EFFECTIVE DATE: 07/22/2010 EXPIRATION DATE: 03/31/2012 

PROGRAM POLICY LETTER NO. P10-V-04 

FROM: KEVIN G. STRICKLIN

 Administrator for 

Coal Mine Safety and Health 

LINDA F. ZEILER John Faini for 

Acting Director of Technical Support 

SUBJECT: Sampling Sealed Areas with Inert Gas Injection 

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, 

miners’ representatives, and other interested parties. 

Purpose

This PPL provides guidance for sampling sealed areas of mines where inert gas has 

been injected to maintain an inert atmosphere under 30 C.F.R. § 75.336. 

Policy 

If a mine operator chooses to inject inert gas into a sealed area to assist in maintaining 

an inert atmosphere, the mine operator must re-evaluate the adequacy of the sampling 

locations in determining if the atmosphere in the sealed area is inert under 

§ 75.336(a)(2). MSHA has stated: 

Many variables affect the atmospheric composition of the sealed area, 

including size, methane liberation, leakage, ventilation pressures, and 

barometric changes. Mine operators must analyze each sealed area 

when determining appropriate sampling locations and frequencies. If 

the mine operator’s analysis indicates that sampling through seal 

sampling pipes does not render an appropriate evaluation of the sealed 

atmosphere, the mine operator must establish additional sampling 
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locations and specify them in the ventilation plan for the District 

Manager’s approval. 73 Fed. Reg. 21182, 21193 (2008). 
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Injection of inert gas is a variable that affects the atmospheric composition in the sealed 

area. When mine operators inject inert gas into a sealed area, the effectiveness of 

sampling locations cannot be compromised by the inert gas that is being injected. 

Therefore, sampling locations should not be in close proximity to inert gas injection 

points. In particular, injection of inert gas into a sealed area should not occur through 

the same seal where samples are collected to evaluate the atmosphere in the sealed area. 

When existing sampling pipes and injection pipes are limited or non-existent in older 

seals, the mine operator may inject inert gas through a borehole that is separated from 

the seal by an appropriate distance, or the mine operator may sample through 

boreholes located an appropriate distance from the inert gas injection in accordance 

with the approved ventilation plan under § 75.336(a)(2). Boreholes may be drilled from 

the surface, through pillars or through either the roof or floor using directional drilling 

methods. In any case, mine operators should observe the precautions listed in PIB No. 

07-29 (2007) addressing “Breaching and Drilling into Sealed Areas.” Inert gas injection 

locations and the information on the injection system, capacity and proposed operating 

schedule must be submitted to the District Manager with any request to approve 

different sampling locations and frequencies under § 75.336(a)(1)(ii) and (iii). 

Background Information

MSHA has investigated several instances of ineffective sampling in conjunction with 

inert gas injection. In one case, a mine operator injected inert gas into a sealed area 

through a pipe and sampled the atmosphere in the sealed area through a smaller 

diameter pipe inside that injection pipe. The injected inert gas had no real effect on the 

composition of the several hundred thousand cubic feet volume of the sealed area; the 

localized concentration at the end of the sampling pipe only affected the validity of the 

gas sample. Similar problems have occurred where a mine operator injected inert gas 

through a water drainage pipe with the sampling tube inlet near the injection point. 

Authority 

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

30 C.F.R. § 75.336. 

Internet Availability

This PPL may be viewed on the Internet by accessing MSHA Home Page at 

http://www.msha.gov, choosing “Compliance Info,” then choosing “Program Policy 

Letter.” 

Issuing Office and Contact persons

Coal Mine Safety and Health, Safety Division 

Erik Sherer, (202) 693-9523 

E-mail: sherer.hubert@dol.gov
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Technical Support, Pittsburgh Safety and Health Technology Center 

John Urosek, (412) 386-6936 

E-mail: urosek.john@dol.gov

Distribution

MSHA PPM holders 

Underground Mine Operators-Coal 

Miners’ Representatives-Coal