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Safety cabinets—the British Standard revised
Journal
of Hospital
Infection
(1993) 23, l-3
EDITORIAL
Safety
cabinets-
the British
Standard
revised
The first issue of TheJournal of Hospital Infection contained an editorial’ on the British Standard (BS) for microbiological safety cabinets (BS 5726, 1979), and serendipity allows celebration of the Journal’s new cover by a discussion of the revised BS 5726, 1992.2m5Manufacturers were quick to design to the 1979 Standard, and the safety cabinet scene was much improved. The Standard required only minor changes and an amendment issued in 1982 provided a new diagram for a Class III cabinet and slight alterations of the specification and test methods. The BS Technical Committee remained in being, and after 5 years confirmed the Standard. A final and significant amendment was made in 1987-namely the requirement that ‘The direction of airflow, as demonstrated by smoke or other visualisation tests shall be inward over the whole area of the working aperture.’ Kennedy6 described a simple method for this test based on the mist of water vapour from an ultrasonic nebulizer. Why revise the Standard? Some problems persisted, primarily with incorrect installations. In our own laboratory the new Class I cabinets did not achieve design airflow until the ridged metal duct was replaced by smooth plastic, and one Class II cabinet we tested had the fan mounted to blow rather than exhaust. Clarke’ described the failure of correctly specified cabinets when placed in a high-risk laboratory equipped with fierce ventilation set for 60 air changes per hour. Users voiced several concerns over size restrictions and failure of monitoring processes. The allowable number of amendments had been made; any more and the Standard would become unwieldy. Finally the British Standards Institute (BSI) approach to standards changed. A Standard can now only cover a single topic-e.g. manufacture of the item, or installation thereof, but not both. All requirements in the Standard must be verifiable. The BSI now has a scientific editing team to apply a final polish to the standards. The first step towards the revision was to circulate a questionnaire among users and makers of cabinets requesting comments on the current standard. Thirty-two replies were received from a wide spectrum of respondents including Health Service users (12), universities (five), manufacturers (five), industrial users (four) and others ranging from architects to the Medical Research Council. ‘I’he main criticisms related to reliability of the Correspondence IIK.
to: S. LV. H. Sewsom,
Papworth
Hospital,
Papworth
Everard,
Cambridge
CR3 XRE,
2
Editorial
electronics: speed controllers, indicators and alarms. A misleading indicator is worse than none, and one that cannot be seen by the operator is useless. Alarms should be ‘fail’ safe. Many commented on the failure of finishes, particularly where corrosive agents such as hypochlorites have been used. Some disquiet was expressed about the KI Discus test system-especially its reproducibility; but many respondents welcomed it as a non-invasive test method. Seals and night doors were mentioned as problem areas. Difficulties with installation and servicing were also highlighed. Armed with this information, the Committee set out to revise the Standard. The final result (BS 5726 Parts l-4) is now complete. How does it differ from its predecessor? The most obvious change is in presentation, which like BS 7258 for fume cupboards is in four parts. Parts 1 and 3 are specifications-Part 1 for design, construction and performance prior to installation and Part 3 for performance after installation. Parts 2 and 4 are recommendations-Part 2 for information to be exchanged between the purchaser, vendor and installer, with recommendations for installation and Part 4 for selection, use and maintenance. The specification for cabinet construction contains two main changes. It is less restrictive, and written in terms of performance tests. These are described in full for stability, vibration and resistance to chemicals. Several alterations of emphasis have been included. Cabinet width is no longer specified except in so far as wider cabinets require extra operator protection tests, and the light intensity required has been reduced to 500 lumens. One major change is the inclusion of cabinets that recycle air into the laboratory provided they do so through two high efficiency particulate air (HEPA) filters (and have Health and Safety Executive approval where appropriate). Recycling cabinets raise the problem of how to exhaust fumigants safely. Either temporary ducting to the outside, or a thimble system leading to the building exhaust ventilation would be required. Part 2, on installation, closely resembles the fume cupboard Standard, and provides a checklist of all the factors that should be taken into account when deciding what sort of cabinet to buy and where it should be installed. A set of useful diagrams showing the space allocations is included. Part 3 is a very slender document giving a specification for performance after installation. The prototype cabinet must be fully tested by the makers, but production models require testing ‘on site’ after installation, hence this specification. While airflow measurements on the original design should last for 5 min per position, this is obviously impractical for the regular checks by laboratory staff or service engineers, so 1 min is allowed for this. Finally, Part 4 is the ‘nitty-gritty’ of cabinet use; originally presented as ‘Notes for Users’ in the original Standard, and echoed in various safety manuals. Where next? Maastricht notwithstanding, European Standards are on the horizon. Once a European Committee is in being with an agreed work programme local Standards activities must cease. Indeed, at one stage there was some doubt as to whether the 1992 revision could be published.
Editorial
3
Laboratory safety has been moved into ‘Biotechnology’; cabinets appear in a long list of potential contenders for the European work programme so a Standard may be some years away. BS 5726 has taken note of the American Standard NSF 49s for Class II cabinets, and the German Standard,’ with respect to test methods, and so should be compatible with standards elsewhere. Other standards have not addressed cabinet installation, merely their construction. When a European Working Group is finally set up, it is hoped that the BS, as the most recently published and comprehensive standard, may be acceptable as a basis for a joint standard, and work will proceed towards that end. S. W. B. Newsom
Papworth Papworth Cambridge
Hospital, Everard, CB3 8RE, UK.
References 1. Newsom SWB. Safety cabinets encounter the British Standard. J Hasp Infect 1980; 1: 11-13. 2. Microbiological Safety Cabinets BS 5276 Part 1: 1992 SpeciJication for Design, Construction and Performance Prior to Installation. British Standards Institute, 2 Park St, London. 3. Microbiological Safety Cabinets BS 5276 Part 2: I992 Recommendations for Information to be Exchanged Between Purchaser, V en d or and Installer and Recommendations for Installation. British Standards Institute, 2 Park St, London. Safety Cabinets BS 5276 Part 3: 1992 Specification for Performance after 4. Microbiological Installation. British Standards Institute, 2 Park St, London. for Selection, Use 5. Microbiological Safety Cabinets BS 5276 Part 4: 1992 R ecommendations and Maintenance. British Standards Institute, 2 Park St, London. 6. Kennedy, DA. Water fog as a medium for visualisation of airflows. Ann Occ Hyg 1987; 31: 255-259. RP. Pers. comm. 1990. 7. Clarke Sanitation Foundation Standard No. 49 for Class II (Biohazard) Cabinetry. 8. National National Sanitation Foundation, Ann Arbor, Michigan, USA 1983. 9. DIN Standard 12 950. Laboratory furniture; safety cabinets for microbiological and biotechnical work; safety requirements, tests. 1991.
of Hospital
Infection
(1993) 23, l-3
EDITORIAL
Safety
cabinets-
the British
Standard
revised
The first issue of TheJournal of Hospital Infection contained an editorial’ on the British Standard (BS) for microbiological safety cabinets (BS 5726, 1979), and serendipity allows celebration of the Journal’s new cover by a discussion of the revised BS 5726, 1992.2m5Manufacturers were quick to design to the 1979 Standard, and the safety cabinet scene was much improved. The Standard required only minor changes and an amendment issued in 1982 provided a new diagram for a Class III cabinet and slight alterations of the specification and test methods. The BS Technical Committee remained in being, and after 5 years confirmed the Standard. A final and significant amendment was made in 1987-namely the requirement that ‘The direction of airflow, as demonstrated by smoke or other visualisation tests shall be inward over the whole area of the working aperture.’ Kennedy6 described a simple method for this test based on the mist of water vapour from an ultrasonic nebulizer. Why revise the Standard? Some problems persisted, primarily with incorrect installations. In our own laboratory the new Class I cabinets did not achieve design airflow until the ridged metal duct was replaced by smooth plastic, and one Class II cabinet we tested had the fan mounted to blow rather than exhaust. Clarke’ described the failure of correctly specified cabinets when placed in a high-risk laboratory equipped with fierce ventilation set for 60 air changes per hour. Users voiced several concerns over size restrictions and failure of monitoring processes. The allowable number of amendments had been made; any more and the Standard would become unwieldy. Finally the British Standards Institute (BSI) approach to standards changed. A Standard can now only cover a single topic-e.g. manufacture of the item, or installation thereof, but not both. All requirements in the Standard must be verifiable. The BSI now has a scientific editing team to apply a final polish to the standards. The first step towards the revision was to circulate a questionnaire among users and makers of cabinets requesting comments on the current standard. Thirty-two replies were received from a wide spectrum of respondents including Health Service users (12), universities (five), manufacturers (five), industrial users (four) and others ranging from architects to the Medical Research Council. ‘I’he main criticisms related to reliability of the Correspondence IIK.
to: S. LV. H. Sewsom,
Papworth
Hospital,
Papworth
Everard,
Cambridge
CR3 XRE,
2
Editorial
electronics: speed controllers, indicators and alarms. A misleading indicator is worse than none, and one that cannot be seen by the operator is useless. Alarms should be ‘fail’ safe. Many commented on the failure of finishes, particularly where corrosive agents such as hypochlorites have been used. Some disquiet was expressed about the KI Discus test system-especially its reproducibility; but many respondents welcomed it as a non-invasive test method. Seals and night doors were mentioned as problem areas. Difficulties with installation and servicing were also highlighed. Armed with this information, the Committee set out to revise the Standard. The final result (BS 5726 Parts l-4) is now complete. How does it differ from its predecessor? The most obvious change is in presentation, which like BS 7258 for fume cupboards is in four parts. Parts 1 and 3 are specifications-Part 1 for design, construction and performance prior to installation and Part 3 for performance after installation. Parts 2 and 4 are recommendations-Part 2 for information to be exchanged between the purchaser, vendor and installer, with recommendations for installation and Part 4 for selection, use and maintenance. The specification for cabinet construction contains two main changes. It is less restrictive, and written in terms of performance tests. These are described in full for stability, vibration and resistance to chemicals. Several alterations of emphasis have been included. Cabinet width is no longer specified except in so far as wider cabinets require extra operator protection tests, and the light intensity required has been reduced to 500 lumens. One major change is the inclusion of cabinets that recycle air into the laboratory provided they do so through two high efficiency particulate air (HEPA) filters (and have Health and Safety Executive approval where appropriate). Recycling cabinets raise the problem of how to exhaust fumigants safely. Either temporary ducting to the outside, or a thimble system leading to the building exhaust ventilation would be required. Part 2, on installation, closely resembles the fume cupboard Standard, and provides a checklist of all the factors that should be taken into account when deciding what sort of cabinet to buy and where it should be installed. A set of useful diagrams showing the space allocations is included. Part 3 is a very slender document giving a specification for performance after installation. The prototype cabinet must be fully tested by the makers, but production models require testing ‘on site’ after installation, hence this specification. While airflow measurements on the original design should last for 5 min per position, this is obviously impractical for the regular checks by laboratory staff or service engineers, so 1 min is allowed for this. Finally, Part 4 is the ‘nitty-gritty’ of cabinet use; originally presented as ‘Notes for Users’ in the original Standard, and echoed in various safety manuals. Where next? Maastricht notwithstanding, European Standards are on the horizon. Once a European Committee is in being with an agreed work programme local Standards activities must cease. Indeed, at one stage there was some doubt as to whether the 1992 revision could be published.
Editorial
3
Laboratory safety has been moved into ‘Biotechnology’; cabinets appear in a long list of potential contenders for the European work programme so a Standard may be some years away. BS 5726 has taken note of the American Standard NSF 49s for Class II cabinets, and the German Standard,’ with respect to test methods, and so should be compatible with standards elsewhere. Other standards have not addressed cabinet installation, merely their construction. When a European Working Group is finally set up, it is hoped that the BS, as the most recently published and comprehensive standard, may be acceptable as a basis for a joint standard, and work will proceed towards that end. S. W. B. Newsom
Papworth Papworth Cambridge
Hospital, Everard, CB3 8RE, UK.
References 1. Newsom SWB. Safety cabinets encounter the British Standard. J Hasp Infect 1980; 1: 11-13. 2. Microbiological Safety Cabinets BS 5276 Part 1: 1992 SpeciJication for Design, Construction and Performance Prior to Installation. British Standards Institute, 2 Park St, London. 3. Microbiological Safety Cabinets BS 5276 Part 2: I992 Recommendations for Information to be Exchanged Between Purchaser, V en d or and Installer and Recommendations for Installation. British Standards Institute, 2 Park St, London. Safety Cabinets BS 5276 Part 3: 1992 Specification for Performance after 4. Microbiological Installation. British Standards Institute, 2 Park St, London. for Selection, Use 5. Microbiological Safety Cabinets BS 5276 Part 4: 1992 R ecommendations and Maintenance. British Standards Institute, 2 Park St, London. 6. Kennedy, DA. Water fog as a medium for visualisation of airflows. Ann Occ Hyg 1987; 31: 255-259. RP. Pers. comm. 1990. 7. Clarke Sanitation Foundation Standard No. 49 for Class II (Biohazard) Cabinetry. 8. National National Sanitation Foundation, Ann Arbor, Michigan, USA 1983. 9. DIN Standard 12 950. Laboratory furniture; safety cabinets for microbiological and biotechnical work; safety requirements, tests. 1991.