Chapter 9: Engineering Controls
Primary Engineering Controls
Biological Safety Cabinets (BSC)
Also Refer to Appendix B for more information on BSCs and other types of hoods.
BSCs constitute one of the most critical pieces of safety equipment in Biosafety Level (BSL) Containment laboratories. Designed to contain aerosols generated from biological material via laminar air flow and high efficiency particulate air (HEPA) filtration, BSCs differ from chemical and laminar flow hoods (clean hoods) in that they always offer personnel projection. They also provide some protection from contamination of the material being handled within the work environment.
There are three types of BSCs (Class I, II, and III); each offers different levels of protection. Open-fronted Class I and Class II BSCs are partial containment devices that provide a primary barrier; significant levels of protection of personnel and environment are obtained when complemented by good laboratory technique. The gas-tight Class III BSC, or glove box, provides the highest level of protection to personnel, environment, and product.
The Class I BSC is suitable for work where there is a need for protection from the biological material, but not for protection of the product. It protects personnel and environment from contaminants within the BSC but does not protect the work within the cabinet from “dirty” room air.
The Class II BSC protects the material being manipulated inside the cabinet (e.g., cell cultures, microbiological stocks) from external contamination. It meets requirements to protect personnel, the environment, and the product. The two basic types of Class II BSCs are Type A and Type B. The major differences between Types A and B may be found in the percent of air that is exhausted or recirculated, coupled with the way exhaust air is removed from the work area.
The gas-tight Class III BSC, or glove box, provides the highest level of protection to personnel, environment, and product. It is the only unit that provides a total physical barrier between the product and personnel. It is used with high-risk biological agents and when absolute containment of highly infectious or hazardous material is required. It is important to note that laminar flow hoods (clean hoods) or chemical fume hoods MUST not be utilized for work with biological agents. Laminar flow hoods provide product protection by ensuring that the product is exposed only to HEPA-filtered air. They do not provide protection to personnel or the laboratory environment.
Chemical fume hoods only provide personal protection by directional airflow into the fume hoods, which prevents chemical fumes from exiting out of the hood. Instead, the air is exhausted to the outside, generally above the roof of the building. They do not provide HEPA filtered air at all, and are therefore unsuitable to protect personnel, product, or environment.
BSC Owners Responsibilities and BSC Maintenance
Proper operation and maintenance of a BSC requires knowledge of how the system operates, as well as training and experience in effective techniques for working within the BSC without compromising its functions. Additional details concerning the design and use of BSCs are provided in Appendix C.
Two specialized forms of quality control are strongly recommended for all BSCs:
- At least daily, or each time the cabinet is operated, the user should observe the Magnehelic gauge and note its relative position. Magnehelic gauges measure the pressure drop across the outlet HEPA filter and are important indicators of filter integrity and loading. The gauge will typically indicate the same measurement over a long period of time. A significant change in the reading over a short period of time may indicate clogging or a leaking filter. In such cases, the hood should not be used until the problem is identified and resolved. If the BSC does not have a Magnehelic gauge, users must understand the operation of the airflow monitor, controls, and alarm settings.
- Annually, the cabinet must be certified by a licensed technician. The certification process ensures that the BSC is meeting its operating specifications and providing maximum protection. In addition, technicians can provide services and preventive maintenance for BSCs and can often forecast expensive requirements like HEPA filter replacements, thereby enabling PIs to budget for the event.
- Annual BSC recertification must be completed before the current certification expires. If the certification lapses, the BSC may not be used for BSL-2 or higher procedures until it is recertified. Laboratory personnel should report lapsed BSC recertification to the Biosafety Officer immediately. The Biosafety Officer will inform the PI and lab workers not to use the BSC, post a “DO NOT USE” sign on it, and will arrange for a technician to recertify the BSC as soon as possible. The certificate expires on the last day of the month in which the certification was performed, one year later (for example, a certificate issued on June 2, 2022 will expire on June 30, 2023).
- BSCs must be recertified after relocation.
- UM offers an annual recertification event for BSCs located on UM main campus, please contact the BSO for more information and assistance.
Secondary Engineering Controls
Facility Design
The design of a laboratory facility is important in providing a barrier to protect both the personnel working within, as well as those outside of the laboratory. It should also protect the surrounding community and environment from accidental release of infectious agents in the lab. Facility design must be commensurate with the laboratory's function, particularly the BSL required for use and/or storage of the biological agents therein.
The recommended secondary barrier(s) will depend on the risk of transmission of specific agents. For example, the exposure risks for most laboratory work in BSL-1 and BSL-2 facilities will be direct contact with the agents or inadvertent contact exposures through contaminated work environments. Secondary barriers in these laboratories may include separation of the laboratory work area from public access; availability of decontamination equipment (e.g., autoclave*); and sinks for handwashing.
As the risk for aerosol transmission increases, higher levels of primary containment and multiple secondary barriers may become necessary to prevent infectious agents from escaping into the environment. Such design features may include specialized ventilation systems to ensure directional airflow; air treatment systems to decontaminate or remove agents from exhaust air; controlled access zones; an airlock at the laboratory entrance; and separate buildings or modules for physical isolation of the laboratory itself.
Autoclaves
- Steam Sterilization is defined as 121C for at least 15 minutes peak temperature. The standard autoclave “cycle” is at least 45 minutes.
- Personnel operating autoclave(s) must be properly trained in its use. This training is provided by an experienced lab personnel or autoclave vendor.
- Biohazardous materials must not be placed in autoclaves overnight in anticipation of autoclaving the next day.
- Wrap packages to allow for steam penetration; aluminum foil may not allow steam penetration, and is not recommended for wrapping.
- Do not overload the chamber.
- Avoid over packing of autoclave bags.
- Do not seal bags or close bottles and other containers tightly.
- Do not stack containers.
- Always place autoclave bags/containers in a secondary container when autoclaving.
- Label waste by writing lab name and date on autoclave tape.
The changes that are seen on autoclave indicator tapes following an autoclave cycle do not guarantee that the contents of containers are sterile: they indicate only that the tape on the outside of the packages has been exposed to a certain amount of heat or steam. Proper autoclave performance is essential for sterilization. The time required for effective sterilization depends on the size of the load, volumes of liquid and density of materials to be autoclaved. Assessing autoclave performance regularly (at least once per month) is critical, the use of a heat-resistant biological indicator (BI) such as Bacillus stearothermophilus, should be used to ensure that the cycle in use really achieves sterilization conditions.