i've used a company named Precision Air Technology based in Raleigh, NC. Make sure whatever testing agency you use, uses an IR gas analzyer with a 0-20,000 cc/min sampling rate (usually set to match the isokenetic tidal volume of the average worker 15,000 cc/min). Do not use any testing companies that use the Qualtek leak detector, as their results will not stand up should you ever go to court with a worker exposure issue.
Also test as hard as you can and fail/eliminate any fume hood that doesn't meet your spillage rate at the "abuse" condition (normally full sash open).
