The Douma chemical attack was an incident that took place on 7 April 2018 in the Syrian city of Douma that reportedly killed at least 70 people.  Reports from the area claimed that a mixture of chlorine (as used in swimming pools ) and sarin was used in the attack.  These social media rumours about sarin use were dispelled by the Organization for the Prohibition of Chemical weapons (OPCW) interim report, published on 6 June 2018, which found no evidnce of sarin or nerve agents. It further admitted they ‘cannot confidently determine whether or not a specific chemical was used as a weapon’. 
Robert Fisk investigated the site of the alleged attack on 16th April and visited the clinic where the video of casualties was taken. Fisk interviewed Dr. Assim Rahaibani from the clinic who claimed the victims were suffering from oxygen starvation & dust inhalation, not poison gas. He claimed that a member of the White Helmets started a panic by shouting "gas" and then recorded the video. Fisk also interviewed civillians in the area and could find no witnesses or evidence of the attack. 
On April 26, Russian and Syrian officials brought 15 Syrians, including Hassan Diab to an OPCW news conference in the Hague who said they had not seen any evidence of chemical weapons being used. 
Eva Bartlett has interviewed Marwan Jaber, a medical student about life under Jaysh al-Islam , who controlled Douma at the time of the attack. He claimed that strangers with video cameras and masks came to an area where regular injuries were being treated and started shouting about chemicals. Jaber confirmed that he witnessed no symptoms of chemical poisoning and saying of Hassan Diab, "if there was a chemical attack, he wouldn't be alive." He also remarked that the strangers that "nobody recognized" who took the video "didn't know medicine" and emphasized his consideration that "they didn't even finish sixth or ninth grade education".