Note that increasing the key figure by 1 causes the particle count to double.
Example: ISO code 18 / 15 / 11 means:
Cleanliness class No. particles / ml Size ranges
18 1,300 – 2,500 > 4 µm
(c)
15 160 – 320 > 6 µm
(c)
11 10 – 20 > 14 µm
(c)
Are found in 1 ml of the analyzed sample
Overview of modifications - ISO4406:1987 vs. ISO4406:1999
“Old” ISO 4406:1987 “New” ISO 4406:1999
Size ranges > 5 µm
> 15 µm
> 4 µm
(c)
> 6 µm
(c)
> 14 µm
(c)
Dimension
determined
Longest extension of a
particle
Diameter of the
area-equivalent
circle
ISO 11171:1999
Test dust ACFTD dust
1-10 µm
ultrafine
fraction
ISO 12103-1A1
SAE Fine,
AC – Fine
ISO 12103-1A2
SAE 5-80 µm
ISO MTD
Calibration dust
for particle
counters
ISO 12103-1A3
SAE Coarse
Coarse fraction
ISO 12103-1A4
Comparable size
ranges
Old ACFTD calibration