No. 2A201-519EN*A
68
However, increasing humidity too much causes humidity hazard.
(Refer to figure A.1.2-1.)
0
2
4
6
8
10
10
20
30
40
50
60
70
80
90
100
R
el
ati
ve
ha
za
rd
ra
tio
Relative humidity (%)
Clean room
55%
Overall hazard ratio
Static electricity hazard
Humidity hazard
Leakage hazard
Corrosion hazard
Annoyance hazard
Figure A.1.2-1 The relation between relative humidity and relative hazard ratio
The above relationship indicates that the relative humidity for systems should be
controlled in the 50% to 55% range as far as possible.
2. Countermeasures using conductive materials
The above method (increasing relative humidity) is not always optimal because
humidity hazard may be caused. Therefore, preventive measures using conductive
materials are outlined below. (An example comparing conductive shoes with normal
shoes is presented.)
500
1000
1500
0
1
2
Walking in place
Standing
<2> Normal shoes
<1> IC shoes (conductive
shoes)
Time (min)
Sta
tic
el
ec
tr
ic
ity
v
ol
tag
e (V)
500
1000
1500
0
1
2
Walking in place
Standing
<2> Normal shoes
<1> IC shoes
(conductive shoes)
Time (min)
Sta
tic
el
ec
tr
ic
ity
vo
ltag
e (V)
Figure A.1.2-2 Nonconductive flooring
Figure A.1.2-3 Conductive flooring
material
material
Figure A.1.2-2 illustrates an example of walking in place followed by standing on a
nonconductive floor with normal shoes and conductive shoes. (The static electricity
voltage may be higher depending on the material of the clothes, etc.) Wearing
conductive shoes makes it possible to decrease the static electricity voltage level.
However, the static electricity voltage even at this level could damage devices, as
shown in the table A.1.2-1.
