Is the high-efficiency filter leak detection instrument suitable for pharmaceutical cleanrooms

The leak detection of HEPA filters usually uses a PAO generator to emit dust upstream of the filter, and uses a photometer to detect the aerosol concentration upstream and downstream of the filter to determine whether the filter has leakage. The purpose of dust is that due to the low concentration of dust particles in the upper reaches of the high efficiency filter, it is difficult to find a leak with only a particle counter in the case of no dust detection, and it is necessary to add dust in order to obviously and easily find a leak.


PAO generator can be divided into two kinds of thermal generation and cold generation, thermal generator is the use of evaporation and condensation principle, atomized aerosol particles vaporized by the heater, and condensed into tiny droplets under specific conditions, remove too large and too small droplets leaving about 0.3μm of mist DOP into the air duct, particle size distribution in 0.1~0.3μm. The cold generator refers to the use of compressed air in the liquid bubble, through the laskin nozzle splash to produce polydispersed phase DOP aerosol, the large distribution particle size of about 0.65μm. Cold DOP is used when scanning filters for leak detection.

There are two kinds of detection instruments, one is the aerosol photometer, the other is the particle counter, the detection instrument commonly used in the high efficiency filter leak detection is the aerosol photometer (hereinafter referred to as the photometer), is a kind of front scattering linear photometer, which is composed of vacuum pump, light scattering chamber, photomultiplier tube, signal processing converter and microprocessor. The principle is that when the air flow is pumped to the light scattering chamber by the vacuum pump, the particulate matter in it scatters light to the photomultiplier tube. In a photomultiplier, light is converted into an electrical signal, which is amplified and digitized and analyzed by a microprocessor to determine the intensity of the scattered light. By comparing with the signal generated by the reference substance, the mass concentration of particulate matter in the gas can be directly measured, so it is very useful. The particle counter, its test value reflects the concentration of the number of particles in the air stream - particle size, and specifies the particle size range, its high sensitivity, suitable for all dust source aerosols, the choice is larger, but less used in the high efficiency filter leak detection, the test results of the two instruments are difficult to compare quantitatively. For the field leak detection of high efficiency filters in pharmaceutical enterprises, the photometer is widely used because it is convenient to use, easy to judge the detection result, and more sensitive to leak detection.

Regulations for leak detection of high efficiency filters

The tested aerosols were polydisperse PAO aerosols with a median mass diameter of 0.5~0.7μm and geometric standard deviation of 1.7.

The test instrument is divided into aerosol photometer and particle counter two kinds, aerosol photometer test is the mass concentration, the unit is μg/L, particle counter test is the particle number concentration, the unit is particle /L, both methods can meet the leak detection requirements. For the field leak detection of high efficiency filters in pharmaceutical enterprises, the photometer is widely used because it is convenient to use, easy to judge the detection result, and more sensitive to leak detection. It is the development trend of efficient leak detection in the future.

When using a photometer, the upstream concentration should reach 20 to 80μg/L, and the fluctuation should not be too large, allowing the fluctuation of 15% above and below the average value.

Detection method

To determine whether the high efficiency filter itself and its installation have obvious leakage, it is necessary to test the following places on the site: the filter material of the filter; The filter material of the filter is connected to the inside of its frame; Between the gasket of the filter frame and the filter group support frame; Support between frame and wall or ceiling. DOP leak detection materials and instruments are: dust source (PAO solvent), AG-1800 series aerosol generator, PM-350 series aerosol photometer.

PAO aerosol was introduced into the upstream side of HEPA to be measured
The area of the part leakage should not be greater than 5% of the total area, otherwise it must be replaced.