Technical consultation on specifications and quality control of netting materials and mosquito nets
Determine the optimum shape and maximum dimensions of holes required to prevent mosquito entry through untreated netting.
Develop alternative, rapid and reliable methods for measuring mesh size, according to the optimum shape and maximum dimension requirements.
3.2 Bursting strength of netting materials
Strength of netting material can be measured as: (a) its bursting strength (the maximum pressure that can be applied to a given surface area of netting before it bursts under the strain); (b) its tensile strength (the strain applied to a material in various directions before it gives way); (c) tear strength (e.g., the weight can be hung from a small hole before the material tears); or (d) as a very crude measurement, by grasping the material in both hands and gauging the effort required to push the thumbs through it.
Bursting strength is currently the only practicable test for which reliable data exist. Netting quality has improved over the past 5 years and the meeting agreed that the minimum bursting strength for acceptable netting materials is 250 kPa, when measured according to ISO 13938-1 (1999) or ISO 13938-2 (1999), using a 7.3 cm2 sample. Experience had shown that this corresponds approximately to the minimum which would satisfy a test using thumb pressure only, although the latter test is subjective and not suitable for testing for compliance with a specification.
According to the ISO standard, bursting strength can be measured on areas of netting material measuring either 7.3 cm2 or 50 cm2, though they do not give identical results. In 2000, 7.3 cm2 was chosen for testing of netting materials. All available routine test data were derived from 7.3 cm2 samples and, at present, there are no validated threshold limits for 50 cm2 samples. A sample size of 50 cm2 could be used for quality testing, subject to the availability of data to support a proposed threshold value.
In a range of netting materials, establish the values obtained from use of a 50 cm² test head that correspond to those measured with a 7.3 cm² test head.
In a range of netting materials, establish whether or not the values obtained with hydraulic equipment (ISO 13938-1) are equal to those obtained with pneumatic equipment (ISO 13938-2).