A ductless hood is an enclosure designed for the handling of contaminants, which limits the propagation toward the operator and other personnel of such contaminants. 

Typically, a ductless hood is not attached to any external exhaust system and equipped with its own independent ventilation system which forces the contaminated air to travel through a filter and recirculates it within the room.

The Scientific Equipment and Furniture Association (SEFA) is an international trade association comprised of manufacturers of laboratory furniture, casework, fume hoods and members of the design and installation professions.

SEFA 9-2010 classifies the ductless hoods into three categories – DH-I, DH-II, and DH-III. Let’s explore what the classification means in this infographic.

To download the specifications and download the brochure follow this link.

TYPE SPECIFICATION RECOMMENDED USE & PRECAUTIONS
DH I
  • Equipped with a filtration device designed to control non-toxic chemicals, nuisance odours, particulates.
  • For use with applications that would normally be performed on the open bench without protection. 
  • DH I Ductless Hoods should not be used with toxic contaminants
DH II
  • Meets all DH-I requirements
  • Equipped with a filtration device designed to filter manufacturer approved toxic contaminants up to filter break through only
  • DH-II is not designed to provide secondary containment beyond primary filter break through.
  • DH II Ductless Hoods should not be recommended for use unless their application has been pre-approved by the manufacturer/supplier using form SEFA 9-A
  • Should only be recommended for use with applications where continuous monitoring and detection of filter break through is available
  • Its use must be suspended once filter break through detection occurs.
DH III
  • Meets all DH II requirements
  • Equipped with a filtration device designed to filter manufacturer approved toxic contaminants beyond primary filter break through by providing secondary back-up protection
  • Should provide a period of time to continue and end an ongoing experiment with its secondary back-up filter system.
  • DH III Ductless Hoods should not be recommended for use unless their application has been pre-approved by the manufacturer/supplier using form SEFA 9-A
  • Should only be recommended for use with applications where permanent monitoring and detection of filter break through is available.

Source: SEFA

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