In a properly controlled cleanroom, there are specified limits for the concentration of airborne particles which must be continually removed from the air. Those particles might be created by the workers, the equipment, the process, or the facility itself. Air filtration and flow is critical to avoid cleanroom contamination. In order to visualize the room’s air flow and to comply with ISO Class 5 specifications, airflow visualization studies, also known as smoke studies, are performed to ensure that the airflow is exiting through the cleanroom HEPA filters in a single direction. In case of contamination, the smoke studies offer visual verification of where the contaminant would move within the room. The studies not only identify problems in the room’s airflow, but can also identify leaks in the exhaust ducts and measure air flow balance in cleanrooms. The methods used for airflow visualization studies, as well as the types of products used for them, depend upon the cleanroom’s function.
How Smoke Is CreatedCleanroom foggers or smoke generators are often used to create the smoke, using either sterile water for injection (WFI), which contains no bacteria, antimicrobial agents or buffers, or water that has had its ions removed (DI). The water is filled into the fogger, and its transducers create pure fog which is released into the room. Some foggers are not suitable for cleanrooms, because they use a glycerin-based smoke which leaves an oily residue not only on the cleanroom walls and floors, but on the cleanroom filters and supplies, personnel, and cleanroom HVAC system.
Best SmokeWater vapor smoke, using either WFI or DI water, is considered to be the best option to create smoke studies in a cleanroom. The water is usually heated and mixed with dry ice or liquid nitrogen. Although the smoke does not last long, it doesn’t leave behind a residue, so cleanup is minimal.
Documenting the Smoke StudyThe smoke study is generally videotaped and photographed, which can prove challenging.
- Cleanrooms are usually all white, so smoke can become invisible. Hanging black sheeting in the background will make the smoke stand out and allow easier visualization of its path.
- If there are stainless steel cabinets or other fixtures, consider their reflective nature. Change the angle of the camera to keep the smoke from sending a false directional appearance.
- Film the beginning first. Where does the smoke enter the cleanroom? Pan down to follow the flow of the smoke through the cleanroom.