Five common leak detection methods for HEPA filters

As one of the items of clean room inspection, leakage testing of high-efficiency filters has received more and more attention since the implementation of the 2010 version of GMP.

It has now become a mandatory inspection project for pharmaceutical companies, and there are more and more units in hospitals, electronics, food, cosmetics and other industries that carry out leakage testing of high-efficiency filters.

The following is to give you a specific introduction to the method of leakage testing of high-efficiency filters.

1.Sodium flame method

Sodium flame method of testing dust source for polydisperse phase sodium chloride salt spray, "amount" for the brightness of hydrogen flame containing salt spray combustion.

Brine in the compressed air under the stirring splash, by drying the formation of tiny salt crystal particles and enter the duct, before and after the filter were sampled.

Containing salt spray air samples to make the colour of the hydrogen flame blue, brightness increased to the brightness of the flame to determine the concentration of salt spray air, and to determine the efficiency of the filter on the salt spray filtration.

The main testing instrument for the flame photometer, the method can only sponge detection sensitivity is not high, can not be detected on the ultra-high efficiency filter.

2.The oil mist method

Oil mist method of testing the dust source for oil mist, "amount" for the turbidity of the air containing oil mist to filter the difference in turbidity before and after the air samples to determine the filter efficiency of the filter on oil mist particles.

Germany provides for the use of paraffin oil, oil mist particle size of 0.3 to 0.5 microns. Oil mist method in the detection of filters, easy to damage the filter, and can not be read directly, wasting time.

3.DOP method

This method used to be the commonly used method for testing high-efficiency filter sponges internationally.

Its test dust source for the 0.3 micron monodisperse phase phthalate dioctyl phthalate (DOP) droplets, also known as "hot DOP", "amount" for the DOP-containing air turbidity.

DOP liquid heated into a vapour, the vapour condenses into tiny droplets under specific conditions, after removing the oversized and undersized droplets, leaving particles of 0.3 microns or so, into the air ducts, through the measurement of turbidity before and after the filter air samples, and thus determine the filter efficiency of the filter on the 0.3 micron dust.

4.Fluorescence method

The test dust source of fluorescence method is the sodium fluorescein dust produced by the sprayer. The test method is first sampled before and after the filter sponge, and then dissolve the sodium fluorescein on the sampling filter paper with water, and then measure the fluorescence brightness of the sodium fluorescein-containing aqueous solution under specific conditions, the brightness of the response to the weight of the dust, which calculates the filter's filtration efficiency.

5. Particle counting method

This method is common in Europe, the U.S. ultra-high-efficiency air filter test method is also relatively similar to the current international mainstream sponge test method.

The dust source is polydisperse phase droplets, or solid dust with a defined particle size. Sometimes, filter manufacturers have to use atmospheric dust or other specific dust according to the special requirements of users.

If a condensation counter is used in the test, a monodisperse phase test dust source with a known particle size must be used. The main measuring instrument is a high-flow laser particle counter or a condensation counter.

The entire air outlet surface of the filter is scanned with the counter, which gives the number of dusts at each point and also compares the local efficiencies at each point.