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Updated WHO specifications for netting materials and mosquito nets - page 11 / 34

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

3.3 Bursting strength of seams

Mosquito nets require seams in the netting material, to give the net the desired shape and to seal against mosquito entry between adjacent panels of fabric. For acceptable performance, the seams must be at least as strong as the netting. At present, there is no documented experience with standardized tension tests for seam quality control on mosquito nets. Therefore, the meeting proposed that the test for bursting strength should also be used to measure seam strength in the net. The equipment for testing bursting strength does not require modification for this purpose.

Research requirements:

  • a.

    Manufacturers should check that the relative bursting strengths of fabric and seams, measured by ISO 13938-1 or -2 (1999), correspond to the results obtained by any other test method used for assessing seam strength.

  • b.

    In a range of netting materials, compare the values obtained from testing seams with 50 cm² and 7.3 cm² test heads.

c. In a range of netting materials, compare the values obtained from testing seams with hydraulic equipment (ISO 13938-1) and pneumatic equipment (ISO 13938-2).

3.4 Dimensional stability

Current tests for dimensional stability are performed with a sample of the netting material treated according to ISO 3759 (1994) and ISO 6330 (2000) and the results are calculated according to ISO 5077 (1984) and expressed as percentages (usually shrinkage, though stretching may also occur). The 2000 WHO specifications state that shrinkage in either direction of the netting material should be no more than 5%. Most commonly netting material is heated and pulled into shape during the production process (“heat-setting”) to achieve the correct mesh count but nonetheless nets can be sensitive to the temperature at which they are subsequently washed.

There are 10 European washing procedures (for front loading machines) specified in the ISO 6330-1984 (E) standard and 11 for the United States of America (for top loading machines). The revised WHO specification relies on the 8A wash procedure (European norm: gentle wash at 30 ºC) and drying procedure C (dry flat). For reproducible results, great care should be taken

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