Effects of environmental temperature and humidity on evaporative heat loss through firefighter suit materials made with semi-permeable and microporous moisture barriers

The goal of this research was to understand how firefighter protective suits perform in different operational environments. This study used a sweating guarded hotplate to examine the effect of environmental temperature (20–45°C) and relative humidity (25–85% RH) on evaporative heat loss through firefighter turnout materials. Four firefighter turnout composites containing three different bi-component (semi-permeable) and one microporous moisture barriers were selected. The results showed that the evaporative resistance of microporous moisture barrier systems was independent of environmental testing conditions. However, absorbed moisture strongly affected evaporative heat loss through semi-permeable moisture barriers coated with a layer of nonporous hydrophilic polymer. Moisture absorption in mild environment (20–25°C) tests, or when testing at high humidity (>85% RH), significantly increased water vapor transmission in semi-permeable turnout systems. It was also found that environmental conditions used in the total heat loss (THL) test (25°C and 65% RH) produced moisture condensation in bi-component barrier systems, making them appear more breathable than could be expected when worn in hotter environments. Regression models successfully qualified the relationships between moisture uptake levels in semi-permeable barrier systems and evaporative resistance and THL. These findings reveal the limitations in relying on THL, the heat strain index currently called for by the NFPA 1971 Standard for Structural Firefighter personal protective equipment, and supports the need to measure turnout evaporative resistance at 35°C (Ret), in addition to THL at 25°C.

Radiative feedbacks on land surface change and associated tropical precipitation shifts

Changes in land surface albedo and land surface evaporation modulate the atmospheric energy budget by changing temperatures, water vapor, clouds, snow and ice cover, and the partitioning of surface energy fluxes. Here idealized perturbations to land surface properties are imposed in a global model to understand how such forcings drive shifts in zonal mean atmospheric energy transport and zonal mean tropical precipitation. For a uniform decrease in global land albedo, the albedo forcing and a positive water vapor feedback contribute roughly equally to increased energy absorption at the top of the atmosphere (TOA), while radiative changes due to the temperature and cloud cover response provide a negative feedback and energy loss at TOA. Decreasing land albedo causes a northwards shift in the zonal mean intertropical convergence zone (ITCZ). The combined effects on ITCZ location of all atmospheric feedbacks roughly cancel for the albedo forcing; the total ITCZ shift is comparable to that predicted for the albedo forcing alone. For an imposed increase in evaporative resistance that reduces land evaporation, low cloud cover decreases in the northern mid-latitudes and more energy is absorbed at TOA there; longwave loss due to warming provides a negative feedback on the TOA energy balance and ITCZ shift. Imposed changes in land albedo and evaporative resistance modulate fundamentally different aspects of the surface energy budget. However, the pattern of TOA radiation changes due to the water vapor and air temperature responses are highly correlated for these two forcings because both forcings lead to near-surface warming.

The Effect of an Equatorial Continent on the Tropical Rain Belt. Part 1: Annual Mean Changes in the ITCZ

The Tropical Rain belts with an Annual cycle and Continent Model Intercomparison Project (TRACMIP) ensemble includes slab-ocean aquaplanet controls and experiments with a highly idealized tropical continent: modified aquaplanet grid cells with increased evaporative resistance, increased albedo, reduced heat capacity, and no ocean heat transport (zero Q-flux). In the annual mean, an equatorial cold tongue develops west of the continent and induces dry anomalies and a split in the oceanic ITCZ. Ocean cooling is initiated by advection of cold, dry air from the winter portion of the continent; warm, humid anomalies in the summer portion are restricted to the continent by anomalous surface convergence. The surface energy budget suggests that ocean cooling persists and intensifies because of a positive feedback between a colder surface, drier and colder air, reduced downwelling long wave (LW) flux, and enhanced net surface LW cooling (LW feedback). A feedback between wind, evaporation, and SST (WES feedback) also contributes to the establishment and maintenance of the cold tongue. Simulations with a grayradiation model and simulations that diverge from protocol (with negligible winter cooling) confirm the importance of moist-radiative feedbacks and of rectification effects on the seasonal cycle. This mechanism coupling the continental and oceanic climate might be relevant to the double ITCZ bias. The key role of the LW feedback suggests that the study of interactions between monsoons and oceanic ITCZs requires full-physics models and a hierarchy of land models that considers evaporative processes alongside heat capacity as a defining characteristic of land.

Thermal and evaporative resistance measured in a vertically and a horizontally oriented air gap by Permetest skin model

This paper is a study of the correlation of the thermal resistance (Rct ) and the evaporative resistance (Ret ) in vertically and horizontally oriented air gaps by using the portable Permetest skin model. Experiments were done in a climatic chamber; an isothermal condition for Ret tests and non-isothermal condition for Rct tests. Foamed polyethylene air gap distance rings were prepared with a thickness of 2, 4 and 5 mm and their combinations to simulate the air gap distance from 0 to 16 mm which is more than the expected average gap in clothing systems. Test samples were woven fabric of 100 percent cotton, 100 percent polyester and their blends plus 100 percent of polypropylene, all have similar weight and structure. Results showed that with the increasing thickness of the air gap, Rct increased in a polynomial trend and Ret in a linear proportional rate up to 12 mm then started to change due to the effect of free convection and the different properties of materials. The surprising positive observation is that results from the horizontally and vertically oriented air gaps are very similar, and most of the results from the vertical air gap are slightly lower than the results from the horizontal air gap in all materials.

A thermal foot manikin as a tool for footwear evaluation and development

This study investigated the relationship between thermal perceptions during human wear trials and thermal foot manikin measurements of heat and vapour resistance for five running shoes varying in material and construction. Measurements of thermal/evaporative resistance were performed using a 12-zone sweating thermal-foot manikin. Eleven males performed running trials on five occasions, wearing shoes of same design, differing in materials and construction, to achieve a range of heat/vapour resistances and air permeabilities. Trials in 20°C/60% RH consisted of three phases: 15 min rest, 40 min running, 15 min recovery. In-shoe temperature/humidity were measured at two sites on the left foot. Thermal sensation/wetness perception/thermal comfort were provided for the left foot and four foot regions. Variations in shoe material and construction resulted in differences in thermal and evaporative resistance. These differences were reflected in in-shoe temperature and in-shoe absolute humidity assessed during wear trials. At the end of the rest period, thermal sensation was strongly related to thermal insulation ( r2 = 0.69, p<0.001). During exercise however, thermal sensation, wetness perception and thermal discomfort were related to both thermal insulation and evaporative resistance. Thermal foot manikins provide a sensitive, effective evaluation of footwear thermal properties, which are also reflective of changes to in-shoe parameters during actual use. This discriminate power may be enhanced using higher, more realistic air-speeds during testing, as well as simulating foot movement. While thermal foot manikins are highly sensitive to design features/attributes of footwear (e.g. ventilation openings, air-permeabilities and coatings), subjective evaluations of footwear do not seem to have the same sensitivity and discriminative power.

Performance attributes relevant to thermal wear comfort of hip protective garment: influence of comprising pad materials, pad thickness, pad area, and pocket fabric structure

PurposeThis study aimed to evaluate the performance attributes relevant to thermal wear comfort of the commercially available hip protective pads and materials intended for impact protection that can be used for the hip protective pad.Design/methodology/approachThe performance attributes relevant to thermal wear comfort (i.e. dry thermal resistance and evaporative resistance) of the pads were tested using MTNW Integrated Sweating Guarded Hotplate (iSGHP).FindingsIt was found that: the pad with more porous structure has more advantages in terms of evaporative resistance; the permeability index will be higher on the pad with an opening such as a segmented pad; the permeability index will be lower on the thicker and larger pad. The pocket fabric with open structure will have lower dry thermal resistance and evaporative resistance.Originality/valueThe study results showed that the properties of the utilised materials influenced thermal comfort performance. These results could be useful for designing and engineering hip protective garments.

Thermal Simulation of Close-Fitting Sportswear

A novel and intelligent product development approach is required in this fast-growing and advanced technological era. Therefore, textile researchers have worked intensively to create efficient and transparent solutions for complex developments by using advanced modeling and simulation tools and techniques. This paper addresses a process for the thermal simulation of sportswear by considering the human thermophysiological model and important thermal properties of fabrics, i.e., thermal resistance, evaporative resistance, and permeability index. The results of the simulation are illustrated in terms of core body and mean skin temperatures. Moreover, results are validated by wear trials showing good consistency. This study is beneficial to the development of clothing for specific sports and the evaluation of comfort and heat stress during different sports activities.