Sources of Particles in Cleanrooms

By Jim Strachan, Sales & Marketing Manager
2 March 2015

The objectives of environmentally controlled cleanrooms are to provide a contamination-free space to test or manufacturer contamination free products.  Nonetheless, contamination has a way of unexpectedly occurring without any indication of its origin.

There are two types of contaminates: viable and non-viable (or inert) particles. 

Non-viable particles, for example, are metal specks or flakes, fiber from clothing, and even dead skin.  These are generally obtained from people, equipment, or tools. 

An adult human will lose about 6-14 grams of dead skin material every day, and lose a complete layer of skin about every four days, which is equivalent to 10,000,000 particles per day. 

In a cleanroom, an adult will generate 100,000 particles per minute when motionless (fully gowned), and will generate 1,000,000 particles per minute when walking in the cleanroom.  As can be seen in the graph, cleanroom personnel are a major source of particle generation. 

Viable particles consists of bacteria, virus, fungal spores, molds, and yeast.  These are generally obtained from people, outside air, water, equipment, tools, excipients, and active ingredients.

Sources for particle generation come from mostly internal sources, which consist of personnel (generally the highest source of contamination), process, air conditioning, introduction of raw materials and equipment, and other materials.  External particle generation comes generally from outside air. Smaller, "respirable" particles remain virtually suspended in air until breathed in.

According to several sources, approximately 75% to 80% of all particles generated in a cleanroom are from manufacturing personnel. About 15% comes from ventilation, and the remaining contamination comes from the room structure, equipment, and various other processes.

Sources of Cleanroom Contamination

Most of the airborne particles emitted from cleanroom personnel migrate up through their cleanroom garment collars or down their legs when walking.  Colognes, deodorants, lotions, makeup and perfumes are definitely not allowed in cleanrooms.

Approximately 98%-99% of all particles by count are in the size range of 5 µm or less.  These particles tend to remain in suspension or slowly settle.  The > 5 µm particle size is important in Life Sciences, given the following: 

Particle Size Microns
Human Skin 0.4 to 10 µm
Human Hair  40 to 100 µm
Bacteria 0.3 to 20 µm
Mold Spores 0.5-20 µm
Fungal Spores 2-100 µm
Pollen 1 5-100 µm
Influenza 1 0.43 µm
Tuberculosis 1 0.86 µm
Strep 1 0.9 µm
Anthrax 1 1.0 µm
Aspergillus 1 3.50 µm
1 Size of a single cell. 

The size of a single bacteria, virus, or mold spore (as shown above) may on the surface appear innocuous. However, these viable organisms tend to form in pairs, clusters, or chains; and therefore tend to aggregate in colony forming units of > 5 µm.



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