The effects of using chlorine as a weapon
Syrian government forces have been accused of injuring 80 people by dropping chlorine bombs on Sukkari, a district of Aleppo.
Chlorine attacks usually come in the form of a "barrel bomb" - often an oil drum, gas cylinder or other improvised container - filled with chlorine.
The use of chemical weapons is illegal.
In 2013, Syria signed the Chemical Weapons Convention (CWC) and agreed to the destruction of its chemical weapons.
It's not the first time in recent years that Syria has been suspected of using chemical attacks.
They were also investigated in August over reports of another attack on Aleppo which killed four people.
Chlorine attacks your respiratory system, eyes and skin
Small amounts can cause irritation to your skin and eyes but more prolonged exposure can result in chemical burns.
That's just if it touches you - the effects of inhalation can be even worse.
Very low levels will irritate your airway, perhaps giving you a sore throat.
This is what is likely to happen if you are using chlorine products to clean your house.
But the amounts used in chlorine bombs can cause choking and breathing problems.
That could eventually result in noncardiogenic pulmonary edema, which is basically fluid on the lungs.
If it's really bad, it can be fatal.
The 1925 Geneva Protocol banned the use in war of asphyxiating, poisonous or other gases
Since the 1920s, the Chemicals Weapons Convention has been adopted and is overseen by the Organisation for the Prohibition of Chemical Weapons (OPCW).
The OPCW's aim is for all countries to commit to a world free of chemical weapons.
Syria is a member of the OPCW.
The organisation said in January that "Veolia, the US firm contracted by the OPCW to dispose of part of the Syrian chemical weapons stockpile, has completed disposal of 75 cylinders of hydrogen fluoride at its facility in Texas".
"This completes destruction of all chemical weapons declared by the Syrian Arab Republic."
And talking about the attacks in August, it said: "These reports are of great concern.
"The OPCW continues to examine any credible reports it receives including pertinent information that might be shared by States Parties to the Chemical Weapons Convention."
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