Fundamentals - Wildland Fuel Fundamentals and Applications - page 29

conductivity is most often used to describe solid fuel particles, but it can also be
modified to describe heat transfer through porous fuelbeds, layers, or components.
Estimates of thermal conductivity for duff, for example, are often used to simulate
heat and temperature dynamics in the soil layer as a result of surface fire (Campbell
et al. 1995 ). Bark thermal conductivity is used to estimate how hot and fast heat
penetrates live tissue to estimate plant mortality (Reinhardt and Dickinson 2010 ).
In general, most fire applications that require an estimate of thermal conductivity
are for research purposes or specialized fire effects models (Reinhardt et al. 1997 ).
The chemical content of fuel particles is also important to most of the fuel prop-
erties presented here and also for other fuel properties that are input to some fire and
fuel management applications. Oils and resins in some fuel particles may increase
heat content (see Sect. 2.3.1.6; Philpot 1970 ), while high concentration of minerals
in leaves and some wood may reduce flammability and dampen combustion (see
Sect. 2.3.1.5; Whelan 1995 ). Other aspects of chemical composition may be impor-
tant from a human health standpoint. Fuel particles might contain mercury or ra-
dioactive elements that, when burned, could create hazardous smoke emissions that
might impact air quality (Canham and Loucks 1984 ). The relative concentrations
of organic compounds, such as cellulose and lignin, influences those fuel properties
that control live and dead fuel moisture dynamics, such as permeability and hygro-
scopy (affinity of cell walls to hold water; Chap. 5) and dictate rates of decomposi-
tion (Chap. 6).

2.3.2 Fuel Component

Most fuel component properties are quantified from a statistical summary of the
fuel particle properties, which is often an average across a fuel component. For
example, the 10 h woody fuel component (Chap. 3) is defined as downed deadwood
particles with diameters greater than 0.6 cm (0.25 in) and less than 2.5 cm (1 in),
so the average diameter ( d ) of the 10 h class is estimated from field measurements
(Brown 1970a ) and SAVR is estimated from d and ρ p (Eq. 2.13). However, there are
two fuel component properties that are measured directly and not estimated from
particle properties.

2.3.2.1 Loading ( W )

Loading is quantified as the dry weight mass of the fuelbed or fuel component per
unit area. Loading estimates are reported in dry weight to eliminate moisture con-
tributions to weight estimates, which can vary wildly over a fire season. The units
used to represent loadings are quite important in fuel management because they are
the context in which many people visualize the weight of fuel loads. Traditionally,
loadings were assigned imperial units of tons acre −1 , but it is difficult for many fire
professionals to envision what a ton of any fuel component looks like, let alone
envision how it is distributed across an area as large as an acre. Moreover, the fuel