Air Flow Smoke Pattern Testing. Written by CriticalPoint
Various standards covering sterile operations including USP <797>, the FDA Aseptic Processing Guide, and State Boards of Pharmacy require an airflow visualization study to prove that the primary engineering controls (PEC) are suitable for the intended activity. The airflow must be unidirectional and devoid of turbulence and updrafts. Historically, compounding pharmacies have turned to their certifier for this critical test, turning it into a checkbox for compliance rather than the important training tool it was intended to be.
We would like you to consider performing this testing yourselves. It also can be incorporated into initial and ongoing training. Training has consistently been proven to be more effective if methods of visual feedback are incorporated.
An airflow visualization (smoke pattern test) should be used to train and instruct compounding personnel in proper aseptic technique for every PEC in which they work. Working in a horizontal flow Laminar Air Flow Workstation (LAFW) is different that working in a vertical flow Biological Safety Cabinet (BSC) or Compounding Aseptic Isolator (CAI). Airflow must be traced from the entrance plane (HEPA filter diffuser) across the Direct Compounding Area (DCA) to the exit plane. The DCA is the area within the PEC where critical operations are conducted.
- The entrance plane in a horizontal flow LAFW is the HEPA filter at the rear of the work surface. The exit plane is the area behind the operator. Air must be traced from the HEPA filter diffuser screen across the critical sites in the DCA to and across the operator and should not reflux back into the work area after passing through it.
- The entrance plane in a vertical flow unidirectional airflow device is the HEPA filter diffuser screen above the work surface. In a unidirectional vertical flow area, the diffuser screen will traverse the entire entrance plane from the front wall to the back wall and from side wall to sidewall. The exit plane in a vertical flow device is the work surface. Air must be traced from the diffuser screen across the critical sites in the DCA to and into the air grilles at the front and rear of the work surface.
- The air in the center of the work area at the work surface of a vertical flow device is typically the worst airflow in many devices.
- The air closest to the front intake grille is often the best airflow within a vertical flow device.
- In both vertical and horizontal airflow, the airflow through the DCA must be shown to be smooth and without turbulence and updrafts.
- Air must be shown to sweep across the critical site.
- Air flowing out of the HEPA filter diffuser screen is considered “First Air” until hits an obstruction such as an IV bar, the operator’s hands, vials, bags, and other supplies. “First Air” must be proven to exist at all critical sites.
An airflow visualization study can be the best aseptic technique training tool in your training and process set-up arsenal. You can use smoke studies to:
- Determine how to place materials within the PEC to minimize turbulence
- Differentiate the area within the PEC where sterile materials are unwrapped before placement in the DCA
- Demonstrate that the air from the particle-generating unwrapping process does not migrate into the DCA
- Demonstrate that the air that passes over the critical sites flows into the air returns or past the operator and does not flow back into the DCA
- Demonstrate how hands must be positioned in vertical flow vs. horizontal airflow
- Demonstrate how vials, syringes and other equipment and supplies used in compounding must be manipulated to ensure first air at the critical site
- Determine how to position large objects within the DCA:
- Large, especially flat objects will create turbulence. Use smoke studies to position objects in a manner that mitigates the turbulence and prevents turbulent airflow from effecting the DCA. Air must flow over, across, and under all objects. Often, feet or risers must be installed to create a gap between the larger objects and the work surface.
- For many years, Baker and Nuaire sold LAFWs with a lip at the back of the work surface. These units can be retrofitted with a diffuser screen that will eliminate turbulence caused by this lip. If you have one of those units (not retrofitted with a diffuser screen), there is a zone of turbulent airflow on the work surface. An EM 2400 compounding device placed in in this LAFW will create a significant area of turbulence and if the air cannot flow under the compounder, it will roll over the top of it in a very turbulent manner. This will prevent “First Air” at the critical sites on top of the compounder. Installing feet on the bottom of the compounder that raise it above this turbulent zone will greatly reduce the refluxing air. The return grilles in a vertical flow PEC must be kept clear but these grilles should be exploited when positioning large objects. Air is more efficiently pulled across an object than blown across it. Positioning an object close to the returns without blocking them will promote a sweeping action over and away from the critical sites.
Smoke studies must be videotaped to properly document the device is suitable for the intended task and that the technicians properly exploit “First Air.”
- Regulators expect to see that every PEC has been properly integrated into the facility and that technicians use “First Air” and display proper aseptic technique. We suggest that technicians demonstrate these skills in every PEC in which they compound.
- Fancy video equipment is not required. A modern cellphone video camera can be used to videotape the visualization study. For slightly better results, consider a Go-Pro camera. If a cellphone is used, it must be vigorously and thoroughly cleaned with a germicidal detergent and followed by disinfection with sterile IPA and the person charged with recording the video must be aware that their hands (and the phone) are highly contaminated and therefore must refrain from placing their phone or hands on ISO 5 or ISO 7 surfaces.
- Practice is needed to determine the best camera angles to show the smoke effect inside the PEC. Often it is not clear what the video was designed to reflect. This can be avoided by making sure the smoke is flowing where the work is being done and that the angle confirms the flow is where you see it when standing at the PEC.
- The video must show where the smoke enters the DCA, as it crosses the critical site, and prove that it does not reflux back into the DCA after exiting.
- Think of Goldilocks when choosing the source of smoke…
- Too much smoke creates a large mass of white smoke that distorts the view and misrepresents what is occurring at the critical site. Refluxes and updrafts are masked by the sheer mass of smoke.
- Too little smoke does not show up well on video. You will not be able to discern the smoke from the background and will not be able to prove a lack of turbulence and updrafts.
- Through years of trial and error, we have found that the “just-right amount” of smoke is best produced by ventilation smoke tubes and a small air pump.
Larger “fog generators” such as the ?C Breeze are available from Degree Controls, Inc. These units create a high volume of fog that will mask some turbulence and is therefore, best used on larger ISO Class 5 systems and not the PECs most often found in compounding pharmacies.
The equipment required to perform a smoke study is not expensive is easy to obtain. Ventilation smoke tubes with a battery-operated fish tank pump, tubing and connectors are all you need. Supplies you’ll need:
1. Ventilation tubes and bulb:
- Drager (appropriate for BSCs and CAIs only) can be purchased online thru Grainger (bulbs, plugs and tubes), Drager, Instrument Depot (aspirator bulb) and Zefon
- Mine Safety Appliances (MSA) are appropriate for all PECs and can be purchased online from Grainger, Medline, and Zoro
2. Battery-Operated Fish Tank Pump
3. Aquarium Tubing and regulator
This article was published in CriticalPoint Pearls in May 2017.