UCD Environmental Health and Safety
Laboratory Health and Safety Program

 

Laboratory Hoods
This information is provided by University of Colorado Denver Environmental Health and Safety Department
Contact 303-724-0345 if you have any questions

There are three main types of laboratory ventilation equipment used at UCD:

• Chemical Fume Hoods (FH)
• Laminar Flow Hoods (LFH) or Clean Benches,
• Biological Safety Cabinets (BSC), and

The design of each type of ventilation unit is specific to the intended application for specific types of materials that will be used within them such as volatile chemicals or biological materials including known or expected infectious agents.  Selection of the appropriate type of ventilation unit is critical and may affect your safety, or the efficacy of your experiment.  Often these units look very similar so it is important to understand the equipment in your lab before using it.

Basic Components
All three types of laboratory ventilation equipment consist of basic components although their orientation and functionality may vary.      

1. A working surface- the counter top or bench, which provides a place for the materials to be worked on
2. Cabinet or Hood- an enclosure to physically contain particulates and vapors from the room where the equipment is contained
3. Sash- the transparent front panel of the “hood”, usually designed to open either vertically, horizontally or both
4. Blower- each unit may contain one or more, used to direct and move air through the hood.

Types of Protection                                                                                                                  (a summery is provided in Table 1)

There are three types of protection that relate to laboratory ventilation equipment:

1. Personal Protection- Arguably the most important, this refers to the ability of the equipment to protect the operator from airborne contaminates (e.g., chemical vapors, infectious agents, or other particulates), by keeping them contained within the unit (cabinet or hood).
2. Product Protection- The ability to keep the product or materials being manipulated within the unit (such as a biological specimen) free from contamination from airborne particles or organisms carried in the air from the laboratory environment.
3. Environmental Protection- Filtration of exhausted air from within the unit (hood or cabinet) before its entrance into the environment.

Chemical Fume Hoods (FH)

Figure 1: Fume Hood (FH)

Characteristics:

• Only provides personal protection.
• Constantly exhausts contaminated air to outside of building through dedicated FH ducts.
• Does not offer protection to product or environment, as there is no filtration of intake or    exhaust air (The only hoods filtered at AMC are specific Radiation Hoods)
• Draws contaminants in the laboratory air directly over product being manipulated (no product protection).

Material Applications:

Materials NOT to be used:

Perchloric Acid Use:
            The use of Perchloric Acid requires a specialized independent hood with a built-in water wash down system.  In addition to being highly corrosive, condensed vapors can react with organic materials such as gaskets, greases, and chemical residues to form explosive perchlorate salts and esters.
            There are no approved Perchloric Acid hoods at AMC.  If you wish to use Perchloric Acid, contact EHS (4-0345) for additional information.  If you have been conducting work with Perchloric Acid, especially concentrated solutions or heated solutions, contact EHS immediately for assessment of ductwork.
Notice in figure 1 the intake air being supplied by the room is being drawn away from where the user would be.  This is negative pressure causing an inflow of air.

 

EH&S provides annual checks of every Chemical Fume Hood on the AMC campus.  Each Fume Hood should have one of our colored stickers (figure 2) on the front near the maximum sash height allowed for that particular hood (which is shown as the arrows on the stickers).
If the Fume Hood in your area does not have a sticker, you feel it is not working properly please contact our Industrial Hygienist Daniel Kerley (303-724-0249) with any questions.

 

Laminar Flow Hoods (LFH)/ Clean Benches

Figure 3: Laminar Flow Hood (LFH)
	HEPA Filter

Laminar Flow Hoods or Clean Benches employ the use of HEPA filters to remove potentially harmful particulates from intake airflow before it is passed over the work area (product) towards the user.  This horizontal laminar airflow is an example of positive pressure or pressure in a space causing an outflow of air (see figure 3).  Clean Benches can also use vertical laminar airflow downward to provide marginal personal protection.  However, clean benches DO NOT offer adequate protection from infectious agents or hazardous chemical vapors.

Characteristics:

• Provide product protection only.
• Product protection is provided by HEPA filtered particulate free unidirectional airflow.
• Discharged air is exhausted directly at operator and into work area.

Material Applications:

Materials NOT to be used:

If you have a Laminar Flow Hood or Clean Bench in your lab it is your responsibility to have it serviced regularly.  Changing the HEPA filters and monitoring its airflow is necessary to ensure proper science.  EH&S will NOT service or check them for you.


Biological Safety Cabinets (BSC)
There are three different classes or Biological Safety Cabinets (BSC):

• Class I
• Class II: is further separated into four types
• A1, A2, B1 and B2
• Class III

All BSC use at least one type of HEPA filtration.  Table 2 provides a summary of particulate protection each type of BSC offers. 

Class I BSC:
Class I BSC DO NOT provide product protection, as they only have HEPA filtration on exhausted air (figure 4).  The air that is drawn over the work area is supplied from outside the cabinet and is NOT free from possible contamination. 

Material Applications for Class I BSC:

• Infectious agents

Materials NOT to be used in Class I BSC:

Note:  Of the three kinds of laboratory ventilation equipment discussed (FH, LFH, & BSC), Class II and Class III BSC are the only types of equipment that can offer all types of protection: Personal, Product and Environmental. 


Class II; Type A1 BSC
            70% of intake air is recirculated in a Class II; type A1 BSC, rendering them incapable for use with hazardous chemicals or radionuclides. A1 exhaust is positive pressure to the room.


Material Applications for Class II; Type A1 BSC:

• Only infectious agents

Materials NOT to be used in a Class II; Type A1 BSC:

Figure 5: Class II; Type A2 BSC

 Class II; Type A2 BSC
            70% of intake air is recirculated in a Class II; type A2 BSC.  Exhausted air is negative pressure to room.

Material Applications for Class II; Type A2 BSC:

Materials NOT to be used in a Class II; Type A2 BSC:

 Class II; Type B1 BSC:
30% of intake air is recirculated in a Class II; type B1 BSC, the cabinet must be hard ducted to building exhaust to ensure proper negative pressure air flow through the cabinet.


Material applications for Class II; Type B1 BSC:

• Infectious agents
• Minute amounts of chemicals and trace amounts of radionuclides only if it is hard ducted to building exhaust

Materials NOT to be used in Class II; Type B1 BSC:

Class II; Type B2 BSC:
            Also known as a Total Exhaust Cabinet as 100% of its intake air is exhausted through a HEPA filter through negative pressure.


Material Applications for Class II; Type B2 BSC:

• Infectious agents
• Chemicals (if hard ducted)
• Radionucleides (if hard ducted)

Materials NOT to be used in Class II; Type B2 BSC:

Class III BSC:
            AMC has no Class III BSC.

Table 2
Type	Personal	Product	Environmental	Particulate Protection
Class 1	X*		X**	None, not for use with vapors and gasses
Class II
AI	X*	X	X**	None, not for use with vapors and gasses
A2	X*	X	X**	None, not for use with vapors and gasses
B1	X*	X	X**	Offers more personal & product protection if the vapor source is located towards the rear of the work area
B2	X	X	X**	Offers personal protection
Class III	X	X	X	Offers personal, product and environmental protection
*personal protection from gasses and vapors only if the BSC is exhausted to facility exhaust system (hard ducted; fig. 6)                                                                  **environmental protection only if the BSC is exhausted to treated facility exhaust system (hard ducted; fig 6), contact EH&S if you have any questions about your particular BSC’s exhaust

           

All Biosafety Cabinets must be certified annually.  HEPA filters and airflow measurements must be taken to ensure safe operating conditions.  EH&S can NOT provide this service.  It is up to each laboratory PI to ensure that their BSC are in compliance.  Please feel free to contact our Biosafety Officer Terry Stinnett (303-724-0235) with any questions or for a list of companies that will provide this service.

Too see the difference of the airflow through each BSC please view the animations in the tutorial at http://www.uchsc.edu/safety/biocabinet/content/unit_3/intro.html.

High Efficiency Particulate Air (HEPA) Filtration       

Laminar Flow Hoods/Clean Benches and Biological Safety Cabinets rely on HEPA filtration.  HEPA filters are 97.97% effective at removing particles smaller than 0.3µm in size.  As the contaminated air stream enters the filter from the BSC or LFH, it encounters the filter fibers (made of glass or polymers) causing the airflow to change direction.  The harmful particles contained within the air stream interact with the filter fibers in different ways (depending on their size).  The largest particles (.5-5µm) having the most inertia are collected by actually impacting into the fibers.  Smaller particles (0.1-1µm) are intercepted, by filter fibers as the air stream passes around them.  The filter fibers are small enough for diffusion from Brownian motion to seize the smallest particles (≤0.1µm).  Brownian motion pertains to extremely small particles that appear to jump or zigzag as they travel; their motion is affected as they are struck by surrounding molecules.  All three capturing methods increase as filter density increases. The more the filter is folded the more tumultuous path the air stream must take to pass through it and more particles are trapped in the HEPA filter.  Even though HEPA filters are believed to be able to capture nanoparticles, little is known and more study is warranted.  Figure 7 provides an illustration of HEPA filter efficiency.

Selecting the right unit:

            Before you begin using the laboratory ventilation equipment it’s important to consider what materials you’re using and how you will be using them.  Ask yourself questions such as:  Am I using hazardous chemicals/vapors?  Am I using known or expected infectious agents?  Does what I’m working with need to be free from particulates?

 

Further Training

http://www.uchsc.edu/safety/biocabinet/start.html

How to Operate RC-1 Fume Hoods (Powerpoint Slide Show - Once the show opens, LEFT-Click your mouse to advance to each new slide. Upon completion, use the BACK button on your browser to return to this page)

References

1.         Committee on Industrial Ventilation.  Industrial Ventilation: a Manual of recommended Practice, 25th Edition, 2004. 
2.         http://www.uchsc.edu/safety/biocabinet/content/home.html
3.         http://www.bakerco.com/resources/introbench.php
4.         Larzelere, John.  New and Novel Technologies in Particulate Filtration, Via:  www.natick.army.mil/Soldier/jocotas/ColPro_Papers/Larzelere.pdf
5.         U.S. Department of Health and Human Services.  Biosafety in Microbiological and Biomedical Laboratories, 4th Edition, May 1999, Appendix A pg. 200-211.