In the plant's control room, Penrice's workers watch crystals form on the outside of a vacuum-drum filter.

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The building had tested negative three times previously for anthrax, but workers from the Centers for Disease Control and Prevention used a special vacuum with a filter developed to detect even the most minute amounts of the deadly bacteria.

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Self-contained vacuum, pump and filter system works without suction lines or other modifications to existing systems.

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Just like the filter in a vacuum cleaner, however, the trap must be cleaned periodically.

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