1 INTRODUCTION 

The occurrence of mine fires continues to be one of 

the most persistent problems facing the mining industry. Since 2000 there have been 19 major mine 

fires (including thermal events) in underground 

mines in the United States (figure 1). The National 

Institute for Occupational Safety and Health 

(NIOSH), in partnership with the Mine Safety and 

Health Administration, is conducting on-going field 

and laboratory investigations that are focused on the 

remote application of extinguishing agents, deployment strategies for firefighting equipment, and permanent and temporary fire containment sealing 

technology. The goals of this research are to evaluate new and existing technologies and to limit miner 

exposure by developing or improving control and 

extinguishment strategies to help ensure the best 

possible outcome during a mine fire. 

Fire fighting foam technology has been available 

for many years, and has been used extensively to 

fight flammable and combustible liquid fires on the 

surface (Colletti, 1992, Brackin et al. 1992, Omans, 

1993a, Omans, 1993b, Omans, 1993c). The application of fire fighting foam in underground mines was 

developed in the 1950’s (Hartman et al. 1958, Nagy 

et al. 1960). Its use has been mostly limited to direct 

fire fighting application using high-expansion foam 

generators located underground to push the foam 

and flood the fire area (Scott and Nagy, 1968, 

Banerjee and Acharya, 1986, Conti, 1995, Conti and 

Weiss, 1998). Other applications include pumping 

of nitrogen-enhanced high expansion foam into gob 

areas to control spontaneous combustion (Komai et 

al. 1989, Voracek, 1993). 

Figure 1. Major underground mine fires in the United States 

(2000-2005). 

More recently, the methods that employ compressed gas foams have been developed, resulting in 

smaller, more uniform bubbles (Grady, 1994). The 

chemicals used to create foam concentrate are 

Mine Fires – Measuring the Efficacy of Gas-Enhanced Foam 

Michael A. Trevits and Alex C. Smith 

National Institute for Occupational Safety and Health, Pittsburgh, Pennsylvania 

Thomas P. Mucho 

Thomas P. Mucho & Associates, Inc., Washington, Pennsylvania 

Alden Ozment and John B. Walsh 

US Foam Technologies, Inc., Longview, Texas 

Michael R. Thibou 

On Site Gas Systems, Newington, Connecticut 

ABSTRACT: The National Institute for Occupational Safety and Health (NIOSH), with US Foam Technologies, Inc. and On Site Gas Systems, Inc., conducted research on the remote application of extinguishing 

agents with the intent of improving deployment strategies to limit miner exposure and to help ensure the best 

possible outcome during a mine fire. Full-scale in-mine were conducted at the NIOSH Lake Lynn Experimental Mine to determine the flow characteristics, stability and fire-suppression capability of gas-enhanced 

foam. The in-mine experimental work was designed to evaluate movement of gas-enhanced foam through 

mine workings closely simulating an underground coal mine environment and how long gas-enhanced foam 

would remain stable. This paper presents results of the experiments and provides valuable insight into mine 

fire deployment strategies for gas-enhanced foam technology. 

Disclaimer: The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health. 
claimed to reduce the surface tension of water, 

greatly increasing the penetrating and wetting abilities of the water used, and significantly increases the 

effectiveness of the water supply (US Foam, 2004). 

The addition of gas to the mixture increases the resulting foam volume to between five and fifteen 

times the volume of water used. 

Foam addresses a fire condition through evaporation of contained water and cooling by energy removal. Foam serves to blanket the combusting material and isolate it from oxygen. As the foam 

collapses, water is released and the temperature of 

the water increases by absorbing heat and eventually 

turns into the water into steam. Water is released 

from foam either through bubble rupture or through 

the effects of gravity distorting the bubble walls. 

Because this process takes time, foam can act as a 

water reservoir, releasing water at a rate that allows 

absorption into the fuel, rather than running off the 

surface (Snuffer Corp, 2004). The four components 

of a fire include: the oxidizing agent (any of the 

various gases that support combustion), the reducing 

agent (any material that is reducible to combustible 

materials thus becoming a fuel), heat from within or 

without the material, and a self-sustaining chemical 

chain reaction (the action of the first three) 

(Gottschalk, 2002). If the foam is enriched with nitrogen gas, then it can serve to remove two components of the fire tetrahedron by robbing the fire of 

heat and removal or displacement of oxygen. Given 

sufficient stability and the capability to efficiently 

move and migrate through a mine opening, it is 

thought that nitrogen-enriched foam could provide 

an ideal technology for addressing mine fire conditions. 

The use of remotely-applied foam from the surface through boreholes is a relatively new concept. 

Because of the lack of experience with this new 

technology, there are uncertainties with respect to 

the foam’s ability to maintain its composition when 

pumped under pressure through deep boreholes and 

its ability to move away from the downhole location. 

In order to quantify these and other parameters, a series of full-scale experiments were conducted in 

NIOSH’s Lake Lynn Experimental Mine (LLEM) 

located approximately 60 miles southeast of Pittsburgh, PA. The LLEM is a world-class, highly sophisticated underground facility where large-scale 

explosion trials and mine fire research is conducted. 

This work is being conducted under the tenets of the 

NIOSH Research to Practice (r2p) initiative which is 

aimed at reducing or eliminating occupational disease and injury by increasing the use of research 

findings in the workplace. During the in-mine experiments, the components of the foam were mixed 

together on the surface and the resulting foam was 

injected through a borehole into the mine void. Experiments were designed to measure the foam’s stability, flow speed and length of flow. In addition, 

the ability of the foam to flow through non-linear 

mine void configurations, through and around obstructions, and over pooled water was evaluated. 

Foam’s fire suppression effectiveness was measured 

against a deep-seated coal fire and a diesel pool fire. 

Lastly, its ability to flow up a sloped entry was 

measured. 

2 FOAM DELIVERY SYSTEM 

US Foam Technologies, Inc. together with On Site 

Gas Systems provided nitrogen gas-enhanced foam 

services during the experiments. US Foam Technologies Inc. offers a specialized gas-enhanced foam 

generating system and On Site Gas Systems provides nitrogen gas for the system using portable 

skid-mounted nitrogen plants that extract nitrogen 

gas from the atmosphere using membrane technology (On Site Gas Systems, 2005). 

US Foam Technologies Inc. owns a proprietary 

nitrogen-enriched foam delivery system known as 

the HellfighterTM which includes a pipeline manifold 

and a sophisticated mixing chamber. Water is 

pumped at a controlled rate and pressure into a line 

that is connected to one of the inlet ports on the 

HellfighterTM. Mine Fire Fighting FoamTM (MFFF) 

concentrate, a proprietary formulation of chemicals 

designed to produce long-lasting foam that can withstand higher temperatures than Class-A Fire Fighting Foam (AFFF), is added to the waterline using 

precision injection pumps. Nitrogen gas from On 

Site Gas Systems’ membrane plant is then injected 

at a controlled rate into another inlet port on the 

HellfighterTM. The fluid (water and foam concentrate) and nitrogen gas is mixed within the HellfighterTM and creates nitrogen-enhanced foam that 

flows from the outlet port of the HellfighterTM to 

wellhead assembly attached to the injection borehole 

and into the mine void. A schematic of the foam 

system is shown in figure 2. 

Figure 2. Schematic of the foam system 

Up to three small HellfighterTM units (or one 

large unit) can be connected to a single borehole de-
pending on the diameter of the hole. Water, foam 

concentrate and nitrogen gas flow rates can be adjusted to produce a variety of foam mixtures from a 

thin water-foam blend to a thick froth similar to 

shaving cream. In addition, the material being injected can be switched (with no downtime) from 

foam to only nitrogen gas simply by closing a valve. 

The gas-enhanced foam and nitrogen membrane 

plant combination provides an ideal platform for addressing mine fires because it can be readily moved 

from one borehole location to another and can be 

deployed using off-road equipment. Bulk liquid nitrogen trucks can deliver more nitrogen in a unit of 

time but their use is limited by rugged road conditions. 

For these experiments, water was stored in a 

10,000 gallon tank at the surface location of the 

borehole and a fire engine was used to pump the water. The foam concentrate was supplied in 250 gallon plastic “tote” containers. The nitrogen was supplied by a 1,000 ft3

/min membrane separation plant. 

Three HellfighterTM units were attached to the injection borehole. 

3 LAKE LYNN EXPERIMENTAL MINE 

A layout map of the LLEM is shown in figure 3. 

The underground mine entries were developed adjacent to an abandoned commercial limestone quarry 

and underground limestone mine. The entries of the 

abandoned limestone mine, labeled as the old workings, are approximately 49 ft wide by 33 ft high. 

The LLEM contains 5 drifts openings called A, B, 

C, D, and E as shown in figure 3. These entries 

were developed to approximate the size of a typical 

Pittsburgh Coalbed mine, about 20 ft wide by 6 ft 

high, and range from 500 to 1500 ft in length. The 

entries, in conjunction with the use of two explosion-proof bulkhead doors that can be positioned to 

open or close an entry, can be made to simulate 

room-and-pillar and longwall mine configurations 

(NIOSH, 1999). 

 

Figure 3. Layout map of the Lake Lynn Experimental Mine. 

The injection borehole penetrated the mine void 

at a depth of 197 ft. The injection borehole intercepts the mine workings in the first crosscut outby 

the face area between the B and C drifts. The borehole is completed to the mine opening with 6-in diameter casing. At the location of the borehole, the 

mine opening is 7-ft high and slopes towards B drift 

on a 1.13 percent gradient. 

4 EXPERIMENT NO. 1 

Experiment No. 1 was designed to evaluate the 

physical characteristics and flow behavior of foam. 

Air was used as the gas in this experiment so researchers could observe foam movement without the 

need to use self-contained breathing apparatuses. 

The parameters studied in this experiment included 

measuring the condition and volumetric changes of 

the foam as it was pumped into the borehole and entered the mine, foam stability, flow speed, length of 

flow, stacking characteristics, movement through 

and around obstructions, movement over a pool of 

water, and flow through non-linear mine configurations. To accomplish this, the multiple entry section 

of the mine was configured as shown in figure 4. To 

evaluate the long-term stability of the foam under 

the typical mine temperature and humidity conditions, a 4.3-ft high concrete block stopping was construct in the closed end of the A drift to create an 

isolated area that could be filled with foam. This 

area measured 92 ft-long by 20 ft-wide. To transport the foam to this area, a flexible hose was attached to the bottom of the injection borehole and 

extended to this enclosure. The volume of this 

chamber to the top of the stopping (7,912 ft3

) was 

then filled with foam. 

Figure 4. Layout map of mine workings for Experiment No. 1. 

A combination of block, plywood, and brattice 

stoppings was used to direct the foam as it exited the 

borehole. A plywood stopping at the outby end of 

the B drift stub and a concrete block stopping in the 

first crosscut between A and B drifts were installed 
to direct the foam down B drift. The second crosscut between A and B drifts was filled rib-to-rib and 

floor-to-roof with broken rock to simulate compacted gob. This area was used to determine if foam 

would penetrate the broken rock mass or if the rock 

only served to block the flow path. Another block 

stopping was placed in the B drift just outby the 

third crosscut. One block was replaced with a window and a camera was located behind the stopping 

window to record the foam movement. Brattice 

stoppings were placed in the second and third crosscuts between B and C drifts and in the fourth, fifth, 

and sixth crosscuts between A and B drifts. Because 

of the slope of the mine floor, this combination of 

stoppings directed the flow of the foam across a broken rock pile in crosscut 3 between the A and B 

drifts. This rock zone was approximately 3-ft high 

and spanned the width of the opening. Three electric resistance heating elements were buried at the 

center of this rock pile to simulate a deep-seated hot 

spot, to determine if the foam could infiltrate the 

broken rock and reduce the temperature of the hot 

spot. 

Two rows of four crib blocks were constructed in 

the A drift between the third and fourth crosscuts 

and a pool of water was created in A drift between 

the fourth and fifth crosscuts. The purpose of the 

pool of water was to determine whether foam would 

move over a body of water, if the pool created a barrier to foam flow, or if the pool served to degrade 

the foam. The water pool was created by constructing a watertight 2-ft high block stopping across the 

width of A drift to act as a dam. Because of the 

slope of the mine floor, a pool of water approximately 50 ft long was made in the A drift. Lastly, a 

26 ft long conveyor belt structure was placed 3.5 ft 

from the rib area in the A drift between the fifth and 

sixth crosscuts to observe the behavior of the foam 

as it flows through or around mine structures. 

The initial attempts to deliver high quality foam 

to the mine entry required some adjustment to liquid 

components and the rate of gas injection. This is 

typical of foam use and is usually done on the surface by the equipment operator. In this case, the adjustment was made through communications between in-mine personnel and personnel on the 

surface at the pump site. After adjustment, foam 

having a shaving cream-like consistency was 

achieved at the bottom of the borehole. The foam 

moved down and around the corner of the first 

crosscut into B drift. The foam reached a height of 

3-to 4-ft through B drift as it moved down slope and 

away from the borehole. 

The first obstacle encountered in B drift was the 

rock pile in the second crosscut between A and B 

drifts. The camera mounted on the A drift side of 

the rock pile showed that foam did not penetrate the 

broken rock mass. Water, however, that apparently 

settled out from the foam was observed flowing 

from the bottom of the rock pile.

The mine stopping configuration then caused the 

foam to turn into the third crosscut between A and B 

drifts, where the foam encountered the 3-ft high rock 

pile with the heating elements. Figure 5 shows the 

temperature profiles for the thermocouples attached 

to the four heating elements located in the rock pile. 

Unfortunately, the heating elements failed after 

reaching temperatures ranging from 28o to 34o C, 

just 15o to 20o C above ambient temperature. Unfortunately, the limited exposure of rock to the heating 

elements did not raise the rock temperature enough 

to measure the effect of the foam on the rock temperature. However, it is clearly obvious that the 

foam quickly infiltrated the rock pile and cooled the 

heating elements within minutes. 

Figure 5. Rock pile heater element temperature profiles. 

After turning the corner into the A drift, the foam 

moved until it encountered the sets of crib blocks. 

Figure 6 shows that the crib blocks formed an effective barrier to the foam, causing it to build up to roof 

height behind the crib blocks. Once past the crib 

blocks, the foam height in the entry was reduced to 

about 2-ft. The foam then approached the water 

pool in the A drift. The water had no apparent effect 

on the foam as it moved over it without any apparent 

affect on foam quality. Finally, the foam encountered the conveyor belt structure. The structure 

acted much like the sets of crib blocks in the A drift, 

causing foam build-up upstream of the structure. 

Since the structure only occupied 4.8 ft of the entry 

width, the foam moved through the unobstructed 

part of the entry similarly to the way it moved 

through the B drift. 

As mentioned previously, the closed end of the A 

drift was filled with foam to a height of 4.3 ft. Figure 7 shows the rate of decay of the foam versus 

time. The foam lasted for 9 days and the rate of decay was linear over the 9 day period at about 900 ft3

. 

It should be noted that this area was not exposed to 

mine ventilation air flow and was strictly a measure 

of the rate of foam degradation. 
Figure 6. Foam flow and build-up in the crib block area. 

Figure 7. Rate of decay of foam volume versus time. 

5 EXPERIMENT NO. 2 

Experiment No. 2 was designed to evaluate the fire 

fighting effectiveness of foam against a deep-seated 

coal fire and a flammable liquid (diesel fuel) pool 

fire. In this experiment, nitrogen was used as the 

gas. The mine configuration to direct the flow of the 

foam was the same as in Experiment No. 1. The obstructions in the A drift were removed since the purpose of this experiment was to evaluate the ability of 

foam to extinguish the test fires. A concrete block 

stopping was placed in the third crosscut to contain 

the foam to B drift. Because of this configuration, B 

drift was not ventilated. The diesel fuel fire was located in the center of the third crosscut in B drift. 

Five gallons of diesel fuel was floated on a 1-in water layer in a 3-ft by 3-ft square metal tray. This fire 

was ignited just prior to the arrival of the foam front. 

The size of fire was approximately 600 kW. The 

deep-seated coal fire was placed just up slope of the 

diesel fuel fire in the center of the mine entry. To 

create the coal fire, approximately 250 lb of coal 

was placed on top of 25 lb of commercial cooking 

charcoal in a 3-ft by 3-ft square metal tray. This fire 

was ignited approximately 60 minutes before the 

foam flow was initiated. Figure 8 shows a layout 

map of the mine for Experiment No. 2. 

Figure 8. Layout map of mine workings for Experiment No. 2. 

The diesel fuel fire was monitored using two 

thermocouples located 4-in above the fuel layer. 

The coal fire was monitored using seven thermocouples located throughout the coal pile. Both fuel and 

coal trays were also monitored by a thermal imaging 

infrared camera that enabled researchers to remotely 

view the fire through the foam. Figure 9 shows the 

temperature-time trace for the thermocouples located 

above the diesel fuel tray fire. The fire was ignited 

and allowed to burn for 10 minutes before the foam 

reached the fire. Temperatures of about 800 oC were 

recorded 4 inches above the fuel layer. When the 

foam reached the fuel tray, it easily enveloped and 

extinguished the fire. 

Figure 9. Temperature-time trace for thermocouples located 

above the diesel fuel fire. 

Figure 10 shows the temperature-time plot for the 

thermocouples located in the coal fire tray. Temperatures near the top of the coal pile reached about 

850o and 625 o C. Other areas of the coal pile were 

between 100o and 250o C, with the exception of the 

two thermocouples located on the outer edge of the 

coal pile which only reached about 50o C. The foam 

reached and enveloped the coal fire tray and quickly 

cooled the hot spots. Temperatures deeper inside the 

coal pile slowly decreased over the next hour.
Figure 10. Temperature-time trace for thermocouples located in 

the coal fire. 

Data from the infrared camera that was used to 

image the fuel and the space above the coal tray 

showed the space above the fire tray was reduced to 

about 15o C. The temperature of the foam downstream from the fuel tray was above the ambient 

temperature of the foam showing that it carried heat 

away from the fire. At the same time, the maximum 

temperature in the coal pile, as measured by the 

thermocouples, was about 90o C. This suggests that 

foam be used to quickly cool the airspace near a 

deep-seated fire, reducing the chance for spreading 

the fire. Furthermore, the nitrogen gas used to create 

the foam reduces the oxygen concentration in the 

airspace, thereby reducing the chance of a methane 

ignition. 

During this experiment, foam reached the roof in 

B drift because of the stopping configuration, which 

essentially closed off B drift. In this confined experiment, foam filled the mine void and then moved 

upslope towards the injection borehole. Foam was 

also observed penetrating through the top of the rock 

pile located in the second crosscut between A and 

B drifts. 

6 EXPERIMENT NO. 3 

Experiment No. 3 was designed to evaluate the ability of the foam to fill a single mine entry. The 500 ft 

long E drift was used for this experiment. A layout 

map of the LLEM for this experiment is shown in 

figure 11. The slope of E drift (6.2 percent) is much 

more severe than in the multiple entry section of the 

mine. In this experiment, concrete stoppings were 

constructed in the crosscut between B and C drifts 

and in C drift to isolate E drift, creating a long single 

entry. Several blocks were removed from the first 

course of blocks in these stoppings to allow water to 

flow from the degradation of the foam. It was 

thought that water could collect in this area possibly 

causing the block structure to fail. A longwall 

shearer was located near the distal end of E drift and 

was utilized to evaluate foam’s ability to move 

around the obstruction after flows a long distance. 

Figure 11. Layout map of mine workings for Experiment 

No. 3. 

The foam was delivered through the borehole and 

filled the closed area (crosscut between B and C drift 

and area that was closed at the opening to the C 

drift) and then began moving up into the E drift. 

The foam reached the mine roof quickly because of 

the severe slope of the entry in this area. The rate of 

advance of the foam plug, as measured by the lowest 

point of the leading edge of the foam, was constant 

at 1.5 ft/min once the foam reached the mine roof 

and began moving up the E drift. Over the first 50 

minutes, the foam had not yet reached the roof since 

it was filling the first crosscut at the intersection of 

C and E drifts. The pressure exerted on the concrete 

stoppings was measured and was approximately 

equal to the foam density. Figure 12 shows the progression of the body of foam along the E drift. 

Figure 12. Progression of the body of foam along the E drift. 

The foam filled the entire length of E drift in five 

hours. The experiment was stopped when the foam 

reached the fan shaft at the end of E drift to prevent 

disruption of the ventilation system. The rate of 

foam dissipation was measured over the next seven 

days, and is shown in figure 13. At the time the 

foam injection was stopped, the length of the E drift 
filled with foam was 469 ft. Initially, the foam was 

quite stable, decaying at a rate of only about 

8.8 ft/day (1,145 ft3

/day) after the first day. The rate 

eventually increased to about 64.7 ft/day 

(8,410 ft3

/day) at seven days. The rate of decay over 

the first three days is comparable to the results from 

the stability test conducted earlier in the A drift stub. 

The rapid increase in decay rate after three days is 

possibly attributed to air pathways developing over 

the top of the body of foam as it degraded allowing 

airflow to pass over the foam. This likely increased 

the rate of dehydration of the foam. 

Figure 13. Rate of foam dissipation in the E drift. 

7 SUMMARY 

The foam experiments were very successful in 

evaluating many of the parameters that can affect the 

use of foam for remotely fighting mine fires. However, these experiments were also limited in scope 

with respect to the type of foam used, the geometry 

and slope of the mine entries, and the size and types 

of fires. Therefore, these results should be used as 

guidelines for the use of foam, and not as design 

specifications for its use. 

The foam used in Experiment No. 1 showed good 

stability over time. Foam stability is a function of 

foam concentrate, water volume, and gas flow, and 

these parameters can be varied based on the particular application. Observations during the experiments 

suggested that the life of gas-enhanced foam is 

highly dependent on the quality of the foam (relative 

ratio of water, foam concentrate and nitrogen gas). 

“Wet” foam had shorter life (from a few minutes to 

a few hours) and “dry” foam lasted as long as several days. During the LLEM experiments when 

“wet” foam was created and the system was shutdown the foam degraded quickly and flowed away 

from the injection borehole. In addition, the life of 

the foam can be dependent on the mine temperature 

and wetness or dryness of the environment, water 

hardness, and pH. However, the effect of varying 

these parameters was not measured in this experiment. This experiment also showed that the foam 

quality can be adequately managed from the surface. 

However, periodic monitoring of the foam consistency on the surface is recommended to ensure stable foam is entering the mine. 

Foam flow, speed, and ability to reach the mine 

roof and fill the entire cross-section of the mine 

opening were shown to be highly dependent on the 

slope of the mine floor. In the first two experiments, 

the foam flowed quickly and did not reach the roof 

of the mine until it was obstructed by the sets of crib 

blocks. In the third experiment, the foam reached 

the mine roof very quickly because of the upslope of 

the mine floor and the obstructions that did not permit down slope flow, but the rate of advancement of 

the foam front was much slower than in the first two 

experiments. 

In confined applications where the objective is to 

flow foam from the borehole to a fire location some 

distance away, this parameter is extremely important. In a situation where the elevation of the fire is 

below the foam entry point into the mine, the foam 

will flow quickly, however an obstruction, such as a 

remotely installed mine seal, will be neededl to 

cause the foam to completely fill the mine void from 

the floor-to-roof. In situations where the foam will 

need to move up slope, it will be critical to get the 

location of the foam injection borehole as close as 

practicable to the fire and position obstructions 

down slope from the foam injection point. Again, 

the use of remotely installed mine seals could be 

necessary. In situations where the mine entry is 

level, foam should flow in all directions away from 

the injection borehole, but the flow will be highly 

dependent on obstructions. Unfortunately, this scenario was not tested at the LLEM. 

The nonlinear configuration of the mine openings 

used in the first two experiments demonstrated that 

foam will flow around corners, but again the major 

influence on its effectiveness was elevation and obstructions. In the first two experiments, foam 

flowed past the rock rubble pile in the second crosscut between A and B drifts, essentially treating it as 

a stopping. The stopping in B drift acted to turn the 

foam into the crosscut between A and B drifts. 

However, when the foam reached A drift, which was 

open in both directions, the foam only flowed in the 

down slope direction. 

The ability of foam to suppress a liquid pool fire 

was shown in the second experiment. However, 

foam’s ability to cool a hot, deep-seated fire was not 

completely addressed in these experiments. Foam 

did cool the high temperatures in the coal fire, but 

this was a relatively small fire. Foam was able to infiltrate the rock pile and quickly cool the heating elements in the second experiment, but the temperatures were not high enough to truly test the foam’s 

cooling ability. Foam’s inability to penetrate 
through the rock pile in the first experiment was 

noted. In the second experiment, foam moved 

through the rock pile near the mine roof when it was 

confined to the B drift. This indicates that the compaction of gob material and other possible pathways 

will determine the foam’s ability to infiltrate and 

penetrate deeply into a gob area. 

ACKNOWLEDGMENTS 

The authors acknowledge the support of Frank A. 

Karnack, William Slivensky, Donald D. Sellers, 

Kenneth Jackson, and Frances J. Goff, and Richard 

A. Thomas in preparation of the experimental setups and data acquisition and analysis, and William 

Monaghan for gathering the thermal imaging data. 

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