Dust Mask Testing

Dust mask testing mainly conducts scientific testing and analysis on filtration efficiency testing, breathing resistance testing, leakage testing, field of view testing, flammability testing and dead space testing, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Filtration efficiency testing: This test aims to evaluate the barrier ability of the dust mask filter media to the specific particulate matter. Sodium chloride (NaCl) or paraffin oil (DOP/corn oil) aerosol is usually used as the test medium, simulating the non-oily and oily particles. During the testing, the aerosol of the specified concentration is passed to the upstream of the filter media at the specified flow rate (such as 85 L/min), and the concentration is measured by the upstream and downstream particle counters, calculating the filtration efficiency percentage. This is the core indicator for measuring the protective performance of the mask.

Breathing resistance testing: This item evaluates the airflow resistance of the mask to the breathing of the wearer, directly related to the comfort and acceptability of the use. The testing is divided into the inhalation resistance and exhalation resistance. At the specified test flow rate (such as 85 L/min), a differential pressure gauge is used to measure the pressure difference between the inside and outside of the mask. An excessively high breathing resistance may cause fatigue or even hypoxia of the user, so the standards have clear limit requirements for this.

Leakage testing (total inward leakage): This test is used to evaluate the degree of fit between the mask and the face of the wearer, i.e., the overall protective performance in the actual wearing state. During the testing, the subject needs to complete a series of actions simulating the work activities as required (such as turning the head, speaking and deep breathing), while the particle concentration inside the mask is detected, calculating the leakage rate. The total inward leakage combines the total of the edge leakage of the filter media and the penetration of the filter media itself, and is the key to the actual protective effect.

Field of view testing: The field of view testing evaluates the degree of obstruction of the downward field of view of the user after wearing the dust mask. A standard perimeter is used to measure the angle difference of the monocular downward field of view before and after wearing the mask. An excessively narrow field of view will affect the operation safety, especially in the industrial or construction environments, so the relevant standards have a lower limit provision for this.

Flammability testing: This test mainly targets the masks that may be used in the environments with flammable and explosive gases or dust. The mask sample is placed under specific flame conditions, and the flame retardant performance of its material is evaluated, recording the afterflame time and afterglow time. The qualified mask material should be able to effectively prevent the flame spread and reduce the risk of the secondary injury in the dangerous environments.

Dead space testing: The dead space refers to the space volume inside the mask that cannot participate in the fresh gas exchange. In the testing, carbon dioxide of the known concentration is injected into the mask worn on a head form, and the dead space volume is calculated by measuring the stabilized concentration. An excessively large dead space will cause the retention of carbon dioxide, increasing the breathing burden and affecting the wearing comfort.

Headband strength and durability testing: This item evaluates the mechanical properties of the mask headbands (including the ear-loop type or head-band type). It usually includes the tensile strength testing, measuring the tensile force at the breakage of the headband; and the cyclic stretching testing simulating the wearing, evaluating its fatigue resistance. It is ensured that the headband will not break or become excessively loose under the normal use and emergency situations, maintaining the effective fit of the mask.

Testing Scope

KN/KP series masks (Chinese standard GB 2626): This standard is the mandatory standard of the Chinese respiratory protection non-powered air-purifying particle respirators. The testing scope covers the KN type (only applicable to filtering the non-oily particles, such as dust, smoke and mist) and the KP type (applicable to filtering the oily and non-oily particles). According to the filtration efficiency, they are graded as KN90/KP90, KN95/KP95 and KN100/KP100, corresponding to the filtration efficiencies of 90%, 95% and above 99.97% respectively.

N/R/P series masks (US standard NIOSH 42 CFR Part 84): This is the certification standard of the National Institute for Occupational Safety and Health of the United States. The testing scope includes the N series (Not resistant to oil, only for the non-oily particles), R series (Resistant to oil, for the oily and non-oily particles, with a time limit) and P series (Oil Proof, for the oily and non-oily particles). The efficiency grades are N95/R95/P95, N99/R99/P99 and N100/R100/P100.

FFP series masks (European standard EN 149): This standard is applicable to the particle filtering half masks of the European market. According to the filtration efficiency, the testing scope is divided into FFP1 (filtration efficiency ≥80%), FFP2 (filtration efficiency ≥94%) and FFP3 (filtration efficiency ≥99%). This standard not only tests the filtration efficiency, but also strictly tests the comprehensive properties such as the total inward leakage, breathing resistance and flammability.

Medical protective masks (Chinese standard GB 19083): This standard is mainly applicable to the medical working environment, used to filter the particulate matter in the air and block the droplets, blood, body fluids and secretions. In addition to the filtration efficiency (divided into grades 1, 2 and 3) and breathing resistance, the testing scope also specially adds the synthetic blood penetration resistance testing, surface water resistance testing and microbiological indicator testing, to meet the special protective needs of the medical environment.

Daily protective masks (Chinese standard GB/T 32610): This standard targets the protection in the air pollution environments in daily life. The testing scope focuses on the filtration efficiency (divided into grades Ⅰ, Ⅱ and Ⅲ), breathing resistance, leakage, protective effect (the particle barrier ability in the simulated wearing state) and the safety indicators such as the formaldehyde, pH value and decomposable carcinogenic aromatic amine dyes, paying more attention to the applicability and safety of the public wearing.

Disposable and replaceable masks: The testing scope is differentiated according to the product structure. The disposable mask is an integral structure, and the filter media cannot be replaced, so it is tested as a whole. For the replaceable half masks, the mask body (exhalation valve, leakage, etc.) and the replaceable filter elements (filtration efficiency, breathing resistance, etc.) need to be separately tested, ensuring that all the components meet the standard requirements.

Testing Methods

Aerosol generation and neutralization method: In the filtration efficiency testing, an aerosol generator is needed to produce the monodisperse or polydisperse test aerosols (such as NaCl and DOP). The generated aerosol usually carries static electricity, and needs to pass through a neutralizer (such as the Kr-85 radioactive source or soft X-ray neutralizer) to reach the Boltzmann charge equilibrium state, to eliminate the interference of the static electricity effect on the filtration test results, ensuring that the test reflects the comprehensive ability of the mechanical filtration and electrostatic adsorption of the material.

Scanning method and counting method: The filtration efficiency testing mainly adopts two methods. The scanning method is to carry out the moving test on the whole surface of the test sample at the specified scanning rate, obtaining the average efficiency, applicable to the initial stage testing. The counting method is to test the efficiency at the most penetrating particle size (MPPS) of the local area of the test sample. The MPPS is usually between 0.1 and 0.5 microns, and the penetration ability of the particles at this size is the strongest. The efficiency measured at this size is the most conservative value, and is the key method for determining the grade.

Head form simulation test method: Used for the tests related to the face adaptation such as the leakage, field of view and dead space. The standard head forms are designed according to the ergonomics data of the target user groups, with different sizes (such as the large, medium and small sizes). During the testing, the mask needs to be worn on the corresponding head form according to the manufacturer's instructions, simulating the real wearing conditions, ensuring the representativeness and repeatability of the test results.

Dynamic breathing simulation method: In the breathing resistance testing, a breathing simulator (sine wave pump or piston pump) is used to simulate the waveforms and flow rates of the human breathing. Through the precision flow meter and differential pressure sensor, under the specified constant flow rate or the simulated tidal volume breathing conditions, the pressure difference change between the two sides of the mask is precisely measured, thereby obtaining the inhalation resistance and exhalation resistance values, more truly reflecting the breathing load during use.

Total inward leakage (TIL) test method: This method requires the real human subjects to wear the mask properly in a test chamber and carry out the specified series of actions (such as normal breathing, deep breathing, turning the head left and right, nodding up and down, speaking and normal breathing). The test chamber is filled with the test aerosol of the specified concentration, and the real-time sampling is carried out through a small tube extending into the mask, calculating the concentration ratio inside and outside the mask, and obtaining the total leakage rate. This is the golden method for evaluating the actual protective performance.

Synthetic blood penetration test method: Mainly used for the medical protective masks. The synthetic blood with a surface tension similar to that of the blood is sprayed to the outside of the mask sample from a certain distance (300 mm or 550 mm) under a specific pressure (such as 10.7 kPa, 16.0 kPa and 21.3 kPa corresponding to the different grades). It is observed whether the synthetic blood penetrates to the inside of the mask, to evaluate its barrier ability to the blood and body fluids.

Testing Standards

Domestic Standards:

1. GB 2626, Respiratory protection — Non-powered air-purifying particle respirators

2. GB 19083, Technical requirements for protective face mask for medical use

3. GB/T 32610, Technical specification of daily protective mask

International Standards:

1. EN 149, Respiratory protective devices — Filtering half masks to protect against particles — Requirements, testing, marking

2. NIOSH 42 CFR Part 84, Approval of Respiratory Protective Devices

3. ASTM F2100, Standard Specification for Performance of Materials Used in Medical Face Masks

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Aerosol filtration efficiency test bench: This equipment is the core test system, mainly composed of an aerosol generator, neutralizer, drying and dilution system, test fixture, laser particle counter (or photometer), vacuum pump and flow control system. It can precisely control the concentration, particle size distribution and charge state of the test aerosol, and automatically complete the scanning test of the filtration efficiency or the most penetrating particle size (MPPS) test at the specified flow rate, with a highly automated data acquisition and processing.

Breathing resistance tester: This equipment usually includes an adjustable flow rate suction pump (or breathing simulator), high-precision differential pressure sensor (with a range generally of 0-1000 Pa), flow meter and test fixture. The system can set the constant flow rates (such as 30 L/min, 85 L/min and 160 L/min) according to the standards, or simulate the tidal breathing waveforms, automatically measure and record the inhalation resistance and exhalation resistance of the mask, directly outputting the test results.

Total inward leakage test chamber: This is a sealed test chamber, with a uniform mixing system inside, which can generate and maintain a stable aerosol test environment (such as salt mist or oil mist). The chamber is provided with a seat and communication equipment for the subjects. During the testing, the subject wearing the mask connected with a sampling tube sits in the chamber, and the sampling tube leads the gas inside the mask to the particle counter outside the chamber, calculating the leakage rate by comparison with the reference concentration in the chamber.

Tensile testing machine: Used to test the mechanical strength of the mask headbands, connecting parts, exhalation valve covers, etc. This equipment can carry out the constant-speed tensile testing, precisely measuring the parameters such as the breaking strength and elongation of the sample. Some equipment also has the cyclic stretching function, which can simulate the durability of the headband after multiple stretches, ensuring that it maintains sufficient elasticity and strength within its service life.

Synthetic blood penetration test device: This device includes an air compression system with adjustable pressure, liquid storage tank, spray nozzle and sample fixing frame. The nozzle diameter and spraying distance are strictly set according to the standards. By controlling the air pressure, a quantitative amount of synthetic blood is sprayed vertically to the mask sample fixed on the fixture at a specific speed. After the spraying, the penetration of the liquid on the inner surface is checked visually or with dedicated equipment.

Field of view test device (perimeter): An arc-shaped or hemispherical perimeter is usually adopted. The chin of the subject or the standard head form is placed on a fixed chin rest, and the eyes look at a fixed point in front. By moving the visual target installed on the arc rail, the boundary angle of the monocular downward field of view before and after wearing the mask is measured. The professional device can automatically record the angle difference, ensuring the accuracy and consistency of the testing.