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Influence of the air gap between protective clothing and skin on clothing performance during flash fire exposure

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Abstract

A finite volume model was developed to simulate transient heat transfer in protective clothing during flash fire exposure. The model accounts for the combined conduction-radiation heat transfer in the air gap between the fabric and skin. The variation in the fabric and air gap properties with temperature and the thermochemical reactions in the fabric are also considered. This study investigates the influence of the air gap in protective clothing on the energy transfer through the clothing and hence on its performance. Different parameters that affect the conduction-radiation heat transfer through the air gap such as the air gap absorption coefficient and the air gap width were studied. Finally, the paper demonstrates that an innovative and potentially significant way to improve protective clothing performance is to reduce the emissivity on the backside of the fabric.

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Abbreviations

A :

Surface area (m2)

a, b:

Finite volume discrete equation coefficient, source term

C :

Heat capacity (J/kg K)

c P :

Specific heat at constant pressure (J/kg K)

\( D_{c}^{l} \) :

Directional cosine integrated over ΔΩl

\( \hat{e} \) :

Unit vector in coordinate direction

G :

Incident radiation (W/m2)

h :

Convective heat transfer coefficient (W/m2K)

I :

Intensity (W/m2)

k :

Thermal conductivity (W/mK)

L :

Thickness (m)

P :

Pre-exponential factor (1/s)

\( q^{\prime\prime} \) :

Heat flux (W/m2)

\( \overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {r} \) :

Position vector (m)

R :

Ideal gas constant (J/mol K)

\( \hat{s} \) :

Unit vector in a given direction

S :

Source function

s :

Geometric distance (m)

T :

Temperature (K)

t :

Time (s)

W :

Fabric width (m)

y :

Linear vertical coordinate (m)

Ω:

Solid angle (sr)

θ :

Polar angle (rad)

\( \varphi \) :

Quantitative measure of skin damage

\( \phi \) :

Azimuthal angle (rad)

ΔE :

Activation energy of skin (J/kmol)

ΔV :

Volume of control volume (m3)

ΔΩl :

Control angle

α :

Air gap absorptivity

ε:

Emissivity

γ:

Extinction coefficient of the fabric (1/m)

κ:

Air gap absorption coefficient (1/m)

ρ:

Density (kg/m3) or surface reflectivity

σ:

Stefan-Boltzmann constant, 5.67 × 10−8 (W/m2 K4)

τ:

Transmissivity

ω:

Blood perfusion rate (m3/s)/m3 of human tissue

air:

Air

amb:

Ambient conditions

b:

Human blood/black body

cnv:

Convection heat transfer

cr:

Human body core

ep, ds, sc:

Epidermis, dermis, subcutaneous human skin layers

exp:

Exposure

fab:

Fabric

fl:

Flame

g:

Hot gases

n, s:

North, south control volume faces

P:

Control volume central node

R, rad:

Radiation heat transfer

x, y, z:

Coordinate directions

A :

Apparent

l :

Index for direction

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Authors and Affiliations

  1. Department of Mechanical Engineering, University of Saskatchewan, 57 Campus Dr., Saskatoon, SK, S7N 5A9, Canada

    Ahmed Ghazy & Donald J. Bergstrom

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  1. Ahmed Ghazy
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  2. Donald J. Bergstrom
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Correspondence to Donald J. Bergstrom.

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Ghazy, A., Bergstrom, D.J. Influence of the air gap between protective clothing and skin on clothing performance during flash fire exposure. Heat Mass Transfer 47, 1275–1288 (2011). https://doi.org/10.1007/s00231-011-0791-y

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