The Quantum Vapor was stored in canisters near the docks in Dakota, which became the sight of a large gang war. When the police attempted to quell the fighting, a tear gas canister accidentally hit the canisters, causing a cloud of the vapor to overtake not only the gangbangers, but others nearby as well.
The vapor caused mutations and transformations in those exposed, causing them to become what were termed as "Bang Babies".
Some time later, Edwin Junior studied and modified a large sample of it, fashioning a suit with bubbles full of it that he could burst at will, granting him a different power with each one.
Several years later, Doctor Donald Todd had finally managed to discover a cure for the vapor and had begun spraying it into the atmosphere, causing several metahumans to begin losing their powers. Desperate not to be nothing again like he was before the Big Bang and enraged in the abandonment of his oldest ally, Talon, Ebon teamed up with Hotstreak and several other Bang Babies to steal a vapor sample and recreate the Big Bang once more. Unfortunately, the plan backfired, and Hotstreak stole the gas for himself. Ebon pursued him and the two fought, setting off the gas. Ebon and Hotstreak absorbed too much of the gas, fusing together into an abominable two-headed monster, which possessed both of their powers.
The Quantum Vapor—so named in "Junior"—is based on Quantum Juice of Milestone Media comics. In order to fight gang violence, Alva and the mayor had ordered to spike tear gas with a radioactive tracer in the hope that it would track gang members. The side-effects of said tracer were that it killed a majority of the people involved in the Big Bang, although many survived and were given metahuman powers.