|Vector and Pest Control in Refugee Situations (United Nations High Commissioner for Refugees (UNHCR) / Alto Comisionado de Naciones Unidas para los Refugiados (ACNUR), 1997, 124 p.)|
In order to calculate the dilution of insecticide for use in impregnation of fabrics, the absorption capacity of the fabric per m2 (which will vary according to its thickness and composition) has be taken into account.
The procedure is as follows:
(a) calculate the total surface area of the fabric to be impregnated;
(b) calculate the quantity of insecticide formulation required according to the following formula:
m2 of fabric X g of a.i. per m2 X 100
concentration (%) of the insecticide formulation
(c) calculate the absorption capacity by soaking the fabric or mosquito net in a basin containing a known quantity of water. Drain the fabric or net over the basin and measure the volume or weight of the water remaining in the basin;
(d) add the quantity of formulation (point (b)) to the quantity of water that was found to have impregnated the fabric after draining (point (c)).
To impregnate a 10 m2 nylon mosquito net having a total absorption capacity of 500 ml water, using permethrin in a 50% emulsifiable concentrate at a dose of 0.5 g a.i. per m2:
10 ml of insecticide will, therefore, have to be mixed with 490 ml of water for each mosquito net (or 1 litre of insecticide with 50 litres of water for 100 mosquito nets).