Performing a Clean Zone Smoke Test

• Direct compounding area (DCA): a critical area within the ISO Class 5—a primary engineering control (PEC) where critical sites are exposed to unidirectional HEPA-filtered air, also known as first air.
• First air: the air exiting the HEPA filter in a unidirectional air stream that is essentially particle-free.
• Critical site: a location that includes any component or fluid pathway surfaces (e.g., vial septa, injection ports, beakers) or openings (e.g., opened ampoules, needle hubs) exposed and at risk or direct contact with air (e.g., ambient room or HEPA filtered), moisture (e.g., oral and mucosal secretions), or touch contamination. Risk of microbial particulate contamination of the critical site increases with the size of the openings and exposure time.

To test a clean zone, there are several issues like smoke reflux, dead spots, and numerous smoke deviations to look for. It is important not to separate the media filter from the wall since the farther it is from the wall, the more reflux can be found. The HEPA filter media should be flush with the walls of the clean zone and the front shield. The lexan shield must be consistent in its area of opening from the HEPA filter through the entire travel of the ISO-5 zone. Providing an incline to expand the area of the opening will lower the velocities and uniformity of the supply velocity. The uniformity of airflow velocity can be affected by the type of filter utilized, like a room side replaceable HEPA or ULPA filter. The typical loss of filter area also lowers the cfm (cubic feet per minute) of the filter, thus lowering the velocities as well as the volume.

To perform this test personally, I have taken 10 measurements (two columns, five rows) of velocity (testing a 2 by 4 ft. HEPA filter) using a termo-anemometer held by a suitable stand to avoid the manual fluctuations.

The test procedure to validate these clean zones requires a thermo-anemometer with a ring stand placing the probe of the anemometer 12 in. under the filter and beginning 6 in. away from the corner in each direction. Then a 12 in. grid is set up with readings taken every 12 in. on center.

Compute the arithmetic mean of the velocities recorded. Ex. average x = (y1 + y2 +…+ yn /n).

Where:
y= Average of each test position
n= Number of test positions
x = Average of filter face velocity
Compute the standard deviation (S)²=((y1 - x)² + (y2 - x)²
+ ….+ (yn - x)²) / (n-1)
Compute the relative standard deviation (RSD)= (standard
deviation (S) / average velocity (x)) * 100

Most compounding pharmacy clean zones have I.V. bars and bags which makes it important to get the relative standard deviation as low as possible. IEST-RP-CC-002.3 Section 6.1.1 states, "The maximum relative standard deviation is typically 15% when using an electronic micro-manometer with multipoint probe."

It's preferable to keep the RSD below 10% to create the effect necessary to pass the smoke challenge without high reflux, dead spots, or airflow that travels sideways as opposed to straight down.

Selecting the filters for the clean zones
Careful consideration of filter manufacturers is recommended as we have seen large discrepancies in uniformity of face velocities among different manufacturers and even filter types, like HEPA to ULPA designs. Uniformity or unidirectional flow is the key to the functionality of these systems as well as a continuous low level return beneath the work zone.

Achieving a deviation of less than 14 degrees in an ISO-5 clean zone
There must be a continuous length of HEPA filter across a wall away from the door with a 4 in. continuous wall return cavity along the back of the area. The clean zone must have 100% coverage of the area, and use a polycarbonate directional flow shield from the ceiling grid to 5 ft. off the floor. The work table or zone should be moved nearer or farther away from the back wall as necessary to cause a waterfall effect on the front and back edges of the work table. A solid table produces an effect similar to a biological safety cabinet centerline smoke split. (Note: Perforated tables are difficult to clean and maintain.) Be sure the table is no more than 30 in. in height and 30 in. or less in width. Once the desired water fall effect is noticed, secure the work table at that location and perform the smoke pattern test.

Performing the clean zone smoke pattern test
Purpose: This test determines that the airflow within the clean zone conforms to the manufacturer's design criteria. This shows the airflow within the DCA moving in a downward direction with no dead spots or refluxing in the critical site. Be sure that the ambient air does not enter the clean zone or other areas except through the supply HEPA filter. Once the air enters the DCA, it must move to the returns without reentry. (Note: This test should be performed following completion of the airflow velocity, volume, room air changes per hour, room pressures, and uniformity tests.)

Apparatus: A source of visible smoke that is generally neutrally buoyant. Chemical smoke tubes or glycol-base smoke generators are examples of acceptable smoke sources.

Good results can be achieved using a theatrical fog generator that has a mixture of glycol with a fan speed controller connected to a delivery tube, supported by a hands-free stand (1 in. diameter PVC with small holes to create a laminar-like curtain smoke pattern). It is recommended that the PVC tube be the same size as the distance between the front shield and the wall.
• Adjustable support stand
• Plumb bob
• Tape measure
• Video or digital camera

Procedure: • Place the delivery tube with the plumb bob.
• Turn on the smoke generator and adjust the fan speedcontrol to get the desire laminar airflow.
• Introduce the aerosol stream isokinetically and, as nearly as practical, isothermally.
• Generate the smoke remotely from the vicinity of the source.
• Move the smoke tube through the entire area to be tested, sliding the hands-free stand slowly so that the whole clean zone area is observed and video recorded.
• With the pointer mounted in the support stand, at the work table exit plane, measure the offset distance (Δs) between the theoretical straight-line flow point and the
center of the source stream. Measure the distance between the delivery outlet tube and the work table exit plane (d).
• Calculate the angle of deflection, Theta (θ). The angle (θ) is found as the arctangent of the ratio expressed as (Δs)/(d) using the equation: θ = Arctangent(Δs)/(d).
• Example: if the distance between the delivery outlet tube and the work table (d) is 4 ft. and the offset distance (Δs) between the theoretical straight-line flow point and the center of the source stream is 1 ft. Using the equation, we have θ = Arctangent (1 ft./4 ft.).
• θ = Arctangent 0.25.
• θ = 14.036°. That means that for every 4 ft. (d) we will have no more than 1 ft. (Δs).

Acceptance: Readings in excess of a 14-degree offset should be discussed with the customer and either approved or corrections made until acceptable.

The clean zone smoke pattern test needs be performed "as built," "at rest," and "operational" phase.

Other tests that need be performed are: airflow volume, airflow velocity, and uniformity test; HEPA filter leak test; airborne particle count test; rooms pressurization test; light level and uniformity test; noise level test; temperature uniformity test; moisture uniformity test; vibration test; microbiological sampling test and air changes per hour (ACPH) calculations. (See IEST-RP-CC-006.3 Section 5.1 and USP 34 (1116) for details.)

References1. IEST RP-CC-001.5, HEPA and ULPA filters.
2. IEST RP-CC-002.3, Unidirectional flow, clean air devices.
3. IEST RP-CC-006.3, Testing Cleanrooms.
4. United State Pharmacopeia (USP) 797, Pharmaceutical Compounding physical test.
5. United State Pharmacopeia (USP) 1116, Microbiological evaluation of clean rooms.
6. ISO 14644.1:1999, Cleanroom and associated controlled environments.
7. Controlled Environment Testing Association (CETA) CAG-003-2006, Revised Jan. 31, 2012,  Sterile Compounding facilities.