ISSUE DATE: 4/1/2011 

PROGRAM INFORMATION BULLETIN NO. P11-19 

FROM: KEVIN G. STRICKLIN

 Administrator for 

 Coal Mine Safety and Health 

 LINDA F. ZEILER

 Acting Director of Technical Support 

SUBJECT: Re-Issue of P08-13 - Use of Single-boom Roof Bolting Machines 

Who needs this information?

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

Administration (MSHA) enforcement personnel should have this bulletin. 

What is the purpose of this bulletin?

The purpose of this Program Information Bulletin (PIB) is to identify the advantages of 

using the “bar” or “beam”-type Automated Temporary Roof Support (ATRS) used on 

dual-boom roof bolting machines as opposed to using the “safety-arm”-type ATRS 

system used on single-boom roof bolting machines. 

What is the background for this PIB?

On June 10, 2005 and January 10, 2006, fatal roof fall accidents occurred in which the 

required support capacity of the ATRS system on two roof bolting machines was 

exceeded. The bolting machines in both of these accidents were single-boom machines 

equipped with “safety-arm”-type ATRS systems required to elastically support a 

deadweight load of at least 11,250 pounds. Although the weight of the roof fall material 

in both cases exceeded this required load, the occurrence of these accidents has 

nevertheless raised concerns regarding the adequacy of such “safety-arm” support 

systems under certain mining conditions. 

Information

Under 30 C.F.R. § 75.209, the required load support capacity of all ATRS systems is based on 

the mine roof area intended to be supported during roof bolt installation. In the United States, 

most roof bolting machines can be categorized into two types: single-
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boom and double-boom. For most single-boom bolting machines, one roof bolt is installed from 

one machine setting and then the machine is re-positioned for the next bolt installation. The area 

intended to be supported for these single-boom machines is a five feet by five feet square 

encompassing the bolt location. A three foot thick layer of rock with a density of 150 pounds per 

cubic foot is assumed to be supported, resulting in a required support capacity under § 75.209 of 

11,250 pounds for the ATRS system on this type of machine.

Dual-boom roof bolting machines with “bar” or “beam”-type ATRS systems are used to 

install multiple roof bolts from one machine and ATRS-setting position. This in turn 

means that the “area intended to be supported” is much larger, resulting in typical 

required load capacities in excess of 33,750 pounds. 

Obviously, with load support capacities at least three times that of single-boom safetyarm ATRS systems, bar-type ATRS systems have a much greater potential to prevent 

roof falls. Also, in addition to their larger support capacity, bar-type ATRS systems 

have several other inherent advantages when compared to safety-arm ATRS systems on 

single-boom bolters. The roof area being supported for a bar-type ATRS, during one 

machine setting, spans the width of the opening. The straight-line beam design of the 

bar system provides a much better “break line” aspect to the support when it comes to 

stopping a roof fall that begins in the unsupported cut inby the ATRS system. On the 

other hand, a safety-arm’s ring or individual roof contact pads are an isolated break 

point around which the fall can continue outby much more easily. 

In addition, as the dual-boom bar-equipped machine is trammed from bolt row to bolt 

row, a consistent effective ATRS position is achieved. In contrast, because single-boom 

machines are squirm-steered from bolt to bolt, they require significantly more machine 

operator attention in order to properly position the ATRS between the unsupported 

roof and the operator. Improper operator positioning has been a contributing factor in 

seven roof fall fatalities involving single-boom machines since 1992. 

 

Another advantage of dual-boom bolters with bar-type ATRS systems compared to 

single-boom bolter systems also results from the time involved. Because far less time is 

spent positioning the machine, and because there are two drill booms compared to one, 

dual-boom bolters can bolt a cut in less than half the time it takes a typical single-boom 

machine. For some types of mine roof, the resulting decrease in roof sag from timely 

bolt installation can greatly improve overall roof control. 

With this in mind, roof bolting operators should consider the following before using a 

single-boom bolter: 

 Bar-type ATRS systems can withstand at least 3 times the load a single-boom 

bolter ATRS can. Whenever possible, use an ATRS bar-equipped bolting 

machine. 
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 Bar-type ATRS systems are much better at acting as a “break line” in stopping 

falls from riding outby. Mine roof that exhibits such “ride-out” characteristics 

when it falls may require a bar-type ATRS system. 

 As the dual-boom bar-equipped machine is trammed from bolt row to bolt row, 

a consistent effective ATRS position is achieved. In contrast, proper 

machine/ATRS position requires significantly more machine operator attention 

when bolting with single-boom bolters. The machine must be properly angled to 

maximize the protection afforded by the ATRS; the ATRS must be between the 

machine operator and unsupported roof. 

 Dual-boom bolters can bolt a cut in less than half the time it takes a typical 

single-boom machine. For some types of mine roof, the resulting decrease in roof 

sag from timely bolt installation can greatly improve overall roof control. 

 Mine roof that is especially susceptible to time-related sag failure may require 

even further limitations with single-boom bolters. Some mines have a cut-depth 

limit of 12 feet when using a single-boom bolter. 

Authority

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

30 C.F.R. § 75.209. 

Internet Availability

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

www.msha.gov then choosing "Compliance Info and then Program Information 

Bulletin.” 

Contact Person(s)

Coal Mine Safety and Health, Safety Division 

Johnny P. Calhoun, (202) 693-9507 

E-mail: calhoun.johnny@dol.gov 

Technical Support 

William J. Gray, (412) 386-6787 

E-mail: gray.william@dol.gov

Distribution

MSHA Program Policy Manual Holders 

Miners' Representatives 
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Coal Mine Operators 

Metal and Nonmetal Mine Operators 

Special Interest Groups