RESEARCH REPORT ON REFUGE ALTERNATIVES FOR 

UNDERGROUND COAL MINES 

Office of Mine Safety and Health 

National Institute for Occupational Safety and Health 

Centers for Disease Control and Prevention 

Department of Health and Human Services 

December 2007 

Purpose 

Section 13 of the Mine Improvement and New Emergency Response Act of 2006 

(“MINER Act”), PL 109-236, required NIOSH to conduct “research, including field tests, 

concerning the utility, practicality, survivability, and cost of various refuge alternatives in 

an underground coal mine environment, including commercially available portable refuge 

chambers.” This report summarizes the findings of such research, focusing on specific 

information that could inform the regulatory process on refuge alternatives. Further, gaps 

in knowledge and technology that should be addressed to help realize the full potential of 

refuge alternatives are also identified. 

Scope 

NIOSH’s research on refuge alternatives was limited to underground coal mine 

applications. Historically, the use of refuge chambers has been more prevalent in 

underground metal/nonmetal mines, and some findings from this research may be useful 

for metal/nonmetal application. Notwithstanding, the underlying differences between 

mining sectors are significant and practices in one sector cannot be generalized to the 

other. Therefore, the information provided here is not intended for rote transfer to 

metal/nonmetal applications. 

This research into refuge alternatives for underground coal mines has identified 

knowledge and technology gaps and the need for new training. While this report 

specifically addresses the elements of refuge alternatives that should be considered in the 

regulatory processes, the completion of the research to fully describe and address the 

above issues is ongoing. 

All discussion in the remainder of this report applies specifically to coal mines and coal 

miners, unless stated otherwise. 

Refuge Alternatives 

Historically, miners trapped underground by a fire or explosion have built a “barricade” 

to take “refuge,” i.e., to isolate themselves from the potentially poisonous environment 

and await rescue. These barricades could be concrete block walls or brattice cloth 

1
fastened to the ribs, roof, and floor, and serve to contain a breathable atmosphere for the 

miners while isolating them from contaminated air. Although barricading is reported to 

have been a useful practice in mines near the beginning of the 20th century, NIOSH has 

no evidence to support the practice of barricading in modern mining operations. 

Barricading is not considered to be a viable refuge alternative. 

Two well-known refuge alternatives are chambers, which can be stationary or portable, 

and in-place shelters, such as safe havens, safe rooms, and bulkhead-based refuge 

stations. Another alternative currently under development is an escape vehicle that could 

also serve as a place of refuge. This report will focus on chambers and in-place shelters, 

and many of the findings can apply to refuge alternatives in general. When there is a 

need to distinguish between chambers and in-place shelters, then the specific refuge 

alternative will be named. 

Chambers typically consist of manufactured rigid or inflatable vessels that are outfitted 

with supplies and equipment to sustain life for a period of time. In-place shelters are 

developed by taking an existing part of the mine, e.g. a crosscut, isolating it with one or 

more bulkheads, and then equipping the shelter similarly to a chamber. Chambers are 

manufactured off-site, delivered to the mine, and moved to appropriate locations 

underground, whereas in-place shelters are constructed within the mine. Two common 

ways of constructing an in-place shelter are: (1) installing a bulkhead at each end of a 

crosscut to create an isolated space; or (2) mining a cut into a block of coal and installing 

a bulkhead to isolate this dead-end heading. 

 

1

 The gap areas were identified at the end of the international survey effort, which was performed during 

July through October 2006. The technical part of the contract to address these areas was completed at the 

end of October. The actual contract award, conducted in compliance with the Federal Acquisition Rules, 

was made in March 2007. Work on this contract will continue through 2008. The contractor was able to 

provide key inputs for the preparation of this report to Congress. 

2

Research Activities 

A literature survey was performed to identify the findings from any past research on 

refuge alternatives and topics related to mine refuge and mine disasters, escape, and mine 

rescue. Visits were made to mines, nationally and internationally, and meetings were 

held with mining experts from labor, industry, and government in the U.S., Australia, and 

South Africa to collect information on refuge alternatives and to discuss contemporary 

issues associated with refuge alternatives. A research contract study of existing 

international practices, regulations, and products was conducted, and more detailed 

studies of practices in Australian and South African coal mines were completed under 

two other contracts. However, this work revealed very little information related to coal

mining refuge applications, and several knowledge and technology gap areas were 

identified within the first four months of NIOSH’s research into refuge alternatives. As a 

result, a major research contract was developed and awarded to address the gap areas, 

including guidance for locating and positioning refuge alternatives and establishing 

specifications for chambers and in-place shelters1

. Concurrently, NIOSH researchers 

examined non-mining applications where survival in confined spaces is critical – notably 
civil defense shelters, submarines, and space capsules – in search of guidance for the coal 

mining application. Overall, NIOSH researchers studied a range of practical issues 

associated with refuge (such as movement of chambers from place to place), collected 

cost data on refuge alternatives and performed cost analyses, and conducted testing of 

refuge chamber performance at the Lake Lynn Experimental Mine. 

Separate research projects were initiated as related gap areas were uncovered and the 

research remains ongoing. For example, one project focuses on the development of 

communications technology specifically for use in refuge alternatives, while another 

addresses the development of training modules for using refuge alternatives during 

escape and rescue. As a final example, a series of user booklets are being developed to 

assist mine operators in the location, installation, inspection, maintenance, and 

provisioning of refuge alternatives. The outputs from these projects are expected to begin 

late in 2008 and continue through 2009. 

Report Format 

The remainder of this report summarizes the findings of the research, and it is organized 

into the categories of utility, practicality, survivability, costs, and testing to correspond to 

the areas specified in the MINER Act. Training has been added to this list, as it is 

assessed to be critical to the successful use of refuge alternatives. Detailed supporting 

information and key references are included in the NIOSH docket, organized under 

docket #125. The docket can be accessed at: http://www.cdc.gov/niosh/docket. 

UTILITY 

The usefulness of refuge alternatives to help save the lives of trapped coal miners was 

investigated as part of the research. An analysis of historical mine disasters was 

performed to assess the effect that the presence of refuge chambers might have had in the 

outcome of these disasters. The results of this analysis are mixed. Given the overall 

small number of disasters and the specialized and mine-specific circumstances under 

which they occurred, it is difficult to make a strong case for or against a specific refuge 

alternative, or even for or against the efficacy of trapped coal miners taking refuge. 

Nevertheless, recent mine disasters have again focused attention on the utility of refuge 

alternatives, and it has been argued that the availability of refuge alternatives may have 

been useful in these disasters. 

The usefulness of refuge chambers has been debated in the U.S. at least since the passage 

of the Coal Mine Health and Safety Act of 1969, PL 91-173. Despite significant research 

by the U.S. Bureau of Mines nearly 30 years ago, the use of refuge chambers had not 

been embraced by industry, labor, or government. The paradigm was to focus on escape. 

Based on the totality of research associated with the utility of refuge alternatives, NIOSH 

believes the significant opportunity today is to recognize that refuge alternatives can be 

extremely useful to facilitate escape from the mine as well as to serve as a safe haven of 

last resort. Moreover, the potential of refuge alternatives to save lives will only be 

3
realized to the extent that mine operators develop comprehensive escape and rescue plans 

that incorporate refuge alternatives. Such an approach would be far superior to one in 

which refuge chambers are simply placed into the mine to comply with a regulation. 

Ultimately, the utility of refuge alternatives will depend upon the suitability of the 

engineering specifications for the intended application, the integration of these refuge 

alternatives into a comprehensive escape and rescue plan, and the implementation of 

appropriate training for mine workers and mine managers. The engineering 

specifications have received considerable attention over the past 18 months, and are 

addressed in upcoming sections of this report. The establishment of escape and rescue 

strategies has received less attention, other than some debate on appropriate locations for 

refuge chambers; notwithstanding, this area is beyond the scope of this report. Work has 

been initiated under a separate research project to examine escape and rescue strategies. 

Training is also a critical component for success, and this report addresses the need for 

training in three areas: operation and maintenance of refuge chambers, expectations for 

the use of chambers, and escape and rescue procedures, i.e., how and when to use 

chambers during a mine emergency. 

The utility of refuge alternatives to facilitate escape, as well as to serve effectively as 

refuge, will be greatly enhanced if two-way communications are provided between each 

refuge alternative and the surface. The technology to accomplish this does not exist 

generally, but is expected to become available over the next few years, and should be 

incorporated into most refuge alternatives as soon as practicable. 

PRACTICALITY 

Refuge alternatives have been successfully installed in underground coal mines abroad 

and to a limited extent in the U.S. Refuge alternatives are available commercially. 

Although no documentation is available to illustrate the successful use of a refuge 

chamber in an underground coal mine in an emergency circumstance, there is no 

evidence to suggest that refuge chambers or alternatives are impractical. It is wellunderstood that the installation of certain refuge alternatives and the moving and 

maintenance of such chambers will require an ongoing effort on the part of mine 

operators, and the costs of these activities are examined as part of the cost analysis that 

follows. There was also concern that the moving of refuge alternatives to advance or 

retreat with mining could be difficult and possibly impractical. After a thorough 

investigation of this issue including numerous site visits, it was found that the movement 

of refuge alternatives can be done safely and practicably. Notwithstanding, it may be 

impractical to implement viable refuge alternatives in the few mines that operate in very 

low coal, e.g. less than 36 inches. 

The finding of the NIOSH research is that refuge alternatives, to facilitate escape and to 

serve as a refuge of last resort, are practical for use in most underground coal mines. 

4
 

2

 Must withstand a pressure wave that rises to 15 psi in 0.10 second and then returns to 0 psi after another 

0.10 second. Any damage to the housing of an inflatable chamber must not affect the deployment time, and 

all associated equipment must be fully functional after the overpressure. Any damage to the housing of a 

rigid chamber must not impair operation or sealing of the access door, i.e. there can be no leakage into the 

chamber from any external point, and all equipment inside of the chamber must remain in working 

condition after the overpressure. 

3

 The pressure from the initial explosion may cause substantial movement with significant translational and 

rotational components. Studies of this issue are ongoing, but in some cases anchor systems could worsen 

damage. 

5

SURVIVABILITY 

Survivability, for the purpose of this report, focuses on the required characteristics of 

refuge alternatives to ensure that workers who must use the alternatives will be able to 

survive for a specific duration. The most crucial specifications address the following 

issues: establishing and maintaining an atmosphere that will support life; maintaining 

structural integrity through an initial explosion and a possible subsequent explosion; and 

providing for the most basic human needs, e.g. water, food, and waste disposal. The 

location and positioning of a refuge alternative can affect its survivability as well. 

The engineering design criteria for acceptable performance are optimally set based on 

experimental observations and/or simulations. A number of factors make optimal design 

difficult with respect to refuge chambers. The reasons for this are varied and include the 

following: complexities of mine explosions and the interaction of the explosion with the 

physical environment; conflicting data in the literature; and the limited number of 

observations of post-explosion environments. Generally, there are significant tradeoffs 

and potential “penalties” when selecting among design criteria options, i.e., optimizing 

one parameter will adversely affect another. The design parameters for refuge chambers 

and in-place shelters are selected with the understanding that the internal environment 

needs to support life for a limited time under emergency conditions, and not to serve as a 

routine workplace. Accordingly, none of the values suggested for refuge alternatives are 

intended to apply to workplaces. 

The key design parameters that apply to portable or stationary refuge chambers and inplace shelters are summarized in Table 1. Additional comments on many of the 

parameters are provided in the footnotes. Except for the “strength” parameter, the values 

were chosen based on the literature, practices in other countries, and guidance obtained 

from the study of non-mining applications. The strength parameter is based on explosion 

experiments at Lake Lynn Laboratory in addition to the review of literature and modern 

practices. The values listed in the table should not be considered as absolute, but rather 

as reasonable starting points for specifications. 

Table 1. Design and performance specifications for refuge alternatives. 

PARAMETER RECOMMENDED VALUE or PRACTICE 

Minimum Rated Duration 48 hr 

Strength2 15 psi overpressure for 0.2 sec 

Anchor System3 Not recommended at this time 
PARAMETER RECOMMENDED VALUE or PRACTICE 

Fire Resistance 4 300o F for 3 sec 

Deployment Time 5 Minimize this time when establishing the location of the refuge 

alternative and consider as part of the travel time

Min Concentration O2 18.5% 

Max Concentration O2 23% 

Max Concentration CO 6 25 ppm 

Gases to be Monitored Inside 

Chamber 

O2, CO, CO2

External Gases to be 

Monitored 

O2, CO 

Max Concentration CO2

7 1.0%, not to exceed 2.5% for any 24-hr period 

Apparent Temperature 8 95o F 

Entry and Exit Provide a means of egress without contaminating the internal 

environment and/or a means to maintain a safe environment 

during and after ingress/egress 

Potable Water per Person 2-2.25 qt per 24 hr 

Durability 9 Structurally reinforced and of sufficient physical integrity to 

withstand routine handling

Purge Air Volume 10 No specific recommendation (see Entry and Exit parameter) 

Food,11 per Person 2000 cal per 24 hr

Human Waste Disposal 

System 

Required

First Aid Kit Required 

Occupant-Activated 

Annunciation 

Battery-powered strobe light or radio homing signal 12 

Communication with Surface13 Survivable post-disaster system 

Minimum Distance to Working 

 Face 

1000 ft 

 

4

This parameter is based on NFPA-2113, but additional investigation is warranted; a fire resistance 

specification should be selected to protect exposed surfaces from the initial, not a subsequent explosion. 5

 This is the elapsed time beginning with the arrival of miners at the location of the chamber and ending 

when the environmental systems within the chamber have begun to function. Additional work is needed to 

establish reasonable boundaries for this time frame. In the interim, deployment time should be considered 

as part of the travel time needed to reach a chamber. 

6

 The concern here is CO contamination during ingress and egress (see purge air volume). 

7

 Scrubber materials must not become airborne or otherwise cause respiratory distress or other acute 

reactions. 

8

 Apparent temperature is a measure of heat stress, but other indices or standards could be used, such as the 

wet bulb temperature. Regardless of the index selected, the numerical value must be assigned to prevent 

heat stroke. Thus, if wet bulb temperature were selected, then a corresponding numerical value of 84 deg F 

would be appropriate, based on available medical evidence. 9

 The expectation is that the structure can withstand the expected number of moves without visible 

evidence of structural damage and without damage to the internal contents. 10 It is unclear whether all commercial chambers can purge contaminated air from the chamber; this will 

require further investigation. 

11 Food stores should be selected to minimize waste and flatulence and to meet basic nutritional needs. 12 This would allow rescue teams to concentrate their efforts on refuge alternatives that are occupied. The 

use of the battery in this application is controversial and additional study is warranted. 

13 Systems are under development and should be applied as soon as they become available. These systems 

should be independent of the mine’s communications system, to the extent practicable. 

6
PARAMETER RECOMMENDED VALUE or PRACTICE 

Maximum Distance from 

Working Face 

Distance that a miner could reasonably travel in 30–60 minutes, 

under the expected travel conditions 

Security Visual indication that a refuge alternative has been entered; 

inspection and maintenance actions required subsequent to 

discovery 

Repair Materials Materials and instructions supplied by manufacturer 

Testing and Approval Required 

Unrestricted Floor Space > 15 ft2 per person

Unrestricted Volume > 85 ft3 per person 

Capacity14 Sufficient to accommodate the maximum number of miners in 

the area to be served by the refuge alternative 

 

7

14 Consideration should be given to short term needs as well, such as at shift change. 

Location and Positioning 

The location of refuge alternatives is best established in the context of an escape and 

rescue plan for each mine. A refuge chamber or in-place shelter should be available and 

readily accessible from each active working section. Additionally, refuge alternatives 

such as in-place shelters may be desirable in more “outby” locations, e.g. between the 

mouth of the panel and the shaft, to facilitate escape or the handling of injured miners. 

However, the presence of escape shafts or other means of exiting the mine could 

effectively eliminate the need and desirability of outby refuge alternatives, and the 

benefit of these additional locations should be evaluated on a mine-by-mine basis. 

The location of the refuge alternative serving each active face is important, but 

establishing the exact location is problematic. It would appear advantageous to place the 

refuge alternative as close to the face as possible to minimize the time and effort required 

for miners to reach it. On the other hand, locating the alternative closer to a possible 

explosion source will increase the chance that it is damaged by either the overpressure or 

flying debris from the initial explosion. It is also argued that refuge alternatives should 

be located farther from the face to encourage and facilitate escape rather than refuge. 

Furthermore, the effects of subsequent explosions, with their more varied possible 

locations, must be considered in addition to the initial explosion. 

An analysis of past disasters as well as various probable scenarios provides conflicting 

evidence to support any particular location for refuge alternatives. Nonetheless, the 

experience of studying mine explosions at NIOSH’s Lake Lynn Experimental Mine, and 

the resulting explosion pressure profiles, suggests that refuge chambers should normally 

be located a minimum of 1000 feet from the working face and in some cases as far as 
2000 feet.15 Distance is an appropriate measure with regard to decay of explosion 

overpressure, for example, but the distance parameter alone cannot account for the time it 

will take miners to travel to the location of the refuge alternative. Lower seam heights, 

difficult bottom conditions, and the presence of smoke, among other factors, will increase 

travel times. Thus, the maximum distance from a working section to the refuge chamber 

or in-place shelter should be based on projected travel time rather than actual travel 

distance. Unless there is a compelling reason otherwise, the refuge alternative should be 

located within approximately 30–60 minutes16 from the face under the expected travel 

conditions, assuming smoke-filled entries and a directional lifeline. 

Arguably, one reason for allowing a greater distance and travel time would be to reach an 

in-place shelter. Typically, an in-place shelter would have a vastly greater volume per 

occupant, better environmental and sanitary conditions, and might be connected to the 

surface by a borehole with its attendant services. However, it is impracticable to move 

these shelters frequently. Therefore, if the in-place shelter is constructed to offer 

significant advantage over a portable chamber, it may be desirable to allow greater 

distances that would require a travel time of 60 minutes or slightly more. 

Refuge alternatives should be positioned in crosscuts rather than entries, or in dead-end 

cuts made specifically for the refuge alternative, and they should be positioned off of the 

intake or return escapeway whenever feasible. They should not be located within 

approximately 1000 feet of any mine seal, nor in or off of track entries whenever 

practicable. Locations near overcasts should be avoided; as should sources of potential 

fire such as belt drives. 

Site preparation is particularly important for portable inflatable refuge chambers. 

Adequate clearances to the roof and ribs must be provided to ensure an unobstructed 

volume for the inflation of the chamber. The area, including the floor, should be free of 

materials that could puncture the chamber, and the floor should be reasonably flat and 

level and free of mud holes, ruts, and rock. Special consideration should be given to the 

condition and stability of the ribs, roof, and floor around all chambers.

 

15 The most likely locations of an initial explosion can be predicted with some certainty, and this 

information can be used to guide decisions on the location and characteristics of refuge alternatives. Minewide ventilation is often disrupted as a result of the initial explosion, and once disrupted, methane can 

accumulate at any number of locations in varying quantities. If there is an ignition source, there could be 

subsequent explosions, although the location and strength of these is more difficult to forecast. 

Accordingly, the discussion here focused more on the events that can be anticipated and therefore be used 

to provide guidance. 

16 This guidance is based on experience with traditional self-contained self-rescuers (SCSR). The style of 

SCSR or the presence of SCSR caches, for example, could be used to justify a change in these times. 

8

COSTS 

A cost analysis of refuge chambers was conducted, with the associated costs separated 

into three segments: (1) purchase, installation, and training; (2) maintenance and 

inspection; and (3) moves. The costs for these segments were quantified and the 

assumptions used in the analysis are summarized in Table 2. Benefits associated with the 
costs of the refuge chamber were not evaluated in this analysis. Information to quantify 

costs was obtained from requests for certification of emergency shelter documents 

submitted to the state of West Virginia by the manufacturers of portable refuge chambers, 

from state regulations for refuge chambers, and by contacting the manufacturers directly. 

Table 2. Assumptions used for quantifying costs for refuge chambers. 

Cost Assumptions for One Portable Refuge Chamber 

Mine operates 24 hours/day for 365 days/year 

Discount rate = 9.5%, 10-year lifespan 

Chamber Purchase, Installation, and Training 

Description Initial Costs Annual Costs 

Refuge Chamber $80,000 

Installation (8 hours using mechanic ($30.21 hour), electrician $700 

($30.04/hour), and laborer ($27.28/hour) 

Safety Training (Initial = 2 hours. Annual after each move = 15 minutes, 60 

times/year) 

 Manufacturer Training ($1000/day) $1,000 

 Personnel Costs (3 continuous miner crews ($223.52/hour per crew) $1,341 $10,058 

Total $83,041 $10,058 

9
Chamber Maintenance and Inspection 

(Daily and monthly performed by mine; all other inspections performed by manufacturer 

twice/year) 

Description Initial Costs Annual Costs 

Personnel Costs 

 Manufacturer Inspection (2 inspections per year at $1000/day) $2,000 

 Mine Personnel Inspections (Monthly 15-minute inspection by mine $140

foreman ($47.52/hour) 

Supplies (All items have a 5-year life, items with 

only) 

* incur costs in 5th year 

 Batteries* $2,500 

 CO2 Scrubber System* $11,500 

 First Aid Kit* $1,000 

 Food and Water $1,400 

 Oxygen* $2,500

Total (Annual cost) $1,400 $2,140 

Total (5th year cost) $19,640 

Chamber Moves 

(60 moves/year calculated from typical mine production rates and maintaining 1000-foot distance 

in a 3-entry room and pillar system) 

Description Initial Costs Annual Costs 

Personnel Costs (4 hours using mechanic ($30.21/hour), electrician $21,007

($30.04/hour) and laborer ($27.28/hour) 

 

Supplies ($100 per move) $6,000 

Total $0 $27,007

10
Net present value calculations were performed on the quantified costs, shown in Table 2, 

over a 10-year life span for the refuge chamber, using various discount rates. Results of 

these calculations are summarized in Table 3. The total costs shown in the table are more 

substantial than the initial purchase price of a chamber, but these present worth costs 

include the quantified costs for the tasks of installation, training, maintenance and 

inspection, and moving. These quantified costs are necessary in order to realize the 

potential benefits of a refuge chamber. 

Table 3. Summary of costs, for varying discount rates, of a portable refuge chamber over 

a 10-year life span.17

 3% Discount 

Rate 

7% Discount 

Rate 

9.5% Discount 

Rate 

Purchase cost $80,000 $80,000 $80,000

 Installation $700 $700 $700

 Training $88,100 $73,000 $65,500

Maintenance and Inspection 

costs 

$34,600 $28,500 $25,400

Moving costs $230,400 $189,700 $169,600

Total $433,800 $371,900 $341,200

Moving costs are a significant portion of refuge chamber expenses, and changes to the 

number of moves can have a significant impact on cost. A sensitivity analysis conducted 

on moving costs showed that, as the number of required moves was varied from 30 to 90, 

the total net present value of the costs ranged from $256,400 to $426,000 with a 9.5% 

discount rate. 

An analysis of in-place shelters using movable bulkheads was also conducted, and as 

expected it is not feasible from a cost perspective to advance in-place shelters with 

mining, as the present worth costs would exceed $7,000,000 per shelter. However, the 

net present cost to install such a shelter in a location that would be moved or abandoned 

once per year is similar to the present worth cost of a portable chamber; if the shelter 

were moved twice per year the present worth cost would increase by approximately 75%, 

using similar assumptions to those for portable refuge chambers. An important function 

of an in-place shelter is its connection to the surface with a borehole, when practicable18. 

However, the costs of drilling this borehole and providing air and communication lines 

were not included in the analyses. 

 

17 OMB circular A-94 requests agencies use discount rates of 3% and 7%. A discount rate of 9.5% 

represents the December 2007 lending rate of LIBOR + 5% for a fixed rate loan. 18 The mine would need to acquire surface rights, and the surface would have to be accessible and free of 

obstructions, e.g. protected structures or a body of water, before a borehole could be considered. 

11
TESTING 

The need for any specific type of testing was undefined at the beginning of NIOSH’s 

research on refuge alternatives. Initially there were no commercially available chambers 

to test and none of the knowledge gaps surrounding refuge alternatives suggested a 

specific type of experimental investigation. Approximately 10 months into the study, the 

State of West Virginia mandated specific performance standards for approval of 

chambers for use in West Virginia coal mines. A NIOSH review of the approval criteria 

established by the West Virginia Office of Miners’ Health, Safety, and Training found 

them to be appropriate, based on a review of the literature and the application of mining 

heuristics. The State’s approval of individual chambers was conditioned upon 

certification by a registered professional engineer. 

NIOSH had concerns that the information needed to approve a chamber could be fully 

obtained from manufacturer-submitted materials and calculations, and that this 

information would need to be supplemented with the results of experimental testing. 

Accordingly, NIOSH began to develop a protocol for testing chambers in the 12th month 

of this study. Although an experiment involving human subjects in the chambers was 

desired, the risks were deemed sufficient that a full human subjects review board review 

and approval would be required. To address many of the issues within the time 

constraints of this study, the decision to simulate human occupancy was made, and a 

protocol was developed, peer reviewed, and then implemented. 

The research goals of the testing were limited to the areas of greatest interest in the 

context of time constraints, and these were to investigate CO2 levels, oxygen flow rates, 

and the heat index (i.e., apparent temperature during chamber operation), and to observe 

the overall deployment and operation of the chambers. The protocol defined the means 

of simulating human occupancy to facilitate the evaluation of the chamber. In the 

simplest terms, the simulation of human occupancy was accomplished as follows: the 

oxygen flow rate into the chamber was set based on the occupancy limit and measured as 

a surrogate for the chamber’s ability to provide adequate oxygen levels; CO2 was injected 

into the chamber based on the respiratory quotient and the CO2 level was then monitored; 

the heat from light bulbs was used to mimic the metabolic heat load of the expected 

occupancy; humidified air was injected into the chamber to simulate moisture from 

human respiration and perspiration, and then the temperature and humidity were 

measured for the calculation of apparent temperature. The tests were conducted 

continuously over a 96-hour period. Four manufacturers provided chambers for testing in 

the 16th month of this study. The testing and preliminary analyses were completed in the 

18th month of the study. Major findings from the experiments are summarized in Table 4, 

and more specific observations are given below. 

The innovation of the four manufacturers is evident in their products, and their ability to 

create new products to fill the gap in the market for portable chambers is commendable. 

12
Notwithstanding, the testing did reveal shortcomings in the chambers. Those 

shortcomings, as outlined in Table 4, are sufficiently serious in three of the chambers to 

require correction before deployment. In most cases, but not all, these shortcomings 

should be correctable, or have already been corrected, with minor technical changes, the 

addition of clear instructions, and/or improved engineering. Major findings of the testing 

are as follows: 

- All four chambers had been approved for use in West Virginia based on 

manufacturer representations and certification by a registered professional 

engineer. Nevertheless, testing revealed potentially serious deficiencies, 

underscoring the fact that computational models and other engineering analyses 

alone cannot be relied upon for approval and certification of complex systems 

such as refuge chambers. The results of the testing indicate the need for 

independent evaluations and testing beyond the chamber manufacturers. 

- Heat dissipation was more of a problem in the steel than the inflatable 

chambers, and the heat stress index19 in both steel chambers exceeded the levels 

established as acceptable by the state of West Virginia. Despite these findings, 

steel chambers are assessed to have certain inherent benefits over inflatable 

ones, such as their ability to withstand subsequent explosions, and it would be 

desirable to correct this observed limitation so that rigid steel chambers can be 

approved for use. The heat created during the exothermic scrubbing process 

would be reduced by allowing higher CO2 values as listed in Table 1. Further, 

an increase in the surface area of the steel chambers would allow more heat loss 

to the environment and the rated occupancy of the chamber could be decreased, 

which would reduce the heat generated within the chamber. It should be noted 

that the ambient air temperature for the tests was approximately 60 degrees F; if 

the steel chambers were used in mines with ambient temperatures closer to 70 

degrees F, as is found in some deep mines, the problem would be exacerbated. 

- The time to deploy20 each chamber varied from a few minutes to more than 30 

minutes in two cases. There is no consensus on the amount of time that is 

reasonable, but the time to deploy a specific chamber should be considered 

when establishing the maximum distance that a chamber can be located from 

the face. 

- Three of the four chambers were unable to maintain CO2 concentration below 

the level specified by West Virginia OMHST, but the levels were within the 

range suggested in Table 1. Two of the four chambers were unable to deliver 

oxygen for the duration of the test. 

 

19 West Virginia specified “apparent temperature” as a measure of heat stress and established an upper limit 

of 95° F, which is reasonable and is conservative. 20 This is the elapsed time from arriving at the chamber until the environmental systems inside the chamber 

have begun to function. This time would include the setup and inflation time for an inflatable chamber in 

addition to the time required to start the oxygen flow and CO2 scrubbing inside of the chamber. 

13
Testing revealed deficiencies with the documentation provided for each chamber, and this 

information has been provided to the manufacturers. Opportunities for improving the 

usability and performance of chambers were noted and will be investigated further. 

Finally, although these research experiments were not intended to be tests that would be 

employed in a certification process, they have provided insights that can be used to 

develop independent evaluations. 

Table 4. Survivability evaluation of four mine refuge chambers. 

 Chamber 1 Chamber 2 Chamber 3 Chamber 4

Chamber 

Type 

Inflatable Inflatable Steel Steel 

Capacity 

(persons) 

20 36 12 26

CO2

Scrubbing 

System 

Passive soda lime 

curtains 

Powered soda lime 

cartridges 

Passive lithium curtains Powered soda lime 

cartridges 

Specifications Basis to 

Change 

Scrubbing 

Materials 

Specified time - 96 hrs Specified time - 24 hrs Specified time - 

variable 

Specified time - 16 hrs 

CO2

Scrubbing 

Criteria 

(0.51 

l/min/man) 

(CO2 level 

<= 0.5%)

Did not meet 

Exceeded maximum 

Met Did not meet 

Exceeded maximum 

Did not meet 

Exceeded maximum 

Comments Exceeded 0.5% 42 hrs 

into test, remained 

above 0.5% from 44 

hrs to end 

Stabilized between 

0.35% and 0.40% 

Maximum reading was 

0.72% (Due to error in 

deployment 

instructions rather than 

failure of scrubbing 

materials) 

Maximum recorded 

reading was 1.34% 

O2 Supply 

Criteria 

(0.62 

l/min/man) 

(O2 >= 

19.5%)

Did not meet, 

Insufficient 

Met Met Did not meet,

Insufficient 

Comments O2 flow ended at app. 

71 hrs 

 O2 flow and conc. 

starting dropping at 

94.5 hrs 

O2 flow ended at app. 

37 hrs 

Apparent 

Temperature 

Criteria21 

(< 95 deg F)

Met Met Did not meet 

Exceeded maximum 

Did not meet 

Exceeded maximum 

Comments Apparent temperature 

app. 76° F (73° F and 

62% RH) 

Apparent temperature 

app. 73° F (70° F and 

69% RH) 

Apparent temperature 

app. 102° F (87° F and 

86% RH). 

Apparent temperature 

app. 110° F (90.5° F 

and 92.6% RH) 

Duration 

Criteria (96 

hours)

Did not meet, 

Less than required 

Met Met Did not meet,

Less Than Required 

Results 

Comments Test continued for 96 

hours 

 Test continued for 56 

hours. Failed scrubber 

containers and loose 

soda lime forced early 

termination. 

21 Apparent temperature computed according to West Virginia Emergency Rule 56-4-4, page 51, 2006. 

 

14
TRAINING 

To ensure the successful implementation of refuge alternatives, mine workers need to be 

trained in their use, and those involved in moving and maintaining chambers would 

require additional training. All miners and mine managers should be trained in the use of 

refuge alternatives in the context of that particular mine’s escape and rescue plan. 

NIOSH research indicates that motor task training, i.e. how to use refuge alternatives, 

should be given quarterly, possibly in conjunction with the mandatory mine evacuation 

training and drills. This would also be an appropriate time to include training on 

decision-making skills, i.e. when to use refuge alternatives. Finally, expectations training 

would be useful to reduce the level of panic and anxiety associated with the use of refuge 

alternatives, and should be included with the other training components described in this 

paragraph. 

The proper movement, maintenance, and inspection of refuge alternatives are necessary 

prerequisites to saving lives with refuge alternatives. Task training would be appropriate 

to ensure that those charged with the responsibility are equipped with the skills to 

successfully complete refuge chamber moves, maintenance, and inspection. 

NIOSH researchers and technical staff are developing training materials to meet the 

needs identified here, and most of the materials are expected to be completed within the 

next 12 months. 

SUMMARY 

Refuge alternatives have the potential for saving the lives of mine workers if they are part 

of a comprehensive escape and rescue plan, and if appropriate training is provided. Two 

viable refuge alternatives have emerged over the past 18 months: in-place shelters and 

portable chambers that are inflatable or rigid. Portable chambers are well-suited to 

providing a refuge alternative to workers as the active face advances or retreats. 

In-place shelters can offer a superior environment for refuge and in many cases could be 

connected to the surface via a borehole to provide vital services. Unfortunately, it is 

impracticable to move in-place shelters frequently, and as such it would be impossible to 

keep them within 1000-2000 feet of the face. However, their strengths compared to 

portable chambers are so significant that consideration should be given to allowing 

extended distances, if in-place shelters are used to provide refuge for face workers. 

NIOSH testing found that some commercially available portable chambers have 

operational deficiencies that will delay their deployment in mines. We conclude that 

approval or certification of refuge chambers based on laboratory and/or field testing is 

necessary for refuge chambers. In-place shelters should also be inspected and certified to 

meet at least the applicable requirements in Table 1. 

15
There are some remaining knowledge or technology gaps for the design and specification 

of refuge alternatives. Nonetheless, the benefits of refuge alternatives and the general 

specification of these alternatives are sufficiently known to merit their commercialization 

and deployment in underground coal mines. NIOSH research suggests that any 

regulations on the specification, location, and conditions of use for refuge alternatives 

should accommodate the rapidly changing state of knowledge and technology. 

16