How is the filtration efficiency of medical masks measured?

The filtration efficiency of medical masks is a key indicator for assessing their protective performance; it reflects the mask’s ability to filter specific particulate matter. The following provides a detailed explanation of its measurement method:

Testing Principle

The basic principle behind measuring the filtration efficiency of medical masks is to pass a test aerosol of a certain concentration through a mask sample, then compare the aerosol concentrations before and after the mask. By calculating the proportion of particles filtered out by the mask, we can determine its filtration efficiency.

Testing equipment

Aerosol generator It is used to generate aerosols with specific particle sizes and concentrations. Common test aerosols include sodium chloride aerosols and di-octyl phthalate (DOP) aerosols. For example, when testing medical protective masks, sodium chloride aerosols are often employed, with a particle size range typically between 0.02 and 2.0 μm.

Particle counter It is divided into types such as optical particle counters and condensation nucleus counters, which are used to measure aerosol concentrations. Optical particle counters count particles by detecting their scattering of light; they offer advantages such as fast measurement speed and relatively high accuracy. Condensation nucleus counters, on the other hand, are suitable for measuring particles with smaller particle sizes.

Mask Filtration Efficiency Tester This is an integrated device that combines an aerosol generator, a particle counter, and a related sampling system. It can automatically perform aerosol generation, sampling, and concentration measurement, and calculate the filtration efficiency.

Test steps

Sample Preparation Select multiple representative samples of medical masks, ensuring that the number and specifications of the samples comply with relevant standard requirements. At the same time, prepare the auxiliary equipment and materials needed for testing, such as sampling tubes and connecting pipelines.

Install the sample Place the mask sample onto the sample fixture of the tester, ensuring that the mask fits snugly against the fixture to prevent air leakage. Generally, the mask should remain flat throughout the testing process and must not have any wrinkles or distortions.

Aerosol Generation and Sampling Start the aerosol generator to produce an aerosol with a specific particle size and concentration, and introduce it into the test chamber. At the same time, use sampling tubes to direct the aerosol—both before and after it passes through the mask—into particle counters for concentration measurement. During the sampling process, ensure that the sampling flow rate remains stable; typically, the sampling flow rate is 85 L/min, which simulates the airflow conditions during normal human breathing.

Data Recording and Calculation The particle counter records aerosol concentration data in real time before and after the mask. Based on this data, the tester automatically calculates the filtration efficiency. The formula for calculating filtration efficiency is: Filtration Efficiency = (1 - Aerosol Concentration After Filtration / Aerosol Concentration Before Filtration) × 100%.

Multiple Measurements and Result Analysis To ensure the accuracy and reliability of the measurement results, each mask sample needs to be measured multiple times, and the average value should be taken as the filtration efficiency result. At the same time, statistical analysis should be performed on the measurement data to evaluate the degree of dispersion and uncertainty in the measurement results.

Filter efficiency requirements for different types of medical masks

Medical protective mask According to GB 19083-2010, under an air flow rate of (85 ± 2) L/min, the filtration efficiency for sodium chloride aerosol with an aerodynamic median diameter of (0.24 ± 0.06) μm shall be no less than 95%, thereby meeting or exceeding the N95 (or FFP2) level.

Medical surgical mask According to the YY 0469-2011 standard, the filtration efficiency for Staphylococcus aureus aerosols with an average particle diameter of (3 ± 0.3) μm shall be no less than 95%.

Ordinary medical mask Although there is currently no nationwide unified standard, the general requirement is that the filtration efficiency for non-oily particulate matter should be no less than 30%.

By employing scientific and accurate measurement methods, we can ensure that the filtration efficiency of medical masks meets the relevant standard requirements, thereby providing effective protection for healthcare workers and the general public.