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A better method for estimating the real strength of LLIN

April 14, 2011 - 11:55 -- Rune Bosselmann

Measuring bursting strength is the standard method for evaluating mosquito net strength. However, in real life use scenarios of nets these are rarely exposed to the kind of strain they are exposed to in this test. It would correspond to, more or less, if you were to grab on to a net by the hands, uniformly and without penetrating the mesh with your fingers, and pull the net apart. Few people can do that. However, if you put the netting on a nail at one end and pull with your hand at the other, a hole will be ripped with very little effort. This type of strain is something nets are exposed quite often and a cause of many a tearing when nets are caught on nails, corners of beds, even finger nails etc.

A new study and article suggest that tension strength measured with a grab or clamp (being the "hand") and a hook put through the mesh (like a nail would) better represent how holes are generated in bed nets in real life. A number of the currently WHOPES recommended nets were subjected to this test.

The results showed a greater difference in strength between multifilament and monofilament than observed using standard bursting strength. This may help to explain differences in durability between the different LLIN type as observed in the field. The explanation is likely that the fine polyester filaments break one at the time when exposed to this kind of uneven and focused strain. This observation is supported by the fact that making the filaments thicker gives a stronger net.

The hope is that this standardized method (it is an ISO method and not one invented for LLIN testing) becomes part of the strength assessment of LLINs so that field durability can be better predicted for each net type. Further, the authors demonstrated that all nets were stronger in one direction of the net than in the other, given the way all nets are made. And that all LLIN manufacturers may improve the actual tear resistance of their products by simply changing the way they sew the net pieces together.

Study published in Malaria Journal

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