Bedding and Clothes Without Machines: A Drying Rule for Mould Risk and a Solar Heat Treatment for Parasites

Where washing is done by hand and drying and pest control must use sun and air, two questions decide whether bedding and clothes stay healthy: how long washed cloth stays wet enough for mould, and whether sunshine alone can heat bedding enough to end the life cycles of lice and mites. This paper models both. Drying follows an exponential moisture model for three loads in nine combinations of climate and hanging arrangement, reporting hours spent above a stated mould-risk moisture level of 0.30 kg of water per kg of dry cloth. A cotton bedding set spread in a single layer outdoors spends 1.31 hours above the risk level in hot dry air (32 °C, 40% relative humidity), 2.05 hours in warm humid air (28 °C, 75%), and 4.22 hours in cool damp air (18 °C, 85%); the same set on an indoor rack in cool damp air spends 15.07 hours above it, and left bunched in a basket indoors it spends 26.37 hours. Spreading in a single layer rather than hanging folded over a line cuts the time above the risk level by roughly half in every climate, and arrangement matters more than the difference between the cotton loads. For the heat treatment, a sealed dark container of bedding is modelled as a lumped thermal mass over an 8-hour sunny day. In strong sun (peak 900 W/m², ambient 32 °C) a thin black bag peaks at 68.8 °C and holds at or above 55 °C for 279 continuous minutes, meeting the stated treatment criterion of 55 °C held for at least 60 continuous minutes; an insulated dark box peaks at 82.5 °C and holds 345 minutes. In moderate sun (peak 650 W/m², ambient 28 °C) the bag peaks at 55.4 °C and holds above 55 °C for only 52 minutes, so it fails the criterion, while the insulated box peaks at 66.4 °C and holds for 250 minutes and passes. In weak or overcast sun (peak 350 W/m²) the box peaks at 46.0 °C and never reaches 50 °C, and in low winter sun (peak 300 W/m², ambient 12 °C) the bag peaks at 25.6 °C: under those conditions the treatment fails outright, and this paper says so rather than recommending it. At an ambient temperature of 28 °C the minimum peak irradiance meeting the criterion is 675 W/m² for the bag and 475 W/m² for the insulated box.