Fume hoods are a central component in most laboratories. Whether designing a new laboratory or renovating an existing one, architects are challenged to incorporate safety, reliability and sustainability. These same issues hold true for laboratory managers when thinking about updating their existing equipment. Traditional ducted fume hoods are no longer the status quo, however. Changes in fume hood technology now give architects and managers more options when choosing fume hoods.
The most commonly used fume hood type is the ducted hood and its derivatives. The ductless fume hood has been used since 1968 with great success for specific, known and predictable chemical handlings. A relatively new category is the filtered fume hood which, while lacking a duct, safely retains a broader range and combination of chemical handlings and provides superior monitoring, safety alarms and communication.
Each category of fume hood contributes to safety, reliability and sustainability in different ways and to differing levels. New technologies provide the means of addressing tomorrow’s laboratory design requirements while safely reducing initial and operational costs. Furthermore, new technologies can reduce the effort, complexity and time of designing and constructing laboratories.
Ducted fume hoods
Traditionally, ducted fume hoods have been considered an effective means of protection for laboratory personnel. They require fairly straightforward pre-verification of the chemicals intended for use, for example, typical wet chemistry, perchloric acid, acid digestion and radioisotopes. Prior to installation, though, extensive engineering studies are necessary to determine proper rooftop ventilation and ductwork requirements, as well as the make-up air system necessary to compensate for the air consumed by ducted fume hoods. Since ducted workstations are tied into the building’s fixed exhaust system, they are rendered immobile.
Reliability is high with ducted fume hoods and their associated mechanical equipment, provided that preventative maintenance is performed on a periodic basis. Complex and expensive variable air volume (VAV) control systems are required to enable energy savings while maintaining user safety.
Ducted fume hoods are large consumers of energy. Although, with today’s level of sophistication, ducted fume hoods have allowed for improvements in regard to reducing the amount of air exhausted into the atmosphere. Redesigned sash openings, restricted openings during use and better containment at lower face velocities have all contributed to energy savings. However, the consumption of heated and cooled make-up air is still relatively high and is the driving factor in energy consumption for laboratories with higher hood densities. For example, a 6-foot hood with the sash vertically open 18 inches will exhaust 37,200 cubic feet per hour (cfh) even with a reduced face velocity of 80 feet per minute (fpm). Considering the high percentage of fossil fuel used in generating electricity, resulting in tons of carbon dioxide, it becomes clear that a more comprehensive and effective global solution to achieve green buildings is necessary.
Ductless fume hoods
A ductless hood is an enclosure fitted with filter technology designed for specific and dedicated applications, for example dilution, transfers or prep work. There is a known, predictable use of small quantities of chemicals which are easily reviewed and a filter type is chosen based upon those chemicals.
Ductless filtering fume hoods have been around for about 40 years and were inspired by the activated carbon technology found in modern gas masks. Ductless fume hoods use the properties of activated carbon combined with catalysts and certain neutralizers in order to filter toxic molecules, therefore, eliminating their dependency upon HVAC as well as external ductwork. Since no ductwork is required, a non-ducted filtered hood eliminates the direct discharge of pollutants into the atmosphere and therefore contributes to the protection of the environment. Ductless fume hoods do not consume any air since they filter and recycle purified air back into the laboratory. Furthermore, ductless hoods do not generate any pollution linked to energy use, unlike a traditional ducted fume hood.
The filter selection process should include a thorough validation review by the manufacturer to determine which specific filter can handle the application and provide the longest life. There are many filter types to choose from and it’s imperative to review each manufacturer’s guide of retained chemicals or chemical listings. It’s also important to make sure that the chemicals used are retained by the filter under the various conditions set by AFNOR NFX 15-211 standard. Filters have a “lifetime”, so filter saturation detection methods need to be provided by the manufacturer.
The filters need to be changed once saturation has been approached or reached. This maintenance effort is straightforward, handled within the operator work zone and requires minimal training. The cost for replacement filters and the disposal of used filters is usually more than offset by the energy saved by not requiring additional costly make-up air. Typical energy savings are two to three times the total filter replacement costs.
Finally, since no advanced planning is required, ductless fume enclosures are immediately available for use—without the necessity of having excessive installation costs. Mobility is inherent with this design as only electrical power and bench top space are required to relocate the ductless hood.
Filtered fume hoods
A filtered fume hood provides the benefits of both ducted and ductless fume hoods in one unit, along with the ability to provide safety and sustainability. The filtration, detection and communication technology in a filtered fume hood allows it to be safely used in a broader range of applications typically served by ducted fume hoods. Filtered fume hoods use advanced filtration media that is capable of capturing a wider range of acids, solvents and bases simultaneously. This enhanced filtration enables the use of one filter type for all applications, simplifying selection and replacement.
In addition, filtered fume hoods use enhanced sensing technology for detection of chemical breakthrough of the primary filter. This automatic filter saturation detection, and all other operating parameters and safety alarms, can be communicated to EH&S and facilities departments via Ethernet, BACnet or other communication protocols. Meanwhile, as detailed in AFNOR NFX 15-211 standard, Class 1 filtered fume hoods have a second layer of filtration offering a safety reserve for use when the primary filter is saturated and a replacement filter is being scheduled.
Filtered fume hoods can replace many conventional ducted fume hoods, while ductless fume hoods remain as a limited-application product. The sustainability of both filtered and ductless fume hoods is very high, as no additional make-up air is required. The safety of filtered fume hoods is enhanced by automatic saturation detection.
As an essential part of user safety, responsible manufacturers should offer assessments and precautions for anyone contemplating the use of filtered or ductless fume hoods. These assessments should include independent third-party testing, comprehensive chemicals lists—those approved and not approved—and individual application review for safety and financial viability. Only then can a recommendation be made for the selection of the most appropriate unit. After installation, there should be a program in place to constantly monitor the unit for the user so that they can focus on their work and not the fume hood.