What Does My Smoke Study Require to Visualize Airflow Turbulence?

Ultrapure, Ultrasonic and CO2 Fogger Discussion

The three types of foggers manufactured for use in the semiconductor and pharmaceutical industry are described below.

Ultrapure LN2 Fogger:
This type of smoke generator or clean room fogger provides the highest volume, density and purity of fog. Purity is created by bringing the water to a high temperature, creating a vapor, while simultaneously using gravity to remove the residual mass from the vapor. This process removes any bacterial agents and residual particulate matter from the vapor. The pure vapor is then passed over an LN2 bath, which naturally boils at room temperature. The water molecules bond with nitrogen molecules, creating a nominal 3um fog droplet. The volume of water and nitrogen molecules that combine is extremely high in quantity, creating a dense, high volume, ultrapure fog output with exit temperatures of about 78 degrees F airflow. The fog is ultrapure leaving minimal, if any, trace particles behind. It evaporates to its gaseous hydrogen, oxygen and nitrogen components, which are natural to the Cleanroom environment. The high density of the fog increases the duration and travel distance of the fog. This fogger can be used in a Class 1 – 10,000 cleanroom environments of pharmaceutical and semiconductor facilities; such as sterile rooms, hospital rooms, medical rooms and cleanrooms.

DI Water Fogger: This type of fogger has less fog density (less capability to visualize airflow) than the UltraPure Fogger described above, but more density than the CO2 fogger described below. The DI water fog is generated by atomizing DI water into water droplets, which are nominally 3-10um in size. The water droplets may contain residual particulate matter remaining in the DI water, but this would be very trace amounts. If the facility manager operates a class 10 to Class 10000 Clean room, the use of a DI Water Fogger poses no problem. However, Cleanroom Engineers who manage facilities operating at Class 1 to Class 10 performance may desire to use an ultrapure fogger. Although some DI Water foggers are described as ultrapure, unless the DI water is vaporized to remove bacterial agents and residual particulate matter, the fog is not ultrapure. The temperature output is typically less than the surrounding room temperature, thus a fog generated from the atomized water droplets will sink momentarily in a typical 70 degree room temperature.

CO2 Fogger, CO2 Ice and DI Water:
This type of smoke generator, CO2 Fogger, is designed for low volume, non-process critical applications such as bench airflow testing. The fog is created using CO2 ice as the fogging agent, combined with DI Water or WFI water. The fog is generated by evaporating CO2 ice with warm water and is ideal to visualize airflow and turbulence for short periods of time. The fog starts out with a large volume of fog at perhaps 10cfm, but as the CO2 ice evaporates, the fog volume then begins to decrease until no CO2 ice remains. The advantage of a CO2 fogger is the high initial density, making it useful for video applications; and the CO2 fogger is portable as it can be taken into a clean area with no power cords required during the fog process. The output starts at about 9-10cfm and slowly decreases to 0 CFM over a period of 8 – 12 minutes, depending on how much CO2 ice volume is placed in the warm water.

Smoke Sticks and Glycol (glycerine) Foggers

Smoke Sticks are used in some Pharmaceutical Clean Rooms around the world. Below is a discussion on the use of smoke sticks used to visualize airflow and turbulence?

A smoke stick is often used visualize airflow turbulence, but smoke sticks are filled with particulates and chemicals. Smoke is created using chemical reactions; thus the smoke is SPUTTERING (sputter) or popping out of the smoke stick in a non-consistent pattern with velocity, but little volume. It is a particle smoke, compared to a visible, pure water based fog, thus smoke sticks are a contaminating smoke. The smoke stick generates an inconsistent flow or pattern of smoke, but it is low cost, which is why some managers allow use of smoke sticks in their Pharmaceutical clean rooms.

Compare a smoke stick to a Clean Room Fogger or an UltraPure LN2 fogger, both which produce a constant volume of fog with a consistent fog output and pure fog. Di Water foggers produce a consistent flow of visible water vapor, which enters the airflow to visualize the airflow patterns and turbulence, then begins to evaporate, returning back to the hydrogen, oxygen and nitrogen components that we breathe. No particulate contamination, no chemical contamination. Water based foggers produce a constant volume of fog at a constant rate, which provides consistent visualization of airflow patterns and turbulence. The Smoke Stick has to be waved around to see what kind of airflow pattern there is, while a Di Water fogger is simply placed in position and produces a flow of fog that can be directed 360 degrees to easily describe the airflow patterns and turbulence. In addition, tubes are now available to create “fog curtains”, or a wall of fog, which smoke sticks can not produce.

How many smoke sticks are used per smoke cycle? How much labor is needed to clean up after smoke stick use. Do you need to Clean all the walls where the smoke stick was used. How did the chemical particulates and particles affect the process area? These are critical questions for a pharmaceutical manager. Did the contaminating particles and chemicals get into the drug process?

How much labor is used to cleanup after smoke stick use and if the cleanup did not get every chemical particle, then some smoke chemical material is added to the Pharma process or trapped in a filter somewhere, until it escapes into the Pharma process. That is a quality control issue for that company using smoke sticks.

The low labor cost of using smoke sticks is the reason facility managers may use smoke sticks, but are the chemical and particulate effects to the pharma process being analyzed? Non-contaminating fog does not emit particulates, requires less labor and does not contribute any unwanted chemicals to the Pharma process. A Di Water Fogger provides these advantages in fog volume, fog consistency and fog purity, which easily outweighs the low cost of smoke sticks, the high cost of labor for cleanup and the detrimental affects to quality control!

Smoke Sticks – quality side of the drug product:
The smoke chemicals are not of the same chemistry as the drug product, thus smoke chemicals and particulates could migrate into the drug process. There is no guarantee the cleaning process removed all the unwanted particulates and chemicals, from for example, a glove box or isolation box. The chemicals and particulates eventually migrate to the air filter system, which is not 100% effective. If this is the case, the quality and purity of the drug process is affected. Drug quality is the basis of product credibility, which is a valuable asset in customer relations.

Smoke Sticks – labor side of the drug product:
The smoke is generated by a chemical reaction, which causes the smoke to sputter into the environment. The smoke is inconsistent in volume, thus the smoke stick is unpredictable for airflow visualization. The chemicals migrate to equipment and walls, which then must be cleaned, and requires an added labor cost. The use of Smoke sticks generates an inefficient smoke, not a consistent fog.

Glycol Foggers – typically use water combined with glycol liquid, which has a long strand, glycol molecule. This combination produces excellent visible fog; however the long strand glycol molecules degrade HEPA filters by clogging the filtration material, which decreases airflow efficiency. An odor builds up eventually in the filter, when using glycol fog. In most clean rooms, glycol is considered a particulate contaminate, as it needs to be wiped clean from the clean room. This requires additional labor and manpower. In a pharmaceutical process, how does one clean 100% of the glycol residue from the clean room? How much of the glycol residue enters the pharmaceutical process?

A Di Water Fogger produces a water (H2O) droplet that evaporates back into hydrogen and oxygen, the air we breathe. No clean up is required, at all. No additional time delays and clean up labor is not required. The fog is consistent in volume and constant in output to describe the airflow patterns and turbulence. These are equipment, quality and application concerns to consider when the need for airflow visualization is considered.