Among other things, the one used in the bombing in Oklahoma city in 1995, when Anders Behring Breivik carried out his terrorist attack in Oslo in 2011 - and in Sweden's first suicide bombing in 2010.

"If the figure given by the Lebanese Prime Minister is correct, that 2750 tons of ammonium nitrate were stored in the port, then the explosion is larger than the one that occurred in 1947 in Texas City where 500 people lost their lives, writes British The Guardian.

• Exactly what started the explosion is unclear. Security sources tell Reuters that this may be a welding job in the warehouse.