After the Second Battle of Hoover Dam, samples were recovered from the Sierra Madre by NCR researchers for purpose as a weapon against the Republic's enemies, but by unknown means was unwittingly release over the greater portion of the Core Region and Mojave Wasteland.
Sierra Madre Cloud (Presumably SM-0)
By 2281 the Cloud released from the Sierra Madre's ventilation systems had engulfed the Casino to the point of blocking out the sun.
An unknown chemical compound smelling and tasting of copper, sulfur, and plastic, it killed many of the Casino's inhabitants and transformed those in hazmat suits into the ghost people. Whatever its nature, the Cloud is a corrosive compound, slowly deteriorating both organic and inorganic matter, which makes gas masks, environmental suits, and power armor ineffective protection.
The Ghost People were Sierra Madre staff trapped in their hazmat suit when the Cloud eroded the suit clasps. Slow exposure to the toxin mutated them, their bodies trapped within their suits and forced to adapt into a stiffening entity composed of pockets of pressurized gas, glowing green fluid, and tissue that seemingly draws nourishment from the Cloud.
A variant of the Cloud designed by NCR scientists in the early 2280's, SM-5 is a more potent alteration of the Sierra Madre toxin.
It kills its victims and corrodes more quickly than the SM strain, as a result none of the Sierra Madre Ghost People are encountered in the Mojave.
Rather those who survive in hazmat suits become creatures analogous to feral ghouls, albeit with a higher degree of intelligence.
Locations and areas affected by or involved with the SM-5 Cloud
- Goodsprings (Possibly linked to the cloud)
- The Boneyard (Was cleared from The Cloud sometime after)
- The Lucky 38
- The Strip