Clean environment is required in various fields such as precision equipment and parts processing and pharmaceuticals. Methods to create cleanliness, conditions to maintain it, etc. This lecture will explain the basics in an easy-to-understand manner.

The four elements of air conditioning

Air conditioning involves adjusting the air conditions to suit the use and purpose of a space. To do this, four elements - temperature, humidity, cleanliness, and airflow - must be adjusted to create a uniform and appropriate indoor environment.

environment standards for general air-conditioning environment

In Japan, various laws stipulate a comfortable air environment to protect the health of the people. Even under general air conditioning, the management targets for temperature, humidity, cleanliness, and airflow are quantified as shown below.
Examples: Building Sanitation Act, Building Standards Act, Building Management Act, Occupational safety and Health Act, etc.

Cleanliness of general air-conditioning environment

In addition, the cleanliness of a general air-conditioned environment requires the removal of airborne particles such as dust, house dust, and pollen from the target space, such as indoors, as well as allergy-causing chemicals such as formaldehyde, and unpleasant odors.

Cleanliness in the manufacturing process

The level of cleanliness in manufacturing processes is generally referred to as cleanliness class, which indicates the degree of air pollution in the target space based on certain standards. A room that achieves and manages a certain level of cleanliness is called a clean room.

clean room

A clean room is defined as:

This is a room where airborne particles and microorganisms are kept below a certain level of cleanliness, and contamination control is carried out to prevent the introduction of impurities and foreign substances.The cleanliness of products, chemicals, and water brought into the room is also maintained, and environment conditions such as temperature, humidity, pressure, and airflow are controlled as necessary to create a comfortable working environment.

(Reference: JIS Z 8122)

Clean rooms are broadly classified into two types depending on their purpose of use.

Industrial Clean Room

It is primarily intended for industrial fields such as semiconductors, liquid crystal displays, electronic components, and precision instruments, and targets particles suspended in the air.

Biological Clean Room

It is primarily intended for use in the medical food industry, including pharmaceuticals, genetic engineering, biotechnology, and operating rooms, and targets airborne microorganisms.

Contamination

Contamination is the contamination of a product or food with foreign matter, impurities, or microorganisms. Contamination control is the process of preventing contamination from occurring.

In the manufacturing process, metal fragments, foreign matter, impurities, contaminants, etc. may be generated from environment the periphery of machinery, equipment, conveyors, etc., and may get mixed in or adhere to products. Especially in the semiconductor, electronics, precision parts, pharmaceutical, and food manufacturing fields, where clean environment management is strict, this can lead to major losses and loss of trust, such as lot-outs and recalls.
Countermeasures for this include the following.

• We will review the materials and change them to specification that are less susceptible to contamination.
• Clean thoroughly.
• Review the cleaning method.
• Use dedicated equipment.
• Conduct thorough inspections.
• Review the process to prevent specific substances from being mixed in.
• Provide thorough employee training.

Clean standards and cleanliness levels (classes and cleanliness levels)

Class (cleanliness) is a standard that defines the amount of particles in the air. Currently, it has been unified into the internationally unified ISO standard, but the previous US federal standard "FED-STD209D" is still widely used. The JIS standard is based on the basic ISO standard.

ISO14644-1 (JIS B9920)

It targets particles of 0.1 μm or larger per cubic meter of air, and is classified into classes 1 to 9. Like the ISO standard, the JIS standard also classifies particles of 0.1 μm or larger per cubic meter into classes 1 to 8.

FED-STD-209D

The classification is based on the number of 0.5 μm particles in the air per cubic foot (1 foot = approximately 30 cm).

■ Table 5. Measurable particle size and upper limit concentration by air cleanliness class

Cleanliness Class		Upper limit concentration (pieces/m3 Upper limit concentration (pieces/m3))
international unified standards ISO 14644-1	Federal Standard FED-STD-209D	Measured particle size
		0.1μm	0.2μm	0.3μm	0.5μm	1.0μm	5.0μm
クラス1		10	2
クラス2		100	24	10	4
クラス3	1	1,000	237	102	35	8
クラス4	10	10,000	2,370	1,020	352	83
クラス5	100	100,000	23,700	10,200	3,520	832	29
クラス6	1,000	1,000,000	237,000	102,000	35,200	8,320	293
クラス7	10,000			352,000	83,200	2,930
クラス8	100,000			3,520,000	832,000	29,300
クラス9				35,200,000	8,320,000	293,000

Cleanliness measurement

The method for evaluating the air cleanliness of a clean room is specified in JIS B 9920. Generally, a particle counter is used to measure the number of particles by particle size.

Cleanliness and air filter

To satisfy the cleanliness (cleanliness) of a target space, there must be air filter that filters airborne particles. Air filter is broadly classified according to its collection efficiency as follows: HEPA is sometimes called quasi-HEPA filter while HEPA high-performance filter is close to HEPA filter.

filter Types	Coarse dust filter	Medium-performance filter	HEPA filter	ULPA filter
Particle size guideline	Slightly coarse grain	Slightly fine particles	Very fine particles
Particle size	10~20μm or more	1~2μm or more	0.3 μm	0.1 to 0.2 μm
Collection rate (approximate)	Approximately 50-90%	Approximately 50-95%	99.97～99.99%	99.999～99.99999%
Initial pressure loss (approximate)	Approximately 5-20Pa	Approximately 20-120Pa	Approximately 90-250Pa	Approximately 130-250Pa

FFU (filter Fan Unit)
A clean air device that combines a HEPA filter and fan motor is called an FFU.

HEPA filter are an abbreviation for High Efficiency Particulate Air Filters, and are defined by the JIS standard as follows:

An air filter with a particle collection rate of 99.97% or more for particles with a particle size of 0.3 µm at rating air flow rate and performance initial pressure loss of 245 Pa or less.

(Reference: JIS Z 8122)

ULPA filter is an abbreviation for Ultra Low Penetration Air Filter, and is defined by the JIS standard as follows:

An air filter with a particle collection rate of 99.9995% or more for particles with a particle size of 0.15 μm at rating air flow rate and performance initial pressure loss of 245 Pa or less

(Reference: JIS Z 8122)

Collection efficiency

weight method

weight captured by filter ÷ total weight flowing into filter
⇒The weight method may not be able to capture fine particles, but it will calculate a high collection efficiency if it captures large dust particles (coarse dust), so it is generally used to measure coarse dust filter.

Counting method

Number of particles of each size captured by filter ÷ Number of particles of each size flowing into filter
⇒The counting method is an evaluation method used for HEPA filter, etc., to count the number of particles and measure how much dust or airborne particles are captured by filter for each particle size.
For this reason, specification for HEPA filter state that they are "more than 99.97% effective against particles of 0.3 μm."

<Notes>
While HEPA and ULPA filter have high collection efficiency, if filter are used in places with a lot of suspended particles and dust, filter itself will become clogging quickly, causing a sudden drop in airflow and resulting in filter needing to be replaced more frequently. Therefore, it is necessary to consider the location of use and whether to use a pre-filter in combination.

filter Pressure Drop

filter have a fibrous mesh structure to capture suspended particles and dust. This creates resistance that hinders the flow of air through filter. The pressure difference is the pressure drop that occurs when the static pressure of a certain volume of air passes through filter. filter Pressure Loss It is called.
Static pressure of air before passing through filter- static pressure of air after passing through filter
⇒Pressure loss can be measured with a differential pressure gauge.

<Notes>
The pressure loss of filter when it is new is called the initial pressure loss, and as filter becomes clogging over time, the pressure loss of filter gradually increases, causing a decrease in collection efficiency and airflow. Also, in the case of fan motor with weak static pressure, using filter with a large pressure loss may cause the desired airflow to not be achieved, so care must be taken.

Four cleanroom principles for maintaining cleanliness

In order to maintain the cleanliness (purity) of a clean room at all times, it is essential to adhere to the "four principles of clean rooms."

Airflow design guidelines for industrial clean rooms

The JIS standard recommends an airflow velocity of 0.2 m/s or more for clean rooms, but clean-related equipment manufacturers tend to select an airflow velocity of approximately 0.3 to 0.4 m/s. In the case of Apiste, it is set to 0.4 m/s.

Cleanliness Class (JIS)	Cleanliness Class (FED)	Airflow type	mean air velocity (m/s)	Ventilation frequency
				(number of times/h)	(number of times/h)
2	-	Unidirectional flow	0.3～0.5	Not applicable	-
3	C1	↑	↑	↑	-
4	C10	↑	↑	↑	-
5	C100	↑	0.2～0.5	↑	200～400
6	C1,000	non-unidirectional flow or in combination	Not applicable	30～90	100～150
7	C10,000	↑	↑	20～40	30～75
		*JIS B 9919	←	←	※FED Hoka

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