The three types of cleanroom foggers used in smoke studies of clean rooms, ISO suites, sterile rooms, barrier isolators, glove boxes and fume hoods are described below.
Ultrapure LN2 Fogger: This type of smoke generator or cleanroom fogger provides the highest fog volumes, best fog density and highest 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 water vapor is then passed over an LN2 (liquid nitrogen) dewar, which naturally boils at room temperature. The water molecules bond with nitrogen molecules, creating a nominal 2-3um 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 75 degrees F. The AP35 and AP100 LN2 foggers provide adjustable fog volume and adjustable airflow to tune the fog output to your room dynamics. The fog is ultrapure leaving minimal, if any, trace particles behind; and it is breathable. It evaporates to its gaseous hydrogen, oxygen and nitrogen components, which are natural to the clean room environment. The high density of the fog increases the duration and travel distance of the fog. Ultrapure Ln2 foggers 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 ultrasonic 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 6-10 microns in diameter. If the facility manager operates a class 10 to Class 10000 Clean room, the use of a DI Water Fogger poses no problem. Although some manufacturers describe their DI Water, ultrasonic foggers as an ultrapure fogger, the term”ultrapure” is applicable only to LN2 foggers using liquid nitrogen. The fog output of most DI Water foggers is a constant output, such as the low cost, CRF2 Cleanroom Fogger. The CRF4 Cleanroom Fogger allows for the fog volume and airflow to be adjusted by control panel input or wireless remote control. 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, and then float with the airflow to visually describe the air patterns and turbulence. The fog is a pure fog based on the quality of the deionized (DI) water used or the WFI (water for injection) used. Both DI water and WFI water are quite pure and the resulting fog leaves no particles in the airflow and the fog is completely breathable. No wipedown is required after using a DI Water Fogger.
CO2 Fogger: This type of smoke generator or 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. The fog contains elements of the CO2 and the user must determine if the residual CO2 components are acceptable in a process environment operating Class 100 to Class 10,000. The 3-5lb output pressure of a CO2 fogger also distorts the airflow patterns, thus adding to the turbulence. The output starts at about 3cfm and slowly decreases to 0 CFM in about 10 – 12 minutes.
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. While use of smoke sticks are certainly very low cost, the resulting labor to clean the process room is quite high. Some companies feel they have more people and consider smoke sticks a low cost solution using people to clean their facilities after a smoke study. But how does the facility manager ensure that all the smoke stick chemicals are removed after a smoke stick is used in a clean room, ISO suite, sterile room, barrier isolator or glove box? That is the advantage of a DI water fogger or LN2 fogger, which uses a pure WFI water or DI water and leaves no contamination at all.
Compare a smoke stick to a Clean Room Fogger or an Ultrapure LN2 fogger, both which can produce much more 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 – Glycol foggers are portab le foggers using a water and glycol liquid. Glycol produces excellent visible fog. If the glycerine is based on a long strand molecule, the resulting glycol fog can degrade HEPA filters by choking the filter material. This reduces airflow efficiency, and eventually an odor within the filter and airflow occurs. If you use a short strand, alcohol glycerine and water mixture, the fog generated is acceptable for use in many pharmaceutical ISO suites and industrial clean rooms. Some Engineers consider glycerine as a contaminate, as the glycol residue needs to be wiped clean, requiring more labor and manpower. In a pharmaceutical process, the facility manager understands his clean room requirements and bases his decision for a low cost portable fogger, a higher volume cleanroom fogger, or the ultrapure LN2 fogger?
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.