Validation of the Ventgraph program for use in metal/non-metal 

mines 

C.J. Pritchard 

National Institute for Occupational Safety and Health (NIOSH), Spokane, Washington, USA 

ABSTRACT: The mine ventilation program Ventgraph has been utilized and validated extensively in coal mines 

in Europe, Australia, and the United States. Ventgraph is used for studying coal mine fires, fighting fires with 

inert gases, spontaneous combustion, and mine emergency exercises. However, it has been used to a much lesser 

extent in metal/non-metal (M/NM) mines. Its application to hardrock mining methods would be beneficial for 

studying M/NM ventilation effects, mine evacuation training, risk analysis of potential mine ventilation changes, 

airborne contaminants, recirculation, and mine fires. In order to determine its applicability to M/NM mine fire 

modelling, Ventgraph was utilized to simulate the 1972 Sunshine Mine fire, where 91 miners perished. The 

Sunshine Mine was selected due to its deep, complex ventilation system, involving ventilation thermal effects and 

recirculation not normally found in single-level coal mines. Information sources such as the United States Bureau 

of Mines (USBM) accident reports, ventilation surveys, books, and publications were examined to recreate the 

pre-fire Sunshine Mine ventilation system. Next, Ventgraph’s network and fire simulation were run using 

assumptions from a USBM contract report to re-create the early stages of the mine fire and contaminant flow. 

Options to better control the ventilation system, evacuation, and early mine rescue attempts were tested. 

Calibration of Ventgraph’s fire simulation module to known events of the fire showed close correlation to 

contaminant levels observed and real-time movement of fire combustion products through the mine. This study’s 

conclusions validate the use of Ventgraph in a deep M/NM mine fire and illustrate its use as a valuable tool in 

mine ventilation, fire, and evacuation planning. 

1 Introduction 

In 2008, the National Institute for Occupational Safety and 

Health (NIOSH) began a research project to reduce the 

incidence rate and severity of fires in metal/non-metal 

(M/NM) mines and to reduce the potential consequences 

of fires in M/NM mines through a better understanding and 

consideration of the products of combustion (e.g., smoke 

and heat) in ventilation and escape planning. 

After examining the available ventilation modelling 

programs for mine fire simulation capability, NIOSH 

researchers chose Ventgraph, developed by the Polish 

Academy of Sciences (Wala et al., 1995, Dziurzynski et 

al., 2006). Ventgraph includes features similar to other 

ventilation programs, such as network simulation and 

contaminant dispersal, but also has additional capabilities 

such as mine fire simulation, compressible flow modelling, 

and real-time on-screen visualization of mine ventilation 

and fire effects. In addition, Ventgraph offers modellers 

considerable flexibility for displaying multiple fire product 

gasses, ventilation system pressures, airflows, and other 

information important to mine safety professionals. Most 

importantly, Ventgraph models can be halted anytime 

during execution, allowing for on-screen changes to 

ventilation system parameters such as fire intensity, 

ventilation structure adjustment, and fan operation. This 

feature is especially beneficial for training, mine 

evacuation, and fire fighting options. 

To demonstrate the capabilities of Ventgraph for 

modelling a M/NM operation, the 1972 fire at the 

Sunshine Mine in Kellogg, ID, was chosen. Ninety-one 

miners lost their lives at the Sunshine Mine, making it the 

second worst hard rock mining disaster in U.S. history. 

The Sunshine Mine fire also represents a turning point in 

public attitude towards mine safety, helping to trigger the 

passage of the Mine Safety and Health Act of 1977. Unlike 

previously studied coal mine fires, the Sunshine Mine was 

a deep operation influenced by significant natural 

ventilation thermal effects (Wala et al., 1995). The 

Sunshine Mine had a complex ventilation system 

incorporating two surface main fans, eleven underground 

booster fans, and compressed air injection. The 

underground booster fans caused high pressure 

differentials, leakage, and recirculation. This, coupled with 

fire-induced bulkhead failures, contributed greatly to the 

large number of fatalities. In essence, due to the above 

factors, the smoke could not be cleared from the mine in 

an effective manner. 

The Sunshine Mine fire had been previously modelled 

by early digital ventilation programs (Hall et al., 1977), 

but without inclusion of fire combustion products and 

thermal effects. At that time, mine ventilation programs 

balanced airflows and pressures, but did not have the 

capability to model mine fire effects and flow of 

combustion products. Natural ventilation effects could be 

calculated and manually inserted into the network. 
 

Since the early 1970s (Greuer, 1977), the United States 

Bureau of Mines (USBM), in cooperation with Michigan 

Technological University (MTU), pioneered efforts to 

define mine fires, their effects on mine ventilation systems, 

and to develop the MFire software to aid ventilation 

engineers in modelling mine fires (Laage et al., 1995). 

Support for MFire was severely reduced with the 

elimination of the USBM in 1995. NIOSH has recently 

begun updating the MFire program code (Yuan, 2008). 

A new generation of ventilation programs that include 

user friendly data entry and graphics has evolved in the 

last 20 years, of which Ventgraph is one. Ventgraph’s 

capabilities to simulate mine fires and make changes in 

real-time make it a valuable tool and its abilities have been 

extensively tested in coal mine applications. The 

opportunity to apply these tools to deep metal mines is 

attractive and a potential benefit to the health and safety of 

underground M/NM miners. Using previous ventilation 

modelling data with Ventgraph will hopefully validate its 

usefulness in this difficult environment which includes 

mine heat sources, natural ventilation effects, fire thermal 

effects and flow of contaminants through the mine. 

2 Description of the Sunshine Mine fire 

2.1 Ventilation System 

An effective model of the Sunshine Mine fire requires an 

understanding of the ventilation system and the sequence 

of events during the fire and rescue. Therefore, this section 

will describe the underground mine and summarize the 

initial fire events. 

The Sunshine Mine was located west of Kellogg, 

Idaho, in the Silver Valley of the Coeur d’Alene mining 

district. Figure 1 shows a schematic of the ventilation 

system at the time of the fire.

Figure 1 Sunshine Mine ventilation and escape system. 

 Primary access to the mine 

was through the Jewell intake shaft at 823 m elevation 

MSL to the 3700 Level (elevations are depth below shaft 

collar in feet), across this level approximately 1.6 km east 

by track haulage to the underground winze vertical No. 10 

Shaft (10 SH) and then to lower work areas. At that time, 

10 SH was extended to the 5800 Level. Raises were 

connected east and west of 10 SH as secondary 

escapeways. Most support services were located on the 

3700 Level at 10 SH. These services included the fourdeck “chippy” cage operated from the 3700 Level, a larger 

double drum hoist that could hoist 9 men was located 

above on the 3100 Level (secondary escapeway), pipe 

shop, supervisor’s office, safety room, maintenance shop, 

electrical shop, and substation. 

Intake air was coursed down the Jewell shaft, across 

the 3100 Level and 3700 Level to 10 SH, and down to the 

working areas. Air was distributed to the levels by booster 

fans. Additional air to the work areas was provided by 

compressed air from the surface. Exhaust return air from 

the bottom workings was coursed up east and west of 

10 SH shaft through raises and ultimately joined on the 

east side of 10 SH at the 3400 Level, where mine level 

boosters were installed immediately above the 3700 Level 

shop areas. The return air proceeded west, then up No. 3 

Shaft (3 SH) to other booster fans at 1900 Level, and to 

surface exhaust fans at 3 SH and Big Hole. 

A new recently completed raise, the No. 12 Shaft 

borehole, (12 BH) located off the Jewell shaft at 

3700 Level was connected to the west end of the 

4800 Level. This raise was planned to be widened and 

used as an intake airway to the lower mine. 

The location of the 3400 return airway between two 

intake levels, combined with high booster fan pressures, 

caused leakage primarily between the 3400 and 

3700 Levels. Because this problem was noted in the fall, a 

1971 USBM ventilation survey (Foster & Andrews, 1971) 

at the time of the fire the USBM’s recommendations to 

reduce leakage and improve mine airflow capacity were 

being carried out 100 m (340 ft) west and downwind of the 

3400 Level booster fans. Further, at the time of the fire, the 

3400 return airway was being enlarged and leakage 

prevention work was being performed. This work involved 

sealing wooden bulkheads between levels that isolated 

mined-out stopes and sealing raises that contained mine 

waste and combustible materials. Drift areas west of the 

3400 Level booster fan installation were smooth-lined with 

wood stulls, covered with plywood and asphaltic mastic, 

and sealed with polyurethane foam to promote smooth 

airflow through airways with rough walls (Day, 2007). 

3 Fire Event 

On May 2nd, 1972, at around 11:40 a.m. after the lunch 

break, smoke was discovered in the 3700 Level shop and 

office area close to the underground hoist at 10 SH. 

Management officials in the nearby office were notified 

immediately. Smoke was traced to about 270 m west of 

10 SH, emanating from the 910 raise (910R), indicating 
 

that the fire was located above the 3700 Level. As per the 

mine fire procedures plan, the decision was made quickly 

to evacuate the mine using the 3100 Level secondary 

escapeway, and to close the fire door to the west on 

3700 Level by the Jewell shaft (Figure 1). Mine 

supervisors feared the smoke would contaminate the intake 

air to the lower levels. 

At noon, surface employees were notified of the fire 

and told that mine evacuation had begun, and the safety 

engineer was directed to bring the McCaa mine rescue 

breathing apparatuses to the 3100 Level. This level was 

where the evacuating miners would be sent, avoiding the 

3700 Level smoke. The 3700 Level was the primary 

travelway into and out of the mine used by miners. Stench 

gas was released into the surface compressor system to 

notify miners of evacuation at 12:05 p.m. Smoke was 

observed coming from the mine exhaust on the surface at 

that time. Underground, smoke levels increased and spread 

quickly from the 910R raise into intake air on the 

3700 Level, and into the active mine workings below. 

At about 12:15 p.m., miners evacuating on the 

3100 Level to the Jewell shaft encountered light smoke 

caused by recirculation from the 3400 Level booster fans 

below. Around 12:18 p.m., an examiner on a routine check 

of the 1900 Level return fans above encountered 

impassable smoke, precluding access to the upper level 

return fans. By 12:30 p.m., smoke was leaking from 

multiple bulkheads into the 3100 Level, inhibiting 

evacuation. Due to smoke-reduced visibility and 

unfamiliarity with the evacuation route on 3100 Level 

(Note: 3700 Level was the primary route), many miners 

had difficulty finding their way out. 

When the McCaa breathing apparatuses arrived at the 

3100 Level at 1:00 p.m., carbon monoxide (CO) levels 

over 3000 ppm were measured by the rescue team 

advancing towards 10 SH near No. 5 shaft. The last cage 

was hoisted to the 3100 Level just after 1:00 p.m., at which 

time the hoist operator was overcome by CO. The rescue 

team encountered and brought out two miners from the 

12:43 p.m. hoist load, and one of those rescuers perished 

due to cumulative CO exposure. 

Miners evacuating on the lower 3700 Level had closed 

the fire door east of the Jewell shaft at 12:00 noon, then 

later (1:15 p.m.) opened the cover that restricted airflow 

down the recently completed 12 BH raise near the Jewell 

shaft and 3700 Level (Figure 1). The 3700 Level was 

connected to the lower levels of the mine at the west end 

of the 4800 Level. This change provided by the open shaft 

would supply the only fresh air, although in small 

quantities, toward the 10 SH area. Saved by this single 

split of fresh air, two survivors were found eight days later 

by rescuers using an emergency hoist capsule down the 

12 BH to 4800 Level. 

4 Modelling 

4.1 References Used 

Information used to generate the Sunshine Mine network 

for Ventgraph was acquired from multiple sources. J.W. 

Andrews (2008), former Mine Safety and Health 

Administration (MSHA) and USBM ventilation engineer, 

maintained an extensive file on the incident. He also 

participated in the original USBM ventilation surveys 

(Foster & Andrews, 1972) of the mine, and the USBM 

Contract Report (Hall et al., 1977) on Ventilation Analysis 

of the Circumstances of the Sunshine Mine Fire. Contract 

participants were ventilation experts from the Colorado 

School of Mines, University of Idaho, MTU and the 

Pennsylvania State University. Other information was 

gleaned from the USBM Final Report on Major Mine Fire 

Disaster, Sunshine Mine (Jarrett et al., 1972), the books 

The Price of Silver (Day, 2007) and The Deep Dark 

(Olsen, 2005), and the online report, The Sunshine Mine 

Fire Disaster – A View from the Inside (Launhardt, 1997). 

These sources were helpful in establishing and 

corroborating timelines during initial stages of the fire and 

evacuation. 

4.2 Modelling Process Used 

Airway data (airflow, resistance, airway, and junctions) 

were generated from the MTU contribution to the USBM 

Report (Hall et al., 1977). The Penn State University and 

University of Idaho also modelled the Sunshine fire and 

their data sets from this report provided equivalent 

confidence when compared to each other and thus would 

have provided similar results if used. 

Airways (Hall et al., 1977) were not to scale and data 

needed for establishment of contaminant transient times 

were unavailable. Data were correlated from USBM 

Report descriptions and schematics to full-scale digitized 

mine drawings (Andrews, 2008). Airway locations were 

determined from descriptions and manually scaled. 

Mine temperature data are required by Ventgraph for 

determination of natural ventilation and fire thermal 

effects. Information on temperature was gathered from 

1971 USBM ventilation survey measurements. These 

temperatures may have been lower than at the time of the 

fire in May; nevertheless, they would not have 

significantly altered the natural ventilation effects and 

airflows in the fire area, and the same data were used by 

Hall et al. (1977). Temperature and elevation data were 

input for each junction, and barometric pressure was 

computed from standard atmospheric tables at elevation 

and not corrected for in-mine pressures. 

5 Model Development 

5.1 Network Model Comparison 

The 1977 USBM model data was modelled in Ventgraph 

with airflow results comparing within 1.6%. Efficiency 

was calculated by summing the differences between 

Ventgraph and the USBM model airflows, and dividing by 
 

 

the sum of all airflows. Because all three USBM 

researcher’s models were comparable, the Ventgraph 

model was believed to provide a good correlation to the 

initial Sunshine conditions. The MTU/USBM model 

utilized fixed pressure airways for fans (no fan curve), 

assuming no short-term change during the initial fire 

stages. As per the USBM ventilation survey estimate, 

mixed-quantity injection airways were used to simulate 

compressed air for mining work areas in multiple 

locations. 

5.2 Ventgraph Fire and Fan Simulation 

Based on the USBM accident investigation, the fire was 

located in the upper 910R (Figure 1). Ventgraph allows for 

the choice of fuel (oil, wood, coal, or belt) for heat value, 

length of fire, and relative fire intensity in the range of 

zero through ten (Dziurzynski et al., 2006). Concentrations 

of CO and hydrogen in combustion products are given as 

10% and 1% respectively as a default value, but may be 

modified. Fire ramp-up time from start to full strength is 

specified by the operator. Specific modelling choices made 

by the author will be discussed in Section 5.2. 

An important asset of Ventgraph is that real-time 

simulation can be started and stopped at any time. Fire 

characteristics can be altered, ventilation structures 

installed, resistances changed, and fan operation adjusted 

on the interactive screen schematic. As the simulation 

advances, smoke movement, various contaminant

concentrations changes, and other data may be observed 

visually and in on-screen output boxes. These boxes are 

chosen by the modeller to visualize desired specific 

information in real-time. Figure 2 shows a snapshot of 

smoke advance in the early fire stage at the time smoke 

was discovered (arrived) at the 10 SH 3700 Level area at 

around 11:40 a.m. The network schematic view may be 

zoomed in or out for more or less detail. 

Figure 2	 Ventgraph schematic visualization of smoke 

travel at the 11:40 a.m. smoke discovery 

(evidenced by bold airways). 

Because a fixed pressure fan could not be used to 

represent drastic changes in the model caused by a failed 

bulkhead, fan curves for the 3400 Level booster and two 

main surface fans were generated from USBM 

simulations. Non-critical fans were left as fixed pressures. 

Accuracy comparison after fan curves changes was 3.3%. 

6 Examination of References for Fire Details 

6.1 Fire start and smoke arrival times used to calibrate 

fire to observations 

The time of observation of smoke is essential to recreating 

the fire event (Jarrett et al., 1972); (Day 1976, 2007); 

(Olsen 2005); (Launhardt, 1997). The day of the fire, 

downwind (west) of the 3400 Level return booster fans, 

miners were blasting to enlarge the return airway until the 

11:00 a.m. lunch time and did not notice any smoke. 

Miners leaving the 10 SH 3700 Level just after 11:30 a.m. 

traveling west to the Jewell shaft passing by the 910R also 

noticed no smoke. Miners on the 3700 Level stated that 

they first observed smoke at around 11:40 a.m. in the shop 

area (illustrated in Figure 3), and on the upper 3100 Level 

at about 12:10 p.m. At 12:18 p.m., heavy smoke was 

observed in the upper return shafts on the 1900 Level. 

Figure 3	 Visualization of fire area (carbon monoxide 

levels) during the early stages of contamination. 

Ventgraph allows the modeller to follow smoke travel 

through the system to ascertain arrival times. After arrival 

times are known, back calculation to fire start-up may be 

determined, and then modelled to fit observations. Hall et 

al. (1977) envisioned a small fire smoldering until it burnt 

through the bulkhead from the backside, with rapid failure 

and increased fire activity driven by high airflows from the 

short circuit caused by bulkhead failure from the 3400 to 

3700 Levels. 

6.2 Fire Event Sequence Development 

USBM investigators determined that the 910R bulkhead 

failed, but how rapidly and its effect on the ventilation 

system needed to be determined for modelling purposes. 

Experimenting with Ventgraph showed that almost total 

failure needed to occur to force smoke and high CO to the 

lower 3700 Level and overcome fire thermal buoyancy 

forces. 
 

To illustrate this scenario, at a 2007 Trona Mine fire 

incident in which the author participated, a small ember 

flew through a wood bulkhead vent hole, landing in 

between bulkhead cribbing, starting a fire that totally 

consumed the structure in 10 minutes. Pressure across this 

bulkhead from the ventilation system was 1500 Pa (6"wg), 

and after failure 85 m3

/s (180,000 cfm) short-circuited to 

the return. Fire and high pressure differentials can rapidly 

consume a bulkhead and very quickly compromise its 

integrity. The Sunshine Mine 910R bulkhead had twice 

this pressure and was modelled to partially fail 5 minutes 

after the fire began and totally fail in 15 minutes. Hall et 

al. (1977) modelled the failure in increments, but no start 

time or timeframe was given. 

In the simulation, Ventgraph fire intensity settings 

from 1 to 10 were used to vary the fire strength. However, 

no defined heat flow values are given for these ranges, 

which are calculated internally. Various fire intensities and 

lengths (extents) were modelled to obtain CO levels and 

ventilation system effects to correspond to USBM study 

results and observations. To adequately model alternate or 

defined fire scenarios, these values need to be quantified 

by Ventgraph or empirically determined by the researcher. 

In this case, the modelled fire was determined to be 

equivalent to a 35 kW fan source upon the ventilation 

system. Heat was also added to the air and rock, making 

determination of the total fire heat output difficult. 

Using Ventgraph fire modelling tools, the following 

scenario was developed to simulate the initial stages of the 

Sunshine Mine Fire: a “Level 10” intensity wood fire 65 m 

long in 910R raise starting at 11:05 a.m., ramping up to 

full strength in 5 minutes, and the 910R bulkhead totally 

failing in the next 10 minutes with the fire growing to 

100 m and then 200 m in length. This scenario matches 

smoke arrival times and observed CO levels in Hall et al. 

(1977). 

To reach approximately 4,000 ppm CO at the surface 

(Jarrett et al., 1972), a considerable fire is needed. The fire 

simulated above resulted in surface fan return CO levels of 

3,600 ppm, rising slowly after 2 hours. Concentrations at 

10 SH bottom were 1,000+ ppm, which would be fatal to 

life in short time. CO levels on 3100 Level initially were 

500 ppm, deteriorating quickly. These figures seem 

reasonable based on the actual fire conditions. USBM gas 

samples about 30 hours after the fire began at the surface 

exhaust were around 4000 ppm CO. Miners at 400 ppm 

can survive 1-2 hours, with death in 4 hours. At 

1,000 ppm, survival is for 30 minutes with death in 2 

hours. The 1,500 ppm level is immediately dangerous to 

life and health (IDLH) (Hartman, 1961). 

6.3	 Time Events in Final Ventgraph Sunshine Scenario 

Time Event 

11:05	 Start wood fire in 910R, 65 m long, ramp up time 

5 minutes to “Level 10” 

11:10	 Fire increases to 100 m long, 910R bulkhead 

partially failed 

11:15	 Fire increases to 200 m long, 910R further failure, 

08 shop door blown open 

11:20	 Fire constant, 910R wide open 

11:40	 Smoke arrives at 3700 Level and at 08 shop door 

11:42	 Smoke at 10 SH 3700 Level 

11:47	 Smoke arrives at surface 

11:49	 Smoke to bottom of 10 SH 

12:00 	 3700 fire door shut at Jewell Shaft 

12:10	 Smoke leaked into 3100 Level 

12:30	 Electricians hoisted to 3400 Level to wait for 

instructions to turn booster fans off 

1:15	 No. 12 BH cover removed to allow additional 

fresh airflow to 4800 Level. 

Modelling the Sunshine Mine fire in this timeframe 

and intensity gives good correlation to observed smoke 

arrival times, evacuating miner CO exposure, and miner 

behavior. Confidence in the developed base model allows 

further use in analyzing various options regarding the 

effectiveness of choices that were made or could have been 

made during the disaster. 

7	 “What if” Scenarios of the Sunshine Mine Fire 

Model 

NIOSH’s goal is to effectively model mine fires to aid in 

evacuation and fire fighting, minimizing injury, loss of 

life, and risk to mine rescue teams. All these goals fall 

within Ventgraph’s capabilities. “What if” scenarios allow 

for analysis of events prior to, during, and after a fire, 

identifying reactions that would have been better for 

escaping miners and factors that would have aided mine 

rescue teams in fighting the fire and locating survivors. 

The following examples illustrate how Ventgraph was 

used to stop the real-time fire simulation and make 

adjustments to fire strength, location, ventilation 

structures, and fan operation. This approach allows the 

researcher to study the applicability and effectiveness of 

each adjustment. 

7.1	 Turning Off the 3400 Level Booster Fan 

A serious question raised by USBM investigators was why 

the 3400 Level booster fans were allowed to continue 

operating, recirculating contaminated mine air. 

Unfortunately, the fan shared its power supply with the 

10 SH 3100 Level hoist and could not be stopped 

remotely. Further, shutting off that power would have 

eliminated evacuation of miners to the upper 3100 Level. 

The only other power disconnect was at the 3400 Level fan 

location, not on the surface. Electricians were hoisted there 

at 12:30 p.m. and succumbed to CO while awaiting further 

instructions. 

Using the Time Event Scenario outlined previously and 

stopping the 3400 booster fan at 12:35 p.m. would have 

cleared the majority of the 3100 Level roadway in less 

than 15 min. The CO level at the 10 SH hoisting station 

remained at approximately 140 ppm for over 80 minutes 

until clearing. Hoistmen and personnel at that location had 

nearly all succumbed to CO by then. Most of the miners 
 

that were hoisted on the last trip at 12:45 p.m. did not 

make it out and may have had too high a CO saturation 

level by then. Lower in the mine, 1000 ppm CO was still 

arriving at the 4800 Level 34 min after the fan could have 

been stopped, with 737 ppm after an hour, indicating that 

the working levels of the mine continued to be heavily 

contaminated. Even after the change, smoke still 

occasionally pulsed into the 3700 Level travelway from 

910R and fire above. 

With quick booster fan stoppage, CO levels would 

have improved to allow a better chance of escape if miners 

could have gotten to the 3100 Level and partway towards 

the Jewell shaft to escape localized contamination. 

The improved conditions on the 3100 Level may have 

allowed Sunshine Mine rescue personnel to access the 

hoist room with the McCaa apparatus and continue 

evacuation and travel down into the mine much more 

quickly. Continued booster fan operation surely 

contributed to maintaining a high fire level by supplying 

increased oxygen to combustible material in mined-out 

stopes and the subsequent deterioration of the mine 

workings that impeded rescuers. 

It should be noted that shutting down main fans is a 

difficult decision, especially for supervisors in the mine, 

who are often without essential information regarding the 

emergency. As a comparison, it took the USBM officials 

over five days to decide to turn off the same fans. 

7.2 Opening and Closing Jewell Shaft Fire Doors 

Evacuating miners on 3700 Level closed the Jewell shaft 

fire door around 12 noon as per the Sunshine Mine Fire 

Plan. This action forced more air across the 3100 Level to 

aid evacuation, but actually increased contamination on 

3700 Level and to the lower mine. 

Later, USBM investigators asked if closing the fire 

door was the correct choice. The question was posed: 

“Should the doors have been left alone, or shut on the 

3100 Level and reopened on the 3700 Level, as was done 

by rescue crews at around 1:30 p.m. when they left the 

mine?” 

Analysis by Ventgraph showed that the best choice to 

maintain fresh air supply to the 3100 Level was to close 

the 3700 Level door per the Sunshine Mine Fire Plan. If 

both doors would have been left open, the 3100 level 

escape route would have suffered from reduced dilution, 

and CO would have increased by almost 70%. Ventilation 

in the lower mine would have been aided by the increased 

airflow and CO would have been reduced by 40%. 

However, since the evacuation was directed toward the 

3100 level, this decision to close the 3700 Level door was 

the correct choice at that time. 

If the 3100 Level door had been shut instead of the 

door at the 3700 Level, CO would have more than doubled 

on the 3100 Level; however, the lower mine areas would 

have seen a decrease in CO due to more air bypassing the 

fire zone. This would have precluded using the 3100 Level 

as an escape route, and neither of the hoist operating sites 

would have had a survivable atmosphere. Miners might 

have survived longer below, but hoist operators and others 

on the 3100 Level would have perished sooner with any 

other door option than the one chosen at the time of the 

disaster. 

The combination of turning off the 3400 Level booster 

fans when electricians were hoisted to the fan level 

(12:30 p.m.) and leaving both doors open would have been 

the best choice. This would have had the effect of rapidly 

lowering CO on 3100 Level from 551 ppm to 260 ppm in 

30 minutes, and to 94 ppm in 45 minutes. This action 

would have been too late for the hoist operator and miners 

at 10 SH, but it may have allowed rescue personnel to 

make it to the 3100 Level hoist room to evacuate more 

miners. It also may have allowed others to escape on the 

3100 Level as conditions would have improved towards 

the Jewell Shaft. Any option that shut the 3400 Level 

booster fans off regardless of fire door choices would have 

improved CO levels deep in the mine due to less 

recirculation of fire combustion products into intake air. 

7.3 Opening the No. 12 BH Cover Earlier 

Opening the 12 BH cover at 1:15 p.m. increased airflow to 

the lower west mine from 0.9 to 2.1 m3

/s, and was the only 

source of fresh air to miners near 10 SH waiting for 

evacuation. The survivors’ safe location was west of the 

shaft, where fresh air arrived from the west and return air 

from the level below flowed up the return raise system. 

Investigators asked the question: “What would be the 

benefit of opening the shaft cover earlier than 1:15 p.m.?” 

The earliest it could have been changed was noon, which 

will be the reference point. 

Based on the Ventgraph analysis, opening up the 

12 BH earlier would have only provided a slight advantage 

of 90 vs. 87 ppm CO at 10 SH on the 4800 Level, where 

the mine atmosphere continued to deteriorate rapidly. 

Airflow down 10 SH is reduced and CO is at a higher 

concentration with 12 BH open, adding to contamination 

from recirculated lower level air. In the short term, while 

miners were evacuating, opening No. 12 BH intake earlier 

would have made no difference at the. 10 SH assembly 

point nor to the lower mine. 

7.4 Placement of Bulkheads to Fight Fire 

Fire growth on the 3700 Level caused ground failures, 

which severed the main power feeder cable and 

compressed air line. If fumes and heat could have been 

diverted from infrastructure critical to mine evacuation and 

recovery, miners may have been able to be saved, or the 

mine may have been recovered earlier. Simulations were 

run with options for opening or closing the 3100 and 

3700 Level doors to see if airflow could be forced to flow 

from 3700 to 3400 Levels, moving the fire away from the 

3700 Level facilities at the bottom of the 910R. 

Unfortunately, with the 3400 Level booster fans either 

running or turned off, no combination of doors opening or 

closing would accomplish this goal. A stopping would 

have needed to be installed past (east of) the 910R raise to 

force air away from the infrastructure, which could not 
 

have been done by rescue teams for a considerable period 

of time. 

The accuracy of the Ventgraph simulation was only 

deemed valid during the initial stages of the fire before too 

much damage to the ventilation system had occurred. 

Ventilation planners should practice with various bulkhead 

placement scenarios to better prioritize mine rescue efforts 

and protect critical mine infrastructure through control of 

airflow to mine fires. 

8 Summary and Conclusions 

The goal to validate the use of Ventgraph for modelling 

M/NM mine fires has been met by verifying that fire 

contaminants and disruption to the Sunshine Mine 

ventilation system were modelled to a degree of accuracy 

that lends confidence to the software and method in this 

particular case. Fire modelling was especially challenging 

in an application that included considerable natural 

ventilation effects and complex underground booster fan 

pressures and recirculation. These issues cause an increase 

in complexity over previously modelled coal mine 

validations, lending credibility to the results. Additional 

work should be done to further investigate the use of 

Ventgraph in M/NM applications. The ability to assign fire 

locations and vary their intensity, along with changing the 

characteristics of ventilation structures and mine fan 

operation in real-time, proved to be an excellent tool to 

study mine fires in M/NM mines. 

More work needs to be done to understand the 

Ventgraph system of Mine Fire Intensity Levels. The 

arbitrary levels from 0 to 10 are expedient, but they make 

it difficult to design and implement modelling of fires and 

determine what heat levels actually correspond to those 

values. A more detailed user manual would also help 

define the actual heat values derived from the Mine Fire 

Intensity Levels and length of fire input values. Modellers 

also need to be aware that not all fires produce CO and 

hydrogen in the default ratio of 10:1, and modellers must 

obtain accurate estimates of the type of fire envisioned. 

Ventgraph modelling of the early stages of the 

Sunshine Mine fire shows that the fire produced CO levels 

in the fire zone of around 16,000 ppm. Ventilation dilution 

reduced that to approximately 4,000 ppm at the exhaust 

fan, comparing closely with USBM measurements. The 

model’s CO levels in the working areas corroborated the 

toxic effects described in the investigation reports. 

In Ventgraph, the 3400 level booster fan airflows after 

the 910R bulkhead failure did not correspond to USBM 

contractor model results. Ventgraph model airflow was 

lower, possibly due to buoyancy effects from the fire 

acting against and restricting airflow from booster fans 

from the 3400 Level down to 3700 Level. The Ventgraph 

simulation may actually be closer to reality, as the USBM 

researchers did not incorporate fire dynamics into the 

network simulation. 

The Mine Safety and Health Act of 1977 required 

remote control of main fans and a separate fresh air supply 

to underground hoisting chambers, which might have 

made a great difference in the number of survivors at 

Sunshine Mine. Realistically, turning off mine fans is a 

difficult decision and, in most cases, leaving the fans 

running is the best option. Turning the booster fans off at 

12:30 p.m. as discussed by Mine Supervisors underground 

would have greatly reduced CO contamination for miners 

escaping and for those trapped in lower levels. 

Unfortunately, there was insufficient time to save those in 

the area of the mine hoist who already had been exposed to 

high CO concentrations. Turning off the booster fans 

might have also aided rescuers’ access to 10 SH. 

Ventgraph allows engineers and safety professionals to 

model an operation after performing a risk analysis of 

mine fire sources. Once identified, risks can be simulated 

to observe the flow paths of the contaminants and the 

effects on the ventilation system. Exposures for evacuating 

miners may be determined and evacuation routes planned. 

“What if“ scenarios to improve escape opportunities or to 

contain the fire may be examined. Fire fighting and mine 

rescue plans may be deployed to take advantage of this 

knowledge. Mine ventilation plans can be expanded to 

include these exercises. 

Advances in mine ventilation modelling such as 

Ventgraph have provided tools to greatly enhance the mine 

ventilation engineer’s ability to effectively plan for and 

provide support during mine fires. Should a fire situation 

arise, an updated ventilation model for that mine can be 

used to simulate fire and ventilation changes. This could 

provide valuable information to mine engineers, 

management, and regulatory authorities to make better 

informed decisions during the event. 

Disclaimer 

The findings and conclusions in this manuscript are those 

of the authors 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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