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Updated WHO specifications for netting materials and mosquito nets - page 25 / 34

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Technical consultation on specifications and quality control of netting materials and mosquito nets

The method to test seam bursting strength is identical to that used to test the fabric, except that 5 replicate tests should be made with a seam centred on the test head. Up to 5 seams may be tested but, if there are <5 seams, replicate measurements should be made on 1 or more seams, to provide a total of 5 measurements.

NOTE 6

Method of preparation before and after the washing test: ISO 3759 (1994). Method of washing: ISO 6330 (2000). Method of calculation: ISO 5077 (1984). Size of test portions: 500 mm x 500 mm; mark off 350 mm x 350 mm within each test portion. Test a total of 4 replicate portions, 2 washed in each of 2 separate loads. Type of washing machine: ISO type A (front loading, horizontal drum). Washing programme: ISO type 8A (gentle cycle 30 ºC). Fill the washer with ballast/dummy load (with fabric as per ISO standard) up to the standard of 2 kg. Detergent: IEC + sodium perborate. Drying: C, flat drying.

20%

11

14

21

15%

15

19

29

10%

22

29

44

5%

45

59

90

1%

231

299

459

Table 1a: Sampling rate based on probability of detection and frequency of non-

Example: A buyer aiming for 90% confidence to detect a non-compliance occurring at 10% frequency would have to collect and test 22 nets per batch.

compliance

Actual frequency of non- compliant nets in the batch

Minimum number of samples per batch required to detect a non-compliant net with a probability of:

90%

95%

99%

Actual frequency of non-compliant nets in the batch

Probability of detecting a non-compliant net by testing 8 nets

44% 31% 25% 10% 5% 1%

99% 95% 90% 57% 34% 8%

Table 1b: Example: the probability of detecting a non-compliant net by testing 8 nets per batch

The probability values given in Tables 1a and 1b assume either random sampling or a random distribution of non-compliant nets, or both. The values are calculated from:

1–p = (1–i)n where: p = probability of detecting a non-compliant net (expressed as a fraction, not %); i = incidence of non-compliant nets in the batch (expressed as a fraction, not %); n = number of nets tested from the batch.

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