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 and ultrapure LN2 fogger has been in production from 2001 and provides the highest volume, highest density and highest purity of fog. There are 4 product models of LN2 foggers: AP35, AP50, AP100 and AP150. Ultrapure fog is created by bringing the water to a about 70C temperature, creating a water vapor, while simultaneously allowing LN2 to boil in a separate dewar, and passing the nitrogen vapor into the separate water chamber, where a visible fog forms at very high fog density. By heating the water and essentially boiling the nitrogen, an ultrapure fog is formed with much smaller droplet diameter, thus allowing very high density of fog per cubic centimeter. The water vapor bonds with the nitrogen vapor, creating a very high density of 2-3 micron fog droplets. Exit temperature of the fog is 75-78 degrees F with an exit pressure of less than 0.2 lbs, so as not to disturb the surrounding airflow. The fog is ultrapure leaving minimal, if any, trace particles behind. It evaporates back to a gas composed of hydrogen, oxygen and nitrogen components, which are natural to the clean room environment, and in the air we breathe. The high density of the fog increases the duration and travel distance of the fog. The AP35, AP50, AP100 and AP150 LN2 Ultrapure Foggers can be used in a Class 1 – 10,000 clean room environments of pharmaceutical and semiconductor facilities; such as sterile rooms, hospital rooms, medical rooms and clean rooms.

Cleanroom, DI Water Fogger: This type of fogger has less fog density (less capability to visualize airflow) than the Ultrapure LN2 Fogger described above. The water based fog is generated using ultrasonic piezos, operating around 1.7 MHz frequency, creating fog droplets from 1 micron on the low end and up to 8-10 microns on the high end of the droplet size curve.

Some manufacturers use the term “ultrapure” with their ultrasonic foggers, but this would be a misnomer.  ultrasonic water foggers are not ultrapure, unless the water is brought to near boiling. The purity of fog is as good as the water being used, such as de-ionized water, sterile water or WFI water. The typical 68 degree F temperature of fog at the 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.

Glycol Fogger: This type of smoke generator is a true smoke generator, in that the glycol is heated to form visible smoke particles to visualize airflow. Glycerine introduced into a cleanroom or controlled ISO Suite should be questioned for use, since glycol foggers are actually introducing particulate matter into the area, and in some cases a film will be generated on surfaces, if the fog output is too close to a surface. Glycol foggers are quite useful in airflow studies conducted in non-cleanroom type environments, such as industrial rooms where contamination is not a concern.

Smoke Sticks

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 sometimes used to 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 an inconsistent pattern with uncontrolled velocity, but little volume. It is a particulate based smoke, a true smoke generator, 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 airflow visualization studies.

Compare a smoke stick to a Cleanroom Fogger or an LN2 Ultrapure fogger, both which produce a constant volume of fog with a controlled velocity. Water based 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 study? How much cleanup labor is needed to clean the walls and cleanroom after smoke stick use? Do you need to Clean all the walls where the smoke stick was used? Did the chemical particulates emitted from the smoke stick affect the process area? These are critical questions for an engineer to consider, when using smoke sticks in an airflow visualization study. Did the contaminating particles and chemicals migrate into a drug process?