Work on the James Webb Space Telescope takes place in the largest cleanroom of NASA's Goddard Space Flight Center. Cleanrooms are like operating rooms in hospitals--pristine areas kept as free of contaminants as possible, since even one speck of dust or an oily fingerprint could severely damage the observatory's sensitive components and instruments. Scientists and engineers who work in cleanrooms have to wear sterile bodysuits, head covers, gloves, boots, and face masks. At the same time, the ventilation systems of Goddard's largest cleanroom circulates nearly 1 million cubic feet of air each minute through 9,000 square feet of filters located along one wall. This provides the cleanroom with a Class-10,000 rating, meaning that any cubic foot of air contains no more than 10,000 particles larger than a half-micron (that's about 200 times narrower than a human hair). Air typically has millions of such particles.