Clean workshop, also known as cleanroom and dust-free workshop, is widely used in pharmaceutical and biological engineering, precision machinery, medical and health, food, electronic materials and other fields. In FED-STD-2, a cleanroom is defined as a room equipped with air filtration, distribution, optimization, construction materials and equipment, in which specific rules and operating procedures are used to control the concentration of airborne particulates to achieve an appropriate level of cleanliness.

The cleanliness and continuous stability of pollution control are the core standards for testing the quality of cleanroom. The scope of testing in clean workshops generally includes cleanroom environmental rating and engineering acceptance in food, health care products, cosmetics, bottled water, milk production workshops, electronic product workshops, GMP workshops, hospital operating rooms, biosafety laboratories, biosafety cabinets, ultra-clean workstations, dust-free workshops, sterile workshops, etc.

Test items includes air speed and air volume, ventilation frequency, temperature and humidity, differential pressure, suspended particles, airborne viable particles, settling bacteria, noise, illumination, etc. For details, please refer to relevant standards for cleanroom testing.

1. Air speed, air volume, and ventilation frequency

The cleanliness of cleanroom is mainly achieved by supplying sufficient amount of clean air to replace and dilute the particulate pollutants generated in the room.  Therefore, it is necessary to measure the air supply volume, average air speed, air supply uniformity, air flow direction and flow pattern of cleanroom or clean facility.
Unidirectional flow mainly relies on clean air flow to push and replace the polluted air in the room and area to maintain the cleanliness. Therefore, the air speed and uniformity of the air supply cross-section are important parameters affecting the cleanliness. Higher and more uniform cross-section air speed can remove pollutants from processes faster and more effectively.
Non-unidirectional flow mainly depends on the clean air to dilute the pollutants in the room and area to maintain its cleanliness. Therefore, the more the number of air changes, the more reasonable the airflow pattern, the more significant the dilution effect, and the corresponding cleanliness improves. The air supply volume and the corresponding air change frequency of non-unidirectional flow cleanroom and clean area are the main air flow test items concerned.
To obtain repeatable readings, record the time-averaged air speed at each measurement point.
Air change frequency: calculated according to the total air volume of cleanroom divided by the volume of cleanroom.

2. Temperature and humidity

The temperature and humidity measurement of cleanrooms or clean facilities usually includes the general test and comprehensive test. The former one applies to the acceptance test in the empty state, and the latter applies to comprehensive performance test in the static or dynamic state. This type of test is suitable for the cleanrooms with strict requirements for temperature and humidity performance and shall be performed after the airflow uniformity test and the air conditioning system adjustment. During this test, the air-conditioning system shall be fully operational and everything be stabilized. At least one humidity sensor should be installed in each humidity control zone, and the sensor be stabilized sufficiently. The measurement should be suitable for the purpose of actual use, and not be started until the sensor is stable, and the measurement time should not be less than 5 minutes.

3. Differential pressure

The purpose of this test is to verify the ability to maintain a specified differential pressure between the completed facility and environment and the spaces within the facility. This test applies to all three states and needs to be done regularly. 
Test requirements:
1）The static differential pressure measurement requires that all doors in the clean area are closed.
2）It is carried out in order from the cleanroom with high cleanliness to those with low cleanliness until to the rooms connected with outdoor.
3）The measuring port can be set anywhere in the room without the influence of airflow, and the surface of the port shall be parallel to the airflow streamline.
4）The measured and recorded data shall be accurate to 1.0 Pa.
Test procedures
1）First close all the doors.
2）Measure the differential pressure between cleanrooms, corridors, corridor and the outside with a meter.
3）Record all the data.
Differential pressure standard
The positive or negative pressure value of the cleanroom under test is determined according to the cleanroom design or process requirements. 
1) The static differential pressure between cleanrooms of different levels or between the clean area and non-clean area shall not be less than 5Pa. 
2) The static differential pressure between cleanroom and outdoor shall not be less than 10Pa. 
3) For the unidirectional flow cleanroom with air cleanliness level higher than Class 5 (Class 100), when the door is opened, the dust concentration of the indoor working surface at 0.6m inside the door shall not be greater than the concentration limit of the corresponding level. 
4) If the requirements of the above standards are not met, the fresh air and air exhaust volume should be readjusted until they are qualified.

4. Suspended particulates

A、Indoor test personnel should not be more than two, must wear clean clothing, stand in the test point leeward side and away from the test point, and remain static. The movement should be light when changing test points, and the interference of personnel on indoor cleanliness should be reduced. 
B、The equipment shall be used within the calibration period.
C、Equipment data shall be cleared before and after detection.
D、In the unidirectional flow area, the selected sampling probe should be close to isodynamic sampling, and the deviation between the air speed entering the sampling probe and that of the sampled air should not exceed 20%. If this is not possible, place the sampling port in the main direction of the airflow. For sampling points of non-unidirectional flow, the sampling port shall be vertical upward.
E、The connection pipe from the sampling port to the particle counter sensor should be as short as possible.

5. Settling bacteria

The measuring point in the working area is about 0.8 to 1.2m above the ground. Place the prepared culture dish at the sampling point, open the cover, expose it for the specified time, then cover the dish, and place the dish in the constant temperature incubator for culture for no less than 48 hours. There should be a control experiment for each batch of culture medium to check whether the medium is polluted.

6. Noise

The measurement height is about 1.2 meters from the ground. If the cleanroom area is less than 15 square meters, only 1 point in the center of the room should be measured; if the area is more than 15 square meters, 4 diagonal points should also be measured which is respectively 1 meter away from the near side wall and oriented to each corner.

7. Illumination

The measuring point plane is about 0.8 meters away from the ground, and the point is arranged at a distance of 2 meters. The measuring point of the room within 30 square meters is 0.5 meters away from the side wall, and that of the room exceeding 30 square meters is 1 meter away from the wall.