Sticks of white phosphorus have to be kept submerged to prevent them igniting
There has been concern that Israel has been using controversial white phosphorus shells during its offensive in Gaza. Doctors in Gaza have reported treating dozens of patients with unusually deadly burns. White phosphorus can have serious, long-term effects on health.
How does white phosphorus cause harm?
In its solid form, white phosphorus burns on contact with oxygen and can reach temperatures of 800C.
As a gas, phosphorus smoke can react with water to form a powerful acid.
What are the effects on the body?
If particles of white phosphorus land on the body, they burn through clothing and stick to the skin, scorching through layer after layer of tissue until their supply of oxygen is cut off.
Even when it is not burning, the chemical effects of phosphorus can be absorbed deeper into the body causing multiple organ failure.
Different patients react in different ways - some will die from a small burn others will survive.
Doctors in Gaza have said patients with 15% burns have surprised them by dying.
How do doctors treat these burns?
Alan Kay, a military burns specialist for the British Association of Aesthetic Plastic Surgeons says the main thing is to keep the burn site wet.
"You keep the wound wet, keeping oxygen away from it. But it not only causes very dangerous heat burns, it also causes chemical problems."
"The key is to surgically remove all the phosphorous particles. To see even the ones not visible to the naked eye you use ultraviolet light which makes the phosphorus glow."
"Some of the chemical effects induced by the phosphorus cause a derangement of the normal physiology of the patient which can have lethal consequences."
He said patients who survive are treated like victims of normal burns. They are given skin grafts and intense monitoring of their heart and the levels of certain chemicals in their blood.
What are the effects of long-term exposure?
This was common in the past in workers in industries which used phosphorus in their processes.
Reports from the 1920s say workers in fireworks factories were prone to a condition known as 'phossy jaw'. Their accidental ingestion of phosphorus led to tooth abscesses and dead tissue in their jaw bones which eventually killed them through blood poisoning.