ISSUE DATE: 12/27/10 

PROGRAM INFORMATION BULLETIN NO. P10-23 

FROM: KEVIN G. STRICKLIN 

 Administrator for 

 Coal Mine Safety and Health 

 JEFFERY H. KRAVITZ

 Acting Director of Technical Support 

SUBJECT: Re-Issue of P08-08 - Precautions for the Use of the Analysis of 

 Retreat Mining Pillar Stability (ARMPS) Computer Program 

Scope 

Coal mine operators, miners and miners' representatives, and Mine Safety and Health 

Administration (MSHA) enforcement personnel should receive this bulletin. 

Purpose 

The purpose of this Program Information Bulletin (PIB) is to provide notice to the 

mining community that a new version of the Analysis of Retreat Mining Pillar Stability 

(ARMPS) computer program is available that incorporates pressure arch theory, more 

complex geometries, and warning messages that correspond with several issues. This 

PIB also alerts the mining community to precautions that should be taken when using 

this new version. The latest version of ARMPS is available at the National Institute for 

Occupational Safety and Health (NIOSH) web site: 

http://www.cdc.gov/niosh/mining/products/product6.htm. MSHA strongly 

encourages mine operators to use the updated program. 

Background 

The ARMPS program was developed by NIOSH (and the former US Bureau of Mines) 

to assist the mining industry in evaluating ground stability during pillar recovery 

operations. Based on panel geometry and several additional user inputs, the program 

calculates stability factors that can be compared to a relatively large database of 

successful and unsuccessful case histories. The program was first introduced in 1995, 
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modified substantially in 2002 when additional case studies (under deeper overburden 

than the original data set) were included and corresponding design criteria 

wereintroduced, and updated again in February 2008 to include warning messages 

when recommended design criteria were not met. A new version was released in 

September 2010 (version 6). 

Information 

ARMPS program users should be alert to the following issues: 

• Coal Strength Input. NIOSH recommends that 900 psi be used for coal 

strength in the ARMPS program if comparisons are to be made with the 

ARMPS database and the recommended stability factors. 

The current version of ARMPS will display the following warning if the user 

selects a coal strength value other than 900 psi: 

The ARMPS case history data base was analyzed with an in situ coal strength of 900 

psi. Stability factors (SF) obtained with a different in situ coal strength may not be 

comparable to the suggested stability factor values obtained from NIOSH’s analysis 

of the data base. Also, NIOSH research has shown that the reliability of the ARMPS 

design method decreases substantially when laboratory coal strengths were used in 

place of the default value. For more information, see Help/Resources/In situ strength 

of coal [available in the ARMPS Help file]. 

Stability factors determined using a consistent strength value other than 900 

psi could be compared to one another to assess relative stability (e.g., to 

compare successful and failed cases at a given mine site). However, these 

stability factors should not be compared directly with stability factors in the 

ARMPS case history database. Coal strengths other than 900 psi will result in 

stability factors that are inconsistent with those analyzed in the ARMPS 

database. 

• Unit Weight Input. Typical unit weights for coal measure rocks range from 

about 150 to 170 pounds per cubic foot. An unreasonably low value (e.g. 

entering coal density rather than rock density or a typographical error) could 

result in an underestimate of applied load and, consequently, inappropriately 

high stability factors. 

The current version of ARMPS will display the following warning if the user 

selects an overburden unit weight other than 162 pounds per cubic foot: 

The ARMPS case history database was analyzed with an overburden unit weight of 

162 pounds per cubic foot. Stability factors obtained with a different overburden unit 

weight may not be comparable to the suggested stability factor values obtained from 

NIOSH’s analysis of the database. 
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• Breadth of Active Mining Zone (AMZ) Input. Users should be aware that 

stability factors determined using Breadth of Active Mining Zone (AMZ) 

values other than the ARMPS default (i.e., five times the square root of the 

overburden) are inconsistent with those in the ARMPS database. Stability 

factors determined using a consistent AMZ value other than the default could 

be compared to one another to assess relative stability but they should not be 

compared directly with those in the ARMPS case history database. Older 

versions of ARMPS provide no warning if a Breadth of AMZ value other than 

five times the square root of the overburden is input to the program. 

The current version of ARMPS will display the following warning if the user 

de-selects the box titled “Set AMZ automatically”: 

The ARMPS case history data base was analyzed with the breadth of the Active 

Mining Zone (AMZ) calculated automatically (AMZ = 5 times the square root of the 

depth of cover). Stability factors obtained with a different AMZ may not be 

comparable to the suggested stability factor values obtained from NIOSH’s analysis 

of the data base. For more information, see Help/Project Input Parameters [available 

in the ARMPS Help file]. 

• Pressure Arch Factor Input. Users should be aware that stability factors 

determined using Pressure Arch Factor (Fpa) values other than the ARMPS 

default (ie., 0.28 times the natural log of the depth-to-panel-width ratio) are 

inconsistent with those in the ARMPS database. Stability factors determined 

using a consistent Fpa value other than the default could be compared to one 

another to assess relative stability but they should not be compared directly 

with those in the ARMPS case history database. Older versions of ARMPS do 

not include this function. 

The current version of ARMPS will display the following warning if the user 

de-selects the box titled “Set arch factor automatically”: 

The ARMPS case history data base was analyzed with the Pressure Arch Factor 

(Fpa) calculated automatically (Fpa=0.28 times the natural log of the depth-to-panelwidth ratio). Stability Factors (SF) obtained with a different Fpa may not be 

comparable to the suggested SF values obtained from NIOSH’s analysis of the data 

base. For more information, see Help/Project Input Parameters [available in the 

ARMPS Help file]. 

• Entry Height Input. ARMPS users should note that the value entered for 

Entry Height is the mined height of the pillars, which is not necessarily equal 

to the seam thickness. 
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• Design Criteria. The new version of ARMPS includes new design criteria. 

NIOSH recommends a universal minimum pillar stability factor with 

minimum barrier pillar stability factors specified at depths greater than 650 

feet. For narrow panels, alternate design criteria can be applied. These 

criteria are summarized in the table below. 

Table 1: Standard Design Criteria 

Depth of Cover 

(ft) 

Panel Width 

(ft) 

ARMPS SF Barrier Pillar SF 

<650 Any 1.5 No 

Recommendation 

>650 Any 1.5 1.5 

Table 2: Alternate Design Criteria 

Depth of Cover 

(ft) 

Panel Width 

(ft) 

ARMPS SF Barrier Pillar SF 

650-1,000 <425 ⎟

⎠

⎞ ⎜

⎝

⎛ − ×−

350

650 20.05.1 H 2.0 

>1,000 <425 1.3 2.0 

Site-specific criteria used in lieu of NIOSH’s recommendations should be 

developed cautiously using multiple case histories with known conditions at 

a given mine. Back analysis is most appropriate for mines that have a proven 

track record of retreat mining. In these cases, proper examination of 

individual mine data may demonstrate that stability factors above or below 

NIOSH’s recommended values are warranted. Proper examination would 

entail an analysis of the broad experience at a mine site rather than a focus on 

isolated case(s) that represent the extreme. Also, it is imperative that back 

analyses consider barrier pillar stability factors as well as pillar stability 

factors (especially at depths greater than 650 ft.). 

ARMPS criteria should be reevaluated if difficult ground conditions are 

experienced or if changes in mining conditions (e.g., geology or roof support 

type or density) are anticipated. Back-calculated stability criteria should be 

used only in conditions that are consistent with the mine-specific case 

histories. For example, an ARMPS stability factor developed from retreat 

mining experience in routinely developed panels of pillars may be 

inappropriate for recovery in older workings (e.g. mains or submains). Often 

these older workings contain irregularly shaped pillars that complicate the 

recovery process and may not be modeled effectively in ARMPS. 

Furthermore, the pillars, floor, roof, and roof supports may have suffered 

deterioration over time, making older workings unsuitable for pillar 

recovery. Site-specific stability factors that are less than the NIOSH 
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recommendations should not be used unless they are appropriate for the area 

to be mined. 

• Mining Between Gobs. Although the ARMPS program allows users to 

evaluate the recovery of panels between two gobs (ARMPS Loading 

Condition #4), this situation should be avoided if possible. This mining 

scenario can be particularly difficult under deep cover as demonstrated by 

the fact that only 7 of the 19 NIOSH deep cover case studies were successful; 

some of these cases were problematic even with substantial barrier pillar 

stability factors. 

The current version of ARMPS will display the following warning if the user 

elects to evaluate an Active Retreat Section and Two Side Gobs scenario: 

In the ARMPS data base, of the 19 case histories of Active Retreat and Two Side 

Gobs under deep cover, only 7 were successful. This extraction sequence should be 

avoided if possible. 

• Designs using Pressure Arch Factor. Users should be aware that in some 

cases ARMPS uses a pressure arch algorithm to estimate the design loadings 

carried by the pillars in the AMZ. The algorithm was derived from statistical 

analysis of the ARMPS data base. Most of the 645 case histories in the data 

base were obtained from mines located in UT, CO, VA, eastern KY, and 

southern WV. The pressure arch behavior of the overburden in these 

locations may differ from that in other mining regions. Users should exercise 

caution, make conservative assumptions, and use prudent engineering 

judgment when applying the pressure arch algorithm in other mining 

regions. 

The current version of ARMPS will display the following warning if the 

stability factors are calculated using a Pressure Arch Factor that is less than 

1.0 : 

The Pressure Arch loading model used in ARMPS v6 was derived from analysis of 

case history data from the Western and Central Appalachian coalfields in the US. 

The overburden rock in these two coalfields is relatively strong. No research has been 

conducted to test the applicability of the pressure arch loading model in other 

coalfields. 

• Complicated Panel Geometries. The ARMPS program was developed to 

accommodate geometries commonly used in room and pillar retreat mining 

operations. However, some complicated geometries cannot be modeled 

directly. The latest version of ARMPS (version 6) can account for a row of 

pillars left to establish a bleeder system adjacent to mined-out panels, 
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opposite mined-out panels, and in adjacent mined-out panels. Older versions 

of the software cannot. Users should exercise caution, make conservative 

assumptions, and use prudent engineering judgment in applying ARMPS to 

geometries that are not standard in the program. 

The ARMPS program is not ideally suited for situations where unusual stress 

conditions are likely to be encountered (e.g., multiple seam settings). In these 

instances, other models or analysis methods in lieu of or in conjunction with 

ARMPS should be used. 

Authority 

The Federal Mine Safety and Health Act of 1977, as amended, 30 U.S.C. § 801 et seq.; 30 

C.F.R. § 75.203. 

Internet Availability 

This PIB may be viewed on the Internet by accessing the MSHA home page at 

http://www.msha.gov "Compliance Info" and "Program Information Bulletins." 

An updated version of the ARMPS can be downloaded free of charge from the National 

Institute for Occupational Safety and Health (NIOSH) at 

http://www.cdc.gov/niosh/mining/products/product6.htm. 

Issuing Office and Contact Person(s) 

Coal Mine Safety and Health, Division of Safety 

Chris Mark (412) 386-6522 

E-mail: mark.christopher@dol.gov

Technical Support 

Joseph Cybulski, (412) 386-6920 

E-mail: cybulski.joseph@dol.gov 

Distribution 

MSHA Program Policy Manual Holders 

Underground Coal Mine Operators 

Coal Special Interest Groups