M4R/10073 Work Package 1 – Breathability of filter material


The differential pressure (breathability) across 2 different sample materials were measured following methods set out in BS EN 14683:2019 (Annex C).

The materials were grouped as described on delivery, as “Material 1” and “Material 2”.

The differential pressure across the samples were measured at 5 different points, with each measurement area being nominally 4.9 cm2 (25 mm diameter circle), at an ambient air flow rate of nominally 8.0 l min-1, 20.0 l min-1, 30.0 l min-1, and 95.0 l min-1 being passed across the measurement area.

The samples were pre-conditioned at nominally 21.0 °C and 85 %RH in an environmental chamber for at least 4 hours prior to measurement.

The measurements were performed by laying each sample flat, in-turn, across the sample holder (between the top and bottom parts of the holder). The samples were then mechanically clamped in place, before passing ambient air across the sample at 8.0 l min-1, until the flow rate equilibrated. After which the differential pressure, flow rate, and ambient conditions, were recorded. The flow rate was then increased to 20.0 l min-1, and allowed to equilibrate before recoding the differential pressure, flow rate, and ambient conditions. This process was then repeated at 30.0 l min-1, and 95.0 l min-1.

These measurements were performed 5 times, and results averaged, for each sample.
Due to limitations in the design of the equipment it was necessary to measure baseline differential pressure readings at each flow rate, without the samples in place. These values were then negated from the measurements made with the samples in place.
All measurements were made under nominal ambient conditions of, relative humidity (52 ± 3) %, barometric pressure (1006 ± 5) hPa, and room temperature (19.7 ± 0.2) °C.


The results of the measurements are given in the following tables:

Table 1: Results of “material 1” measurements

* The measured differential pressure at 95.0 l min-1 exceeded the maximum measurable pressure (>10 kPa)

Table 2: Results of “material 2” measurements

The reported expanded uncertainties are based upon standard uncertainties multiplied by the coverage factor k given in Tables 1 and 2, providing a coverage probability of approximately 95 %.

These values include the following type A uncertainties: The reproducibility of the calibrated mass flow meter during the measurements, and the reproducibility of the differential manometer during the measurements, and the following type B uncertainties: the calibration of the mass flow meter, the resolution of the mass flow meter, the area of the test sample, the ambient conditions, the uncertainty of the differential manometer, and the resolution of the differential manometer.

The results and uncertainties given in this report are valid for the specified samples tested and refer to the measurements made during testing only.

Reference: M4R/10073_1