Rescue blankets hamper thermal imaging in search and rescue missions

Abstract

Thermal imaging for unmanned aerial vehicles is used to search for victims in poor visibility conditions. We used a gimbal-mounted camera for thermo-radiation measurements of body temperature from persons covered with rescue blankets in the hibernal wilderness setting. Long-wave infrared radiation in the spectral range between 7500 and 13,500 nm was evaluated. Parts of this research have previously been published in a review on electromagnetic radiation reflectivity of rescue blankets (https://www.mdpi.com/2079-6412/10/4/375/htm). Surface temperature measurement was diminished by clothing, namely by 72.6% for fleece, by 82.2% for an additional down jacket and by 92.3% for an additional all-weather jacket, as compared to forehead temperature. Furthermore, we detected that a single-layer rescue blanket is sufficient to render recognition of a body shape impossible. With three layers covering a clothed body infrared transmission was almost completely blocked. However, rescue blankets increase visibility for thermal cameras due to high gradients in temperature. Conspicuously low temperatures from objects of 1 to 2 m length may indicate reflections from rescue blanket surfaces in a cold environment. Ideally, rescue blankets should be removed from the body to increase the chance of being located when using thermal imaging to search for victims in search and rescue missions.

Prehospital Use of Ultrathin Reflective Foils

“…If the insulation is effective, radiation from the outer layer to the foil is minimal. 11 In addition, emissivity of fabric is lower than that of skin, limiting radiation of heat. 13 Conduction through clothing or other coverings is affected by the properties of the fabrics and by the construction of the textile assemblage with fabric layers and trapped air.…”

“…If the insulation is effective, radiation from the outer layer to the foil is minimal. 11 In addition, emissivity of fabric is lower than that of skin, limiting radiation of heat. 13…”

“…8 Transmission of radiation by URFs in near, middle, and far infrared wavelengths is very low. 11,12 It does not matter whether the gold side or the silver side is facing outward when a rescue blanket is used to protect against hypothermia in a wilderness emergency. 9,12…”

“…9 More recently, it became apparent that reflection of visible light by URFs increases detectability in search and rescue missions performed when there is good visibility, while reflection of infrared radiation increases detectability when there is poor visibility. 11,12 Metallized foils transmit only 1 to 8% of visible light and about 1% of ultraviolet B radiation (280-315 nm). URFs can provide protection from snow blindness from high solar radiation.…”

“…The amount of insulation generally increases with the number of covering garments. 11,20,23 Thermal insulation is directly proportional to the thickness of the ensemble (about 1.3-1.5 clo•cm -1 ). Maximum heat flux is reduced by up to 80% when the air gap is increased from 0 to 1 mm.…”