Hechmi Hamouda

Effects of Moisture on the Thermal Protective Performance of Firefighter Protective Clothing in Low-level Radiant Heat Exposures

This paper describes research on the effects of absorbed moisture on the thermal protective performance of the fire fighter turnout materials exposed to thermal assaults lower than flashover conditions. A thermal testing platform and sensor are used to measure thermal protective performance of turnout systems exposed to a sub flashover heat flux range 6.3 kw/m2 (0.15 cal/ cm2 s). The effects of moisture level on predicted second-degree burn injury for turnout systems having different moisture vapor permeability and total heat loss are discussed. Heat transfer analysis and experimental results show that, for selected test conditions, moisture negatively impacts protective performance most severely when the amount of added moisture is at a comparatively low level (15–20% of turnout system weight).

Modeling the Thermal Protective Performance of Heat Resistant Garments in Flash Fire Exposures

This research developes a numerical model to predict skin burn injury resulting from heat transfer through a protective garment worn by an instrumented manikin exposed to laboratory-controlled flash fire exposures. This model incorporates characteristics of the simulated flash fire generated in the chamber and the heat-induced changes in fabric thermophysical properties. The model also accounts for clothing air layers between the garment and the manikin. The model is validated using an instrumented manikin fire test system. Results from the numerical model help contribute to a better understanding of the heat transfer process in protective garments exposed to intense flash fires, and to establishing systematic methods for engineering materials and garments to produce optimum thermal protective performance.

Fatigue Cracking Resistance of Fiber-Reinforced Asphalt Concrete

The influence of fibers on the fatigue cracking resistance of asphalt concrete is investigated using fracture energy. Nylon, a popular facing yarn of carpets, is used for the actual recycled carpet fibers in asphalt pavement. The experimental program is designed with two phases: the single fiber pull-out test and the indirect tension strength test. Through pull-out tests of 15-denier single nylon fibers, the critical fiber embedded length is determined to be 9.2 mm. As for indirect tension strength tests, samples of asphalt concrete mixed with nylon fibers of two lengths, 6 and 12 mm, based on results of the pull-out tests (critical embedded length) and three volume fractions, 0.25, 0.5, and 1%, are prepared and tested. Asphalt concrete samples fabricated with fibers of 1% and 12 mm results in 85% higher fracture energy than non-reinforced specimens, showing improved fatigue cracking resistance. Although an optimized asphalt mix design with fibers has not been developed for this study, the increased fracture energy represents a potential for improving asphalt fatigue life, which may be facilitated through the use of recycled carpet fibers.

Sulfonated Polystyrene Fiber Network-Induced Hybrid Proton Exchange Membranes

A novel type of hybrid membrane was fabricated by incorporating sulfonated polystyrene (S-PS) electrospun fibers into Nafion for the application in proton exchange membrane fuel cells. With the introduction of S-PS fiber mats, a large amount of sulfonic acid groups in Nafion aggregated onto the interfaces between S-PS fibers and the ionomer matrix, forming continuous pathways for facile proton transport. The resultant hybrid membranes had higher proton conductivities than that of recast Nafion, and the conductivities were controlled by selectively adjusting the fiber diameters. Consequently, hybrid membranes fabricated by ionomers, such as Nafion, incorporated with ionic-conducting nanofibers established a promising strategy for the rational design of high-performance proton exchange membranes.

The Design of a Surface Heat Flux Transducer for Use in Fabric Thermal Protection Testing

From theoretical considerations, a custom slug calorimeter heat flux transducer was developed for experimental use in the measurement of heat fluxes transferred through layers of fabric to the surface of a human mannequinduring simulated flash fire conditions. This paper describes the determination of the transducers physical size, its limitations and heat loss considerations, a computer simulation of transducer operation and the evaluation of transient heat flux measurements. The transducers loss factors were predicted numerically and determined experimentally. The overall performance of the transducer was also examined under varying simulated applied heat flux input.

Thermal and Fire Protective Fabric Systems

Fabric systems that include all clothing and other textile-based goods are altered when exposed to intense heat or flames; however, the characteristics of these changes are vastly different depending on the fiber type, cloth structure, the nature of finish applied, amount of moisture trapped within the garment, and the compactness of its various components. Burning of fabric swatches, an old trade method for quick fibers identification, would illustrate that cloth composition and fiber compactness dictates the effortless motion of gases within a structure. Loosely woven knitted light fabric or nonwoven mats promote a propagation of fire within the material in a much faster procession than a tight heavy fabric structure would support. Cloth system flammability is also affected by the surface morphology of the fabric as well as the moisture trapped within the structure or absorbed by the fiber materials. A high amount of free fiber ends extending beyond the plane of the fabric would also support a prompt fire spread throughout the cloth. Fire-retardant chemical additives are usually applied to natural fibers to essentially delay the combustion onset and, therefore, provide additional time to control or attenuate the flames.

Thermal protective clothing

Publisher Summary This chapter reviews some of the major concepts and mechanisms used to investigate, characterize, assess, and enhance the performance of total protective clothing (TPC) in extremely hot or fire-prone environments. First, the major fabric materials used as outer shells for TPC are reviewed, and then the various stages of the exposure process are described. The major testing methods, evaluation tools, and computing models are also discussed, including the associated thermal sensors and burn damage evaluation schemes. Heat effects on the dermal layers of the skin and the modeling of human skin burn injuries is presented. There is no extensive numerical/empirical modeling of thermal mechanisms in TPC when exposed to intense heat sources because of its complexity. Most of the existing models are based on simplified, steady state, one-dimensional heat transfer processes that can be assessed in a bench-top thermal protective performance (TPP) evaluation environment. A calorimeter- type sensor, such as the TPP sensor, which tracks the heat flux trough the TPC fabric, has a copper disk of a considerable size that disturb the thermal balance during heat flux measurement.

Stability analysis of a growing horizontal thermal layer subject to sudden bottom heating

Abstract The hydrodynamic stability considered here is formulated in terms of a two-point boundary-value, eigenvalue problem derived by assuming periodic small disturbances superimposed on a time-dependent base-state which is the quiescent growing conduction layer resulting from a step in surface heat flux. Since the local heat flux field is similar, a dimensionless similarity parameter arises. The assumed disturbance form is guided by previous stability investigations The stiff equations are integrated to obtain the neutral stability curve with an extreme at Gr = 202.19, α = 1.151, and Cr = 0.0 Although the postulated disturbance form allowed for time-dependent periodic oscillation, the computed disturbance wave velocity is found to be identically zero for the entire curve. Thus, it is presumed that the assumed oscillatory component of the perturbation is not time dependent, during the instability onset, at least for the calculated range (202 ⩽ Gr ⩽ 1000). Thus, unlike analyses for steady base-states, these results prohibit ‘tracking’ disturbances along constant frequency paths. Nevertheless, experimental results suggest that the wave number should decrease with increasing Gr as the neutral curve is crossed by the perturbation.