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Mitigating Health Risks with Laboratory Fume Hoods (Part III) : Ductless Fume Hood

Ductless Fume Hood, a Safe and Sustainable Solution

Traditional ducted fume hoods are no longer the only solution offered to laboratory. The development of filtration technology for the past 48 years now gives laboratory workers more options when choosing a new fume hood without compromising their safety.

Inspired by the activated carbon technology found in modern gas masks, a ductless fume hood is a vented enclosure fitted with filter cartridges designed to retain the chemical vapours handled inside. Ductless fume hood are therefore no more dependent form any external ductwork, auxiliary air supply systems, and can be easily installed anywhere on any existing work bench. Since no ductwork is required, a ductless fume hood eliminates the direct discharge of pollutants into the atmosphere, fully contributes to the protection of the environment and do not consume any laboratory air-conditioned air since it recycle the purified air back to the laboratory room.

In terms of safety, ductless fume hood is subjected to the same requirements as for conventional ducted fume hood in respect to air face velocity (between 0.4 – 0.6 m/s) and containment efficiency (below 0.05 ppm of SF6 tracer gas). Additionally, it shall also offer full guarantee at the filtration level to avoid any release of chemical into the laboratory room. The filtration efficiency of ductless fume hoods are ruled by International Safety Standards, such as the AFNOR NFX 15-211 (France), the SEFA 9 (USA), the JG/T385 (China), and DIN 12927 (Germany). These standards

establish specific performance criteria for the quality of the filtered air that a ductless fume hood can return into the laboratory room.

First, the concentration of a chemical downstream the filter shall not exceed more than 1% of the PEL-TWA of this chemical.

Secondly, the ductless fume hood manufacturer shall provide an exhaustive list of common chemical agents that he certifies can be manipulated in its ductless fume hood and indicating the retention capacity for each chemical at a filtration efficiency of 1% of the PEL-TWA of the chemicals.

Thirdly, a thorough chemical assessment must be conducted by the manufacturer with each user to ensure the filtration efficiency, to determine the most suitable filter (including filter lifespan), and to advise the most suitable filter saturation detection system to be employed.

Lastly, a certificate must be placed at the front of ductless fume hood unit after installation, mentioning the chemicals authorised to be used and the filter life.

Using a ductless fume hood requires discipline from the chemists. They must ensure that any chemical handling have been validated beforehand by the manufacturer and to follow operations as described in the initial assessment. On the other side, fume hood featuring filtration technology allows complete flexibility to laboratory workers since it can be installed anywhere in the laboratory and easily relocated. Ductless fume hood enclosures require no advance planning and are immediately available for use with almost no installation costs. Mobility is inherent with this design as only an electrical socket and adequate bench top space are required to locate the ductless fume hood.

Conclusion

Obtaining a good protection of the chemists in a laboratory requires a good understanding of the safety issues with chemical exposure, the safety criteria of fume hoods and disciplines required of the chemist using it. Such a safety approach is not simple : ducted fume hoods are complex to install and require high expertise from manufacturers to make them working efficiently. Ductless fume hoods are easy to install, offer an excellent containment, but require a high expertise from manufacturers to offer excellent filtration efficiency and high retention capacity.

Both ducted and ductless system shall be combined and employed in the laboratory to provide the most adequate safety to the chemists. Ducted fume hoods are mainly for performing duties involving large emission of chemicals. Whilst, ductless fume hoods shall be used for small and medium duties, involving well controlled emissions of chemicals.

(This article is contributed by Teddy Pitiot, Erlab)

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