“About half of the fume hoods we ship are customized in one way or another,” says Chip Diefendorf, director of business development at Mott Manufacturing (Brantford, ON).
Physical dimensions are the number one modification specified by Mott’s customers. “They want them taller, wider, shallower, or deeper to accommodate whatever is going on inside,” Diefendorf adds. Some dimensional modifications are minor—for example, shaving an inch off a five-foot-wide hood so it will fit into an area 59 inches wide.
The next most common request involves the amount and type of see-through area used in the sash. Clear, laminated safety glass is by far the most frequently used material, and it is most often configured for the full height and width of the sash. But some customers request a smaller viewing area or colored glass. Purchasers who work with hydrofluoric acid, which etches glass, might request see-through polycarbonate.
Standard fume hoods feature a modest array of electric outlets, a small sink, a house vacuum, and house nitrogen. All may be upgraded—for example, to higher voltage, for accessing vacuum pumps below the hood floor or for introducing specialty gases from generators.
Less common modifications include location flexibility and accommodation for disabled workers.
Moveable hoods are part of the trend toward flexible lab configurations. These units tend to be smaller than fixed-location hoods and they require either flexible utility lines or multiple-location access to water, gas, exhaust, etc., which adds a great deal of cost to lab design.
Some lab directors specify that hoods comply with Americans with Disabilities Act workplace design specifications. Mott, for example, sells hoods with flexible service connections, including exhaust, that allow raising and lowering the hood as needed.
Flow, explosion proofing
Beth Mettlach, sales engineer at Labconco (Kansas City, MO), says customers frequently specify airflow monitors. One would think this feature would be standard, as the American National Standard for Laboratory Ventilation ANSI/AIHA Z9.5-2003 3.3.3 states that “All hoods shall be equipped with a flow indicator, flow alarm, or face velocity alarm indicator to alert users to improper exhaust airflow.” Yet the extremely popular variableair- volume fume hoods already have monitors built in. “Having a built-in monitor would add unnecessary costs for those customers,” Mettlach says.
Many customers already own airflow monitors; even handheld thermal anemometers satisfy regulations and industry best practices.
Another popular customization is explosion proofing, which consists of removing all potential sources of sparks—for example, from electrical switches. Interestingly, fireproofing protects not the inside of the fume hood but the lab where it resides. The National Fire Protection Agency (NFPA), through its NFPA 45-2015 Fire Safety in Research Laboratories directive, states that due to the high influx of room air “… chemical fume hood interiors shall be considered as unclassified electrically …” Unless, of course, an unusual hazard is identified.
“The room is electrically rated, not the fume hood,” Mettlach stresses. “It’s a common misconception among lab managers that if they’re working with flammable substances inside a hood, they need explosion proofing.”
NFPA goes to significant lengths to explain lab explosion hazards. In practical terms, storage or manipulation of large quantities of flammable liquids within the lab environment is sufficient. If your facility’s environmental safety team designates a lab as an explosion hazard and you’re installing a hood, it should be of the explosion-proof variety.
For additional resources on fume hoods, including useful articles and a list of manufacturers, visit www.labmanager.com/fume-hood