What is 100 Class (Grade A) area ?

A cleanroom or clean room is an environment, typically used in manufacturing or scientific research that has a low level of environmental pollutants such as dust, airborne microbes, aerosol particles and chemical vapors. More accurately, a clean-room has a controlled level of contamination that is specified by the number of particles per cubic meter at a specified particle size.

Don’t get confuse about 100 class clean room. Several regulatory agencies in this world regulate the pharmaceutical industry. USFDA, MHRA, EU, TGA, WHO are few major regulatory body those who regulate the major pharma market. Basic concept is same but sometimes terminology or way of expression is different, so we should clear about the idea of 100 Clean room concept. In pharma industry the clean room concept mainly fit with parenteral division where the maintenance of area and segregation between different areas is necessary to avoid cross contamination and maintain sterility of product.

A Grade 100 clean-room is designed to never allow more than 100 particles (0.5 microns) per cubic foot of air. Class 1000 and Class 10,000 clean rooms are designed to limit particles to 1000 and 10,000 respectively. 

Now a day’s current industry pattern is that, they avoid maximum particles/ft³ concept. Major guidelines and regulatory agency are giving their focus on maximum particles/m³. As per major regulatory body only 0.5 µm and 5 µm particle are considered for maintain the clean room practice. (At rest condition)

EU GMP	ISO 14644-1 cleanroom standards	US FED STD 209E cleanroom standards	Metric System	maximum particles/ft3 ≥0.5 µm	maximum particles/m3 ≥0.5 µm
Grade A Grade B Grade C Grade D	ISO 5 ISO 5 ISO 7 ISO 8	100 Class 100 Class 10000 Class 100000 Class	M 3.5 M 4.5 M 5.5 M 6.6	100 100 10000 100000	3520 3520 352000 3520000

ISO 14644-1 (per cubic meter)
Fed Std. 209 E USA (per cubic foot)
ISO standard requires results to be shown in cubic meters (1 cubic meter = 35.314 cubic feet)

So no difference between 100 Class room and ISO 5 or Grade A, these words are used for same principle. 

Reference:

1. WHO TRS 961 , annex. 6  (http://apps.who.int/medicinedocs/documents/s19959en/s19959en.pdf)
2. EU annex 1 (http://ec.europa.eu/health//sites/health/files/files/eudralex/vol-4/2008_11_25_gmp-an1_en.pdf) 
3. USFDA aseptic guidance 2004 (http://www.fda.gov/downloads/Drugs/.../Guidances/ucm070342.pdf)