Videos of fiery white smoke falling over the Azovstal has led many to speculate that Russia is using white phosphorus in its conflict against Ukraine.

White phosphorus is a self-igniting chemical that can burn at upwards of 4,800 degrees Fahrenheit once it makes contact with air and can cause horrific human injuries.

It has been used in conflicts across the world including, allegedly, by the U.S. army (article link contains graphic images).

The footage from Azovstal was quickly shared as evidence of the chemical's use on the besieged plant in Mariupol. However, some questioned whether the video really depicted the infamous munition.

On May 15, 2022, aerial footage shared on social media showed showering explosions of fiery white plumes igniting and settling over the Azovstal steel and iron works plant, from which several hundred Ukrainian soldiers were evacuated days later.

A translation of a Telegram post with more than 365,000 views, associated with the Mayor of Mariupol, said that "incendiary or phosphorus bombs" had been used.

Commentators on Twitter furthered claims white phosphorus was being used by Russia in the conflict.

Russia fired white phosphorus munitions in response to Kalush Orchestra's call to save Mariupol at the @Eurovision. These missiles are prohibited by international law. Cynically, Russian troops even signed these bombs with "Save Mariupol" and "Save Ukraine." pic.twitter.com/WQXesnZhjb

Russia trying everything they can to get to the brave #Azovstal defenders. Possible white phosphorus and cluster munitions. I still have lots of hope! The defenders have many advantages. God speed to them holding. Russia losing on many fronts. #SlavaUkraini #Mariupol https://t.co/PyQaZpw5ww

This is not the first time that Russia has been accused of using phosphorus bombs during the conflict in Ukraine.

In March 2022, Russia was said to have deployed it in the north suburbs of Kyiv (although this piece of footage has not been verified).

The same month, Ukrainian officials also alleged that Russia had deployed white phosphorus munitions in the eastern city of Kramatorsk.

The U.K.'s Ministry of Defense said in April 2022 that Russian forces had used it in the Donetsk Oblast region which it said "raises the possibility of their future employment in Mariupol as fighting for the city intensifies."

The Convention on Conventional Weapons (CCW) Protocol III carries a number of restrictions on the use of incendiary weapons in warfare.

In an article explaining the use of incendiary weapons, Humans Rights Watch (HMW) states that the protocol excludes multipurpose munitions that are "primarily designed" for other uses, such as marking, obscuring or signaling. This includes white phosphorus.

It also states that while the convention prohibits the use of air-dropped incendiary weapons in a concentration of civilians, it allows the use of ground-launched incendiary weapons in the same scenario where the military target is "clearly separated from the concentration of civilians and all feasible precautions are taken."

HMW says elsewhere: "White phosphorus munitions produce similarly cruel injuries to other incendiary weapons, despite falling outside CCW Protocol III's definition.

"White phosphorus can burn people to the bone, smolder inside the body, and reignite when bandages are removed."

While some accounts reported the munitions in the Azovstal video were white phosphorus, others claim it was another type of incendiary weapon.

Here you can once again see Russian 9M22S incendiary submunitions. (Thermite) #Azovstal ...It's not white phosphorus, like some people like to claim over and over again. #Ukraine️ #Russia #RussiaUkraineWar https://t.co/GmMgGV0tLx

Whether the video of Azovstal shows the use of white phosphorus is not entirely clear.

According to the U.S.' Centers for Disease Control and Prevention: "The military uses white phosphorus in various types of ammunition as an incendiary agent, because it spontaneously catches fire in air."

In the video, there appear to be ignitions in mid-air and on the ground.

Videos of its alleged use in other conflicts show only a white plume of smoke and no ignition, while others also show explosions in the air.

Newsweek spoke to experts at the U.K.'s Cranfield University, a provider of specialist defense education, to get their take on the video.

Jacqueline Akhavan, Professor of Explosive Chemistry and Director of Education for Cranfield Defence and Security, said: "It looks like white phosphorus because it is combusting in air and producing a white flame. There is not much smoke, which suggests that this is not a white smoke composition and therefore this may just be pure white phosphorous."

Trevor Lawrence, Director and Senior Lecturer in explosives and munitions at Cranfield Ordnance Test and Evaluation Centre, added: "It is possible that WP filled munitions could be initiated by a proximity or time fuse producing the in-air events seen in the video.

"From what I can see from the footage, it is quite likely that the substance deployed is white phosphorous, although I would have expected to see more smoke from a WP munition.

"It may be phosphorous, but it certainly is the deployment of an air-burst incendiary, whatever the type."

Rob Lee, a Russian defense policy specialist at King's College London, also posted the Azovstal video on Twitter, tweeting "Reportedly Russian 9M22S incendiary munitions from Grad MLRS being used on Azovstal."

According to a translation of the viral Telegram post, the Ukrainian soldiers holed up in the Azovstal steel plant said rockets similar to these were used in the attack.

In March 2022, a non-government think tank, the Ukrainian Military Center, assessed the type of munitions used in Popasna, in the Luhansk region of Ukraine. There photos showed explosions of white clouds with fiery fragments. Here, they concluded (based on rocket blueprints and similar attacks in 2014), the weaponry used was 9M22S projectiles.

Specialist technical intelligence consultancy Armament Research Services states 9M22S rockets are magnesium and thermite-based and can ignite fires in flammable military targets, such as fuel depots. It added that while white phosphorus can be used as an ignition source, it is most often used for marking and screening.

Lawrence agreed that it could be an alternative type of munition, adding: "The lack of a typical phosphorus smoke does support the possibility of a magnesium thermite.

"For the people underneath it is not really a great deal of difference. (It's) still nasty stuff.

"The delivery system would certainly fit with the footage."

Whatever munitions were used, the footage indicates that very likely a type of incendiary weapon is being deployed at the Azovstal plant. There is a clear argument that it could be white phosphorus, though it may well be another type of incendiary rocket.

Regardless, videos such as those of Azovstal highlight the opportunity for speculation, unverified information and misinformation to spread on social media during conflict.

The Russian Ministry of Defense was approached for comment.

The munitions used in the video have not been verified as white phosphorus. Experts say the video shows the use of an incendiary device. The composition of the explosion suggests that it could be white phosphorus, or potentially another type of incendiary explosive. While government sources outside of Ukraine and Russia have suggested Russian forces have used white phosphorus, videos alone are not sufficient evidence, particularly without additional verification. We rate this as half-true because experts say an incendiary explosive was used, and there is evidence suggesting it may be white phosphorus, but it could be another type of incendiary, such as thermite, and so further verification is needed.

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