E-cigarette blows up in his face
US man in critical condition in hospital
She was lying in bed with her two-year-old child in their Florida home, when she heard a blast. Ms Ema Richardson also smelt smoke.
She left the room to find the source of the smoke, and was horrified by what she saw.
Her brother, Evan Spahlinger, was lying on the bedroom floor covered in soot, Mail Online reported.
The electronic cigarette he was smoking had blown up in his face.
The 21-year-old was taken to hospital and placed in a medically induced coma and is said to be in a critical condition.
Ms Richardson told local TV station Wink News: "I found my brother not breathing, with his whole face and neck burned. He was trying to throw up a little or maybe he was gasping for air."
She believed that Mr Spahlinger suffered internal and external burns, as well as damage to his lungs from the explosion and possibly the e-cigarette's mouthpiece.
She said when the cigarette exploded the mouthpiece went down his throat and possibly exploded again.
Mr Spahlinger was flown to a Miami hospital and on Tuesday and underwent cosmetic surgery, NBC 6 South Florida reported.
The explosion is being investigated. Authorities believe the explosion could have been caused by the e-cigarette's lithium battery.
Mr Spahlinger's family said they do not know what brand of e-cigarette he was using at the time of the blast.
Meanwhile, Ms Richardson said he told her that he will never smoke an e-cigarette again.
She said: "He said, 'I'm done, that's it'."
That's the only thing he told her after the incident, the New York Daily News reported.
Added Ms Richardson: "Luckily I was here. I think it was the most traumatic experience of my life."
Though rare, the explosion is not the first of its kind for the battery-powered device.
Earlier this month, a California woman was awarded nearly US$2 million (S$2.81m) after she was badly burned by an exploding e-cigarette in 2013.
Last year, a 65-year-old British grandmother was left fighting for her life after her oxygen supply blew up as she puffed on an e-cigarette.
That same month, a video captured an e-cigarette exploding in an English pub and nearly igniting a barmaid.
On Monday, the US Department of Transportation banned the battery-powered portable devices from all airline passengers' checked luggage because of past incidents of fire.
"Fire hazards in flight are particularly dangerous. Banning e-cigarettes from checked bags is a prudent safety measure," it said in a statement.
The rule still allows e-cigarettes in carry-on bags, but passengers cannot recharge the devices on the plane.