Some standard content:
National Standard of the People's Republic of China
Performance test methods for facepiece of filter type respiratorSubject content and scope of application
GB/T 2891-.1995
Replaces GB2891.1~2891.682
This standard specifies the performance test methods for filter type respirators, such as wearing leakage coefficient, actual dead space, field of view, assembly air tightness, exhalation valve air tightness, exhalation valve resistance to air, lens transmittance (transmittance ratio) and facepiece inhalation resistance. This standard is applicable to the test and evaluation of the performance of filter type respirator facepieces (hereinafter referred to as facepieces), and other related products can also be used as a reference. 2 Reference standards
GB/T528 Rubber tensile strength test method
GB2410 Transparent plastic transmittance and haze test method GB2426 Chinese adult head shape series
3 Technical content
3.1 Test method for leakage coefficient of mask wearing (oil mist method)3.1.1 Principle
After a person wears a mask, the ratio of the concentration c of harmful substances that leak into the mask through the mask sealing frame, exhalation valve and mask parts assembly parts to the external concentration c. is called the leakage coefficient of the mask, expressed as a percentage (%). 3.1.2 Test device
The test device system is shown in Figure 1.
Approved by the State Administration of Technical Supervision on June 28, 1995, and implemented on January 1, 1996
GB/T2891-1995
Figure 1 Leakage coefficient test device diagram
1\Oil mist generator; 2--Coarse oil mist settler; 3-Glass or plastic oil mist chamber; 4-Subject wearing a mask; 5-Oil mist instrument; 6-Buffer bottle 3.1.2.1 Oil mist generating device: Use No. 30 or No. 22 turbine oil to generate aerosol oil mist with a flow rate of 30-60L/min, with a large-particle oil mist separator and various components for controlling working conditions. 3.1.2.2 Oil mist chamber: A closed room with glass walls, the size of which should allow the test personnel to complete the specified actions, with an oil mist inlet and overflow, and allow the sampling pipeline to pass through, and the test personnel's inhalation air flow to pass in from the outside. The oil mist chamber can also be made of wood, plastic, etc. 3.1.2.3 Oil mist turbidity meter: YW-4590 or other types of oil mist turbidity meter, the measurement accuracy should be less than 10-6. 3.1.2.4 Sampling device: mainly composed of a suction pump, a buffer bottle, a regulating valve and other pipeline systems, and the sampling airflow used with the oil mist turbidity meter is 4~10 L/min.
3.1.3 Test conditions
Ten people with head and face sizes that meet the matching range of each mask are selected for wearing test. The subjects should shave their beards.
The mask should be worn according to the subject's feeling of fit, and the headband should not be adjusted too tight or too loose. During the test, the subject completes the following actions according to the instructions: stay calm for at least 1 minute;
Swing the head up and down and left and right for at least 1 minute; talk and take deep breaths for about 1 minute.
3. 1. 3.4
The oil mist concentration in the oil mist chamber is within the range of 1000～2500mg/m2. The oil mist filtration efficiency of the gas filter canister is higher than 99.995%. During the test, measures are taken to make the gas filter canister absorb the air outside the oil mist chamber. The air tightness of the exhalation valve and assembly of the test mask should meet the standard requirements. The sampling tube is installed on the test mask, and the interface should ensure airtightness, and the tube end should be close to the mouth and nose area. 3.1.4 Test steps
3.1.4.1 Preparation
3.1.4.1.1 Prepare the test mask, install the sampling tube, take measures to absorb the outdoor air of the oil mist through the gas filter canister, and prepare the alcohol cotton balls for disinfection;
3.1.4.1.2 Select the test personnel, register their selected head and face size and special features, and tell the test requirements; 3.1.4.1.3 Check all instruments and equipment to ensure that they are in normal working condition. 3.1.4.2 Test
GB/T 2891—1995
3.1.4.2.1 Pass the oil mist into the oil mist chamber to make its concentration reach the requirement and be basically stable. Start the vacuum pump to take air flow samples and measure them with the oil mist turbidity meter, and adjust the instrument indication to 100%, which is co; 3.1.4.2.2 The subject wears the mask, performs a preliminary airtightness check according to the instructions, adjusts it appropriately, and connects the sampling tube to the turbidity meter; 3.1.4.2.3 Start the vacuum pump and measure the concentration of the air flow when the subject breathes in the smoke-free air outside the oil mist room. Take 5 samples and average them to get the background concentration ce
3.1.4.2.4 Let the subject The test subject enters the oil mist chamber and performs the actions specified in 3.1.3.3. The concentration of the airflow is measured in each case, with 5 data points each, and the leakage concentration c is obtained on average;
3.1.4.2.5 Replace the test subject and repeat 3.1.4.2.2~3.1.4.2.4. 3.1.5 Test results
3.1.5.1 The leakage coefficient of the nth test subject in any state of stillness, movement or speaking is calculated according to formula (1) and formula (2): k = 2℃ × 100
Wherein; k.-
are the leakage coefficients when stillness, movement or speaking respectively. The leakage coefficient for the subject is:
3.1.5.2 The result of a certain mask is obtained by formula (3): 0
+动+k说出)
（1）
（3）
Note: The leakage coefficient test is based on the oil mist method. It is allowed to use sodium chloride smoke and adopt corresponding test equipment and instruments, but it must be calibrated and corrected with the oil mist method.
3.1.6 Test report
The test report should include the following:
Sample name or code;
Test environment conditions;
Test method;
Test results;
Tester's signature;
Test date.
3.2 Test method for actual dead space of mask
3.2.1 Principle
Correctly wear the test mask on the standard head shape, and use a mechanical lung to simulate breathing under specified conditions so that the exhaled air is CO2 gas with a high concentration a. A part of it is retained in the actual dead space and the "respiratory dead space". During inhalation, it is diluted by the air inhaled through the gas filter canister (assuming its CO concentration is c), and becomes gas with a concentration b that enters the mechanical lung. Therefore, the actual dead space size can be calculated as follows: p=
Wherein: P
actual dead space, mL;
-1 inhaled volume, mL;
(b - c)V
_"respiratory dead space" volume, mL, which can be obtained in advance by water filling, sand filling or calculation; CO2 concentration in exhaled air, %;
b--CO2 concentration entering the mechanical lung, %; C--CO2 concentration in the inhaled air after filtering by the canister, %. · (4)
3.2.2 Test conditions
3.2.2.1 The mask should be worn on the standard head shape for the test. The airtightness of the sealing frame should meet the standard requirements. Auxiliary sealing measures can be taken when necessary. 107
GB/T 2891—1995
3.2.2.2 The test is carried out in a well-ventilated environment so that the high concentration of exhaled CO2 can be discharged in time. The CO concentration in the air around the mask should be less than 1%.
3.2.2.3 The breathing rate of the mechanical lung is 21~24 times/min, and the breathing volume is 24±1L/min. 3.2.3 Device
3.2.3.1 The sampling device is shown in Figure 2. The main components are: Standard head type: It should comply with GB2428, and the head type is equipped with a breathing tube that can be connected to the mechanical lung; a.
b. Mechanical lung: It is a double-cylinder synchronous piston type with a flexible and reliable synchronous reverse valve. Respiratory frequency and breathing depth can be adjusted to meet the requirements of Article 3.2.2.3;
Gas storage bags: 3, each with a gas storage capacity greater than 30L, 1 for high-concentration CO, 2 for rotating storage of inhaled gas samples; Gas storage cylinder: CO2, concentration not less than 95%; Auxiliary equipment: stopwatch, electric fan, etc.
Figure 2 Diagram of actual harmful space test device
0, Analyzer
1, 5--CO gas storage bag and inhaled gas sample storage bag respectively; 2-two valves running synchronously, 1, 7 are connected during inhalation, 3, 6 are connected; 7, 3 are connected during exhalation, 6, 5 are connected; 3 ventilation pipe; 4-standard head shape wearing the test mask; 6, 7 have the same structure and two cylinders moving synchronously, forming a mechanical respirator
3.2.3.2CO2 analyzer: the accuracy is not less than 0.1%. 3.2.4 Test steps
3.2.4.1 Preparation
Install the sampling device according to the diagram, connect the CO2 cylinder to the air inlet of the air storage bag; adjust the breathing rate and breathing depth of the mechanical lung to meet the requirements; measure or calculate the volume K of the "respiratory dead space" of the test system; according to the instructions of the selected CO2 analysis instrument, put the instrument in working condition; start the ventilation equipment to keep the indoor CO2 concentration no more than 1%. 3.2.4.2
Unscrew the CO2 cylinder, inflate the air storage bag 1 for about 3 to 5 seconds, and then discharge it. Rinse twice in this way, then fill bag 1 to about 3/4 of its volume and slow down the inflation speed;
Put the test mask on the standard head shape, pay attention to wearing it correctly, with appropriate looseness and tightness, and close the frame to be airtight; b.
Start the mechanical lung to breathe for about 0.5 minutes, then remove the air storage bag 5 to exhaust, and do this twice. At this time, the concentration of the air bag and the mechanical lung sampling system reaches a stable balance:
GB/T2891—1995
d. Stop the mechanical lung operation 1 minute after the formal breathing sampling, and take off the test mask; e. Supply CO from the air storage bag 5, and the analyzer detects the concentration of the gas sample. Each sample gas is analyzed 3 times, and the average value is calculated. 3.2.4.3 Retest
For each mask, follow the steps of 3.2.4.2 and repeat 3 to 4 times; a.
b. During the test, samples were taken from the environment around the mask to analyze the concentration of C () and obtain c. If c is not greater than 0.5%, c can be ignored when calculating P according to formula (4).
3.2.5 Test results
The average and standard deviation of each mask were calculated from the 4 to 5 P values obtained. 3.2.6 Test report
According to 3.1.6.
3.3 Test method for mask visual field
3.3.1 Principle
A low-voltage bulb was installed at the eyeball position of a standard head shape so that the solid angle of its light emission was equal to the solid angle of the average visual field of Chinese adults. When the mask is put on, the outgoing light cone is limited by the mask eye window and is reduced. The percentage of light that is preserved is equivalent to the visual field preservation rate of the standard head shape after wearing the mask. The visual field map after the mask is put on is measured with a medical visual field meter. The total visual field map area of the two eyes and the binocular visual field map area of the common part of the two eyes are measured. Calculate their corresponding percentages when not wearing a mask, and use the correction coefficient to correct them to obtain the total visual field preservation rate and binocular visual field preservation rate. The lower visual field (degrees) when wearing a mask is determined by the position of the lower intersection of the visual field diagram of both eyes. 3.3.2 Test device
3.3.2.1 Visual field meter: It consists of three parts: a.
Semicircular arc bow: The radius is 300-340mm, which can rotate around the horizontal radius passing through the midpoint 0°. There are scales every 5° on both sides starting from 0° and extending to 90°. A slidable white sight mark is installed on the arc bow; b. Recording device: The recording needle is linked to the sight mark through the shaft wheel and other components, and the direction and angle of the sight mark are recorded on the visual field drawing accordingly;
c. Frame: It is used to support the semicircular arc bow and fix the recording device. 3.3.2.2 Standard head shape: It should comply with GB2428, with black paint on the surface, and 6.3V small bulbs installed at the pupil positions of both eyes. The line connecting the vertices of the bulbs should be 7 ± 0.5mm behind the midpoints of both eyes. The visual field of the head shape itself should comply with the average visual field of Chinese adults. The position of the standard head shape installed on the workbench should enable the left and right eyes to be placed at the center of the semicircular arc respectively, and look directly at the "0" point. 3.3.2.3 Recording paper: It is used in conjunction with the recording device, and the average visual field curve is printed on it. 3.3.2.4 Planimeter: It measures the area of the figure with an accuracy of 0.1cm2. 3.3.3 Test conditions
3.3.3.1 According to the number of the test mask, select the standard head shape with the corresponding number. 3.3.3.2 The test work is carried out in a dark room. 3.3.3.3 Wear the mask correctly, the headband is not too tight or too loose, and pay attention to the left and right symmetry of the eye window. Each mask must be taken off and put on for 3 times, and the average result is taken.
3.3.4 Test steps
3.3.4.1 Check whether the perimeter, recording device and sight mark are working correctly, and calibrate them carefully. 3.3.4.2 Install the recording paper correctly on the recording table. 3.3.4.3 Wear the test mask on the standard head form and adjust it correctly, not too loose or too tight. 3.3.4.4 Place the standard head form with the mask on the seat, so that the left (or right) eye is at the center of the arc, and turn on the light bulb of the eye. Measure one point every 15° to 30° from any vertical or horizontal position (depending on the change in the visual field) until all directions are measured. 3.3.4.5 Move the head form, measure the other eye according to 3.3.4.4, and then remove the recording paper. 3.3.4.6 Take off the mask, readjust it, and repeat the test 3 to 4 times according to 3.3.4.2 to 3.3.4.5. 109
3.3.5 Results
GB/T 2891--1995
3.3.5.1 Connect the points recorded on each recording paper into a closed curve according to the left and right eye fields. Except for special points, the curve should be smooth and natural.
3.3.5.2 Use a planimeter to measure the area S of the binocular visual field map and the total visual field map on each recording paper. Assume the corresponding average visual field map area S without wearing a mask, and measure the visual field preservation rate t. 100
Where: t--visual field preservation rate, %;
-correction coefficient, given by the figure;
S,--area of binocular visual field map and total visual field map, cm2S--average visual field map area, cm2.
Total standard field
Binocular standard field
Figure 3 Total field of view and binocular field of view correction coefficient S./s
3.3.5.3According to the position of the lower intersection of the left and right field of view curves of each field of view diagram, obtain the lower field of view value (degrees). 3.3.5.4 Calculate the average value and standard deviation of the multiple field of view results of the test mask. 3.3.6 Test report
According to 3.1.6.
3.4 Test method for air tightness of mask assembly
(5)
3.4.1 Principle
Create a certain positive pressure in the assembled mask. If the mask is deflated, the pressure value inside the mask will decrease. The amount of gas leakage can be measured by the pressure drop over a certain period of time.
3.4.2 Test device
The test device is shown in Figure 4.
3.4.3 Test steps
GB/T 2891--1995
Figure 4 Mask assembly air tightness test device
1--Screw clamp 2--Piston 3-Mask; 4-Vent plug; 5-Clamp; 6--Pressure gauge 3.4.3.1 Check the air tightness of the instrument pipeline. First, clamp the rubber hose leading to the air plug (4) with a clamp to prevent air leakage. Open the piston (2) to make the internal pressure reach 4.7±0.5kPa. Close the piston (1). The pressure gauge does not drop within 0.5min, which means it is airtight. 3.4.3.2 Adjust the compressed air pressure, loosen the screw clamp (1), open the piston (2), gradually open the compressed air, block the vent plug (4), and slowly tighten the screw clamp (1) to make the pressure gauge (6) indicate a value of 5.0±0.1kPa. 3.4.3.3 Remove the breathing valve and protective cover of the mask, close the exhalation hole, clamp the mask on the special clamp (5), and insert the vent plug into the inhalation port, open the piston (2) to inflate the mask so that the internal pressure value is maintained at 5.0 ± 0.1 kPa, close the piston (2), and record the pressure drop within 1 minute.
3.4.4 Test results
Each test mask is qualified if the pressure value drops by less than 50Pa within 1 minute. 3.4.5 Test report
According to 3.1.6.
Note: The assembly air tightness of the headband mask can be tested by wearing the mask on a standard head shape (or simulated head shape) and passing compressed air. When the internal pressure of the mask is 2.0 ± 0.1 kPa, the joint should be airtight. 3.5 Exhalation valve air tightness test method
3.5.1 Principle
Install the exhalation valve on the constant volume cavity, evacuate to the specified negative pressure, and measure the speed of change of the negative pressure value due to the leakage of the exhalation valve or the time required to return to zero to evaluate its air tightness.
3.5.2 Test device
GB/T 2891
Figure 5 Exhalation valve air tightness tester
1-Water column pressure gauge; 2-Constant volume cavity; 3-Tested exhalation valve; 4-Exhaust control valve; 5-Air flow meter; 6-Flow regulating screw clamp; ·-Exhaust pump 3.5.2.1 Air tightness test device is shown in Figure 5.
3.5.2.2 Constant volume cavity: volume is 150±10mL. 3.5.2.3 Pressure gauge: range is 0~2000Pa; accuracy is 1Pa. 3.5.2.4 Gas flow meter: range 0~2000mL/min; accuracy 10mL/min. 3.5.2.5 Stopwatch: accuracy 0.1s.
3.5.2.6 Suction power: vacuum pump or suction bottle. 3.5.3 Test conditions
3.5.3.1 Environment
Temperature is 17~~30℃; air pressure is 101.325kPa; relative humidity is less than 75%. 3.5.3.2 Sample
The exhalation valve to be tested should be cleaned with alcohol cotton and air-dried or blown dry. a.Www.bzxZ.net
The connection between the exhalation valve to be tested and the constant volume cavity should be airtight and perpendicular to the horizontal plane, and the valve plate should not be deformed due to force. 3.5.4 Test steps
3.5.4.1 Check the airtightness of the instrument system. Close the through holes of the constant volume cavity and the exhalation valve, evacuate to a negative pressure of 1180Pa, and no pressure change can be observed within 2 minutes after closing the exhaust control valve. 3.5.4.2 Prepare the test sample according to the test conditions. 3.5.4.3 Install the exhalation valve on the constant volume cavity. 3.5.4.4 Evacuate air at a flow rate of no more than 500mL./min until the negative pressure in the constant volume chamber reaches 1250Pa, and close the control valve. 3.5.4.5 From the negative pressure of 1180Pa, start the stopwatch and record the change in negative pressure at 45s or the time required to return to 0. Replace the exhalation valve and repeat the above test.
3.5.5 Test results
Unqualified if any of the following conditions exists: a.
The exhaust flow rate has reached 500ml/min, but the negative pressure does not reach 1180Pa. The negative pressure change of the full-face mask exhalation valve within 45s is greater than 590Pa. The time for the half-face mask exhalation valve to return to normal pressure is less than 20s. 3.5.6 Test report
According to 3.1.6.
3.6 Test method for air flow resistance of exhalation valve 3.6.1 Test device
3.6.1.1 See Figure 6 for the test instrument.
Compressed air
GB/T 2891—1995
Figure 6 Test diagram for air flow resistance of exhalation valve
1—adjusting screw clamp; 2—air filter bottle; 3—air flow meter; 4—pressure measuring tee; 5—micromanometer; 6—exhalation valve seat; 7—tested exhalation valve 3.6.1.2 Flow meter: range is 0～401/min, accuracy is 0.5L/min. 3.6.1.3 Micromanometer: range is not less than 294Pa, accuracy is 2Pa. 3.6.1.4 The inner diameter of the pressure measuring tee is 16±0.5mm, the length is 100mm, and the opening of the pressure transmission hole in the air flow pipe is not more than 6mm. 3.6.2 Test conditions
3.6.2.1 The test airflow is 30±0.6L/min and should be purified and filtered before passing through the exhalation valve. 3.6.2.2 The test environment is normal.
3.6.3 Test steps
3.6.3.1 Preparation
Check the air tightness of the test system, pass clean air with a large flow rate, and use soapy water to test for leaks; put the flow meter and micromanometer in working condition. 3.6.3.2 Test
Pass air flow and adjust it to the specified value, and measure the resistance P1 when the exhalation valve is not installed; a.
Install the exhalation valve into the test system, readjust the air flow to the specified value, and measure the resistance P2 at this time. b.
3.6.3.3 Replace the exhalation valve sample and repeat the test in 3.6.3.2. 3.6.4 Test results
The resistance of each exhalation valve sample to air flow is: P= P, - P,
3.6.5 Test report
According to 3.1.6.
3.7 Test method for inhalation resistance of mask
3.7.1 Test apparatus
3.7.1.1 See Figure 7 for the test apparatus for inhalation resistance of mask. 113
Suction pump
GB/T 2891-1995
Figure 7 Diagram of test apparatus for inhalation resistance of mask
1 Adjusting screw clamp; 2 Air flow meter; 3-Inclined micromanometer; 4-Pressure measuring tee; 5~-Standard head type; 6-Test mask 3.7.1.2 Flow meter: The range is 0~~40L/min, and the accuracy is 0.5L/min. 3.7.1.3 Micromanometer: range not less than 294Pa, accuracy 2Pa. 3.7.1.4 Standard head type: in accordance with GB2428. Inhalation
3.7.1.5 Pressure measuring tee: inner diameter 16±0.5mm, length 100mm, pressure transmission hole opening not more than 6mm. 3.7.1.6 Suction pump: suction flow rate not less than 30L/min. 3.7.2 Test conditions
3.7.2.1 For masks with detachable gas filter canisters, the gas filter canisters must be removed. For structures that cannot be disassembled (such as filter element bags), the air flow resistance of the separate filter element shall be deducted from the test results to represent the inhalation resistance of the mask. 3.7.2.2 The standard head type used in the test matches the mask number and is worn correctly. The sealing frame should not leak, and the air guide tube is bent 180°3.7.2.3 The continuous airflow of the test is 30±0.6L/min. 3.7.3 Test steps
3.7.3.1 Check that all the connection parts of the test device are airtight. 3.7.3.2 Make the flow meter and micromanometer work normally. 3.7.3.3 Start the vacuum pump, adjust the screw clamp to make the air flow rate 30±0.6L/min, and measure the system resistance P1. 3.7.3.4 Wear the mask according to the requirements of 3.7.2.2, adjust the vacuum flow rate to 30±0.6L/min, and measure the resistance Pz. 3.7.4 Test results
The resistance value of a single mask is:
3.7.5 Test report
According to 3.1.6.
3.8 The test method for the light transmittance (light transmittance ratio) of the mask lens is the same as GB 2410.
The test report is according to 3.1.6.
3.9 The test method for 300% tensile strength, breaking strength and breaking elongation of hood-type masks (rubber) before aging is the same as GB/T 528.
The specimen is cut from the edge of the hood-type mask sealing frame and the head. The test report is in accordance with 3.1.6.
3.10 Hot air aging test method for exhalation valve 3.10.1 Principle
GB/T 2891—1995
After the exhalation valve sheet with qualified air tightness is aged for a certain period of time under the action of hot air at normal pressure and specified temperature, its air tightness performance is measured.
3.10.2 Test device
The hot air aging box should meet the following requirements: The temperature fluctuation range of the test area in the box is ±2℃; a.
There should be a continuous air blowing device in the box;
There should be an air inlet and an exhaust port.
3.10.3 Test conditions
Aging temperature: 100±2℃;
Aging time: 8h.
3.10.4 Test steps
3.10.4.1 Adjust the temperature in the aging box to 100±2℃. After the temperature stabilizes, place the test sample on the valve seat and seal it in the aging box in a free state. The distance between the samples shall not be less than 5mm; the distance between the sample and the box wall shall not be less than 50mm. 3.10.4.2 Put the sample into the constant temperature aging box as required for 8h and take it out. After placing it at room temperature for 4h, check whether it is sticky or deformed, and test its air tightness according to 3.5.
3.10.5 Test results
According to 3.5.5.
3.10.6 Test report
According to 3.1.6.
3.11 Test method for bonding strength between mask, air duct and canister (box) 3.11.1 Principle
A rubber tensile machine is used to measure the bonding strength between the mask and the air duct, canister (box) or between the air duct and canister. 3.11.2. Test device
The tester is a pendulum rubber tensile machine, and the technical requirements are: measuring range: 0~980N;
The pulling speed of the lower clamp: 100±5mm/min. 3.11.3 Test steps
3.11.3.1 Clamp the lower part of the Y-shaped tube of the mask that has been assembled and placed for 24 hours into the upper clamp of the tensile machine, and the direction of the clamp should be perpendicular to the Y-shaped tube.
3.11.3.2 Clamp the lower end of the air duct into the lower fixture so that the lower fixture is about 20 to 30 mm away from the Y-shaped pipe mouth, turn on the tensile testing machine, and stop the test when the reading on the load dial is greater than the specified value. 3.11.3.3 The test of the bonding strength between the mask and the canister (box), and between the air duct and the canister can be fixed with auxiliary measures and carried out in accordance with 3.11.3.1 and 3.11.3.2.
3.11.4 Test results
The bonding strength values are read from the load dial respectively. When the reading is greater than the specified value, it is qualified. 3.11.5 Test report
According to 3.1.6.
Note: The bonding strength between mask parts can also be tested by static hanging weight method. The test weight of duct-type mask is 15kg, and the test weight of direct-type mask is 5kg115
Additional instructions:
GB/T2891—1995
This standard is proposed by the Ministry of Labor of the People's Republic of China. This standard is under the jurisdiction of the National Technical Committee for Standardization of Labor Protection Products. This standard is drafted by Beijing Labor Protection Science Research Institute, PLA 57605 Unit, Labor Protection Science Research Institute of the Ministry of Labor, and Shanxi New Chemical Factory.
The main drafters of this standard are Liu Liugui, Bao Guoqing, Cheng Xingren, Zhang Xueli, Teng Jinshan, Sun Wenjie, Zhang Xitian, and Liu Zhonghua. 116
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