EFFECTIVE DATE: 3/23/2011 EXPIRATION DATE: 3/31/2013

(Reissue of P09-V-13)

PROGRAM POLICY LETTER NO. P11-V-07

FROM: KEVIN G. STRICKLIN

 Administrator for 

 Coal Mine Safety and Health 

 LINDA F. ZEILER

 Acting Director of Technical Support 

SUBJECT: Two-Way Communication and Electronic Tracking System:

 Potential Interference of RF Electromagnetic Fields with Electric

 Blasting Circuits 

Scope

This Program Policy Letter (PPL) applies to Mine Safety and Health Administration 

(MSHA) Coal Mine Safety and Health (CMS&H) personnel, coal mine operators,

manufacturers of communication and electronic tracking systems, and other interested 

parties. 

Purpose

This PPL provides guidance concerning minimum safe distances necessary to prevent 

interference with blasting circuits by electromagnetic waves produced by Radio 

Frequency (RF) from communication and electronic tracking systems. PPL P09-V-01, 

Guidance for Compliance with Post-Accident Two-Way Communications and Electronic 

Tracking Requirements of the MINER Act , provides that communication and electronic

tracking systems should be installed to prevent interference with blasting circuits and 

other electrical systems. 

Policy

Shot-firers in mines using electric initiation to produce coal by conventional mining 

methods or using electrical initiation for other purposes need to work in close proximity 

to electric blasting circuits. 30 C.F.R. § 75.1323(a) requires blasting circuits to be 
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protected from sources of stray electric current. Thus, when shot-firers and other 

miners are wearing or carrying RF transmitting devices, consideration must be given to

the total RF energy transmitted by these devices and the corresponding safe distances 

required to prevent the potential for RF interference with electric blasting circuits. 

Operators must also account for other sources of RF, such as leaky feeder cables, and 

their impact on electric blasting circuits, whether they are used in inby or outby areas. 

Mine operators must specify these safe distances in their ERPs in accordance with 

manufacturers’ instructions and account for the total amount of energy transmitted 

from all devices and other sources used in the vicinity of blasting circuits. 

Mine operators also should specify in the ERP the administrative controls that must be 

used to eliminate interference with blasting circuits and other electrical systems while 

maintaining effective communication and tracking capability. Examples of these 

administrative controls include the use of manual tracking methods while blasting and 

the practice of leaving communication devices at a safe distance from blasting circuits 

when miners are working in close proximity to electric blasting circuits. 

Background Information

The guidance given in PPL P09-V-01 provides that wireless communication and 

electronic tracking systems should be installed to prevent interference with blasting 

circuits and other electrical systems. Coal mines that use conventional mining methods 

utilize explosives in the face area to separate the coal from its natural deposit. 

Underground coal mines also utilize explosives to construct overcasts, create additional 

height for conveyor belt drives, clean up roof falls, etc. Communications and electronic 

tracking systems are sources of RF energy that can interfere with blasting circuits. 

MSHA’s Approval and Certification Center requires, as part of the approval provisions 

for communication and electronic tracking systems and components, that 

manufacturers specify the minimum safe distances that must be maintained between 

their equipment and blasting circuits to prevent interference and unintentional 

initiation of blasting circuits. MSHA has approved in ERPs a separation distance of up 

to 50 feet between components of communication and tracking system and blasting 

components when the mine operator was unable to specify a safe distance based on 

manufacturer’s recommendation. 

MSHA conducted testing using the L-3 Communications ACCOLADE Communication 

and Tracking System in an underground anthracite mine to determine whether the 

radio frequency output levels of the system components and the resulting inducted 

current on a simulated blasting circuit would pose a hazard to miners. MSHA 

concluded that the radio frequency outputs from the L-3 components did not result in 

induced currents sufficient to detonate blasting caps. MSHA will require that certain 

separation distances between components of communication and tracking system and 

blasting components be maintained to provide additional protection. 
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The Institute of Makers of Explosives (IME) Safety Library Publication No. 20 (SLP-20) 

provides recommended minimum separation distances between RF sources and 

explosives, based on power and frequency. This publication was intended to apply to 

surface blasting where RF energy propagates in free space. RF energy, however, may 

behave differently in underground coal mine environments. 

SLP-20 bases the distances in the tables and graphs between RF sources and blasting 

circuits on a 40-mW "no-fire" level for the electric detonator. The "no-fire" power level 

is that DC power delivered directly to the detonator such that the probability of not 

initiating the detonator is 0.999 at a 95% confidence level. The actual amount of energy 

extracted from a RF field by an electric detonator and its blasting circuit is a function of 

transmitting power, transmitter frequency, distance between the RF source and the 

blasting circuit, the antenna gain of the source antenna, and the orientation, size and 

impedance of the blasting circuit (acting as a receiving antenna). Therefore, RF fields 

from tags and other electronic devices may or may not pose a threat to the detonator 

and its circuit. 

It should be noted that the IME is developing safety guidance similar to SLP-20 that will 

be applicable to underground environments. While this guidance ultimately may be 

instructive, it is incumbent on manufacturers of communications and electronic tracking 

systems and mine operators to specify minimum safe distances that prevent 

interference with electric blasting circuits in the underground mining environment. 

Authority

Section 316 of the Federal Mine Safety and Health Act of 1977, as amended, 30 U.S.C. § 

876; 30 C.F.R. §§ 18.23, 75.1312, 75.1313, and 75.1323. 

Internet Availability

This PPL may be viewed on the World Wide Web by accessing MSHA Home Page at 

(http://www.msha.gov), choosing "Compliance Info," and then choosing “Program 

Policy Letter.” 

Issuing Office and Contact persons

Coal Mine Safety and Health, Safety Division 

John Arrington, (202) 693-9525 

E-mail: arrington.john@dol.gov

Technical Support, Approval and Certification Center 

David Chirdon, (304) 547-2026 

E-mail: chirdon.david@dol.gov

Distribution
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MSHA Program Policy Manual Holders

Coal Mine Operators

Manufacturers of Communications and Electronic Tracking Systems

Miners’ Representatives

Special Interest Groups