The increasing improvement in efficiency of foul air treatment systems, which can often achieve 99.9 percent odor removal, is wasted unless the fugitive emissions are well contained and captured at the source. Off-site odors are recurrently the result of such fugitive or non-captured emissions. This paper presents a comparison of stack emissions versus area or fugitive source emissions, illustrated by air dispersion modeling examples. It then discusses current design guidelines for foul air containment and collection systems by including theoretical and practical examples on the following topics: • Building pressurization • Negative pressures in covered vessels • Exhaust hoods • Ventilation rates to meet design codes • Fan design • Materials of construction