The requirements outlined below must be met when cytostatics are prepared. However, they also apply to other substances, e.g. other CMR substances, genetically modified organisms and microbiological organisms in the BSL1 (BSL = Biosafety Level) 2–4 risk category.
When one or more safety cabinets are installed in a room, they must not be allowed to have a negative effect on their respective protective function or on that of other cabinets in the room.
For this reason, the minimum requirements for a room in which a safety cabinet is to be installed are outlined in "Quality Standard for the Oncology Pharmacy Service" (QuApos):
For further information on minimum clearances, please refer to the British Standard BS 5726 Part 2, 1991 (see Figure 19).
It has been proven that persons walking past the front of the cabinet have the greatest impact on the protective function of the cabinet. For this reason, particular activities should be refrained from in the room when critical work steps are being carried out. The protective function is also impacted by the user moving his/her arms.
When safety cabinets are used during the processing of substances that are hazardous to health, the exhaust air must never be returned to the room. Safety cabinets that cannot be directly connected to the exhaust system are an exception. In such cases, the exhaust air must be filtered twice using H13 or H14 filters. At the same time, it must be proven that materials from the safety cabinet cannot escape into the surrounding room. For this reason, it is important to ensure that newly installed safety cabinets can be connected to the exhaust air system. Experience has shown that the exhaust fan performance of central air-handling systems tends to fluctuate: as a result, a permanent connection is not advisable. An increase in the volume of extracted air can mean that the product is no longer protected. A decrease in the air volume can lead to back pressure in the cabinet, with the result that the protection of personnel can no longer be maintained. For this reason, an open connection is normally given preference over a permanent one, allowing the air volume balance to be extracted from the room. The two vent pipes are aligned centrally in one another leaving a gap through which the balance of air can be sucked in (see Figure 20).
It must be ensured that the volume of air sucked in by the ventilation system is always greater than the volume of exhaust air from the safety cabinet. At the same time, the gap should not be too big. This means that the air velocity, which is used to ensure that exhaust air from the safety cabinet does not escape into the room, remains sufficiently high. An alarm must be automatically triggered if the central ventilation system fails, and work within the cabinet must be stopped immediately. Normally, acoustic and visual alarm signals are used to ensure that it is perceived by all members of staff.
This design is also useful if the cabinet is not used on a 24-hour basis, e.g. only during the day or as required. The air balance for the room in which the safety cabinet is installed should always be the same so that the control unit of the central air-conditioning system is not overtaxed.
When the cabinet is in use, an air volume of 400 m3/h is sucked from the room through the aperture into the cabinet. This air volume is equal to the exhaust air volume from the safety cabinet. Because the outgoing air volume must be larger, a larger value is selected, for example 500 m3/h. In this case, the air volume balance is 100 m3/h. When the cabinet is not in use, 400 m3/h of outgoing air is missing and the air volume balance is 500 m³/h. This compensation can only be achieved without the use of control technology if the previously described construction design is used.
The text is an excerpt from GMP Series Sterile Manufacturing: Barrier Systems, Isolator and Safety Cabinets
Don’t miss ordering your copy of Sterile Manufacturing: Barrier Systems, Isolator and Safety Cabinets
Andreas Nuhn, Dr. Hans H. Schicht