Exposure controls include equipment and procedures designed to minimize inhalation, skin absorption, or ingestion of hazardous materials. Fume hoods and biosafety cabinets are two common pieces of lab equipment that can greatly decrease the potential for inhalation exposures to hazardous chemicals or biological agents. Although they may look similar, laboratory fume hoods and biosafety cabinets are designed and function very differently and must be used appropriately to afford the user protection. Many additional hazard-specific or process-related controls are available. Consult with EH&S (9-2553) to discuss control options.

Laboratory Fume Hoods

Biosafety Cabinets

Laboratory Fume Hoods

A properly operating and correctly used fume hood can reduce or eliminate exposure to volatile liquids, dusts, and mists. It is advisable to use a laboratory hood when working with all hazardous substances. In addition, a laboratory hood or other suitable containment device must be used for all work with "particularly hazardous substances."

Each fume hood should have a current calibration sticker and a marker indicating the highest sash height to be used when working with hazardous materials. Contact EH&S for a hood evaluation if these labels are missing.

Each fume hood must be equipped with at least one type of continuous quantitative monitoring device designed to provide the user with current information on the operational status of the hood. These devices are typically a Magnehelic pressure gauge or a TSI digital flow meter. The fume hood is operating correctly when the Magnehelic gauge indicates the pressure level at the time of certification or when the TSI gauge reads 100 fpm or greater.

The following work practices are always required when using chemical fume hoods; more stringent work practices may be necessary in some circumstances.

Safe Fume Hood Work Practices

• Conduct all work and keep all apparatus at least 6 inches back from the face of the hood. A stripe on the bench surface is a good reminder.
• Keep the hood sash closed as much as possible.
• Keep the hood slots and baffles free of obstruction by apparatus or containers.
• Do not permanently store apparatus or chemicals in the hood. Large equipment used inside the hood should be placed on blocks to allow airflow under the equipment. Store chemicals in an approved safety cabinet.
• Do not put your head in the hood when contaminants are being generated.
• Do not use the hood as a waste disposal mechanism. Solvent bottles in the fume hood must be capped when not in use.
• Conduct any processes that may generate air contaminants at or above the Permissible Exposure Level (PEL) inside a hood.
• Minimize foot traffic by the face of the hood. Do not make fast movements when taking items in and out of the hood.
• Keep laboratory doors closed (exception: some laboratory designs require lab doors to be open).
• Do not remove hood sash or sash panels except when necessary for apparatus set-up. Always replace sash or panels prior to working in the hood.
• Do not place electrical receptacles or other spark sources inside the hood when flammable liquids or gases are present. No permanent electrical receptacles are permitted in the hood.
• Use an appropriate barricade if there is a chance of explosion, implosion or eruption.

Resources

Fume Hood Fact Sheet - for labs in PSB

Fume Hood Fact Sheet - for labs in CBB

Fume Hood Fact Sheet - for all other labs

Title 8, California Code of Regulations, Section 5154.1 (8 CCR 5154.1), "Ventilation Requirements for Laboratory-Type Hood Operations"

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Biosafety Cabinets

The biosafety cabinet (BSC) is an essential piece of safety equipment for many laboratories conducting biological research. The BSC is designed to provide both personnel and environmental protection from potentially infectious materials and human pathogens. BSC's are manufactured in three different classes (Class I, II and III). The common feature in all BSCs is the high efficiency particulate air (HEPA) filter. HEPA filters can remove particles down to 0.3 microns with 99.97% efficiency and will trap most bacteria and viruses. Vapors (from ethanol, formalin, etc) and gases will not be captured and removed by the HEPA filter.

Class I Biosafety Cabinet

Provide personnel and environmental protection, but do not provide a sterile work surface. Airflow in a Class I BSC is similar to a chemical fume hood, with air being drawn away from the worker and across the work surface. The exhaust from the cabinet is HEPA filtered and this protects the environment. Class I BSC are useful for work that requires containment but not product sterility.

Class II Biosafety Cabinet

Provide personnel, product and environmental protection. Air is drawn around the worker into the front grill of the BSC, providing operator protection. HEPA filtered sterile air flows down onto the work surface, minimizing the potential for cross-contamination. Exhaust air passes through another HEPA filter before being released into the surrounding environment. Class II units are further divided into four types; A1, A2, B1, and B2, based on the percentage of air that is recirculated and exhausted.

Class III Biosafety Cabinet

Class III BSCs are designed to provide maximum protection to the worker and the environment. Sometimes called Class III glove boxes, these units are gas-tight enclosures with a non-opening view window. Intake air is filtered through a HEPA filter and exhaust air passes through two HEPA filters before being released.

Safe Biosafety Cabinet Work Practices

1. Plan your experiment. Gather all materials you need to conduct your experiment, including personal protective equipment and waste disposal containers. Think through the steps of your experiment and lay out materials in a logical manner that prevents excessive arm movements and moving items in and out of the cabinet.

2. Turn on the cabinet. Make certain the BSC runs for at least 15 minutes prior to beginning work. This cylce will purge the work area of any particulates before you begin working.

3. Disinfect the work surface. Use a disinfectant appropriate for the work being conducted in your lab. 

4. Prepare to begin work. Line the work surface with plastic-backed absorbent towels. Place your supplies in the cabinet, as far back from the sash as possible. All operations should be performed on the work surface at least four (4) inches from the inside edge of the front grill.

5. Work from clean to dirty. Organize your supplies so that you can segregate your work from the clean side of the cabinet to the dirty side. Avoid moving dirty items over clean ones to prevent cross-contamination of your experiment.

6. Protect vacuum lines. If you will be using a vacuum, be sure to use a HEPA filter and in-line disinfectant flasks to protect your vacuum system from contamination. The in-line flasks will catch any overflow, and the HEPA filter will prevent aerosols and particulates from entering the vacuum system.

7. Collect waste materials. Waste materials should be collected inside the cabinet. Repeatedly moving arms in and out of the cabinet to deposit waste in a container outside the BSC will compromise the air flow and containment provided by the BSC. Be sure to seal bags and cover open containers before removing them from the cabinet.

8. Clean up. Wipe down all materials with disinfectant before removing from the BSC. After the cabinet is emptied, wipe down the interior cabinet surfaces with disinfectant. Allow the BSC to run for 15 minutes before turning it off.

Common BSC Work Practice Errors

• Do not cover the front and rear grills with supplies, absorbent paper or materials as this will compromise the cabinet's airflow and lead to potential contamination issues or personnel exposure concerns.
• Do not store supplies on top of the BSC. The HEPA filter is located there and disturbance or damage can lead to problems with the BSC.
• Do not use an open flame in the BSC. Open flames create significant turbulence that disrupts the laminar air flow in a BSC. The combination of an open flame and 70% ethanol (disinfectant) is responsible for many significant lab fires and destruction of BSCs. Use sterile disposable supplies or an electric bacticinerator instead.
• Avoid moving arms in and out of the cabinet during your experiment and try to minimize activities that can cause eddy currents (opening doors, personnel walking near cabinet, etc.). Small pockets of turbulence can compromise air circulation in the BSC.

Resources

Title 8, California Code of Regulations, Section 5154.2 (8 CCR 5154.2), "Ventilation Requirements for Biological Safety Cabinets"

Biosafety in Microbiological and Biomedical Laboratories (BMBL) 5th Edition

Appendix A - Primary Containment for Biohazards: Selection, Installation and Use of Biological Safety Cabinets

Workinig safely with Biosafety Cabinet videos:

UC Davis 

Cornell

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