Carbon Monoxide Production in Compartment Fires: Reduced-Scale Enclosure Test Facility.
Carbon Monoxide Production in Compartment Fires:
Reduced-Scale Enclosure Test Facility.
(3357 K)
Bryner, N. P.; Johnsson, E. L.; Pitts, W. M.
NISTIR 5568; 214 p. December 1994.
Available from:
National Technical Information Service
Order number: PB95-231700
Keywords:
compartment fires; carbon monoxide; acute toxicity;
fuel/air ratio; combustion products; fire chemistry;
flashover; room fires; scale models; global equivalence
ratio; oxygen concentration
Abstract:
The formation of carbon monoxide during room or
compartment fires has been investigated using natural
gas fires burning within a reduced-scale enclosure
(RSE), an 0.98 m x 0.98 m x 1.46 m (w x h x d) room with
a single door opening centered in the front wall. This
series of 125 fires ranging in heat release rate (HRR)
from 7 to 650 kW and global equivalence ratio from 0.2
to 4.2, respectively, has demonstrated that the upper
layer is nonuniform in temperature and gas species, and
that upper-layer oxygen is depleted for underventilated
fires with high-temperature upper layers. For fires
having HRR exceeding 400 kW, carbon monoxide
concentrations of up to 3.5 percent have been observed
in the front portion of the upper layer. Carbon
monoxide concentrations in the rear were consistently
lower being on the order of 2.0 percent for equivalence
rateo > 2. While oxygen concentrations approached zero
in both the front and rear of the upper layer for
underventilated burning conditions, temperatures were
generally 200 deg C to 300 deg C higher in the front of
the upper layer than in the rear. Both the high
temperatures and high carbon monoxide concentrations in
the front of the upper layer are consistent with oxygen
being transported directly into the upper layer as well
as entering through the fire plume for the large fires.
This oxygen appears to react with unburned fuel to form
carbon monoxide, instead of being fully oxidized to
carbon dioxide. As the unburned fuel is oxidized,
additional energy release occurs which provides an
explanation for the higher temperatures observed in the
front of the RSE. The exact mechanism for transporting
oxygen directly into the front portion of the upper
layer is ot yet understood. The results of these RSE
fires clearly indicate that higher levels of carbon
monoxide can be generated in post-flashover scenarios
than suggested by earlier laboratory hood experiments or
earlier enclosure studies designed to generate a stable
two-layer structure. Current fire models do not
adequately simulate the temperature and gas species
nonuniformities nor the high levels of carbon monoxide.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899