Page 453 - Air pollution and greenhouse gases from basic concepts to engineering applications for air emission control

434 14 Indoor Air Quality

into Eq. (14.2), we get

2:08
! 2:08
0:1 2 0:1 3
N
c ¼ 10 ¼ 10 ¼ 100=m

p
d p 0:1
3
Since the volume of the room is 300 m , the total number of particles larger than
100 nm in diameter cannot exceed 30,000 in total. That is an extremely clean room!
For the ease of practice, the cleanroom classes and their corresponding maxi-
mum particle number concentrations are computed using Eq. (14.2) and they are
summarized in Table 14.3. In this table, the values are the maximum concentrations
for the particles size or greater. The greater the class number, the higher allowable
particle concentration can be.
For a given class, all limits for all particles sizes must be satisfied. For a Class 1
clean room, the concentration of particles greater than 0.2 μm should be 2 or less
3
3
particle/m . Meanwhile, the particles ≥0.1 μm should not exceed 10 #/m .
Cleanroom is important to the quality of many industries, such as medical,
manufacturing, and packaging. Cleanrooms were first developed for aerospace
applications to manufacture and assemble satellites, missiles, and aerospace elec-
tronics. Most applications involve clean airspaces of large volumes with cleanliness
levels of ISO Class 9 or cleaner. Recent advances in electronics industries continue
to drive the design of cleanrooms. Most recently designed semiconductor clean
rooms are ISO Class 5 or cleaner. In addition, preparation of pharmaceutical,
biological, and medical products all require clean airspaces to control airborne
bacteria and viruses to prevent contamination. Furthermore, some operating rooms
in hospital may be classified as cleanrooms, but their primary function is to limit
particular types of contamination rather than the quantity of particles.

Table 14.3 Cleanroom classes
3
ISO class Maximum particle number concentration (#/m ) for particle size
number (N) 2:08
c ¼ 10 N 0:1

p d
p
0.1 μm 0.2 μm 0.3 μm 0.5 μm 1 μm 5 μm
ISO Class 1 10 2
ISO Class 2 100 24 10 4
ISO Class 3 1,000 237 102 35 8
ISO Class 4 10,000 2,370 1,020 352 83
ISO Class 5 100,000 23,700 10,200 3,520 832 29
ISO Class 6 1,000,000 237,000 102,000 35,200 8,320 293
ISO Class 7 352,000 83,200 2,930
ISO Class 8 3,520,000 832,000 29,300
ISO Class 9 35,200,000 8,320,000 293,000