However, if you take a closer look you have biological hoods, radioactive hoods, chemical hoods, environmental hoods; the list goes on and on. Within Chemical hoods there are a whole host of specialty enclosures that are meant to safely contain various chemical hazards and applications. And then you have a very obvious delineation… hoods that are ducted and hoods that are ductless.
Over the last 2 decades, ductless hoods have developed a schizophrenic reputation. For users and lab managers, ductless hoods are heroes; meanwhile, for safety personnel ductless hoods are “goats.” The advantages of the ductless hoods are well known: they are turnkey, they are flexible and adaptive, they don’t require ductwork, they are small, etc… Their limitations are based on the chemistry behind their oft carbon-based filters. Here are the simple 1, 2, 3’s of ductless hoods (DH) as outlined by the Scientific Equipment and Furniture Association (SEFA 9-2010).
Ductless Hood I – These enclosures are typically small and provide primary containment of nuisance chemicals only. Most common applications include clinical or educational histology and pathology, slide staining, and other uses of ‘bench chemistry’. Filters may be generic activated carbon, or they may be specific to the application. These hoods do not have active chemical detection and should not be used for handling hazardous chemistry.
Ductless Hood II – Hoods in this class are what most people think of when they think “ductless hood.” Varying filtration types are determined by the chemistry to take place within and applications are vetted by the hood manufacturer. Only manufacturer approved hazardous chemistry should be used in a DH II. These hoods have a method for detecting and communicating chemical breakthrough beyond filtration to the operator.
Ductless Hood III – Quite simply, these are DH II with backup filtration. The language defining this hood is funny. It requires the aforementioned backup filter after the chemical detection to be of the same type and efficacy. Efficacy meaning efficiency, not filter size and chemical capacity. The benefit of a DH III is that once the sensor detects breakthrough, protection remains constant long enough to obtain replacement filters.
BONUS Hood: Filtered Fume Hood – The current pinnacle of ‘ductless’ hoods is an enclosure that vastly exceeds the defined design and application requirements of a DH III. Filtered fume hoods look like a prototypical ducted fume hood, with valves, electrical duplexes available on corner posts, and have vertical rise full opening sashes. Their safety features are driven by safety, not by user input, meaning that regardless of who is using the hood and what they are working with, unsafe operations will be communicated to the operator, lab manager, administrator and/or safety officer. The filters used by these hoods have comprehensive application suitability, meaning they can simultaneously handle a large array of different chemicals from different chemical groups. Finally, filtered fume hoods utilize an array of sensors that detect small concentrations of chemicals across multiple chemical families, and do so while maintaining safe operating conditions.
Some industry experts are quick to point out that these different ductless hoods should not and cannot be compared to each other, or that it is akin to comparing a cordless phone to a smart phone (both devices are not tethered to a wall, yet their capabilities are far from similar). Others see the differences from the perspective of the lab and those needing the enclosure. What is being done in the lab? What is being used in the lab? What are the requirements regarding laboratory safety? Answering these questions before looking into ductless and filtered fume hoods is critical to having a safe laboratory.
So there you have it, the 1, 2, 3 (AND 4) of hoods without ducts.
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