Environmental, Health and Safety Services

Biosafety Cabinets (BSC) / HEPA-Filtered Equipment


  • BSCs are specialized pieces of lab equipment designed to safely contain biohazardous agents/ materials. Also, all but one class of BSCs protect sterile items and culture materials from contamination when they are manipulated in the BSC work space. Different classes and types of BSCs meet different, specific needs. Choosing the right BSC for purchase should be based on a thorough risk assessment of all material (biological and chemical) being handled and the procedures involved with the work.
  • BSCs must not be confused with chemical fume hoods, laminar flow hoods or tissue culture hoods. In most cases, BSCs and chemical fume hoods have distinctly different functions and cannot be used interchangeably.
    • Chemical fume hoods utilize directional air flow to protect lab workers from exposure to toxic chemical fumes or particulates by venting them to the outside.
    • Material or items inside a chemical fume hood are not protected from room air contamination.
    • Chemical fume hoods should never be used for containment of biologicals.
    • Minute amounts of volatile chemicals/ radionuclides may be used ONLY with certain types of BSCs which exhaust them to the outside.

HEPA Filter

  • The HEPA filters are important features of the BSC, capturing potentially infectious particles from your work as well as room air contaminants, and contaminants that you may shed. HEPA filters should be replaced by the BSC's service provider every 3-5 years, depending on cumulative hours of operation, the cleanliness of the lab, and the materials being used in the BSC. Changing or cleaning the pre-filter on a regular basis extends the life of a HEPA filter.
  • The HEPA-filtered directional air flow in a BSC
    1. protects the work material from contaminants,
    2. protects the worker from exposure to aerosols, and
    3. prevents release of aerosolized material into the environment. IMPORTANT: BSC HEPA filters do not entrap or filter chemical vapors or gases; they entrap particulates.

Magnehelic Gauge

  • The magnehelic gauge on the BSC shows the air pressure difference across the HEPA filter, and can indicates when the air flow system and filter are not operating properly.
  • BSC users should know their BSC's acceptable gauge readings and limits; ask your service provider, or look on the BSC certification label for this information.
  • Before each work session, check the gauge and look for changes higher or lower than this acceptable range. A higher resistance reading indicates the filter is loaded or blocked; a lower resistance reading may indicate a hole or tear in the HEPA filter. In either instance, do not use the BSC; contact a service provider.

Classes and Types

C1 Biosafety Cabinets

  • The Labconco Purifier Axiom Class II, Type C1 biosafety cabinet is a relatively new product that is designed to be more flexible than other biosafety cabinets. It can be used as a re-circulating Class II Type A2 cabinet for standard microbiological work, or it can be ducted to the outside (or used with a manifold exhaust system) for working with small amounts of volatile chemicals and radionuclides, as with a Type B2 cabinet.
  • This cabinet does not have the full functionality of a chemical fume hood, and must not be used as a substitute for a chemical fume hood.
  • Special HVAC requirements may be involved with the installation of this type of cabinet and all manufacturer's recommendations must be followed.
  • Specific EHS training is required for new users of C1 biosafety cabinets to ensure full understanding of the limitations and proper uses of the C1 cabinet.

Using Volatile Chemicals/ Radionuclides in a BSC

  • In general,
    • Minute amounts can be handled in Class II Type A2 or B1 BSCs vented to outside.
    • Small amounts can be handled in Class II Type B2 BSCs vented to outside.
  • Specifically,
    • Check the Safety Data Sheets for volatile chemicals to learn explosion limits, and avoid approaching those concentrations, as chemicals can volatilize and concentrate to hazardous levels inside a BSC, or in ductwork after being pulled through HEPA filters.
    • Make sure the volatile chemicals you use will not damage HEPA filters.
  • You have exceeded the quantity of a volatile chemical you can safely use in your BSC if you can smell or otherwise detect chemical fumes out in the lab. In these circumstances, discontinue use of that BSC; instead, locate and use a BSC that exhausts most or all air to the outside.


  • Choosing the right BSC for purchase should be based on a thorough risk assessment of all material (biological and chemical) being handled and the procedures involved with the work.
  • Key questions to consider:
    • What type and quantity of biological and chemical material will be used in the BSC?
    • What biosafety level (and containment level) will be required?
    • Are you working with biologicals only, or with minute/small amounts of volatile chemicals/radionuclides?
    • What type of exhaust (recirculating, or ducted to the outside) will be needed?
  • Contact EHS (231-3600) for assistance in evaluating needs for a BSC purchase.

Room Location

  • Room location is important to the proper functioning of a BSC:
    • Ideally, BSCs should occupy lab space that is removed from other work areas, especially high traffic areas.
    • Cabinet should be placed 12-14 inches from ceiling and walls.
    • Cabinet should be placed away from windows, air supply vents, lab features creating air movement (chemical fume hoods, centrifuges, vacuum pumps), and entry points into lab.

Required Certification

  • All new BSCs to be used for handling potentially infectious/biohazardous material (BSL-2, BSL-3; ABSL-2, ABSL-3; ACL-2, ACL-3) must be certified before being used; certification involves a standardized check of proper function, performed by a qualified technician.
  • Cabinets must be re-certified:
    1. following a major relocation (change of building, campus, state, country);
    2. when a HEPA filter is replaced;
    3. following any other repair or service to the unit.

BSC Certification Vendors at Virginia Tech

  • Principal Investigators can chose from these three providers for cabinet certification services.
  • A Purchase Order (PO) must be obtained through the PI's departmental business office for this service; the procedure for this is outlined in the next item.

Invoicing Procedure For Contract Work Performed On BSCs, Laminar Flow Hoods, And Other HEPA Filtered Equipment

  • Before any services are provided, a "PO" number must be obtained and emailed to the contractor. Please make sure the device Make, Model, Serial Number, and location (Building and Room Number) are listed on your PO.
  • Upon receipt of Purchase order, someone will contact you by phone or email to set up scheduling for when one of their certifiers will be on campus.
  • After services are rendered, your certification report will be provided to you. Once you have received your report(s), an invoice will be sent directly to you or your department for payment of services. Each department/College/PI will be responsible for paying their particular invoice.

Obtaining Purchase Order Numbers On HOKIEMART

  1. Click on Non-Catalog item.
  2. Where it says "enter supplier", type contractor's name and it should come up.
  3. Under product description list the service being provided. (e.g., Biosafety Cabinet (BSC) certification, BSC repair, BSC decontamination, Laminar flow hood certification)
  4. Add Quantity which would usually be one (1).
  5. Amount – you have to put something here, some amount. Controllers will contact you if the invoice is 10% or more than what is in Hokie Mart. If it's less than what is in Hokie Mart then they will pay what's due and usually release the rest.
  6. Service costs are listed in the individual sheets for each contractor.
  7. Click Save & Close. If you have more than one cabinet being certified or more than one type of service being performed then you would need to click Save & Return, and go through steps 3-5 above again.
  8. To get to the next screen click in the upper right hand corner. That's the active cart.
  9. You can rename the cart if you wish.
  10. Down in the bottom right corner there's a block that says "select contract". Click that and select the contract.
  11. Then click Save.
  12. Then click Proceed to Checkout.
  13. Enter your fund information and Submit the order.
  14. Once the order has been placed, someone within your dept will approve it and that will generate a PO#.
  15. You must send a copy of the PO# with the list of corresponding cabinet #'s to the contractor prior to scheduling so your cabinet(s) can be added to the certifier's work list.

General Decontamination Procedure

  • Biosafety cabinets must be properly prepared prior to the certification technician's arrival, or prior to any service visit. Prepare a BSC by removing all items and disinfecting all work area surfaces, including vertical side and back surfaces, and sash glass.
  • Decontamination of all reachable surfaces, inside and out, is usually sufficient for certification, in situ repairs and moves within a building.
  • Gas or vapor decontamination of the entire unit (including inaccessible areas--plenums, etc.) by a qualified contractor is required:
    • prior to a major relocation to another building, campus, state, country, etc.
    • prior to going to surplus
    • after receiving extensive repairs
    • following a high-volume spill
    • if unit will be used in a lower containment lab (e.g., from BSL-3 to BSL-2)
  • Disinfecting agents typically used by professionals include formaldehyde gas and vaporized chlorine dioxide.
  • If you need assistance in determining whether whole-unit decontamination is needed, or for information on scheduling decontamination service with a contractor, contact EHS.
  • Whenever you have decontaminated a BSC (by either method listed above), you must attach a completed Lab Equipment Decontamination Form to the unit prior to the date you are expecting the movers, certification vendor, etc. Please follow the directions on the back of the form.

Guidelines for BSC Use

  • Preparing for a Work Session
    • Start up and run the cabinet for at least 3-5 minutes prior to working to replace the atmosphere in the cabinet with filtered air.
    • Check the magnehelic gauge to ensure it is within acceptable limits for use before any work session in the BSC.
    • Ensure that you are equipped with the disinfectant that is effective with the agents you will be using.
    • Always use electric heat blocks, bead sterilizers, incinerators or disposable loops instead of an open flame; open flames disrupt the protective air flow and cause heat damage to the cabinet's HEPA filters.
    • Ensure that vacuum lines are connected to 1) an overflow collection flask that contains an appropriate disinfectant, and 2) an in-line HEPA filter. This assembly should be inside the BSC.
    • Before beginning work, adjust stool height so that your face is positioned in front of the BSC glass and is well above the opening below the glass that accesses the BSC work surface.
    • Disinfect your gloved hands prior to starting work.
  • Preparing the BSC Work Surface
    • Use 70% ethanol or other appropriate disinfectant to disinfect the work surface floor, sides, back and interior sash glass; do not disinfect the supply filter diffuser. If using bleach solution, follow with 70% ethanol to remove corrosive bleach residue from metal surfaces.
    • Place all material you will need within the cabinet before starting work. The surfaces of all materials and containers placed into the cabinet must be wiped/sprayed with 70% ethanol or other appropriate disinfectant to reduce the introduction of contaminants into the cabinet environment.
    • Arrange material so that your work flow is from ‘clean' to ‘dirty.'
    • Waste containers should be inside the cabinet, including trays, boxes or bags for pipette disposal.
  • During The Work Session
    • Do not block the front grille or the back grille while you work.
    • Perform your work at least four inches back from the front grille.
    • Organize your work materials on the BSC work surface so that your flow of work goes from clean to dirty.
    • Spray disinfect your gloved hands at routine intervals during your work session.
    • Avoid rapid movement of your arms into and out of the cabinet, which compromises containment provided by the BSC. Move your arms in and out slowly, perpendicular to the face opening of the cabinet. Manipulation of materials should be delayed for approximately 1 minute after placing the hands/arms inside the cabinet, which allows cabinet's air flow to stabilize.
    • Equipment that causes air turbulence (e.g., centrifuge, vortex, etc.) should be placed in the back 1/3 of the work surface. All other work in the cabinet should stop while equipment is running.
    • Personnel activities in the room (e.g., walking back and forth behind someone working at a BSC, entering/exiting lab, opening/closing lab doors, etc.) may also disrupt the cabinet air barrier. For this reason, access to the work area should be restricted when work is in progress.
  • Following The Work Session
    • Spray-disinfect everything coming out of the cabinet; remove clean items first, then ‘dirty' items. Do not leave items in the BSC as a place to store them.
    • Remove waste items last, but before you disinfect BSC surfaces.
    • At the end of the work session, disinfect the cabinet's work surface, the interior sides and back, and the interior glass.
    • Run the cabinet's blower for 3-5 minutes after final decontamination.
    • Properly dispose of gloves and remove lab coat.
    • Wash your hands before doing anything else or leaving the lab.
    • UV Lamps --- EHS does not recommend using UV radiation as a means of disinfection in BSCs. However, for those who choose to use UV radiation in addition to required disinfection procedures for BSC work surfaces, duration of use should not exceed 30 minutes, and should occur as a final step following a work session.
      • UV is no substitute for decontaminating the work area with disinfectant.
      • UV has no penetrating ability and thus decontaminates surfaces only.
      • UV use in a BSC for more than 30 minutes does not increase the effectiveness of UV's decontaminating ability. If routinely left on overnight, a UV lamp's potency (disinfecting effectiveness) will be reduced.
      • A UV lamp's effectiveness is diminished if it is not cleaned weekly to keep it free of dust.
      • To avoid eye/skin exposure to UV radiation, UV should only be activated in a BSC when personnel are not in the immediate vicinity.

Further Information and Guidance: