What is preferable when handling toxic gases—a ductless filtering fume enclosure or ducted fumehood? Truthfully, it is impossible to give an answer in favor of either concept without objectively analyzing the disadvantages and advantages of both systems. It is also impossible to give an answer without prior knowledge of the intended usage. Therefore, to help make a qualified decision, it is important to examine how and where the hood will be used. Equally as important will be to determine what will happen within the hood and how each hood type affects its environment. Objectively analyzing the disadvantages and advantages of both systems requires exact knowledge of chemical usage and project type. Only once the usage scenario has been clearly established can a decision be made in favor of using either system. Aside from helping make the right decision, the goal of this article is also to eliminate any preconceived negative notions against one system or the other so as to allow users to find the best solution in terms of environmental impact, cost, and adaptability of use, without losing sight of the fact that the solution retained should ultimately ensure their safety.
Ducted fumehoods
All laboratory personnel are knowledgeable about ducted fumehoods. In fact, the basic concept dates back to the Middle Ages, when the alchemists used the chimneys of their own homes to perform experiments. Since then this concept, which never ceased to evolve, has finally turned into the modern ducted fumehoods of today’s laboratories.
Ductless filtering fume enclosures
Far more recent, ductless filtering fume enclosures have only been around for about 40 years. Created in 1968, their technology is directly inspired from the activated carbon technology found in the modern gas mask. Today, ductless filtering fume enclosures use the properties of activated carbon combined with catalysts and certain neutralizers in order to filter toxic molecules, therefore eliminating their dependency on HVAC and the need to be connected to external ductwork.
Disadvantages and advantages of ducted fumehoods
Disadvantages
The installation of a ducted fumehood is complex. Extensive engineering studies are needed beforehand to determine proper rooftop ventilation and ductwork requirements along with the make-up air system that will be necessary to compensate for the air consumed by one or more fumehoods.
Since a ducted fumehood consumes more energy per year than an average house, the consumption of heated or cooled air is high and can represent for a modern fumehood an average of 20,000 ft3 (600 m3) per hour and per fumehood. Recently updated figures show that this energy consumption translates to an estimated average of $5600.00 per fumehood per year or $4.2 billion of energy required annually nationwide. (See official studies such as the Lawrence Berkeley National Laboratory Report on High-Performance Laboratory Fume Hood Field Test at the University of California, San Francisco. Final Report for Pacific Gas and Electric Company, Oct. 2001) and LBNL report on Energy Use and Savings Potential for Laboratory Fume Hoods, April 2006).
Lastly, their working principle forces ducted fumehoods to eject toxic substances directly into the atmosphere, and their fixed nature and tie-in to the HVAC system render them immobile.
Advantages
Today, ducted fumehoods have reached a high level of sophistication with regard to saving the air exhausted into the atmosphere and containing the fumes around the work area. They do not require a preverification of the chemicals intended for use, aside from those prohibited by laws and regulations, which as of today do not limit ducted fumehoods on the amount of chemicals they can exhaust into the atmosphere.
Traditional fumehoods have been long recognized as an effective means of protection for laboratory personnel, although recently they have been identified as a large consumer of energy that cannot be ignored.
Disadvantages and advantages of ductless filtering fume enclosures
Disadvantages
The frame of use of a ductless filtering fume enclosure is limited to certain chemicals. This limitation can vary between manufacturers, which is why it is important to consult each manufacturer’s guide of retained chemicals or chemical listing. As an example, companies like ERLAB (North Andover, MA), a leading manufacturer of ductless filtering fume enclosures, publishes a listing of 600 chemicals.
There is a quantitative limitation of chemicals dependent on filter retention capacity. The allowable front sash opening available for handlings is limited by the volume of air treated and is directly linked to filter design. Again, this can vary between manufacturers. It is necessary to monitor filter saturation in case a reliable detector is not present. It is necessary as well to periodically replace the filter after saturation and determine the timeframe, which should be calculated by the manufacturer scientifically prior to the sale or when a procedure changes.
Advantages
(Important notice: The advantages described here are only valid if the manufacturer certifies that its ductless filtering fume enclosures are in compliance with the requirements of a serious standard developed by specialists in molecular filtration, ventilation, and general fumehood design and in collaboration with end users and industrial hygienists responsible for the publishing of official threshold limit values. This is, for example, the case of the very stringent NFX 15-211 standard, whose committee was made up of such recognized specialists.)
Ductless fumehoods do not consume any air since they filter and recycle the air back into the room in which they are set up. (Please note: If in compliance with the NFX 15-211 standard, the air exhausted by the ductless filtering fume enclosure is free of chemical substances and filtered at an efficiency level that is 100 times below official permissible exposure limits. This 100 times below the official permissible exposure limit concentration level is required since basic limit values are set for one chemical at a time and cannot be cumulated.)
Ductless filtering fume enclosures do not require rooftop exhaust ducts or make-up air systems since they recycle and filter the laboratory air at an average rate of 6000 ft3 per hour. Ductless filtering fume enclosures do not exhaust chemical pollutants into the atmosphere. They are mobile and can evolve along with their changing laboratory environment. Ductless filtering fume enclosures are immediately available for use without lengthy or costly installation requirements. They can be temporarily stored and dispatched where needed by a safety officer for a scheduled class or project and also be placed anywhere at a moment’s notice to protect users in cases in which the need suddenly arises.
A few important words of caution
The fact is that when an application falls within the intended frame of usage, as set by the manufacturer, one cannot help but be drawn to the advantages of a ductless filtering fume enclosure. However, it is very important at this moment to verify that the manufacturer has answered all of the necessary questions that must be asked prior to making a final decision, such as:
- Is the chemical or groups of chemicals I am using retained by the filter under the conditions set by a performance standard like the AFNOR NFX 15-211?
- If so, what will be the lifetime of the filter in relation to the frequency of my handlings and their evaporation rate?
- Will I have access to a reliable automatic filter saturation detector?
- If not, what will be the detection methods provided?
- Will the manufacturer provide me with a sustainable cost savings study concerning the advantages of using a ductless filtering fume enclosure over time comparing energy savings against filter replacement cost?
- Will the manufacturer keep me safe by offering services or programs that will monitor my application changes and preserve the intended usage of my ductless filtering fume enclosure?
- Finally, is the manufacturer willing to provide answers to these questions in writing?
If each and every one of these questions receives a positive response, one’s decision is documented and should now be easy to make. However, attention must be given to the fact that certain ductless filtering fume enclosure manufacturers do not hesitate to provide positive answers to all of these questions for the sole purpose of making a sale. It is therefore advisable to deal strictly with manufacturers that are able to show official proof of compliance with a performance standard like NFX 15-211 and that commit in writing to provide a ductless filtering fume enclosure that will comply with the answers of the aforementioned questions.
This indispensable precaution will help protect the buyer from certain companies involved in this emerging profession, which still needs more rigorous product design and sales approaches. Complying with a stringent safety standard can only benefit all parties involved and primarily guarantees the safety of end-users.
Conclusion
In the event that satisfactory responses cannot be provided to ensure the safe usage of a ductless filtering fume enclosure, a decision should certainly be made in favor of selecting a ducted fumehood. Without a doubt, safety must remain the first priority when making this decision. However, while ducted fumehoods have been the industry standard for containment of toxic gases for years, their tremendous infrastructure, usage, and environmental costs cannot be ignored any longer. At the same time, some ductless fumehood manufacturers have recently emerged with safety services and product evolutions, which, under the right circumstances, can provide a viable solution in the laboratory. In today’s world, the decision between the two styles needs to be made with a careful eye on safety, the environment, and energy consumption and a conclusion can be made that it is worthwhile to try and determine where both products have their place. Given the extreme rise in energy costs and the benefits of using green technologies, taking the time to figure out which system is best where, and determining the applications most suitable to each can have a significant impact on one’s budget and on the environment.
Mr. Hauville is President, ERLAB Inc. North America, ERLAB Group, One Elm Sq., 1980 Turnpike St., North Andover, MA 01845, U.S.A.; tel.: 800-964-4434; fax: 978-975-2730; e-mail: [email protected].