When handling chemicals, viral microbes, bacteria, and other potentially harmful substances, it is important to know whether the substance can become airborne. During the experimentation and research process, many chemical and biological agents have the potential to release droplets, fumes, or toxic vapors, which can be inhaled by lab personnel. 

While some chemical fumes may be harmless in small amounts, inhaling various chemicals day-in and day-out can have lasting effects, even if they are not immediately noticeable. Similarly, airborne viral droplets may be easy for the immune system to fight off, but researchers working with highly infectious agents may not be so lucky.

A fume hood is used to all but eliminate the risks associated with working with chemicals and viral compounds by drawing airborne droplets and fumes away from the lab environment and into a filtration system. Using suction, fume hoods collect potentially toxic vapors, directing them through a series of filtration systems before recirculating the air.

Labs are a risky environment. Between the sharp objects and beakers lined up in rows, workers have to constantly be aware of their surroundings. Personal protective equipment and other controls are part of what keep them safe, and fume hoods are no exception.

Fume hoods are an engineering control in labs, meaning they control the hazard. When scientists are working with dangerous materials that emit hazardous vapors, gas, and dust, a fume hood will move it away from their faces and out of the area through an exhaust system.

Without getting too deep into the weeds about the inner workings of the mechanism, it's essential that they are always in working order. Professionals should thoroughly inspect and document fume hoods on an annual basis. A quick visual inspection should be done every time it's used. If there is any suspicion that a fume hood is not working correctly, it's imperative to get in touch with someone ASAP.

No air flow. A quick way to check to see if there's air movement is to tape a piece of tissue to the sash. Turn on the hood. A tissue "flapping in the wind" is indicative of ample air movement - good news.

Weird noises. Occasionally, the fan or motor will need some TLC. Unusual noises are are good indicators to shut the hood down until it can be serviced.
Immediately tag the fume hood as "DO NOT USE" and contact the responsible party to get it repaired if any red flags arise.

Flow visualization consists of two tests known as local smoke and gross smoke. These names are self-explanatory in that the tester utilizes smoke to check for leaks, or cracks in the fume hood, structural defects, air flow inefficiency or other issues that may allow gas to escape. A smoke gun is used to perform this test but the gross smoke measurement is done on a macro level in which a smoke bomb is detonated in the middle of the fume hood. If any smoke escapes out of the front of the hood during either test, the fume hood will receive a "fail" rating and appropriate action must be taken to rectify it.

Face velocity is the measurement of air flow through the fume hood. Different fume hoods have face velocity specifications for ventilating gases and it's important that the fume hood maintain these levels. Otherwise, it's considered compromised and unsafe. This test is performed with the sash open 25%, 50% and 100% using a device that measures air flow at different place within the hood. Those readings are then compared to the manufacturer's specifications for that fume hood to ensure complete functionality.