Insulation boards fitted to the outside of Grenfell Tower gave off highly toxic hydrogen cyanide gas which may have contributed to the deaths of some of the 79 confirmed victims.
Fire toxicity experts have told Sky News the insulation boards installed during a refurbishment of the tower produce the deadly gas when they burn, and their positioning meant every flat could have been filled with enough gas to kill those inside.
At least three of those injured in the fire have been treated with an antidote for hydrogen cyanide poisoning in hospital, and the number of those affected may be higher.
The gas could have incapacitated some residents, but establishing its role in the cause of death may be impossible because of the condition of the victims.
King's College Hospital confirmed to Sky News that three of the 12 patients it received from the fire were treated with the hydrogen cyanide antidote Cyanokit.
Four other hospital trusts declined to comment on the treatment administered to those injured in the fire.
An initial 68 patients were taken to six hospitals across London, with 18 receiving critical care and some put into induced comas to aid in the recovery of damaged airways.
As of Wednesday morning, 10 people were still being treated in four hospitals, six of them in critical care.