Why does Preston give such a detailed description in the following lines?

"The gas penetrated the air ducts, soaked the offices, got into drawers in the desks, and got inside pencil sharpeners in the drawers. It infiltrated Xerox machines and worked its way inside personal computers and inside the cushions of chairs and fingered down into the floor drains until it touches pools of lingering bleach in the water traps." (356)