Clean rooms and Indoor Air Purifiers

We are often asked about the basis for the technology that is used in the indoor air purifiers that we market.  Most of these products share a common thread of using HEPA filter technology and some form of activated carbon to clean.  Interestingly enough HEPA technology comes to us from industry and government.  While the first HEPA air purifiers were used and defined by the Atomic Energy Commission they were quickly adopted by several industry segments.  These are semiconductor and hard disk fabrication from the high-tech sector and the drug manufacturing.  In all of these industries a very minor particle impurity could potentially destroy and entire run of products.

So back to our home systems:  In a home HEPA system the airflow is drawn though the HEPA filter and activated carbon and them blown back into the room.  In a Cleanroom all of the airflow in the room is moved though the HEPA filters and then back into the room.  The sealed Cleanroom is actually kept a positive pressure to keep any contaminants from entering the workspace.

As with most technical subjects today the ISO (International Standards Organization) has organized the ratings of cleanrooms to better communicate the needs of the user community.  The following chart explains how clean the room must be for each rating.

Cleanroom ISO Standard Ratings

CLASS	Number of Particles/M3
ISO	0.1 um	0.2 um	0.3 um	0.5 um	1 um	5 um
1	10	2
2	100	24	10	4
3	1,000	237	102	35	8
4	10,000	2,370	1,020	352	83
5	100,000	23,700	10,200	3,520	832	29
6	1,000,000	237,000	102,000	35,200	8,320	293
7				352,000	83,200	2,930
8				3,520,000	832,000	29,300
9				35,200,000	8,320,000	293,000

While this does not address any of the needs in the home of an allergy or asthma sufferer we thought that is would be interesting to see where the technology in your indoor air purifiers come from.

Ted Zajac, Jr.
MSE Johns Hopkins University