U.S. BUREAU OF MINES TECHNOLOGY APPLICABLE TO DISASTER 

RESPONSE, URBAN SEARCH ANN DSCUE 

J. G. Kovac, H. Dobroski, and D. Litton 

U.S. Bureau of Mines 

P.O. Box 18070 

Pittsburgh, PA 15236 

ABSTRACT 

Since 1910, the U.S. Bureau of Mines 

(USBM) has investigated practical ways of 

dealing with the consequences of major fires and 

explosions in underground mines. The results of 

this research have had a significant positive 

impact on the mining community by enhancing 

mine workers\hances of surviving an 

underground mine disaster. 

Today, the Buleau continues to conduct 

research in mine disaster mitigation. Much of 

this work has direct application to search and 

rescue situations, such as: emergency evacuation 

through smoke-filled or otherwise unbreathable 

atmospheres, locating and rescuing survivors from 

rubble piles, and fire fighting in confined spaces. 

Three USBM research areas are discussed: 

(1) Life Support -- This effort is directed toward 

research into and development of closed-circuit 

breathing apparatus for use in hazardous 

environments which are likely to be encountered 

in the aftermath of a mine disaster. 

(2) Trapped Miner Location -- A mine disaster 

may result in the entrapment of miners whose 

normal escape rouEes are cut-off. This research 

activity resulted in the development of 

transportable seismic technology that can be used 

to locate trapped miners. 

involves developing practical techniques for 

remotely monitoring how the atmosphere inside a 

mine changes during a fire, in order to estimate 

the spread and severity of an underground fire. 

This information is critical in deciding how best 

to fight a mine fire, or whether it is safe to mount 

a rescue and recovery mission. 

INTRODUCTION 

At the turn of the century, mine disasters 

were a commonplace event. It was not unusual 

for hundreds of lives to be lost in a single instant 

when an explosion erupted in a mine. The 

camage reached such a level that congress 

established the USBM with the intent to improve 

technology and give the mining industry the 

mans to provide a safer work place. 

In the years that have passed since then, the 

mining industry assisted, by the USBM, the Mine 

.Safety and Hedth Administration (MSHA), and 

other Federal and State agencies, has greaEly 

improved its safety record. The overdl accident 

rates for mining have greatly decline, and fms 

and expIosions no longer account for the majority 

of work related deaths. Although the frequency 

of explosions has diminished to nearly zero, they 

still occur. It is against these occurrences that the 

USBM performs research into post-disaster 

technologies. 

LEE SUPPORT 

(3) Mine Fi Diagnostics -- This research In a mine fire or expIosion, the mine 
atmosphere can quickly become nnbreathable. 

Along with smoke, there will be carbon monoxide 

and the possibility of toxic byproducts from other 

burning materials. Depending on ventilation 

conditions, the atmosphere may also become 

deficient in oxygen. 

To protect escaping miners, Federal mining 

law (Title 30 CFR, part 75.1714) requires that 

every person that enten an underground cod 

mine be supplied with a Self-Contained, SelfRescuer (SCSR). An SCSR is an emergency 

breathing apparatus designed specifically for the 

purpose of mine escape. The law also calls for 

these SCSR's to meet certain minimum 

requirements in order to be approved for use. 

Among these requirements it is specified that the 

SCSR be able to provide at least a @)-minute 

supply of oxygen (0,). The National Institute for 

Occupational Safety and Health (NIOSH) and 

MSHA act jointly in providing certification for 

SCSR's. 

Description of the Basic Technolorn 

Part of the USBM effort in life support is to 

lead the drive for improved SCSR technology. 

By working cooperatively with manufacturers, the 

Bureau was able in 1989 to introduce secondgeneration SCSRb to the mining industry. 

Second-generation SCSR's are both smaller and 

lighter than the fmt-generation SCSR's that they ' 

are replacing, but are still able to meet the same 

performance criteria. 

The main advantage derived from this 

improvement comes in deployment. The previous 

SCSR's were too large to carry and had to be 

stored in the mine near the locations at which 

people regularly work. One disadvantage of this 

deployment scheme in an emergency is the delay 

in escaping while an individual travels to a 

storage location to look for an SCSR. Since 

second generation SCSR's are prson-wearable, 

miners can begin their escape immediately. 

All second generation 1 - hr SCSR's approved 

for use at this writing employ mainly potassium 

superoxide (KO,), a solid, as the oxygen source 

and as a carbon dioxide (CO,) absorbent. 

Figure 1 is an engineering drawing of a 

chemical oxygen SCSR. One significant feature is 

that SCSR's deliver a breathable atmosphere 

through a mouthpiece, rather than a mask or face 

piece. A mouthpiece combined with nose clips 

provide a high degree of user protection without 

the penalty of custom fitting. 

I C 

Figure 1.--Typical Chemical 0, SCSR 

Three of the four manufacturers who held 

current certifications for their original SCSR's 

have designed and gained approval for secondgeneration SCSR's. All three of these are 

chemical oxygen units. These devices are smaller 

and lighter than the ones they replaced. The sizes 

and weights of these devices, compared to their 

first-generation counterparts, are given in 

Table 1. 

Although SCSR" were specifically designed 

for mint escape, they can also be used for escape 

or evacuation in other hazardous situations, such 

as a chemical plant fire or tunnel fwe. Compared 

to other closed-circuit breathing apparatus 

intended for emergency use, SCSR's have a 

number of advantages: small size and weight, 

low maintenance, Iong service life, easy and quick 

donning, no custom fitting, and relatively low 

deployment costs. 
Table 1.--Size and Weight Comparison of Firstand Second-Generation SCSR's 

Weight Size 

0%) 

Draeger 

1st OXY-SR 60B 

2nd OXY K plus 

MSA 

1st 60-min SCSR 

2nd Portal-Pack 

CSE 

1st AU9-A1 

2nd SR-100 

TRAPPED M?NER LOCATION 

In some cases escape may be impossible due 

to injuries or damage to the fine. The only 

alternative may be to seek out the safest place 

possible, wait, and hope for rescue. 

In such a situation, time is of the essence. 

The toxic gases from a fire or explosion will 

often eventually migrate throughout the entire 

mine. Experience has shown that unless rescue is 

accomplished in a matter of hours, the trapped 

miners will likely perish. Therefore, the key to 

successful rescue is to verify that some miners 

have survived, and to determine their location. 

With such knowledge, rescue teams can focus 

their efforts more efficiently, and the likelihood of 

successful rescue is enhanced . 

above the disaster site. The location of the 

subarrays must be accurately sited by surveying. 

These geophones are designed to detect seismic 

signals generated by underground trapped miners. 

Signals detected by the submays are transmitted 

by wireline or radio link to a seismic 

instrumentation truck that contains computers, 

recorders, CRT displays, and other equipment. 

The truck can be driven or airlifted to disaster 

sites. For the seismic system to be effective, 

trapped miners must be trained to respond in a 

certain manner. This training can be provided by 

MSHA or company safety instructors. As an aid 

ad reminder, a sticker hat summarizes this 

training can be affixed to the inside of hardhats. 

I 

In 1970, the National Academy of Engineers Figure 2.--Trapped miner seismic detection 

recommended that a seismic system be built and system. 

tested as a means of detecting and locating 

trapped miners. Via contracts and in-house 

efforts, the Bureau developed such a system, 

which is shown in Figure 2. It consists of an Initially, the trapped miners should take 

array of geophones, arranged in subarrays, action to improve their chances of survival. This 

deployed on the surface of a mine, approximately includes keeping cdm, gathering food and water, 

and possibly barricading to provide some degree 
of protection from toxic gas. Miners must also 

recognize that it may take hours (perhaps days) 

for the seismic system to arrive on the ,surface 

and be deployed. Therefore, it is important that 

they conserve strength, resources, and hope until 

then. 

The first signal given when the seismic 

system is in place above them is three shots 

(explosions) detonated at the surface. These shots 

can easily be heard underground. At this signal, 

the trapped miner(s) must pound 10 times on the 

mf of the mine with a heavy object like a 

timber. This pounding is repeated every 15 

minutes. This creates a pattern of seismic signals 

that propagate through the earth and reach the 

subarrays at the surface. The signals from each 

subarray are amplified and telemetered to the 

seismic truck, where they are filtered to reduce 

interferences, amplified, and recorded on analog 

magnetic tape. They are then band-pass filtered 

from 20-200 Hz and displayed on an oscillograph 

recorder. 

The operator observes the record and decides 

whether or not the seismic signals ate the result 

of underground pounding. The key, of course, is 

the series of 10 events repeated every 15 minutes. 

If such signals are observed, that portion of the 

magnetic tape is input into a computer which 

processes the data, taking into account the relative 

arrival times at the various subarrays. These data, ' 

along with information concerning the location of 

the subarrays, and the seismic velocity of the 

geologic strata, are used to calculate the location 

of the underground source. Under favorable 

conditions, the system can detect these seismic 

signals from a distance of about 600 m (2000 ft), 

with a location accuracy of about 30 rn ( lOO ft). 

When the surface seismic team has ascertained 

the location, they detonate 5 explosive shots. 

This is the signal to the trapped miners that they 

have been detected and located. They should now 

stop pounding, and wait for rescue. 

Seismic systems have application for 

detecting persons buried in landslides and 

collapsed buildings as a result of earthquakes or 

other natural disasters. However, a surface 

disaster is quite different from a mine disaster. In 

a mine disaster, the victims are trapped perhaps 

hundreds of meters from where geophones can be 

deployed. Also, there is no way of knowing 

exactly where the miners might be. In such a 

situation, detection is not enough. Accurate 

location is needed dso. Both of these 

requirements can be met using seismic techniques, 

because the nature of the seismic path between 

the mint and the surface can be measured. In a 

surface disaster situation, the most important 

aspect is to verify whether or not there are 

survivors within a localized area. Rescuers 

generally know approximately where to look, 

because the distances involved are measured in 

tens of meters, not hundreds. Computer-based 

seismic location techniques, such as those used in 

the mine disaster situation, would not likely be 

successful in the surface case because of the 

chaotic and unconsolidated nature of the material 

between the victim and the geophones. These 

circumstances call for a different kind of seismic 

system, such as the one built by MSHA and 

successfully used in the Mexico City earthquake 

rescue efforts in 1985. This system, known as the 

" mini-seismic" system, was originally built for ik 

mine use, and can be carried by an advancing 

rescue team. It consists of three geophones, three 

preamplifiers, three filters, and a chart: recorder. 

It is a detection system only, and has no 

computer-based location capability . 

The human operator visually examines the 

magnitude of the three seismic signals, and 

decides which is the greater. The assumption is 

that the geophone registering the largest signal, is 

the one nearest the seismic source. By a series of 

measure and move operations, the system can 

zero in on the location of the seismic source. 
Mine fire diagnostics are a set of techniques 

by which the mine air is sarnpIed for combustion 

products to determine: 1) during the early stages 

of a fire, the status of the fire, in terms of its size 

and possibly the primary combustibles involved; 

or 2) after a mine, or a section has been sealed, 

whether or not a fire still exists, and if so, 

whether or not the fire is smoldering or flaming. 

It is important to realize that in addition to 

diagnostics fur fires, similar diagnostic procedures 

are also used to determine the explosibility of the 

mine atmosphere due to the accumulation of 

methane and other explosive gases. For either 

type of diagnostic, fm or explosibility, the basic 

techniques are the same. These techniques consist 

of obtaining gas samples from various mine 

locations, analyzing these samples, and 

interpreting the meaning of the resultant gas 

concentrations as they apply to either a fire or the 

explosibility of the gaseous mixture. 

The differences in these techniques, as they 

apply to either of the two situations, are the result 

of the time-scales involved which dictate that 

different sampling, analysis, and interpretation 

procedures be used. 

Situation No. 1 

Diagnostics that are intended to determine fire 

status, fire Iocation, and possibly the primary 

combustible involved must be rapid. h this 

instance, particularly with regard to fire-fighting 

strategy, time is critical. As much information as 

is possible regarding the fire must be obtained in 

a minimum amount of time. To implement a 

successful fire-fighting mission, several factors 

are critical: 

1) Location 

23 Accessibility 

3) Fire Size and Growth 

4) Combustible Type 

Once the location of a fire is known, a 

determination of Its accessibility must also be 

made. In very general terms, most fires are 

limited in their accessibility due to the smoke 

produced which reduces visibility. In particular, 

if the ventilation air velocity in the fire-affected 

entry is less than some critical level, reverse, 

stratified flow of smoke and other product gases 

can occur, thus limiting accessibility from the 

upstream side of the fire. This critical velocity is 

predictable from the expression 

where: g = 9.8 m/s2 

h = entry height (m) 

For instance, if the location of the fm is in an 

entry with a height of 1.5 rn (5') and the air 

velocity in that entry is 0.50 nzls (100 fpm), then 

the fm-fighting team should expect to encounter 

smoke and reduced visibility from the upstream 

side of the fire, since the critical velocity for this 

entry is 1.2 rm's (240 fpm). This does not 

necessarily mean that some effort should be made 

to increase the air velocity because increasing the 

air velocity may enhance the flame spread of the 

fire in many cases, such as conveyor belt fires. 

The decision to increase ventilation can more 

realistically be made if the fire size is known, or 

if the type of fire is lcnown (i.e., flaming vs 

smoldering). This information can be obtained by 

measuring the levels of the gases, CO and CO,, 

downstream of the fire. The Ievel of CO, is m 

excellent indicator of the intensity of the flre. 

Some benchmark values of the CO, level can 

provide insight as to the stage of the flaming fue, 

and the ratio of CO to CO, can provide additional 

information on the type of fire. For a typical 

mine entry cross-section of 9.3 m2 (100 fitz) these 

IeveIs are: 

a) ppm CO, < 150 and COICO, 1 0.5 indicates 
a smoldering fire in its early stages of 

development; 

b) 150 < ppm CO, < 1500 and COICO, < 0.10 

indicates a localized flaming fire that is not 

spreading; 

c) ppm CO, > 1500 and COICO, 5 0.10 

indicates a spreading fm that is fuel-lean; 

d) ppm CO, > 1500 and COICO, > 0.10 

indicates a spreading fre that is fuel-rich. 

In addition, the absolute levels of CO provide 

information relevant to the toxicity of the 

atmosphere. For CO levels less than 250 ppm, no 

severe toxicity hazard is present hm the C0. 

However, if combustibles other than liquid fuels, 

coal, or wood are involved some high level of 

toxicity may exist due to other gases. For 

instance, if chlorinated combustibles such as PVC 

or Neoprene conveyor belt are involved, elevated 

levels of HCl may be present; if nitrogen-based 

combustibles such as polyurethane foams are 

involved, elevated levels of HCN may be present. 

It should also be mentioned that elevated levels of 

smoke, in excess of some critical level for 

visibility, often exist at very low levels of CO. In 

fact, the critical level of visibility for human 

escape is generally accepted to be 3.7 an (12 ft). 

This level of visibility occurs at a CO level of 20 

ppm. In other words, severe reductions in 

visibility due to smoke can usually be expected, 

and often occur at relatively low levels of CO and 

other toxic gases. 

It should be noted that the ventilation airflow 

serves to dilute the combustion product gases and 

smoke. As n result, when it is necessary to base 

some decision on the absolute level of either CO 

or CO,, every effort should be made to make this 

measurement at a location downstream of the fire 

where the gas levels ate due only to the 

ventilation airflow within the affected entry that 

is affected and not at some location where these 

gases may have been diluted by airflows from 

adjacent entries. 

A11 of the above information applies to rescue 

operations, as well as fire-fighting. However, in 

assessing the feasibility of rescue operations, it is 

aIso necessary to obtain information about the 

level of 0, present in order to assess the 

breathability of the atmosphere. Diagnostics for 

explosibility are also necessary. 

These initial diagnostics need to be acquired 

rapidly and reliably because decisions need to be 

made quickly. As a result, the use of handheld 

gas analyzers for the primary gases CO, CO,, 

CH,, and 0, is usually required. Such devices are 

generally available comrnerciaI~y, 

Situation No. 2 

Usually, the sealing of a mine, or section of a 

mine, is done as a last resort following 

unsuccessful local fire-fighting efforts. The intent 

of sealing is to allow the fite to self-extinguish as 

the supply of 0, is gradualIy depleted. Unlike 

diagnostics for the early stages of a fire, time is 

not a critical factor in this situation. The Bureau 

of Mines has developed various gas ratios to 

assist in determining the status of fires in mines 

that have been sealed. Gas ratios are used instead 

of absolute concentrations because: 1) sealed 

areas enclose large volumes, so ratios are used in 

order to eliminate dilution effects; and 2) the 

typical time scale for attempting to recover a 

sealed mine is genemIly in the range of 2 to 12 

months, but can be longer, and trending of gas 

ratios during this period is extremely beneficial. 

The important thing to remember is that the 

'bulk of necessary information for effective mine 

fire fighting can be obtained from the 

measurement of only four gasses: CO, CO,, O,, 

and CH,. Only in fire emergencies involving 

gasses more toxic than CO, is it necessary to 

monitor these other gasses. These same 
techniques have direct application for attacking was to mitigate the consequences of mine 

fms in any confined space, specifically, tunnels, disasters which are caused by underground fues 

and underground storage facilities. or explosions. However, much of this work has 

direct application to search and rescue situations, 

CONCLUSION such as: emergency evacuation through smokefilled or otherwise unbreathable atmospheres, 

Three USBM research areas were discussed: locating and rescuing survivors from rubble piles, 

Life Support; Trapped Miner Location; and Mine and fire fighting in confined spaces. 

Fire Diagnostics. The genesis of this research