Footwear for cold environments Thermal properties, performance and testing

Present standard on safety footwear (EN 344) checks the insulation only at one point in the shoes by means of measuring the temperature change. A method that uses thermal foot model allows to measure footwear insulation simultaneously at various locations and for whole footwear as well. In the present work the method of heated foot model was developed further. It is possible to simulate sweating and evaluate reduction of insulation of footwear due to wetting and evaporative heat loss. The conditions with various sweat rates, wear length and foot motion were tested. Footwear with various insulation levels (from thin rubber boots to thick winter boots) was evaluated. Some footwear was manufactured both with and without steel toe cap and this allowed to study the thermal effect of steel toe cap in different conditions. Comparative studies between various methods (thermal foot model, humans, EN 344) for evaluating footwear thermal properties/insulation were carried out. Field studies were carried out for evaluation of footwear and feet conditions in real wear situation. The insulation of footwear can vary depending on region and insulation level of the footwear. Heavy winter boots had lowest insulation in toe zone and thin boots had heel zone as the coldest region. Sweat rates of 3 g/h can reduce footwear insulation considerably (9-19 % depending on initial dry insulation). At higher sweat rates (10 g/h) the reduction could be up to 36 %. Combined effects of sweating, walking and wind could reduce insulation by about 45 %. Reduction was bigger in warm winter boots. Only small amount of moisture evaporates from winter footwear during use. Insulation reduction levelled off over longer periods of use. The reduction can be calculated by simple equations. The thermal foot model gave similar insulation values as measured on human subjects in thermal comfort. The insulation values were used for validation of a mathematical model for foot skin temperature prediction. The results obtained with a thermal foot model give more useful information on footwear than does the present standard for footwear thermal testing. Thus, the thermal foot method is recommended for use as a standard. A steel toe cap in a footwear seems to have no influence on insulation, but may modify the heat losses from the foot. The influence could be related to the Òafter effect" that probably depends on the mass of steel toe cap and its thermal inertia. Some recommendations for use and choice of footwear are given.Nuvarande europeiska standard för test av skyddsskor (EN 344) mäter den termiska isolationen bara i en punkt i skon genom att mäta en temperaturändring. En termisk fotmodell möjliggör mätning av isolationen hos skor både i olika zoner och i hela skon. I detta forskningsprojektet har metoden med rörlig uppvärmd fotmodell vidareutvecklas. Metoden kan simulera svettning och bestämma ändring i isolation av skor beroende på fukt och värmeförlust genom avdunstning. Betingelser med olika svettningsgrad, mättid och simulerad gång testades. I projektet undersöktes stövlar med olika isoleringsnivåer (från tunna gummistövlar till tjocka vinterstövlar). Några av stövlarna var tillverkade båda med och utan stålhätta och den termiska påverkan av stålhättan under olika betingelser studerades. Jämförande studier mellan olika metoder genomfördes (termisk fotmodell, EN 344, mätningar på människor). För att bedöma termiska egenskaper hos stövlar användes data från försökspersoner och fotmodell tillsammans. En matematisk modell provades för att förutsäga hud temperaturen på foten. Fältstudier genomfördes för att värdera stövlarnas klimatskydd under verkliga förhållanden. Skodelarna hade olika isolation beroende främst på tjocklek och material. Varma vinterstövlar hade den lägsta isolation vid tårna medan den kallaste delen av gummistövlar var hälen. Även en låg svettningshastighet (3 g/h) minskade isolationen hos alla stövlar (9-19 % jämfört med den ursprungliga torra isolationen). Vid högre svettningshastighet (10 g/h) minskade isolationen med upp till 36 %. I kombination med svettning, rörelse och vind kunde isolationen hos stövlar minska ca 45 %. Minskningen var störst i vinterstövlar. Isolationsförändringen var stor under de första 2 timmarna av 8-timmars mätning, men blev betydligt mindre efter hand. Avdunstningen var generellt mycket liten från vinterstövlar. Enkla samband för att beräkna isolationsminskningen har utarbetats. Den termiska fotmodellen gav lika isolationsvärdena som de som uppmättes på människor vid termisk komfort. Värdena kan användas i matematiska modeller för att förutsäga hud temperaturer, exponeringstider och välja fotbeklädnad. Resultat från försök med termisk fotmodell ger mer användbar information än nuvarande standardmetod för termisk provning av skor. Därför kan termiska fot metoden rekommenderas att användas som standard. Det förefaller som om stålhättan har en påverkan, om än liten, på fotens hudtemperatur och modifierar värmeförlusterna från foten. Påverkan kan relateras till den s.k. Òefter effekten", vilken troligen beror på ståltåhättans stora och termiska tröghet. Rekommendationer för användning och val av skor gavs slutligen. Nyckelord: termisk fotmodell, svettning, skyddsskor, stövlar, termisk isolation, kyla, fot, hud temperatur, temperaturupplevelse, smärta

Testing Sleeping Bags According to EN 13537:2002: Details That Make the Difference

The European Standard on sleeping bag requirements (EN 13537:2002) describes a procedure to determine environmental temperature limits for safe usage of sleeping bags regarding their thermal insulation. However, there are several possible sources of error related to this procedure. The main aim of this work was to determine the influence of the various measuring parameters on the acuity of the respective parameters in order to judge the requirements. The results indicated that air velocity, mattress insulation and time between unpacking the bag and measurement had a significant impact on the result, with a difference of up to 5–15% in thermal insulation between minimum and maximum allowable parameter levels. On the other hand, manikin weight, thickness of the artificial ground and presence of a face mask were found to have a negligible influence. The article also discusses more general aspects of the standard including the calculation methods used

Testing Sleeping Bags According to EN 13537:2002: Details That Make the Difference

The European Standard on sleeping bag requirements (EN 13537:2002) describes a procedure to determine environmental temperature limits for safe usage of sleeping bags regarding their thermal insulation. However, there are several possible sources of error related to this procedure. The main aim of this work was to determine the influence of the various measuring parameters on the acuity of the respective parameters in order to judge the requirements. The results indicated that air velocity, mattress insulation and time between unpacking the bag and measurement had a significant impact on the result, with a difference of up to 5–15% in thermal insulation between minimum and maximum allowable parameter levels. On the other hand, manikin weight, thickness of the artificial ground and presence of a face mask were found to have a negligible influence. The article also discusses more general aspects of the standard including the calculation methods used

Effect of Sweating on Insulation of Footwear

The study aimed to find out the influence of sweating on footwear insulation with a thermal foot model. Simultaneously, the influence of applied weight (35 kg), sock, and steel toe cap were studied. Water to 3 sweat glands wassupplied with a pump at the rate of 10 g/hr in total. Four models of boots with steel toe caps were tested. The same models were manufactured also without steel toe. Sweating reduced footwear insulation 19-25% (30-37% in toes). During static conditions, only a minimal amount of sweat evaporated from boots. Weight affected sole insulation: Reduction depended on compressibility of sole material. The influence of steel toe varied with insulation. The method of thermal foot model appears to be a practical tool for footwear evaluation

A Comparison of Two Methods of Determining Thermal Properties of Footwear

The present European Standard for footwear testing (Standard No. EN 344:1992; European Committee for Standardization [CEN], 1992) classifies footwear thermally by a temperature drop inside the footwear during 30 min at defined conditions. Today, other methods for footwear thermal testing are also available. The aim of this study was to compare EN 344:1992 with a thermal foot method. Six boots were tested according to both methods. Additional tests with modified standard tests were also carried out. The methods ranked the footwear in a similar way. However, the test according to standard EN 344:1992 is a pass-or-fail test, whereas data that is gained from the thermal foot method gives more information and allows further use in research and product development. A change of the present standard method is suggested

Effect of Footwear Insulation on Thermal Responses in the Cold

The influence of footwear insulation on foot skin temperature in the cold at low activity was investigated. Simultaneously, the thermal and pain sensations, and the influence of steel toe cap were studied. Eight participants were exposed for 85 min to 3 environmental temperatures ( + 3, — 12, and —25°C) wearing 5 different boots. Insulation of footwear was determined with a thermal foot model. The study showed the importance of insulation forkeeping feet warm. Other factors, such as wetness and vasomotor response, however, modified the thermal response. The most affected parts were toes and heels. Cold and pain sensations were connected with considerably lower temperatures in these local points. No significant differences were observed between boots with and without steel toe cap

Determination of Heat Loss from the Feet and Insulation of the Footwear

This study compared the methods of determining footwear insulation on human participants and a thermal foot model. Another purpose was to find the minimal number of measurement points on the human foot that is needed for insulation calculation. A bare foot was tested at 3 ambient temperatures on 6 participants. Three types of footwear were tested on 2 participants. The mean insulation for a bare foot obtained on the participant and model were similar. The insulation of warm footwear measured by the 2 methods was also similar. For thin footwear the insulation values from the participants were higher than those from the thermal model. The differences could be related to undefined physiological factors. Two points on the foot can be enough to measure the insulation of footwear on human participants (r = .98). However, due to the big individual differences of humans, and good repeatability and simplicity of the thermal foot method, the latter should be preferred for testing