13 May, 2008
Session 3b – Control
13:30 p.m. - 15:00 p.m  

Control Performance of Ventilated Safety Weighing Cabinets for Potent Pharmaceuticals

Presentation by: Michael C. Perry

Objectives:
The objective of this study was to conduct a detailed evaluation of the control performance capability of four design variations of a ventilated safety weighing cabinet.  The evaluations were carried out under controlled conditions using a surrogate active pharmaceutical ingredient (API).

Safety weighing cabinets (SWCs) are small ventilated enclosures used mainly for small scale laboratory weighing operations.  These devices have design features aimed at delivering laminar airflow with the dual objective of providing good control performance and weigh balance stability, balance stability being a problem in traditional devices such as fume cupboards.  SWCs offer the potential to control small scale laboratory manipulations where potent pharmaceutical materials with occupational exposure limits below 100 ng/m 3 are being handled.

The presentation will introduce the design concepts of these devices and their intended use.  The results of area and personal surrogate airborne sampling will be discussed, as well as commissioning, ergonomic and behavioural factors which may impact on the control performance of the devices.

Method:
Naproxen sodium was chosen as the surrogate material as it offers a more rigorous challenge to control performance than other commonly used surrogates such as lactose.  Naproxen sodium is a fine crystalline material which readily becomes airborne, is of low toxicity, and for which a sensitive analytical method with a limit of detection of 0.25 ng per filter is available.  This allowed the control performance of the SWCs to be evaluated against an approximate control performance target concentration of 10 ng/m 3.

Area and personal samples of airborne surrogate material were collected during the undertaking of a standardised weighing procedure.  The procedure comprised approximately ten repeat weighings of 1 g of the surrogate, followed by cleaning operations and disposal of contaminated waste.  The procedure was conducted and evaluated three times for each SWC, and different operators were used for each of these evaluations to assess variability in control performance due to operator practice.  In addition to the measurements collected outside the devices, measurements were also taken inside one SWC with the aim of evaluating the surrogate challenge concentration.

An important aspect of this work was the training provided to operators.  This included safe handling techniques for potent pharmaceutical powders, with the objective of minimising releases of airborne particulate material during the weighings.

Results:
The working space available in each of the SWCs varied considerably.  The smallest SWC presented the greatest organisational challenge to the operators, and consequently posed the greatest risk of accidental exposure.  Physical attributes of operators, such as arm length also affected the positioning of equipment for individual working comfort.  There is evidence to suggest that working distance inside the unit can influence control performance.  However, neither SWC size or operator physical attributes could, on this occasion, be conclusively related to results arising from the evaluations.

Of the 70 air samples collected, 69 were found to be below the 0.27 ng limit of quantification, resulting in airborne concentrations of 3 ng/m 3 or less.  Indicative control performance concentrations ranged from 11 ng/m 3 to 32 ng/m 3. Concentrations measured inside one SWC ranged from 226 – 6,126 ng/m 3.

Conclusions:
The results suggest that safety weighing cabinets are capable of providing suitable control for highly potent API’s, with occupational limits of less than 100 ng/m 3, for low-intensity and small scale laboratory powder handling activities such as weighing and solution make-up.   With appropriate use, professional support, training and monitoring programmes, these devices can provide a viable alternative to isolators where handling of potent APIs is infrequent and/or involves handling small quantities.


Michael C. Perry, MFOH, Senior Occupational Hygienist, European Operations. SafeBridge is a professional technical firm of health professionals and other scientific consultants providing EH&S services to pharmaceutical, fine chemical, and biotechnology industries.

About the British Occupational Hygiene Society

What is the aim of BOHS?
Every year in Britain alone, more than two million people experience symptoms of ill-health believed to have been caused or made worse by work and the latest figures published by the Health & Safety Executive show that an estimated 30 million working days are lost annually due to work-related ill-health (compared to nine million due to workplace injury). Established since 1953, BOHS’s aim is simple: to help to reduce work-related ill-health. We do this by promoting public and professional awareness, good practice and standards, and by researching and advancing education in the science of occupational health and hygiene.

For more information:
Tel.: David Riordan, +44 1332 250718

Email: david@bohs.org
URL: http://www.bohs.org/eventDetails.aspx?event=123

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