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

Aim. Products for on-site urine drug testing offer the possibility to perform screening for drugs of abuse directly at the point-of-care. This is a well-established routine in emergency and dependency clinics but further evaluation of performance is needed due to inherent limitations with the available products. Methods. Urine drug testing by an on-site product was compared with routine laboratory methods. First, on-site testing was performed at the laboratory in addition to the routine method. Second, the on-site testing was performed at a dependency clinic and urine samples were subsequently sent to the laboratory for additional analytical investigation. Results. The on-site testing products did not perform with assigned cut-off levels. The subjective reading between the presence of a spot (i.e. negative test result) being present or no spot (positive result) was difficult in 3.2% of the cases, and occurred for all parameters. The tests performed more accurately in drug negative samples (specificity 96%) but less accurately for detecting positives (sensitivity 79%). Of all incorrect results by the on-site test the proportion of false negatives was 42%. The overall agreement between on-site and laboratory testing was 95% in the laboratory study and 98% in the clinical study. Conclusion. Although a high degree of agreement was observed between on-site and routine laboratory urine drug testing, the performance of on-site testing was not acceptable due to significant number of false negative results. The limited sensitivity of on-site testing compared to laboratory testing reduces the applicability of these tests.

Holographic optical tweezers are used to make comparative measurements of the hygroscopic properties of single component aqueous aerosol containing sodium chloride and ammonium sulfate over a range of relative humidity from 84% to 96%. The change in RH over the course of the experiment is monitored precisely using a sodium chloride probe droplet with accuracy better than ±0.09%. The measurements are used to assess the accuracy of thermodynamic treatments of the relationship between water activity and solute mass fraction with particular attention focused on the dilute solute limit approaching saturation vapor pressure. The consistency of the frequently used Clegg-Brimblecombe-Wexler (CBW) treatment for predicting the hygroscopic properties of sodium chloride and ammonium sulfate aerosol is confirmed. Measurements of the equilibrium size of ammonium sulfate aerosol are found to agree with predictions to within an uncertainty of ±0.2%. Given the accuracy of treating equilibrium composition, the inconsistencies highlighted in recent calibration measurements of critical supersaturations of sodium chloride and ammonium sulfate aerosol cannot be attributed to uncertainties associated with the thermodynamic predictions and must have an alternative origin. It is concluded that the CBW treatment can allow the critical supersaturation to be estimated for sodium chloride and ammonium sulfate aerosol with an accuracy of better than ±0.002% in RH. This corresponds to an uncertainty of ≤1% in the critical supersaturation for typical supersaturations of 0.2% and above. This supports the view that these systems can be used to accurately calibrate instruments that measure cloud condensation nuclei concentrations at selected supersaturations. These measurements represent the first study in which the equilibrium properties of two particles of chemically distinct composition have been compared simultaneously and directly alongside each other in the same environment.

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.

Data from a group of 20 subjects with normal baseline pulmonary function, who were exposed for 2 h to a test atmosphere containing a complex mixture of pollutants, have been contrasted with data from two other groups exposed to presumably non-toxic control atmospheres. Group 1 was exposed to clean air, group 2 was exposed to clean air containing sodium chloride aerosol at 270 micrograms m-3, and group 3 was exposed to the complex atmosphere containing sodium chloride (332 micrograms m-3) and zinc ammonium sulfate (23 micrograms m-3) aerosols plus nitrogen dioxide (0.5 ppm) and sulfur dioxide (0.5 ppm). These atmospheres (ranked according to the presumed relative toxicities of the components; clean air = 0, sodium chloride = 1, complex mixture = 2) were contrasted using multiple regression and partial correlation analyses. The effects of exposure to the complex gas-aerosol mixture on forced expiratory performance were not significantly different from those observed in subjects exposed to clean air or to sodium chloride aerosol.

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.

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.

The reaction coefficients of nitrogen dioxide and nitrous acid with monodisperse sodium chloride and ammonium sulphate aerosols have been measured in a flow reactor at atmospheric pressure. These experiments were performed at relative humidities above and below the deliquescence points of both aerosols (r.h. 50 and 85%) at 279 K. The results for NO2 afford a reaction coefficient in the range (2.8–10) × 10-4 and for HONO, (2.8–4.6) × 10-3. For both species, there appears to be an enhancement of the reaction coefficient on sodium chloride aerosol at 50% r.h. The results are compared with reaction coefficients determined by other experimental methods. A good agreement is found for both gases between this method and the coated denuder method previously developed in our research laboratories (Msibi et al., 1993) and with the majority of other published data for NO2. In the case of HONO, our estimate of reaction coefficient is smaller than, or at the lower limits of the ranges reported by other published studies.

We have previously demonstrated that inhalation of the dust produced by dual frontal airbag deployment can result in significant bronchospasm in approximately 40% of mild to moderate asthmatics. This study was performed to determine the cause of the asthmatic response. Controlled laboratory study. Asthmatics who were previously tested for their response to airbag effluents were exposed for twenty minutes to either 1) airbag effluents from airbag systems in which the airbag was insulated from the hot deployment module; 2) non-sulfur containing airbag effluents; 3) sodium chloride aerosol; or 4) sodium carbonate-bicarbonate aerosol (pH 10). Pre-exposure, post-exposure, and 2 hour post exposure pulmonary spirometry and mechanics were measured. Subject's filled out symptoms questionnaires before exposure, 2, 4, 8, 12, and 19 minutes into the exposure, immediately post-exposure, and 2 hours post-exposure. Prevention of the pyrolysis of the passenger-side bag as it rested on the hot module after deployment did not diminish the asthmatic response. Removal of sulfur-containing oxidants from the airbag pyrotechnic chemistry, which may have led to sulfite production, similarly did not alleviate the asthmatic response to the airbag effluents. Lastly, when asthmatics were exposed to sodium chloride and sodium carbonate-bicarbonate aerosols at approximately the same concentration (approximately 220 mg/m3) as the airbag aerosol concentration that occurred in the in-car tests, they had responses similar to those produced by the airbag exposures. We conclude that the amount of soluble particulate contained in the aerosol discharged into the passenger compartment by dual frontal airbag deployment is largely the cause of the observed evoked asthmatic attacks. The alkaline pH of the airbag and carbonate aerosols may have added an additional degree of provocation.

Frusemide inhaled by asthmatic subjects before a variety of indirect bronchial challenges inhibits the airway response to these challenges. Since inhalation of hyperosmolar saline is an indirect bronchial challenge, the effect of inhaled frusemide and its vehicle on airway sensitivity to a 4.5% sodium chloride (NaCl) aerosol challenge was investigated. Eleven asthmatic subjects (five females, six males) who had a 20% fall in forced expiratory volume in one second after 4.5% NaCl challenge were enrolled in this double blind controlled crossover trial. Sensitivity was measured as the dose of aerosol required to provoke a 20% fall in FEV1. Frusemide (33.2 mg) or its vehicle was delivered through a Fisoneb ultrasonic nebuliser and inhaled 10 minutes before challenge with 4.5% NaCl. A Mistogen ultrasonic nebuliser was used to generate the 4.5% NaCl aerosol and FEV1 was measured before and one minute after each challenge period of 0.5, one, two, four, eight, eight and eight minutes. The doubling dose difference for PD20 was calculated. Frusemide or vehicle had no effect on baseline lung function. The geometric mean PD20 after vehicle was 1.3 ml with a 95% confidence interval of 0.7-2.3 and after frusemide was 8.2 ml with a 95% confidence interval of 4.7-14.1. This represented a 2.6 doubling dose increase in PD20 after frusemide inhalation. In five of the 11 subjects an increase from baseline FEV1 occurred after exposure to 4.5% NaCl challenge in the presence of frusemide. This transient bronchodilatation may be caused by the release of prostaglandin E2. Inhalation of frusemide is very effective in delaying airway narrowing induced by an aerosol of 4.5% NaCl in asthmatic subjects.

Is ≥ 100% the magic number to rule out the laboratory diagnosis of von Willebrand disease based on initial testing?

To test a performance of the microbiological safety cabinets (MSCs) according to the type of MSCs in microbial laboratories. Tests were carried out to assess the performance of 31 MSCs in 14 different facilities, including six different biological test laboratories in six hospitals and eight different laboratories in three universities. The following tests were performed on the MSCs: the downflow test, intake velocity test, high-efficiency particulate air filter leak test and the airflow smoke pattern test. These performance tests were carried out in accordance with the standard procedures. Only 23% of Class II A1 (8), A2 (19) and unknown MSCs (4) passed these performance tests. The main reasons for the failure of MSCs were inappropriate intake velocity (65%), leakage in the HEPA filter sealing (50%), unbalanced airflow smoke pattern in the cabinets (39%) and inappropriate downflow (27%). This study showed that routine checks of MSCs are important to detect and strengthen the weak spots that frequently develop, as observed during the evaluation of the MSCs of various institutions. Routine evaluation and maintenance of MSCs are critical for optimizing performance.

Containment facilities for pathological material

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.

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.

Microbiological Safety Cabinets (MSC) designed to minimize hazards inherent in work with agents assigned to biosafety levels 1, 2, 3, or 4by keeping hazards work in controled area via filtered air flow. This work defines the tests that shall be passed by such cabinetry to meet the EN 12469 standard. In this work, 5 different types of MSCs' were tested according to the EN 12469 standards and 5 different test methods were analysed.