Immediately under the roof and its trusses are the exhaust ducts. These pipes draw contaminated air from the floor below. Most often, the "contamination" consists of acid fumes or undesirable organic solvents.
At one time, exhaust was simply sent up tall smokestacks. Instead, in this modern plant, exhaust is piped to the towers on both sides of the building. These towers contain "scrubbers" that trap or neutralize harmful chemicals.
