TECHNICAL
Controlled Environments and Cleanrooms
Prevent Contamination in Service Centers
By Tom Bishop, P.E.
EASA Senior Technical
Support Specialist
Like this
article?
Check out the
EASA Resource
Library at
go.easa.com/
library
for more
valuable
resources.
Occasionally we hear the term “cleanroom”
used for a winding area that is physically isolated
from the remainder of a service center (Figure 1).
The main purpose of such an enclosure is to
prevent windings and winding material from being
contaminated with any dust and dirt (Figure 2)
that may be in other parts of the service center.
Some service centers construct these enclosures
because they strive to provide the cleanest practical environment for winding work, and some also
use the enclosure for the bearing installation process. Cleanroom type enclosures can also benefit
facilities by helping minimize quality problems and
increase the volume of acceptable product.
Here we will explore the distinction between
a controlled environment and a cleanroom, the
requirements for both, and provide details to help
you determine if you want to add a controlled
environment or a cleanroom to your facility.
What is a controlled
environment?
A controlled environment is an area with
precisely regulated environmental factors; specifically, pressure, temperature and isolation.
For example, many laboratories are considered
controlled environments, as they have controlled
temperature and pressure and are separated
from other operations, such as manufacturing or
shipping and receiving. Unlike cleanrooms, con-
Figure 1: View of entrance/exit from inside
a controlled environment or cleanroom for
service center winding area.
EASA Currents
g
© 2022 EASA. All rights reserved.
g
easa.com
trolled environments do not usually have to meet
standards for particle contamination.
What is a cleanroom?
A cleanroom is a type of controlled environment
but with more stringent requirements. Cleanrooms
require temperature and pressure control, as
well as separation (isolation) from the outside
environment and other operations, and these
parameters must be controlled in accordance with
specific standards. Cleanrooms are classified by
the maximum acceptable numbers of particles (by
size) in the air per cubic meter and must be regularly tested to ensure compliance to that standard.
Most cleanrooms work on a positive pressure
method. Air is pumped into the cleanroom through
high-powered, high efficiency particulate air (HEPA)
filters that remove the contaminants. The air then
flows down and is pushed out through vents in or
near the floor. The operating principle is that any
particles that exist in the cleanroom are forced
out of the room by the flow of air.
Cleanroom standards
The current accepted standards for cleanroom
classifications are ISO (International Standards
Organization) standards. The primary standard
is ISO 14644-1 Cleanrooms and associated controlled environments – Part 1: Classification of air
cleanliness by particle concentration. This is the
classification system standard most widely accepted internationally, and the U.S. officially switched
to it in 2001. There are nine ISO 14644-1 classes:
Class 1 (the cleanest) to Class 9. The lower the
ISO class number, the cleaner the environment.
The maximum allowed particles columns in
Table 1 are from ISO 14644-1. They indicate
that cleanrooms are classified by the number of
contaminants that exist in them. Contamination is
measured in parts per cubic meter (per m3). For
example, if your cleanroom must be certified
to meet an ISO Class 8 level, which is rated at
3,520,000 parts per cubic meter, you can have
no more than 3,520,000 particles greater than
0.5 microns in size per cubic meter of cleanroom
space (volume). The last two columns in Table 1
are typical ranges based on some industry guidelines and are not from any published standard.
In the cleanroom environment, air particles
April 2022
1
control temperature and humidity,
and increase air filtration with a HEPA
filter. There is, however, no control on
the particle size, thus making Class
9 a potentially certifiable alternative
to a “controlled environment,” which
would not have an ISO cleanroom
class distinction. To clarify, the particle sizes described in Table 1 for ISO
Class 9 could be found in untreated
air, such as outside air in an urban
environment.
Figure 2: Microscope photos of clean magnet wire (A) and dust-contaminated wire (B).
Design considerations
for cleanrooms
Cleanrooms are designed to meet
the specific needs of the industry and application they serve.
Cleanroom contractors (e.g., HVAC firms) consider a wide range
of factors when determining the construction materials and
required environmental regulating equipment. Considerations to
ensure that the facility is properly equipped include the following:
● Level of required cleanliness (e.g., ISO class)
● Environmental conditions
● HVAC requirements
● Dimensional specifications
● Construction materials
● Pass-thru units
● Fire protection
● Light and air supply and filtration
● Equipment hookups and special equipment. g
are measured in microns (one micron equals one-millionth of
a meter.) Micron-sized particles are smaller than a living cell
and can be seen only with the most powerful microscopes. To
put this in perspective, one small dust particle seen in a ray of
sun equates to approximately 60 microns, and the human eye
cannot consistently see objects less than 50 microns in size.
A typical indoor air sample may contain from 20 million to 40
million particles per cubic meter of air.
To achieve the required environmental conditions, the air in a
cleanroom is purified using High Efficiency Particulate Air (HEPA)
filters. Air is forced through the filters, which remove particles
as small as 0.5 microns. The filtration system used depends
upon the required level of cleanliness.
ISO Class 9: A compromise alternative?
A goal of the ISO 14644-1 standard was the creation of
ISO Class 9 as a controlled environment method. Features of
a controlled environment include the ability to exert pressure,
Table 1. Cleanroom Classification Requirements.
Class
Maximum allowed particles (per m3)
≥ 0.1 µm ≥ 0.2 µm ≥ 0.3 µm ≥ 0.5 µm
≥ 1 µm
≥ 5 µm
Air
changes
per hr
Average
airflow
velocity
(m/s)
ISO 1
10
2.37
1.02
0.35
0.083
0.0029
360-600
0.30-0.50
ISO 2
100
23.7
10.2
3.5
0.83
0.029
360-600
0.30-0.50
ISO 3
1,000
237
102
35
8.3
0.29
360-540
0.30-0.45
ISO 4
10,000
2,370
1,020
352
83
2.9
360-540
0.25-0.45
ISO 5
100,000
23,700
10,200
3,520
832
29
240-480
0.20-0.40
ISO 6
1.0 x 10
6
237,000
35,200
8,320
293
70-160
0.13-0.40
ISO 7
7
1.0 x 10
2.37 x 10
83,200
2,930
30-70
0.05-0.08
ISO 8
29,300
10-20
0.005-0.04
ISO 9
293,000
1-20
0.0-0.025
2
102,000
6
1.02 x 10
7
1.02 x 10
1.0 x 10
8
2.37 x 10
1.0 x 10
9
2.37 x 10
April 2022
8
6
352,000
7
3.52 x 10
1.02 x 10
8
6
832,000
7
8.32 x 10
3.52 x 10
6
EASA Currents
g
© 2022 EASA. All rights reserved.
g
easa.com