Comparison of the Behavior of Foams and Gels Exposed to Fire.
Comparison of the Behavior of Foams and Gels Exposed to
Tafreshi, A. M.; diMarzo, M.
NISTIR 6242; October 1998.
National Institute of Standards and Technology. Annual
Conference on Fire Research: Book of Abstracts.
November 2-5, 1998, Gaithersburg, MD, Beall, K. A.,
Editor(s), 59-60 pp, 1998.
Sponsor:National Institute of Standards and Technology,
Available from: National Technical Information Service
Order number: PB99-102519
fire research; fire science; fire suppression; foam
extinguishing systems; fire behavior; gels; experiments;
Water is the principal component of both foams and gels
used as fire protection agents. The foam is expanded to
several times its original liquid volume with air. Data
from a previous study show that, when the foam is
subjected to a radiant heat input of 18 kW/m2, the peak
of the radiant heat absorption is at about 30 mm in the
depth of the foam layer while radiant heat penetrates to
depths up to 60 mm. The reason for this behavior is the
decreasing density of the foam near its exposed surface
as the water is evaporated away from the foam matrix.
As the density decrease, so does the extinction
coefficient leading to lower absorption of the incoming
radiation. In the depth of the foam layer, as the
thickness and the density both increase, the radiant
heat is absorbed causing the water to vaporize in-situ
since the contribution of thermal diffusion is small.
In contrast with this phenomenology, the behavior of the
gel, in a similar situation, is dominated by thermal
diffusion. The radiant heat input is absorbed in the
immediate proximity of the gel surface and the exposed
surface approaches saturation conditions for the
duration of the transient. These differences result in
significantly different fire protection behaviors.
These observations complemented with other, more
qualitative considerations will identify a rationale for
recommending the proper agent for the specific fire