In-mine study of high-expansion 

firefighting foam

L.L. Chasko 

Physical science technician, National Institute for 

Occupational Safety and Health, Pittsburgh, PA

R.S. Conti 

NIOSH, Pittsburgh, PA (Deceased)

R.L. Derick 

Consultant, Derick Mining & Safety, L.L.C., Fort Collins, Colorado

(Retired from Twentymile Coal Company)

M.R. Krump 

Atlanta, Georgia (Retired from Twentymile Coal Company)

C.P. Lazzara, Ph.D. 

Pittsburgh, PA (Retired from NIOSH)

Abstract

A mine fire is one of the most challenging safety issues facing a mine operator and can occur at any 

location underground. The National Institute for Occupational Safety and Health (NIOSH) and the 

Twentymile Coal Mine, CO, conducted in-mine experiments to determine the capability of high-expansion 

foam for addressing underground fires. The tests were conducted in sloping entries with high-capacity 

diesel-powered foam generators. The following results were observed: a well-designed, maintained and 

properly operated high-expansion foam generator can propagate a foam plug hundreds of feet in steep 

upward-sloping (20%) multiple entries against a ventilation pressure; stoppings and partitions designed 

to contain the foam plug in upward-sloping entries must be substantially constructed; and the predicted 

quantity of foam concentrate can be significantly less than the actual amount used, due to foam losses, 

such as bubble breakage on dry surfaces. This paper describes the production of high-expansion firefighting foam and discusses the in-mine experimental tests and results. 

Introduction

When an underground mine fire cannot be directly attacked 

due to heat, smoke or hazardous roof conditions, high-expansion 

foam may be one way to control the fire from a remote, safe 

underground location. High-expansion foam is a blanketing 

and cooling agent produced by a combination of water, air and 

foam concentrate. High-expansion foam is a means of conveying 

water directly to the fire, diluting the oxygen concentration by 

producing steam and blocking both air currents to the fire and 

radiant energy from the burning fuel. The foam concentrate, 

combined with proper amounts of air and water and expelled 

through an application device, will form finished foam appropriate for firefighting applications. The foam expansion ratio 

is the volume of foam to the volume of foam solution required 

to produce the foam. High-expansion foam has an expansion 

ratio greater than 200 to 1.

This paper details how foam generation can be used to 

combat large fires in underground mines and describes experiments conducted by the National Institute for Occupational 

Safety and Health (NIOSH) and the Twentymile Coal Mine, 

Colorado. The underground tests were conducted in sloping 

mine entries with high-capacity diesel-powered foam generators 

and three test scenarios are reviewed, along with their potential 

applications to mine fires.

Background on foam generation and firefighting 

in mines

In its simplest form, a large capacity, blower-type highexpansion foam generator >142 m3/min (>5,000 cfm) is made 

up of an electric or diesel-powered fan, a screen and a foam 

concentrate proportioner. The proportioner mixes the foam 

concentrate with water at the desired rate. The solution is discharged through nozzles onto the screen. The high-expansion 

foam is formed as air from the fan passes through the screen 
wetted with the solution. Additional design information on 

high-expansion foam systems can be found in National Fire 

Protection Associaton Standard 11, Low-, Medium-, and HighExpansion Foam (NFPA, 2005).

Before a foam system is implemented, the mine operator 

should consider the training and equipment needed, and the 

amount and type of foam concentrate required. Once the equipment and supplies are purchased, a plan must be developed for 

using foam in the mine. Foam-generating equipment should 

be compatible with the mine water system in regards to pressure and fittings. Whether using foam or another means of fire 

extinguishment, the mine operator should have an organized 

strategy for fast response, including a group of well-trained 

miners ready for an emergency situation. The mine should 

also have periodic drills to test the effectiveness of the firefighting plan.

Foam concentrates are designed to cover the widest possible 

range of firefighting applications. Selection of foam concentrate 

should be based on foam characteristics that are appropriate 

for each particular fire hazard and the water quality. Some of 

the foam concentrates available include: aqueous film-forming 

foam for flammable liquid fires, aqueous film-forming foam 

for both hydrocarbon and water-soluble liquid fuel fires and 

high-expansion foam for three-dimensional fires where total 

flooding is the objective, such as in coal mines. 

Once the proper foam concentrate is selected, it must be 

mixed in the right proportion with water. Foam concentrates 

are available for mixing with water in various concentrations, such as 2%, 6%, etc. Foam proportioners are designed 

to introduce the proper amount of foam concentrate into the 

water stream. Eductors that work on the Venturi principle are 

the most common form of proportioning equipment. Water 

is introduced, under pressure, at the inlet of the eductor. The 

eductor reduces the orifice available for the water to pass 

through and thus increases the water velocity. This creates 

a pressure drop that, in turn, applies suction to the pickup 

tube. As the foam concentrate is pulled up the tube, it passes 

through a metering valve that introduces the correct amount 

into the water stream. In-line eductors are matched systems 

that require specific water pressures for operation. Therefore, 

the manufacturer’s recommendations for hose size, hose length 

and water pressure must be considered before purchasing an 

in-line eductor system.

An adequate supply of foam concentrate should be readily 

available at the mine in 19-L (5-gal) pails, 114-L (30-gal) drums 

or 208-L (55-gal) drums. If drums are used, transportation and 

compatibility of the eductor should be considered. Arrangements should also be made beforehand to obtain additional 

foam concentrate from nearby mines or a local distributor. 

When storing foam concentrate, the manufacturer’s recommendations should be followed. Storage temperatures at the 

mine should be in the recommended range. Foam concentrate 

should not be stored outside if there is a risk of freezing. A typical 

temperature range for foam concentrate storage is 1.7° C (35° 

F) to 49° C (120o F). The cloud point, or when the concentrate 

becomes gelatinous, is usually below the lowest temperature 

specified. When foam concentrate becomes cloudy, it cannot 

produce quality foam. This same temperature range should 

be maintained when transporting the foam concentrate. Care 

must be taken to ensure that plastic containers are not cracked 

or dented and 19-L (5-gal) plastic pails of foam concentrate 

should not be stacked more than three containers high. 

High-expansion foam cannot control a fire unless the foam 

plug reaches the fire. A fire is considered under control when 

the burning is reduced to the point that extinguishing the fire by 

direct attack with water lines is easily and safely accomplished. 

Attempts have been made to push foam plugs into the burning 

entry ahead (downwind) of large fires. The tremendous heat 

and hot gases on the downwind side of the fire will break the 

foam and most of it will be heated into steam and blow down 

the entry away from the fire. However, if foam is pushed into 

the fire on the upwind side of the fire, the foam will reach and 

cool the fire. It should also be noted that high-expansion foam 

generators may not produce high quality foam if the intake air 

is heavily contaminated with smoke. 

Once the foam-making process is initiated, the foam 

generator should not be turned off unless this decision is 

carefully analyzed, or unless the fire is controlled. Even if 

the water supply fails or the foam concentrate is depleted, the 

foam generator itself should be left on to maintain a positive 

pressure against the foam plug. When the foam generator is 

turned off, the foam plug has a tendency to relax, creating a 

void space near the roof along the length of the foam plug. 

This void space may cause a sudden rush of air to the fire 

area. Additional information on the use of high-expansion 

foam and other methods to combat mine fires can be found in 

various references (Mitchell, 1996; Bird et al., 1999; Conti, 

1994; Havener, 1975; Nagy et al., 1960).

Foam generator partitions and operators

To effectively use high-expansion foam for remotely fighting fires in underground mine entries, it is often necessary to 

construct, at some distance from the fire, a partition or stopping 

in fresh air to separate the foam generator and its operators 

from toxic fire products and to contain the foam. If this is not 

done, the high-expansion foam could flow back over the foam 

generator and never reach the fire. This problem is especially 

acute when the fire is found uphill in a sloping entry. The 

partition also limits mine ventilation air from reaching the fire. 

Concrete block, wood, plastic sheeting, mine brattice or similar 

materials have been used for such partitions. Construction of 

such partitions can be a time-consuming and labor-intensive 

process. Often, mine entries have irregular dimensions to 

which the partition must conform to avoid leakage around 

the periphery. After the partition is constructed, a hole must 

be cut through it to allow passage of the high-expansion foam 

from the foam generator to the fire. During an underground 

training exercise for mine rescue teams and fire brigades in an 

operating coal mine, it required more than an hour to construct 

a partition from wood, metal and brattice, and to start the foam 

propagating up the mine entry. 

To address some of the difficulties of constructing a partition 

for high-expansion foam generators, an inflatable feed-tube 

partition (IFTP) was developed (Conti and Lazzara, 1995; Conti, 

1995). The IFTP is a lightweight, nylon rectangular bag that 

can be inflated by a permissible fan, a compressed air line or 

an inert gas source. The device can rapidly block large underground mine openings in 15 min and simultaneously provide 

a feed tube for high-expansion foam. This allows firefighting 

foam to freely flow to the fire site and control the fire. Despite 

its advantages, the IFTP would not be useful when pushing a 

foam plug a significant distance up a steeply sloping entry (>8 

percent). In this case, a more substantial partition is required.

As high-expansion foam moves down an entry, a continuous 

shrinkage process occurs. A foam bubble cannot exist once 

touching a dry surface; it will collapse, wetting the surface so 
that the next foam bubble can replace it. Thus, as a foam plug 

advances, there is a constant bubble collapse. This shrinkage 

takes place on the leading edge of the foam plug. Due to this 

continuous shrinkage, water starts to collect under the foam 

plug. In an upward sloping entry, the water flows back towards 

the foam generator on the low side of the entry. A considerable 

amount of water can build up on the foam side of the partition, 

causing some partitions to fail. To reduce the water buildup, a 

pipe must be laid on the floor along the low side of the entry 

and under the partition. The water flows through the pipe and 

down the entry. The size of pipe is scaled to the output of the 

foam generator. For example, at least a 15-cm (6-in.) diameter 

pipe should be used with a generator that produces 170 m3/

min (6,000 cfm) or greater. 

The high-expansion foam generator at a mine site would 

most likely be operated by members of the fire brigade or 

mine rescue team. The operators should actually test the foam 

generator in their mine during training drills and propagate 

high-expansion foam in the passageways. This also entails 

erecting a suitable partition to be interfaced with the foam 

generator and/or other stoppings to contain the foam plug. 

They should ensure compatibility of the foam concentrate and 

mine water supply, proper fittings and an adequate supply of 

foam concentrate. 

Foam firefighting efforts during mine fires

Due to its unsuccessful use at the Wilberg Mine Fire, UT, in 

December 1984, some doubt has arisen about the effectiveness 

of high-expansion foam for controlling a large underground 

coal mine fire (Huntley et al., 1987). However, there is also 

some question as to whether the optimum foam concentrate 

was being utilized with the foam generator, whether the foam 

concentrate was in proper condition and whether simultaneous 

rock dusting was taking place. Small and numerous particles of 

rock dust can quickly destroy the foam bubbles. In fact, an easy 

and effective way to walk through a plug of foam is to create 

a path by hand-spreading rock dust into the blanket of foam.

Probably the largest attempt to use high-expansion foam 

to fight a very large underground fire occurred at the Orchard 

Valley Coal Mine, CO, in June 1986 (Timko et al., 1987). 

Miners started fighting the fire with a supply of fifteen 208-L 

(55-gal) drums of foam concentrate. Additional foam concentrate was obtained during the ordeal from several other mines 

and a local vendor. Unfortunately, sufficient quantities of foam 

concentrate to quench the fire were unavailable and as soon as 

the concentrate was depleted, control of the fire was lost. It is 

likely that this effort would have been successful if the foam 

concentrate supply were not exhausted. At one point during the 

fire, 1,700 m3/min (60,000 cfm) of high-expansion foam was 

being pumped into the mine through three portals and shafts. 

Since gas chromatograph samples were obtained during the 

initial hours of the fire, valuable information was learned during this firefighting effort. When the foam concentrate supply 

was exhausted, the oxygen decreased and the carbon monoxide 

increased as the fire grew in size and changed from a fuel-starved 

fire to a fuel-rich fire. This indicated the effectiveness of the 

foam in limiting the spread of the fire. Further, the additional 

safety benefit for miners potentially trapped inby a fire while 

a large-scale firefighting effort is underway was apparent due 

to the lower carbon monoxide concentration measured during 

the application of the foam.

The Deserado Mine Fire, CO, in February 1996 (Gore, 

1997) occurred in the tailgate area of a longwall face. The use 

of high-expansion foam was proposed by the operator as part 

of the firefighting plan. However, the plan was not accepted 

by the U.S. Mine Safety and Health Administration (MSHA). 

Several concerns surfaced, including: 1) whether the foam 

plug would travel from the headgate along the face up an 8% 

incline to where the fire was located; 2) lack of information 

on the possible downwind gas constituents as the fire was suppressed by the high-expansion foam and 3) the effect the foam 

plug could have on restricting the ventilation and the potential 

that methane might migrate out of the gob to the fire, creating 

an explosion risk to underground personnel. 

Calculating foam concentrate and water supply 

needs

A few common questions arise regarding the use of highexpansion foam for controlling an underground mine fire, 

including, “What is an adequate water supply?” and “How 

much foam concentrate is required?” In the context of a 24-

hr period, these questions can be answered by considering the 

mine’s characteristics, such as entry size and water supply. 

The following example is used to illustrate how much water 

and foam concentrate would be needed to sustain firefighting 

efforts for Twentymile Mine with a specific foam generator. 

In this example, a Jamison 510 m3/min (18,000 cfm) dieselpowered high-expansion (expansion ratio of 1,000 to 1) foam 

generator is used. According to the operating manual (Jamison, 

1993), this generator requires 500 L/min (132 gpm) of foam 

solution (water and foam concentrate), FS.

The foam concentrate flow rate can be determined by the 

following equation: 

FFR = FS FC (1)

where: 

FFR = Foam concentrate flow rate, L/min (gpm)

FS = Foam solution, L/min (gpm)

FC = Foam concentrate, percent

For this example, for a 2% foam and 500 L/min (132 gpm) 

of foam solution, the flow rate of foam concentrate, from Eq. 

(1), is 10 L/min (2.6 gpm). 

The water flow rate can be determined by the following 

equation:

WFR = FS - FFR (2)

where: 

WFR = Water flow rate, L/min (gpm)

When FS is 500 L/min (132 gpm) and FFR is 10 L/min (2.6 

gpm), the water flow rate, from Eq. (2), is 490 L/min (129 gpm).

For the above example, in one hour of firefighting, approximately 600 L (159 gal) of foam concentrate and 29,400 L (7,770 

gal) of water are required. The amount of high-expansion foam 

produced from these quantities with the 510 m3/min (18,000 

cfm) generator would fill approximately 30,600 m3 (1,080,000 

ft3) of entry. However, foam quality, foam bubble breakage 

and foam turning into steam as the foam plug approaches the 

fire and contacts the burning material will significantly reduce 

the predicted volume. For a 24-hr period, about 705,600 L 

(186,400 gal) of water and approximately 14,400 L (3,800 gal), 

or one hundred and twenty-six 114-L (30-gal) barrels, of foam 

concentrate should be on hand or be able to be acquired from 
other mines or distributors within that period. Table 1 summarizes the above information for the given example. 

Table 1 — High-expansion foam calculations.

Foam generator parameters Requirements for

1 hr, L (gal)

Requirements for

24 hr, L (gal)

m3/min

(cfm)

Foam solution

(water and foam) 

L/min (gpm)

Foam concentrate

WFR , L/min 

% (gpm) Water Foam concentrate Water Foam concentrate

FFR, L/min 

(gpm)

510 500

2

10 490 29,400 600 705,600 14,400

(18,000) (132) (2.6) (129) (7,740) (159) (186,000) (3,800)

Underground high-expansion foam experiments

In partnership with the Twentymile Coal Company (Oak 

Creek, CO), a series of experiments was conducted with highexpansion foam in underground mine passageways. Twentymile Mine is a slope mine that uses continuous and longwall 

mining methods to extract the Wadge Seam, a high-volatile C 

bituminous coal. Only the most significant tests are described 

in this section, with three scenarios reviewed to represent the 

different experiments.

Scenario 1 – Foam propagating up dip against the 

ventilation pressure. The objectives of the experiment were 

to evaluate the following: 1) a partition (constructed from wire 

mesh, brattice and roof jacks) that can be used with a Jamison 

510 m3/min (18,000 cfm) diesel-powered high-expansion 

foam generator (shown in Fig. 1) and a Kennedy steel panel 

stopping erected in an adjacent entry; 2) foam leakage around 

a stopping door into the beltline and 3) propagation rates of 

high-expansion foam moving a distance of 304.8 m (1,000 

ft) against the ventilation pressure and up an average slope of 

20% with steep downward pitching crosscuts of 17% into the 

adjacent entry. 

Figure 1 — Jamison 510 m3/min (18,000 cfm) high-expansion foam generator with 

attached expandable shroud and screen.

 Fig. 2 depicts the underground entries where 

the experiment was conducted. 

Table 2 — Airflow measurements.

Entry No.

Entry cross-section, 

m2 (ft2)

Airflow, m3/min (cfm)

No partitions Partition No. 3 entry

Partitions Nos. 3 and 2 

entries

1 17 (180) 518 (18,300) 960 (33,900) 4,020 (142,000)

2 18 (197) 1,720 (60,800) 2,410 (85,100) leakage

3 17 (180) 2,000 (70,500) leakage leakage

The foam generator and partition were positioned in the No. 

3 entry, approximately 15.2 m (50 ft) outby a crosscut. This 

location is noted as the origin of the scale at 0,0. A Kennedy 

steel panel stopping was constructed in the No. 2 entry, again 

15.2 m (50 ft) outby a crosscut. The beltline was located in 

No. 1 entry. This entry was mainly used for personnel travel 

in the test area. Table 2 gives the cross-sectional area and the 

airflows in each entry, before and after the partitions were in-
stalled in Nos. 3 and 2 entries. The airflow was measured with 

a handheld vane anemometer where the partitions were to be 

built in Nos. 3 and 2 entries. As seen in the table, the airflow 

was significantly increased in the beltline when partitions were 

constructed in Nos. 3 and 2 entries.

Figure 2 — Diagram of underground foam test site with the 

generator located near the bottom of the upward-sloping 

No. 3 entry.

Magnehelic gages were mounted near the roof on the inby 

side of the foam generator partition, at the Kennedy stopping, 

and at the stopping door of the first outby crosscut in No. 1 entry, 

to measure the pressure differential due to the production of the 

high-expansion foam. Each inlet tube for the Magnehelic gage 

protruded through a hole in the partitions to the opposite side 

(foam side) and pointed towards the floor. Mine rescue team 

members, wearing breathing apparatus to simulate an actual 

emergency, monitored the readings at 2-min intervals during 

the experiment. Rescue team members, also under apparatus, 

recorded the time that the leading edge of the foam plug reached 

key areas, such as the crosscuts in each of the two entries.

Based on measurement of the mine entries (including the 

crosscuts) and the foam generator output, it was estimated that 

approximately 11,700 m3 (413,000 ft3) of mine passageways 

were to be filled with high-expansion foam in 23 min. The 

calculations from Eq. (1) indicated that the foam concentrate 

flow rate for this foam generator is 10 L/min (2.6 gpm) and, 

thus, about 228 L (60 gal) of foam concentrate would be required 

to completely fill the mine entries, assuming no foam losses. 

Figure 3 shows the fire brigade members constructing a 

partition for the foam generator in the No. 3 entry. 

Figure 3 — A partition being built for the foam generator.

 Once the 

foam generator was brought underground and positioned in 

the center of the entry (Fig. 3a), it was then leveled and a 

functional test was conducted. The shroud and screen assembly were pulled away from the generator to its operating 

position. The screen assembly was fixed to the floor in the 

center of the entry with roof jacks, as shown in Fig. 3b. After 

being secured to the floor, additional roof jacks were mounted 

in the entry adjacent to both sides of the screen assembly. Two 

sections of wire mesh, 1.5 m high by 6 m wide (5 ft high by 

20 ft wide), were then secured to the screen assembly, roof 

jacks and the two ribs, facing away from the foam generator. 

Once secured with wire ties, hose clamps and spads, the wire 

mesh was cut away from the screen assembly, so that it did not 

interfere with the foam production. Brattice, shown in Figure 

3c, was mounted to the wire mesh structure and to the ribs and 

then cut away from the rectangular 1.4-m-high by 1.8-m-wide 

(4.5-ft-high by 6-ft-wide) screen assembly to allow the foam to 

flow through the partition. Figure 3d shows the polyurethane 
foam applied to the perimeter of the brattice and wire mesh 

partition (roof, floor and ribs) to reduce foam leakage. A 15-

cm (6-in.) diameter drainpipe was laid on the low side of the 

entry on the floor, and extended 9 m (30 ft) inby (down dip) 

past the partition and foam generator. A row of rock dust bags 

was placed on the mine floor against the partition to direct the 

broken-down foam and water into this drainpipe. This can 

also be seen in Fig. 3d.

Figure 4 illustrates the construction of the steel panel stopping 

in the No. 2 entry by mine rescue team members.

Figure 4 — Construction of a Kennedy steel panel stopping in the No. 2 entry.

 The construction methods were those typically used at the mine. The holes 

for the horizontal rails of the stopping were dug 7.5 cm to 10 

cm (3 in. to 4 in.) deep into both ribs at 45 cm (18 in.) and 90 

cm (36 in.) from the floor and the same distance from the top 

of the roof. Because of the cross pitch of the entry, wooden 

wedges were placed under the bottom of each panel to make 

them level and wooden timber cap pieces were placed at the 

top of the panels. A single panel was also butted up against a 

de-energized power cable. A 15-cm (6-in.) diameter drainpipe 

was laid on the low side of the entry on the floor, and extended 

30 cm (1 ft) inby the stopping. As seen from Table 2, when the 

steel panel stopping was completed, the airflow was diverted 

into the No. 1 entry. The differential pressure across the foam 

generator partition in No. 3 entry was approximately 1.9 cm 

(0.75 in.) of water at the start of the test.

When the rescue team members were in position in the No. 

2 entry with their breathing apparatus donned, the fire brigade 

started the diesel-powered foam generator in the No. 3 entry. 

The foam generator throttle was set to produce an airflow at 

the end of the shroud of approximately 510 m3/min (18,000 

cfm). After a few adjustments with water flows and pressures, 

high-expansion foam was being made with a 2% foam concentrate water solution. Noise levels on the outby side of the 

foam generator partition were quite loud (117 dB); however, 

once the foam started to exit the foam generator shroud filling 

the entry, the sound from the foam generator was completely 

muffled on the outby side. The extent of the high-expansion 

foam plug at 7 and at 13 min into the test is shown in Fig. 5. 

Figure 5 — Foam propagation seven and 13 minutes into the test.

When the leading edge of the foam plug reached the first crosscut 

in the No. 3 entry (Fig. 6) the foam started rolling down the 

steep pitching crosscut into the No. 2 entry as expected. The 

foam plug continued to flow down the No. 2 entry to the steel 

panel stopping. Once the foam plug started filling up the No. 2 

entry, the foam plug in the No. 3 entry once again continued to 

advance. The pressure differentials across the generator partition, Kennedy steel panel stopping and the stopping door in 

the first outby crosscut in the No. 1 entry, were approximately 

5.8 cm (2.3 in.) of water 13 min into the test.

The leading edge of the foam plug on the floor led the foam 

plug at the roof by about 6 m (20 ft) throughout the experiment, as shown in Fig. 7. The figure also shows the foam in 

the No. 2 entry flowing through the wooden cribs and into the 
crosscut towards the No. 1 entry stopping. Figure 8 shows 

the position of the foam plug at 23 min and at 30 min into the 

test. As can be seen in Figs. 8 and 9, the leading edge of the 

foam plug in No. 3 entry led the leading edge of the foam plug 

in the No. 2 entry. 

Figure 6 — Leading edge of foam plug in No. 3 entry, 

first crosscut on left.

Figure 7 — Foam plug in No. 2 entry.

Figure 8 — Foam propagation 30 and 23 minutes into the test.

Figure 9 — Leading edges of foam plug in entry No. 2 

and from crosscut on right.

Usually, as the foam flowed down the crosscut from the 

No. 3 entry into the No. 2 entry, the leading edges of both 

high-expansion foam plugs joined within a couple of meters. 

The pressure differentials across the foam generator partition, 

steel panel stopping and the stopping door in the No. 1 entry 

crosscut were approximately 9.4 cm (3.7 in) of water 23 min 

into the test. A few minutes later, foam started to spurt out 

through the bottom of the stopping door in the first outby 

crosscut of the No. 1 entry.

As the high-expansion foam plug was approaching the goal 

of 304.8 m (1,000 ft) in No. 3 entry, plans were being made 

to extend the test to determine exactly how far the foam plug 

would advance. Approximately 32 min into the test, without 

any warning, the foam plug rapidly dropped from the roof to 

within several centimeters from the floor in No. 3 entry, approximately 304.8 m (1,000 ft) from the foam generator. At 

the same time the airflow in the entry increased. It was later 

learned that the steel panel stopping in No. 2 entry had failed. 

The rescue team member who was monitoring the pressure 

gage at the steel panel stopping observed that as the pressure 

increased, popping and cracking sounds were heard. When the 

pressure differential across the stopping reached 12 cm (4.6 

in) of water, the stopping failed and the foam flowed down 

the passageway. Prior to the failure, the two mine rescue team 

members reported that the high-expansion foam was ankle deep 

in that area because foam was leaking from the polyurethane 

seal around the power cable and the drainpipe. When the steel 

panel stopping failed, they were immediately engulfed in foam. 

Team members proceeded into the crosscut leading into the 

beltline and out of the foamed area. A later inspection of the 

stopping indicated that it failed along the bottom. 

Results indicated that 342 L (90 gal) of foam concentrate 

were required to fill approximately 738 linear m (2,420 linear 
ft) of entries, or 11,500 m3 (405,000 ft3) in 32 min. The foam 

propagation rate was 34 m/min (112 fpm) over the first 46 m 

(150 ft) and then averaged 22 m/min (73 fpm) over the remaining distance as the No. 3 and No. 2 entries were being filled. 

The foam plug propagated approximately 304.8 m (1,000 ft) 

in two entries, with an increase in elevation of about 60.9 

m (200 ft) - the equivalent of a 20-story building. The foam 

generator partition and stopping door had minor leaks around 

their perimeters. 

During the experiment, the revolutions per minute (rpm) 

of the diesel engine were increased from 1,700 rpm (start) to 

2,500 rpm (end) to maintain the optimum airflow for foam 

making. This foam generator can produce quality foam at 

pressures up to 25.4 cm (10 in.) of water. Figure 10 shows 

the differential pressure across the foam generator partition in 

No. 3 entry with time. 

Figure 10 — Differential pressure across the foam generator 

partition versus time.

The pressure continued to rise linearly 

with no indication of leveling off until a sharp falloff occurred 

with the failure of the stopping in the No. 2 entry. 

Figure 11 illustrates foam concentrate usage with respect to 

time. 

Figure 11 — Foam concentrate usage rate.

The quantity of foam concentrate used was estimated at 

2-min intervals as the amount extracted from a 114-L (30-gal) 

barrel. The flat portion in the actual data (Fig. 11) was due to 

a delay in replacing an empty barrel with a full one. Note the 

relatively good agreement between predicted foam concentrate 

usage rate and the actual rate of foam concentrate used. The 

triangle on the x-axis indicates the time that the steel panel 

stopping failed. Figure 12 depicts the high-expansion foam 

plug filling the volume of the mine passageways with respect 

to time. 

Figure 12 — Volume of foam that filled mine entries 

versus time.

 The predicted values (circles) illustrate ideal conditions for propagation of the foam plug from the 510 m3/min 

(18,000 cfm) foam generator with no foam loss. The actual 

values (diamonds) show the real manner in which the highexpansion foam plug propagated through the passageways and 

crosscuts. As time increases, the actual volume of foam-filled 

entries deviates further away from predicted values for these 

mine conditions. 

Approximately 342 L (90 gal) of foam concentrate were 

required to fill the mine entries compared to the estimate of 

228 L (60 gal), a 114-L (30 gal) or 50% increase. This was 

mainly due to foam bubble breakage on dry surfaces and foam 

leakage. The weight of the foam plug being up dip from the 

generator would also compress the plug. These data clearly 

indicate the need to consider foam losses when estimating 

the amount of concentrate to fill a known mine volume with 

high-expansion foam.

Overall, the test showed that high-expansion foam (expansion ratio 1,000 to 1) could propagate in steep upward dual 

entries and that under these conditions the stoppings that contain 

the foam need to be well-built. The stoppings separating No. 

1 and No. 2 entries were constructed from dry stacked cinder 

block and coated with a plastic sealant that contained fibers 

for better bonding. These stoppings were constructed previously and were in an area of significant roof convergence. The 

pressure differential across the cinder block stopping in No. 1 

entry crosscut was similar to that of the steel panel stopping, 

and there was also some water that accumulated behind the 

stopping. The loss of a critical stopping while applying foam 

to control a fire could alter the ventilation and result in fire 

gasses being swept back over the fire site, creating a potential 

explosion risk. It should also be noted that stopping doors need 

to be secured. In previous experiments, the foam plug pushed 

open unsecured stopping doors. The test also demonstrated the 

need to account for foam losses when estimating the quantity 

of foam concentrate required to fill a mine volume with foam.

Scenario 2 – Foam experiments with an inflatable 

partition. In another test, an inflatable feed-tube partition 

(IFTP) was successfully inflated in an underground mine entry 

(7% up dip slope) in an airflow of 47 m/min (155 fpm). The inlet 

shroud to the IFTP was connected to a Mine Safety Appliance 
Company (MSA) 680 m3/min (24,000 cfm) high-expansion 

foam generator. After the foam plug reached 23 m (75 ft) (in 

less than 2 min), excessive water accumulated in the shroud 

and water and foam spurted out of the generator’s air intake. 

The generator was stopped and water in the shroud released. 

The experiment continued and the foam plug advanced to 35 

m (115 ft), when the same problem occurred. The pressure 

differential across the generator at this time was 2.3 cm (0.9 

in) of water.

After discussions with mine personnel on the cause of the 

failure, the test was stopped. Visual observations of the foam 

plug revealed that the foam was very dense, similar to shaving 

cream. Several suggestions were offered on the probable cause: 

defective water sprays on the generator, incorrect percentage 

of water and foam concentrate, transport of the foam concentrate during extremely cold weather and a recent additive to 

the mine water supply to increase its wetting ability. Water 

samples were collected and analyzed and MSA was contacted 

to evaluate the foam generator. 

The underground water supply for Twentymile Mine is 

obtained from three independent aboveground sources, and 

varies considerably in hardness from 700 mg/L up to 3,100 

mg/L (200 mg/L is normal for drinking water). Previous experiments showed that a 2%, high-expansion foam concentrate 

produced quality foam with the MSA 680 m3/min (24,000 cfm) 

foam generator. However, follow-up experiments showed 

that poor quality foam was produced with the same generator 

and concentrate. Samples of the foam concentrate were tested 

by the manufacturer, who indicated that the concentrate was 

not compromised and that the foam generator was operating 

within specifications. Water tests showed that the sample collected was extremely hard and not compatible with the foam 

concentrate. A saltwater foam concentrate for the hard water 

was recommended. In spite of the problems encountered, it 

was important that these issues surfaced during testing rather 

than during a mine fire.

Scenario 3 – Foam propagating down dip with the airflow. 

Due to the water and foam quality issues previously described, 

experiments were conducted to determine the effectiveness of 

two types of foam concentrates with the Jamison 510 m3/min 

(18,000 cfm) high-expansion foam generator. Two underground 

tests were performed in a downward sloping (4 to 5%) entry 

with crosscuts about every 30.4 m (100 ft). A Kennedy steel 

panel stopping and a brattice curtain were used to isolate the 

foam plug from the generator, and the airflow in the entry was 

diverted through the inlet of the generator after the partition was 

erected. The average dimensions of the passageway were 3.0 m 

high by 6.7 m wide (10 ft high by 22 ft wide). Approximately 

114 L (30 gal) of 2% foam concentrate and 80 L (21 gal) of 2% 

saltwater foam concentrate were used. The entry was washed 

down before and after each test. A Magnehelic gage (0-5 in. of 

water) measured the pressure differential across the partitions. 

The results of the experiments are shown in Table 3.

Table 3 — Tests of high-expansion foam (HEF) propagating down dip – 510 m3/min (18,000 cfm) generator.

Foam concentrate

Rate of

foam advance

[First 152.4 m 

(500 ft)],

m/min (fpm)

Time foam 

concentrate

depleted,

min

Rate foam 

concentrate 

used,

L/min (gal/

min)

Length of

foam plug,

m (ft)

Linear ft of 

foam filled 

entry

per L (gal) of 

concentrate

Max. pressure

differential,

cm (in) of H2O

2% HEF;

114 L (30 gal)

29.3

(96) 10.7

10.6

(2.8)

278

(839)

106

(28)

2.8

(1.1)

2% HEF saltwater;

79.5 L

(21 gal)

20.4

(67) 8.4

9.5

(2.5)

229

(750)

136

(36)

1.6

(0.65)

 In both tests, the crosscuts were filled and the high-expansion 

foam started leaking back through the partition and over the 

foam generator. The results indicated that with the water supply used, the foam quality produced by both concentrates was 

good, with the 2% saltwater concentrate producing finished 

foam that filled about 20% more entry per liter than the 2% 

high expansion foam concentrate. However, to ensure that high 

quality foam is produced with any of the three aboveground 

water sources, the use of saltwater foam concentrate should 

be considered.

Additional considerations

Additional topics, not covered here, need to be considered 

for high-expansion foam generators to be used with greater 

confidence during a large underground mine fire. These include: 

1) the significance of the water-gas reaction that could occur 

when the foam reaches a hot coal fire and turns into steam that 

reacts with carbon, producing combustible gases (C + H2O →

CO + H2); 2) a practical method to generate high-expansion 

foam with an inert gas, such as N2, to replace the present foam 

that contains air and 3) the preparation of a handbook related 

to foam generation and propagation guidelines for various 

mine configurations (up dip, down dip, with and against the 

mine airflow, in a dead-end entry) and examining mine fire 

scenarios for which more than one foam generator could be 

used. Such information would be used to define optimum and 

limiting conditions for combating underground mine fires with 

high-expansion foam.

Summary

High-expansion foam is a means of conveying water to 

remote areas of mine passageways to control fires. However, 

before a high-expansion foam system is implemented, the mine 

operator must consider the training and equipment required to 

use foam, foam generator partitions and the type and amount of 

foam concentrate to have available. Results of the Twentymile 

Mine tests indicated the following:

• A properly designed, maintained and operated highcapacity foam generator can propagate a high-expansion 
foam plug at least 304.8 m (1,000 ft) in steep (20%) 

upward multiple entries against a ventilation pressure. 

• The actual amount of foam concentrate required to fill 

a given volume of mine entry with high-expansion 

foam could be significantly more than the estimated 

amount. This is due to the mine-specific conditions, 

bubble breakage and foam compression. In the in-mine 

tests in steep upward sloping multiple entries described 

in this report (Scenario 1), the actual amount of foam 

concentrate required to fill about 738 linear m (2,420 

linear ft) of entries exceeded the predicted amount by 

50%—228 L (60 gal) predicted, 342 L (90 gal) actual.

• Temporary and permanent stoppings need to be wellconstructed to minimize foam leakage and withstand 

the pressure created by the foam plug. Foam generator partitions and other stoppings may require a drain, 

especially in upward sloping entries, to relieve water 

buildup behind the structures. Stopping doors need to 

be well-secured or the foam plug can force the door 

open and allow the foam to pass through.

• Compatibility issues of the high-expansion foam concentrate and water supply, such as water hardness and 

acidity, must be addressed to ensure the production of 

high-quality finished foam. Foam concentrate should 

be stored at recommended temperatures.

• On-site foam generators must be tested underground at 

regular intervals to ensure their proper operation and 

maintain the skill levels of the operators. The mine 

should have a strategy for fast response and a group 

of well-trained miners ready on all shifts for an emergency situation. 

Dedication

This report was initially prepared by Ronald S. Conti and is 

dedicated to his memory. Ron passed away unexpectedly on 

October 28, 2003. His efforts to enhance the training, safety, 

and effectiveness of mine emergency responders have been 

recognized worldwide.

Acknowledgements

The authors wish to acknowledge the contributions of Gary 

Braselton and the fire brigade and mine rescue team members 

from Twentymile Coal Mine who assisted with the experiments.

Disclaimer 

The findings and conclusions in this report are those of the 

author(s) and do not necessarily represent the views of the 

National Institute for Occupational Safety and Health (NIOSH). 

Mention of any company or product does not constitute endorsement by NIOSH.

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