Study of Technology for Detecting Pre-Ignition Conditions of ... - NIST

msc-HG95-1145
because a candidate signature must exist for each type of food if it is to have potential as input
to a universal pre-cooking-fire sensor. Diverse range types were of interest because of potential
variation in i~ition modes due to a proximate flame on the gas range, although in these
experiments, the ranges functioned primarily as sources of heat. The use of the different ranges
selected was expected to have some effect on the time lag of the behaviors of the recorded
variables because of the varied levels of heat flux output associated with each range. The rangehood
status was of interest for two reasons. l?irs~ the flow caused by an active range hood might
obscure the signature(s) of interest preceding ignition. Second, the different flow patterns might
alter entrainment of air wh~ch could effect the mechmism and location of ignition and thus the
preceding set of signatures as well.
The selected foods and ranges were chosen because they were typically used for cooking
in households and were representative of cooking fire scenarios that have actually been reported.
More uncommon range models, food types, and styles of cooking could have been tested, but
their results are less relevant at this stage.
2.1.1 Facility Constm~ion
A small, stand-alone laboratory was built in Building 205, the Large-Fire Facility, at NIST
to acmmmodate these experiments. A schematic of the room is shown in Figure 1. The interior
dimensions of the room are as follows: 3.66 m (12 ft) width, 2.44 m (8 ft) depth, and 2.44 m
@ ft) height. The room was outfitted with double-tide doors, 163 cm (64 in) wide by 207 cm
(81 in) high, and fluorescent lighting. Access holes were made for external supplies of electrical
power and natural gas. The stmcture consists of 2.44 m (8 ft) lengths of 8.9 cm (3.5 in) by
3.2 cm (1.3 in) galvanized steel studding on the outside with 40.6 cm (16 in) centers supporting
1.3 cm (0.5 in) thick gypsum drywall with the interior painted white. A set of white wooden
cabinets with overhead cupboards and a countertop with cupboards below were installed. A space
in the center was reserved for range installation.
A range hood (described in Section 2.1.2) was installed above the range location. A
25.5 cm (10 in) wide by 8.9 cm (3.5 in) high rectangular hood duct passes through the wall
directly behind the range hood to an elbow that transitions to a 15 cm (6 in) diameter round duct.
The round duct is vertical for about 0.6 m (2 ft) where it connects to an elbow, traverses about
1.8 m (6 ft) horizontally to another elbow where the end is directed upwards and is positioned
approximately 10 cm (4 in) below a large 41 cm (16 in) diameter duct which connects to tie
draft hood afterbmer system.
A box hood, 188 cm (74 in) wide by 58 cm (23 in) deep by 91 cm (36 in) high, was
constructed over the doorway to capture most of the smoke produced by the experiments. The
hood was made of 9 mm (3/8 in) thick plywood. From 46 cm (18 in) above the bottom of the
hood to 67 cm (26.5 in), the width of the box tapers from 188 cm (74 in) to 30 cm (12 in). The -top
24 cm (9.5 in) of the hood is 30 cm (12 in) wide by 58 cm (23 in) deep. The hood is
connected at the side of the top section to a 20 cm @ in) diameter, 4.3 m (14 R) long duct which
leads to a fan which pulls the exhaust into the duct of the afterburner system.
Electrical power was provided from two sources. AH of the instimentition was supplied -
120 V electricity from a portable electric sub-panel box with a 60 amp rating which split 240 V
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