The Potassium Iodide Method for Determining Protection Factors in Open‐fronted Microbiological Safety Cabinets

Containment facilities for pathological material

In many biological research laboratories, besides the paramount need to protect the workers from infection, there is also an important requirement to maintain clean or sterile conditions for the work being handled. It should be noted that potentially hazardous biological material used in microbiological safety cabinets generally can be rendered safe by decontamination methods such as fumigation with formaldehyde gas. Filter testing methods, although playing a vital part in the safety performance of many containment systems are outside the scope of this chapter. It is now fully described in BS 5726 for testing microbiological safety cabinets; in addition, it is widely used to measure the operator protection of a whole range of other containment systems including laboratory fume cupboards. National Standards for safety cabinets and microbiological safety cabinets specify methods for assessing operator protection and these techniques can be used for risk assessment as is required by many regulatory authorities in many countries.

The testing of HEPA filters fitted to microbiological safety cabinets: a comparison of methods

Sensitivity tests of biological safety cabinets' contaminant contention to variations on indoor flow parameters in biosafety level laboratories

The biological safety cabinet is the one piece of laboratory and pharmacy equipment that provides protection for personnel, the product, and the environment. Through the history of laboratory-acquired infections from the earliest published case to the emergence of hepatitis B and AIDS, the need for health care worker protection is described. A brief description with design, construction, function, and production capabilities is provided for class I and class III safety cabinets. The development of the high-efficiency particulate air filter provided the impetus for clean room technology, from which evolved the class II laminar flow biological safety cabinet. The clean room concept was advanced when the horizontal airflow clean bench was manufactured; it became popular in pharmacies for preparing intravenous solutions because the product was protected. However, as with infectious microorganisms and laboratory workers, individual sensitization to antibiotics and the advent of hazardous antineoplastic agents changed the thinking of pharmacists and nurses, and they began to use the class II safety cabinet to prevent adverse personnel reactions to the drugs. How the class II safety cabinet became the mainstay in laboratories and pharmacies is described, and insight is provided into the formulation of National Sanitation Foundation standard number 49 and its revisions. The working operations of a class II cabinet are described, as are the variations of the four types with regard to design, function, air velocity profiles, and the use of toxins. The main certification procedures are explained, with examples of improper or incorrect certifications. The required levels of containment for microorganisms are given. Instructions for decontaminating the class II biological safety cabinet of infectious agents are provided; unfortunately, there is no method for decontaminating the cabinet of antineoplastic agents.

Open fronted Class I and II microbiological safety cabinets (MSCs) are required by the British Standard 5726 to provide similar levels of operator protection (viz. 10(5). In laboratories that are naturally ventilated large numbers of both types of cabinets have been shown to exceed this requirement consistently over a number of years. The designs of some mechanically ventilated laboratories, however, produce excessive turbulence and draughts that can prejudice containment at the front aperture. On-site commissioning tests to determine operator protection factor are now well established and are recognized as being essential to the setting up of all open fronted cabinets in both ventilated and unventilated laboratories. This paper shows that where environmental conditions induce unsatisfactory cabinet containment, adjustments to air supply and exhaust systems can be made which will enable both Class I and II cabinets to produce operator protection factors in excess of 10(5). When compatibility is achieved between the local environment and the cabinets it is demonstrated that disturbances at the front aperture, caused by operator working procedures or by disturbances due to personnel movement within the room, have similar effects on both Class I and II cabinets. Once performance levels have been satisfactorily achieved, regular containment testing has shown that consistent performance can be maintained. These aspects of open fronted safety cabinet performance are discussed in relation to ventilated laboratories suitable for work with the human immunodeficiency virus (HIV). Of paramount importance in the future is the necessity to design laboratory air systems that will be compatible with satisfactory safety cabinet performance--a relatively new requirement in ventilation system specifications.

Introduction:The operator protection factor (OPF) of four biological safety cabinets (BSCs) has been measured under standard and suboptimal conditions.Methods:The OPF for one BSC1, two BSC2, and an acid-fast bacilli staining station (AFBSS) was measured using the potassium iodide method for in situ testing of BSCs (CEN12469) over a range of inflow velocities under standard conditions and with common interfering factors (fans, opening doors, and walk pasts).Results:The BSC1 and the AFBSS gave a high level of protection under standard test conditions at all airflows (down to 0.3 and 0.38 m/s, respectively). During interfering processes, the BSC1 and AFBSS gave a high level of protection (OPF >105) at the specified inward airflow. At lower airflows, there was a predictable deterioration in performance. There was a significant difference in performance between the two BSC2s tested, with one model passing all tests under all interfering conditions at all airflows. The second BSC2 failed the standard test at the lowest airflow and provided poor levels of protection (OPF <105) in all tests carried out with interfering processes.Conclusion:Although BSC2s are capable of giving a high level of performance, this is design dependent and the BSC1 and AFBSS give a more predictable level of performance due to their simpler design. In environments where BSC certification is not possible, they may provide more robust and sustainable primary containment.

A modified microbiological safety cabinet which can be used as a class II and a class III safety cabinet has been bacteriologically tested. This cabinet makes use of a high-speed down-flow air curtain in the front opening to minimize the amount of air escaping over the arms of the operator. By using artificial aerosols and a dummy or a test person placing his arms into the working opening of the cabinet, a transfer from the inside to the environment was detected only when the highest concentration of the test aerosol was used. Since the number of bacteria detected was very low, this is considered to be acceptable. When the cabinet was used as a class III type, with a glove panel mounted in the front opening, leakage from the environment occurred. This could be completely prevented by fixing tape over the hinge of the front panel. The conclusion is drawn that this type of biohazard hood can be safely used as a class II and a class III microbiological safety cabinet, provided the construction of the hinge of the front panel will be adapted to prevent transfer from the environment to the working area.

A recent resolution of the Parliamentary Assembly of Europe (No. 986–1992) emphasizes that technical innovation is an important and continuing feature of modern society and that it will act as the driving force in commercial and industrial competition for a long while to come. The public draws substantial benefits from this technological progress but has also developed a keen awareness of the supposed effects of certain technologies on the ethical values on which society is based, on health and on the environment. In this context, the issue of risks (particularly those present in certain new technologies) becomes more complex. Despite a general improvement in safety levels and a substantial reduction in traditional risks, new types of risks, far more difficult to calculate and predict, are emerging. This is especially true in the chemical, pharmaceutical and biotechnology industries where these difficulties have been recognized and where safe systems of work and equipment are therefore being developed that can effectively contain potentially hazardous material. Of particular significance over the last 10 years in this area has been the marked improvement in the design and performance of safety cabinets and related containment systems for microbiological use. In the UK this has been due to a number of factors including the implementation of the requirements of BS 5726 1979 (Microbiological safety cabinets) (Anon. 1979) which have been complimentary to the COSHH (Control of Substances Hazardous to Health) Regulations (Anon. 1988) which themselves reinforced the Health and Safety at Work Act (Anon. 1974). Taken together, this framework has been responsible for significant improvements to the manufacturing technologies for safety systems, the management of containment systems within laboratories and the awareness by users of the functional requirements that all containment systems must now have.

Flexible film isolators: microbiological safety tests

Background: Technical protection measures for laboratory activities involving biological agents include biological safety cabinets (BSC) that may be contaminated. In the case of diagnostic activities with SARS-CoV-2, this may also affect BSC that are operated at protection level 2; therefore, decontamination of all contaminated surfaces of the BSC may be required. In addition to fumigation with hydrogen peroxide (H2O2), dry fogging of H2O2-stabilized peroxyacetic acid (PAA) represents another alternative to fumigation with formalin. However, to prove their efficacy, these alternatives need to be validated for each model of BSC.Methods: The validation study was performed on 4 different BSCs of Class II A2 using the “Mini Dry Fog” system.Results: An aerosol concentration of 0.03% PAA and 0.15% H2O2 during a 30 min exposure was sufficient to inactivate SARS-CoV-2. Effective concentrations of 1.0% PAA and 5% H2O2 were required to decontaminate the custom-prepared biological indicators loaded with spores of G. stearothermophilus and deployed at 9 different positions in the BSC. Commercial spore carriers were easier to inactivate by a factor of 4, which corresponded to a reduction of 106 in all localizations.Conclusions: Dry fogging with PAA is an inexpensive, robust, and highly effective decontamination method for BSCs for enveloped viruses such as SARS-CoV-2. The good material compatibility, lack of a requirement for neutralization, low pH – which increases the range of efficacy compared to H2O2 fumigation – the significantly shorter processing time, and the lower costs argue in favor of this method.

Comparative tests to measure operator protection factors in microbiological safety cabinets in accordance with British Standard 5726 have demonstrated good agreement in the results obtained by a microbiological method using a Collison nebulizer and the technique producing an aerosol of potassium iodide. Either method is suitable for testing for operator protection factors in Class I and Class II safety cabinets.The Collison nebulizer should be considered as the standard aerosol generator for the microbiological method; alternative nebulizers meeting the general requirements of BS 5726 should be compared in performance with this nebulizer if they are to be used for containment tests.Any microbiological safety cabinet specified for a new installation should have been ‘type’ tested to ensure compliance with BS 5726. However, in order to ensure adequate performance, on‐site commissioning tests (and routine maintenance checks thereafter) are necessary to verify that air velocity, filtration and operator protection factor requirements are met.

Biological safety cabinets are frequently relied upon to provide sterile work environments in which hazardous microorganisms can be safely handled. Verification of correct airstream velocities does not, by itself, ensure that adequate protection will be achieved under all users. Instead, the concentration of microorganisms in a cabinet operator's breathing zone must be measured during typical cabinet use conditions to determine whether the exposure is below acceptable limits. In this study, cabinet operator exposures were measured with a personal air sampler. Bacterial spores were released inside a cabinet as a uniform challenge aerosol, and the number of escaping spores was measured for several cabinet arrangements during a number of typical operations. The following were studied to determine their effects on aerosol containment: inflow air velocity, size of access opening, type of operator movements, location of operator's hands, and pace of activity. Other experiments examined differences in aerosol containment for eight typical microbiology operations when performed by six operators who covered a range of body heights and volumes.

Protection factor (PF) of a respirator is a number that describes the effectiveness of various classes of respirators in providing protection against exposure to airborne contaminants (including particulates, gases, vapors, and biological agents). The PF is derived from the ratio of the concentration of an airborne contaminant (e.g., hazardous substance) outside the respirator (Co) to the concentration inside the respirator (Ci) (i.e., Co/Ci). As the PF increases, there is an increase in the level of respiratory protection provided to employees by the respirator. PF Test Facility for the estimation of PF for various respiratory protective equipment was designed, fabricated, and installed at the Respiratory Protective Equipment Laboratory of Health Physics Division. The test facility consists of established air flow at a breathing rate through respirator darn on a human dummy and two identical tapings for iso-kinetic sampling from outside and inside the respirator. These tapings are coupled to two identical optical particle counters (OPCs) for the measurement of aerosol concentration simultaneously, and data acquired by the two OPCs are analyzed for estimating PF for different particle sizes using GRIM AEROSOL software. The results obtained from the studies carried out using this unique setup – air-purifying respirators such as half face mask, full face mask, and powered air-purifying respirators – were found offering a PF of 14, 112, and 1328, respectively, for selected range of 0.28–0.3-μm size standard sodium chloride (NaCl) aerosols. Standard NaCl aerosols used in experiments are polydispersed. However, the 0.3 μ size range (0.28–0.3) was selected as a benchmark for efficiency ratings and PF of respirators because it approximates the most difficult particle size for filters to capture and the least filtration efficiency is obtained in this range. This article brings out the details of design features of the setup and studies and results obtained for various types of respirators used in nuclear facilities.

Aseptic handling is the procedure to enable sterile products to be made ready to administer using closed systems (EU Resolution CM/Res(2016)2). Microbiological monitoring (MM) and media fills are used for environmental and process control.In this study, the application of MM methods during aseptic handling inside, or related to working in, a laminar airflow cabinet or safety cabinet in hospital pharmacies is described and evaluated. Results are expressed as colony forming units (cfu) and Contamination Recovery Rate (CRR; the rate at which MM samples contain any level of contamination -USP<1116>-). For trend analysis, a rolling CRR is developed (a rolling CRR calculates a CRR using a predetermined number of most recent samples).Of all MM methods, glove print is the most informative. The added value of air sampling is doubtful. Because of microbiological as well as statistical considerations, the use of CRR for assessing MM results is advised. Glove prints, in general, give the highest CRR. A CRR < 10% is a realistic limit for MM during aseptic handling in hospital pharmacies. A rolling CRR, calculated using the last 100 samples, is a good compromise between reliability of the CRR value and timely prediction of process changes.