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Hoods, hoods and more hoods

Laboratory hoods are a staple in the scientific industry and beyond. How do you know which is the best fit for your application?

There are several categories of hoods that we will describe, summarize, and hopefully demystify! These include:

  1. Chemical Fume hood
  2. Biosafety Cabinet
  3. Clean Bench
  4. PCR Cabinet

 

Specific uses and applications for different types of lab hoods, cabinets, and enclosures are briefly discussed.

 

Type Hazard Protection Personnel Protection Product Protection
Chemical Fume Hood Chemical vapors Yes No
Biosafety Cabinet Biohazards, Limited chemical vapors for ducted hoods Yes Yes
Clean Bench None No Yes
PCR Cabinet None No Yes

What is a Chemical Fume Hood?

A chemical fume hood is a partially enclosed workspace that is exhausted to the outside of the building. Hazardous gases and vapors generated inside the hood are captured before they enter the breathing zone.

Chemical fume hoods come in all shapes and sizes. There are 4 types and these include:

  1. Conventional Fume Hoods
  2. Bypass Fume Hoods
  3. Auxiliary Air Fume Hoods
  4. Specialty Hoods
Basic Fume Hoods
Type Description Benefits
Conventional Fume Hood All air enters through the hood opening as defined by the bottom of the sash, sides of the hood and the work surface. The face velocity increases as the sash is lowered. Original and most simple design.
Bypass Fume Hood A grill opening is located above the fume hood sash so as the sash is raised or lowered, portions of the grill are covered or exposed. The face velocity will remain constant regardless of height sash. Better than standard fume hood as it reduces the chance for turbulence and loss of containment as sash is lowered.
Auxiliary Air Fume Hood Similar to standard hood except some additional outside air is ducted to the face of a bypass hood Benefit of this is energy savings, but operating costs outweigh energy benefits.
Specialty Fume Hoods
Type Description
Perchloric Acid Fume Hood Constructed with anti-corrosive stainless steel and equipped with a special wash-down system that prevents build-up of highly explosive acid salts and organic matter.
Radioisotope Fume Hood Constructed to accommodate heavy lead bricks used to shield radioactive material. Work surface is usually stainless steel or have a liner that can accommodate radioactive material. HEPA and/or charcoal filters are typically installed to ensure removal of volatile particles.

 

What is a Biological Safety Cabinet (BSC)?

A Biological Safety Cabinet (BSC) was developed as a primary means of containment when working with infectious organisms. BSCs are designed to provide personnel, environmental, and product protection when good practices and procedures for cell culture work are followed. There are 3 classes of cabinets that have been designed to meet the various research and clinical needs: Class I, Class II, Class III.

BSC Class

Protection Provided

Application and Risk Assessed

Personnel

Environment

Sample

Class I Yes Yes No To enclose equipment with potential to generate aerosols such as centrifuges, harvesting equipment, fermenters; or procedures that generate aerosols such as cage dumping, culture aeration, tissue homogenization that are assigned BSL 1-3
Class II
Type A1
Type A2
Type B1
Type B2
Yes Yes Yes Designed for work involving microorganisms assigned to BSL1-3
Class III Yes Yes Yes For highly infectious microbiological agents (BSL-4)

 

BSC Class Face Velocity (lfm) Airflow Pattern Non-volatile Toxic Chemicals and Radionuclides Volatile Toxic Chemicals and Radionuclides
I 75 In at front through HEPA; Exhausted to room through HEPA Yes No (unless exhausted outdoors)
II, A1 75 70% recirculated to cabinet through HEPA; 30% exhausted to room through HEPA Yes1 No
II, A2 100 Similar to A1 Yes No (unless exhausted outdoors)
II, B1 100 30% recirculated to cabinet through HEPA, 70% exhausted through dedicated duct to outside through HEPA. Yes Yes1
II, B2 100 0% recirculated; 100% exhausted through dedicated duct to outside through HEPA Yes Yes1
III n/a Yes Yes1

1Should be ducted to the outside with an in-line charcoal filter an explosion proof motor and other electrical componets. Permitted for only small amounts of volatile toxic chemicals.

 

What is a Clean Bench?

A Clean Bench, like a BSC, is a laminar flow hood with an ISO Class 5 rating. However, “clean benches” are not BSCs. These cabinets only provide product protection. Because they do not provide personnel protection they should not be used with applications that contain biohazardous material, toxins, or radionuclides.

There are 2 types of clean benches: 1) horizontal flow and, 2) vertical flow.

Type

Description

Protection

Benefits

Personnel Environment Sample
Horizontal Pushes air through HEPA filter from the back, horizontally over the work surface at constant speed. There is no sash. No No Yes Taller and larger work area allow for instruments to be placed inside. Typical applications include media plate preparation, electronics inspection, medical device assembly pharmacy drug preparation.
Vertical Pushes air through HEPA filter located on top of the cabinet. Air is directed downward over the work surface at constant speed. No No Yes Glass sash offers a physical protective barrier from splashes. Typical applications include microbiology, forensics, plant tissue culture, pharmacy drug preparation.

What is a PCR Enclosure?

Polymerse Chain Reaction is a simple method that is used to focus on a piece of DNA and copy it a billion times over. It is used to diagnose diseases, identify bacteria and viruses, match criminals to crime scenes. Avoiding cross contamination with other DNA in the environment is critical for this method to be successful. That way you can be confident you’ve amplified the DNA that you want!

PCR enclosures are used to minimize sample cross-contamination. There are two types of PCR Enclosures: 1) Filtered and, 2) Non-Ventilated. Note that BSCs with UV light may also be used as a PCR work environment.

Type

Description

Protection

Benefits

Personnel Environment Sample
Filtered HEPA-filtered air flows downward or horizontally over work area to provide ISO Class 5 conditions. Also has UV light to deactivate DNA and RNA contaminants. No No Yes Taller and larger work area allow for instruments to be placed inside. Typical applications include media plate preparation, electronics inspection, medical device assembly pharmacy drug preparation.
Non-Ventilated Basic non-ventilated enclosure with UV light to denature DNA and RNA during periods of non-use. No No Yes Glass sash offers a physical protective barrier from splashes. Typical applications include microbiology, forensics, plant tissue culture, pharmacy drug preparation.