Protection Against Cold in Prehospital Care—Thermal Insulation Properties of Blankets and Rescue Bags in Different Wind Conditions

Abstract

In a cold, wet, or windy environment, cold exposure can be considerable for an injured or ill person. The subsequent autonomous stress response initially will increase circulatory and respiratory demands, and as body core temperature declines, the patient's condition might deteriorate. Therefore, the application of adequate insulation to reduce cold exposure and prevent body core cooling is an important part of prehospital primary care, but recommendations for what should be used in the field mostly depend on tradition and experience, not on scientific evidence. Objective: The objective of this study was to evaluate the thermal insulation properties in different wind conditions of 12 different blankets and rescue bags commonly used by prehospital rescue and ambulance services. Methods:The thermal manikin and the selected insulation ensembles were setup inside a climatic chamber in accordance to the modified European Standard for assessing requirements of sleeping bags. Fans were adjusted to provide low (< 0.5 m/s), moderate (2-3 m/s) and high (8-9 m/s) wind conditions. During steady state thermal transfer, the total resultant insulation value, I tr (m 2°C /Wclo; where °C = degrees Celcius, and W = watts), was calculated from ambient air temperature (°C), manikin surface temperature (°C), and heat flux (W/m 2 ). Results: In the low wind condition, thermal insulation of the evaluated ensembles correlated to thickness of the ensembles, ranging from 2.0 to 6.0 clo (1 clo = 0.155 m 2°C /W), except for the reflective metallic foil blankets that had higher values than expected. In moderate and high wind conditions, thermal insulation was best preserved for ensembles that were windproof and resistant to the compressive effect of the wind, with insulation reductions down to about 60-80% of the original insulation capacity, whereas wind permeable and/or lighter materials were reduced down to about 30-50% of original insulation capacity. Conclusions:The evaluated insulation ensembles might all be used for prehospital protection against cold, either as single blankets or in multiple layer combinations, depending on ambient temperatures. However, with extended outdoor, on-scene durations, such as during prolonged extrications or in multiple casualty situations, the results of this study emphasize the importance of using a windproof and compression resistant outer ensemble to maintain adequate insulation capacity.

Evaluating Cold, Wind, and Moisture Protection of Different Coverings for Prehospital Maritime Transportation–A Thermal Manikin and Human Study

“…It has been shown that a moderate wind speed (3 m/s) decreases the thermal insulation of low insulation covers by 20% to 40%, and that of high insulation covers by 15% to 25%. 9 It has been shown that high wind speeds (12 m/s to 18 m/s) will decrease the thermal insulation of highly impermeable clothing ensembles by 30% to 40%. The decrease of the thermal insulation in wind is caused mostly because of boundary layer breakdown and compression effects.…”

“…These results correspond with the literature. 9 Wet garments inside the coverings increased evaporative heat transfer from the skin. Therefore, the dry thermal resistance of the coverings declined.…”

“…According to Henriksson et al, the insulation capacity of blankets and rescue bags at high wind speeds is best preserved by ensembles that are windproof and resistant to the compressive effect of the wind. 9 During maritime prehospital transportation, casualties may be exposed to splashes and rain. Clothing may also be wet from water or body fluids.…”

The prehospital management of avalanche victims

“…Instead, evaporative heat loss may be minimised by adding an airtight vapour barrier immediately outside the wet clothing 52. Recent studies have suggested that the optimal packaging method for wet conditions is a combination of a vapour-tight inner layer followed by a dry insulating middle layer covered in a wind-resistant and water-resistant outer wrapping 53 54. Obtaining vascular access may be difficult due to hypothermic and/or hypovolaemic vasoconstriction.…”

The effect of metallisation, porosity and thickness on the thermal resistance of two-layer fabric assemblies

“…Recent research investigating rescue blankets using a supine thermal manikin, dressed in thin underwear, identified that materials with a metallic coating had higher thermal resistance than would be expected from their thickness [4]. For example, a 0.01-mm thick dual surface (gold/silver) metallic laminated plastic foil blanket had the same thermal resistance as a 5.5-mm thick felted wool blanket (2.9 AE 0.1 Clo and 2.7 AE 0.1 Clo, respectively).…”