Israel Allegedly Used White Phosphorus Munitions in Gaza and Lebanon. Here’s What to Know

White phosphorus is a particularly incendiary weapon. When exposed to the air, the chemical ignites, creating flames that burn as hot as 1499°F. The thick smoke it produces can serve as a handy obscurant for militaries. But for the civilians on whom it rains down, it can cause severe fires and deep burns that go down to the bone.

On Thursday, Human Rights Watch accused Israel of using white phosphorus munitions in its ongoing military operations in Gaza and Lebanon. The allegations, which HRW based on verified video and witness accounts from Oct. 10 and 11, have been rejected by Israel’s military as “unequivocally false.”

Israel has previously been accused of using white phosphorus on a civilian population. During the 2008-9 war in Gaza, dubbed Operation Cast Lead, the Israeli military admitted to having used munitions containing the toxic agent on Gaza, but denied that doing so contravened its legal obligations. While it is considered legally legitimate to use white phosphorus as a smokescreen or for signaling, international law forbids its use in populated areas. In a place like Gaza, one of the world’s most densely-populated places, such areas are difficult, if not impossible, to avoid.

Omar Shakir, the Israel and Palestine director at Human Rights Watch, spoke with TIME by phone to discuss how they verified the allegations, the effect white phosphorus has, and what its use means for the millions of people living in Gaza.

TIME: This is not the first time Human Rights Watch has accused Israel of using white phosphorus, is it?

Omar Shakir: Yes, so Human Rights Watch has documented the Israeli armed forces’ use of white phosphorus in previous conflicts in Gaza, including in 2009. And actually, there has been some litigation in the Israeli court system, all the way up to the High Court of Justice. The military said it would no longer use white phosphorus in populated areas, except in two narrow situations, which were not specified.

It’s been used in previous conflicts, but certainly not in the most recent several conflicts we've seen in the last few years.

Can you walk us through HRW’s process of verifying that white phosphorus was used?

We’ve been closely monitoring [the situation in Gaza]. We have a team on the ground, we have teams that are reviewing social media, that are doing interviews. So we had a several-step process. The first thing that we did, when we saw the videos, was to run it by our munitions experts. Some of the videos we had seen were not conclusive enough for us to make a claim.

For the one on Gaza Port and the ones in Lebanon, our munitions experts were able to make a conclusive assessment that it was white phosphorus, but we still needed two things: one was verifying the authenticity of the video, so we have a digital investigations lab that went through the process of authenticating the time and the date and the location; we were able to get GPS coordinates based on that process for the locations. The other was, in Gaza, we wanted to be able to speak to people who were in the area and might have been able to experience what it looked like, smelled like, et cetera. So we were able to get in touch with two people who were in the area and whose account of what they experienced were consistent with where white phosphorus was used.

Those were the three steps: our specialized team of experts on munitions reviewing the video footage, authenticating the location and the time of the video, and then speaking to witnesses in the affected area who provided an account based on the questions we asked. We’ve done this work in other contexts, which allowed us to confirm that what was experienced was consistent with what we saw in the verified videos.

What exactly does white phosphorus do?

White phosphorus has multiple uses. It can be used for essentially signaling, obscuring, or marking. Or it can be used as a weapon that burns people and objects. But the main thing is it has an incendiary effect. Basically, what happens is it ignites when exposed to atmospheric oxygen and continues to burn until it’s deprived of oxygen or exhausted. It can create heat that goes up to 800°+ Celsius, or like 1500° 

Fahrenheit. It creates light and smoke. And then upon contact, it can burn people thermally and chemically down to the bone, as it’s highly soluble in fat and therefore in human flesh. So it can exacerbate wounds, even after treatment. It can enter the bloodstream, it can cause organ failures. Even dressed wounds can reignite when dressings are removed and it’s exposed again to oxygen. Even minor burns can be fatal. And it can create long-term suffering because of scarring and physical disabilities. And that’s not even to mention the trauma of all of it.

It can also burn structures, not just individuals. So you can have a situation where it burns homes, fields, civilian objects.

In a statement to the Washington Post, the Israeli military said that it is “currently not aware of the use of weapons containing white phosphorus in Gaza.” What do you make of that denial?

Weapons containing white phosphorus. Implicit in it is almost an admission of sorts, because white phosphorus can also, as I said, be used for signaling, obscuring—not necessarily as a weapon. The wording of their statement is done carefully.

Let’s say Israel was using white phosphorus within its legal capabilities, as it claims to have done in 2009. Is it possible, in a place such as Gaza, to use it safely?

No. In populated areas, it should be banned without exceptions. I mean, Gaza is one of the most densely populated areas on Earth. There are no safe places in Gaza. The other thing to note is there are readily-available, non-lethal alternatives to white phosphorus smoke shells, including some that are produced by Israeli companies, which the Israeli army has used in the past. They have the same effect and dramatically reduce the harm to civilians. So there really is no justification for using it in densely-populated areas.

How does the use of white phosphorus stack up against the other serious challenges affecting people in Gaza right now?

Obviously this raises significant legal issues, but there are many other issues also that are taking place, including the cutting of electricity, food, and water. The dire humanitarian situation, the dropping of thousands of bombs on Gaza's population and wiping out buildings, neighborhoods, the wiping out of families. Israel has a long track record of targeting civilian infrastructure, of disproportionate and indiscriminate attacks.

There has been significant attention in the media and otherwise to this publication, which is important. But it's also important to understand that there are many other issues taking place at the same time.

This interview has been edited for style and length.