Introduction:- Control of airborne contamination requires certain measures to be adopted, which are usually dictated by the type of product required at the end of the preparation process. Pharmacy clean room facilities are designed, constructed and operated to minimize the risk of microbiological and physical contamination by non-viable airborne particulates to the products prepared. Measurement and determination of the number and size of airborne particulate contamination is essential to ensure that a suitable environment is maintained for the preparation of aseptically prepared products. In the event of an air handling system or clean air device failure or shutdown (controlled) it is important to know when the room or device environment is back within specification. Steps should be taken to determine when the facility or device has returned to its normal operating grade i.e. how quickly the facility or equipment cleans-up. Guidelines for determination of clean-up time for clean rooms and clean air devices following shut down of air handling units/devices are contained in a separate document. The guideline covers many of the aspects described below for routine monitoring.
 
Equipment:- It is standard practice to utilize modern technology and use an optical particle counter where the air sample is drawn into the instrument and passed through a light scattering device. The signal that this generates is electronically processed to display particle counts at different size ranges. The sampling rate can vary but the most likely sample volumes are 0.1ft³ or 1ft³. Particle counters can count a range of particle sizes ranging from 0.3μm up to 25μm. Pharmaceutical standards quote limits for the total number of particles equal to or greater than 0.5μm and 5μm, and these are the particle sizes that are usually measured. Counts of other particle sizes may be useful for investigation in the event of problems occurring.
 
Sample locations and volumes
Clean rooms:- The operational condition is the most important condition to be measured as it reflects the actual contamination when the area is working; it should be noted that monitoring in the operational condition will give the highest particle counts. It is necessary to take sufficient samples within the clean room to have confidence that the room is performing within the limits set by the standards. A statistical technique may be employed to give a mathematical basis to this confidence. Using this technique the number of sampling locations reflects the size of the room and its cleanliness e.g. the larger and cleaner the room the more sampling locations that must be taken. However the most common method for selection of the number of sampling locations can be determined using the formula:-
NL = √A
Where,
NL is the minimum number of sampling locations (rounded up to the next whole number).
A is the floor area of the clean room in m².
The sample locations selected should be evenly distributed within the area under test and at a position related to the working activity (typically at bench height 1m from the floor). A site plan should be prepared indicating sampling locations. The minimum volume to be sampled is 27L (approx 1ft³). The sampling rate can vary but most particle counters operate at a fixed sampling rate of either 0.1ft³ or 1ft³ per min. The sampling rate and the volume of air sampled should be recorded.
Where the sampling rate is 1ft³ per min, 1-minute samples should be taken and this should be repeated at least five times per sample location. It is common to take more samples at each location to allow equipment to settle down following the initial start-up. Where the sampling rate is 0.1ft³ per min, at least 1ft³ of air should be sampled at each location.
Clean air devices:- Measurements must be made in clean air devices where the contamination level is critical. It should be stressed that the sampling procedure must not interfere with work zone air quality or airflows when monitoring in the operational state. It is suggested that a grid approach is adopted for the work zone. The sampling rate and volume of air sampled should be as specified for clean rooms. Where the sampling rate is 1ft³ per min, 1-minute samples should be taken and this should be repeated at least five times per sample location in the clean air device. Where the sampling rate is 0.1ft³ per min, at least 1ft³ of air should be sampled at each location.
 Frequency of sampling:- In order to comply with cGMP the minimum frequency for monitoring of non-viable particulates is three monthly.
Note: It is preferable that sampling takes place with the facility in the operational condition i.e. personnel present and normal operations being carried out or in a condition specified. The operational condition for unidirectional airflow cabinets/isolators and transfer devices can be considered to be when an operator is working in any part of the clean air device. Sampling in the ‘at rest’ condition may be continued at an agreed frequency to monitor baseline contamination levels.
Method of sampling
Clean rooms:-

1. Set up the monitoring equipment to give total particle counts according to the operating procedure.
2. Record the name and number of operators working in the area being tested and their activity at the time of testing, where possible. Any changes in activities must be documented.
3. Carry out sampling at the locations marked on the site plan with the probe positioned facing upwards at normal working height i.e. approximately 1m. If this is not possible, place on the floor and record this. When testing in the “at rest” condition it is preferable if work progresses from “dirty” to clean areas. In all monitoring, steps should be taken to ensure that the sample probe does not pick up particle counts from the motor/exhaust of the test instrument or from adjacent operations.
4. Following the procedure for operating the particle counter, start the count.
5. Observe the first count to ensure the particle counter is operating correctly. Where appropriate check the first printout produced to ensure information is printed clearly.

Note: In carrying this out a greater proportion of particles will be observed due to the presence of the operator.

6. Where appropriate write sample location next to the counts on the printout. If equipment is operating satisfactory, continue the count, and vacate the room unless involved in the work session, for sufficient time to allow the appropriate number of samples to be taken.
7. If equipment is not operating satisfactory determine what the fault is by checking the standard operating procedures.

Clean air devices:-

1. Clean air devices (such as a unidirectional airflow cabinets or safety cabinets), which may have been switched off, should be switched on and allowed to run for the time specified in the local operating procedure or for the validated clean up time for the device before any particle counts are made.
2. Follow the appropriate transfer procedure ensuring the probe, probe stand, tubing and particle counter, where appropriate, are swabbed with sterile alcohol wipes before placing into the clean air device.
3. Set up the monitoring equipment to give total particle counts according to the operating procedure.
4. Record the name of operator(s) working in the clean air device being tested and their activity at the time of testing, where possible. Any changes in activities must be documented.

Note: In order to avoid sampling procedures causing interference to the work zone air quality or air flows during the preparation of products for administration to patients it is recommended that the operational sampling be performed during operator or process simulation testing.

5. Position the probe isokinetically in relation to the air flow (facing the air flow), ensuring the probe is halfway into the device being monitored. Other probe positions, e.g. facing work, may be used for monitoring specific activities, where this is deemed necessary.
6. Following the procedure for operating the particle counter, start the count.
7. Observe the first count to ensure the particle counter is operating correctly. Where appropriate check the first printout produced to ensure information is printed clearly. Note: In carrying this out a greater proportion of particles may be observed due to the presence of the operator.
8. Where appropriate write sample location next to the counts on the printout. If equipment is operating satisfactory then continue the count to allow the appropriate number of samples to be taken.
9. If equipment is not operating satisfactory determine what the fault is by checking the standard operating procedures.

Note for Isolators:- Where the isolator has an access port for the sampling tube this should be used and a suitable seal achieved so that the device may be monitored as described above. Where the isolator has no access port it is possible to monitor the device by cutting off one of the glove fingers, passing the sampling tube through this and then sealing it appropriately. This is not ideal as it means that the device cannot be monitored in the operational state (especially if it is a two glove isolator) and the device will require a replacement glove at the end of the test
period with a thorough clean down of the device to remove any possible contamination that may have entered by deliberately breaking the barrier. Alternatively small battery operated particle counters can be used to monitor the internal conditions of isolators in the operational state where no access port is available. The volume of air sampled with such equipment should be recorded.

Results and interpretation of results
Clean rooms:- Examine the results for each sample location. Determine the first and last counts in each location and discard as the equipment operator can often influence them. Select five consecutive counts at the end of the sampling period and calculate the mean of the 0.5μm and 5μm counts per m³ or other particle sizes under consideration. Record these calculations on the worksheet/record sheet and repeat for all sample locations in the clean room.

 
Clean air devices:- Examine the results for each sample location. Determine the first and last counts in each location and discard. Select five consecutive counts at the end of the sampling period and calculate the mean of the 0.5μm and 5μm counts per m³ or other particle sizes under consideration. Record these calculations on the worksheet/record sheet and repeat for all sample locations.

Interpretation of results:- Current clean rooms standards state that the room or device will be accepted as having passed the test if the particle concentration at each of the locations falls below the class limit. Therefore, if the mean number of particles per cubic metre for each particle size under consideration at each sampling position is equal to or less than the appropriate number given in Table 1.1., the controlled space (clean room or clean air device), under the conditions specified, is deemed to have a satisfactory level of environmental cleanliness.
(a) Limits for background environment for negative pressure isolators with type A, B, C1 transfer devices or background environment for positive pressure isolators with type A transfer devices.
(b) Limits for isolators to be sited in a grade D background or the background environment for negative pressure isolators with type C2, D, E, F transfer devices or the background environment for positive pressure isolators with type B, C1, D, E, F transfer devices.
(c) The conditions given for the “at rest” state should be achieved after a short “clean up” period of 15 – 20 minutes (guidance value) in an unmanned state after completion of operations.
(d) These areas are expected to be completely free from particles of size greater than or equal to 5μm. As it is impossible to demonstrate the absence of particles with any statistical significance the limits are set to 1 particle/per m³. During clean room qualification it should be shown that the areas can be maintained within the defined limits.

Action:- It can be appreciated that the airborne contamination level of a given clean room is dependent on the particle generating activities in the room. If the room is at rest, very low particle concentrations can be achieved closely reflecting the quality of the air supplied to the room and hence the efficiency of the filter system. If the room is operational there will be a greater particle concentration, which is wholly dependent on the number of staff and the activities they are performing. It is expected that a drop in classification will occur as a result of those activities. This information should be available when interpreting the data generated during the monitoring as it may allow problems to be pinpointed. It is difficult to replicate conditions when monitoring environments in the operational state and this should be considered when interpreting data and deciding whether or not an investigation and corrective action are necessary. Where limits are exceeded for clean air devices an investigation into the problem should always be carried out. Any corrective action taken as a result of investigations should be recorded. Retesting may be carried out immediately in clean rooms, where there is a known reason for the failure e.g. due to a certain activity or task being carried out, and if the results are acceptable the facility will be considered to have passed.
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Reference links
https://www.emlab.com/s/sampling/env-report-02-2010.html
https://www.pda.org/docs/default-source/website-document-library/chapters/presentations/missouri-valley/regulations-concerning-airborne-particle-counting.pdf?sfvrsn=4