Settle plates and contact plates are commonly used for environmental monitoring of cleanrooms. The ISO 14698 guideline states: “When culture media are used in cleanrooms, the external surface of their containers shall be maintained in a in a state of cleanliness to their use.” This requirement is usually discussed with regard to the microbiological contamination risk of these products.
Furthermore, all cleanrooms are qualified and monitored for particles that define the cleanliness of the air. The topic of this study is the particle emission of the packaging material of ICR plates in cleanrooms.
The ICR culture media in settle or contact plates are designed for use in cleanrooms, RABS and isolators. They are triple-bagged in a transparent and VHP impermeable bag. The inner bag is sealed with 10 media plates and a desiccant sachet.
After removal of the 2 outer bags in material locks, the innermost single bag is ready for use in a cleanroom ISO 5 or isolator. The inner bag is removed within the cleanroom environment. This study shall verify that the removal of the inner packaging material including the desiccant will not emit 0.5 µm particles that exceed the limits for an ISO 5 cleanroom environment.
The particle emission test was performed following ISO 14644-14 for the assessment of the suitability for use of equipment regarding airborne particle concentration. 30 bags each of either 10 contact or settle plates were used. 5 test runs were performed per batch of culture media. The selection of the media batches was performed regarding the maximum variety of different desiccant batches from 2 different suppliers.
A background read in the laminar flow hood with the particle counter was performed before starting a set of particle emission tests (5 tests per plate batch) After unwrapping the outer two bags outside of the hood, the innermost bag was placed 10 cm away from the isokinetic probe of a particle counter and the particle measurement was started. 15 seconds later, the bag was torn open and the plates were removed. The desiccant sachet was then placed on the top of the plate empty bag.
The workflow is illustrated below.
Figure 1. Performance of particle emission test at a distance of 10 cm.
1.1. Test setup - particle emission test
1.2. Opening of the plate staple
1.3. Removal of bag
1.4. Moving desiccant to the top
The average particle emission upon opening if the inner bag of 10 plates including movement of the desiccant should conform to ISO class 5 conditions: ≤ 3520 particles per m3 at a size of 0.5 µm.
The background read was zero in all cases. All tests conformed to the specified particle limit of a maximum of 3520 particles at a size of 0.5 µm per m3. All single results are shown in Figure 2. The highest single count was 250 x 0.5 µm particles. The average of all 30 test runs was 19 x 0.5 µm particles, which were emitted during the process of unpacking culture media and moving the desiccant sachet.
Figure 2. Number of 0.5 µm particles emitted during unpacking plates and removing desiccant sachet.
These results confirm the suitability of the ICR plates with desiccant in cleanroom environments up to ISO 5 classification
Nevertheless, it is recommended to perform the unpacking of the culture media plates as far away from critical manufacturing areas (i.e. open product) as possible.