[Federal Register Volume 71, Number 95 (Wednesday, May 17, 2006)]
[Rules and Regulations]
[Pages 28581-28585]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 06-4391]


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DEPARTMENT OF LABOR

Mine Safety and Health Administration

30 CFR Parts 6, 7, and 18

RIN 1219-AB42


Evaluation of International Electrotechnical Commission's 
Standards for Explosion-Proof Enclosures

AGENCY: Mine Safety and Health Administration (MSHA), Labor.

ACTION: Final rule; equivalency determination.

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SUMMARY: MSHA reviewed the requirements of the International 
Electrotechnical Commission's (IEC) standards for Electrical Apparatus 
for Explosive Gas Atmospheres to determine if they are equivalent to 
the Agency's applicable product approval requirements or can be 
modified to provide at least the same degree of protection as those 
requirements. MSHA has determined that the IEC's standards for 
explosion-proof enclosures, with modifications, provide the same degree 
of protection as MSHA's applicable product approval requirements. 
Applicants may request that MSHA grant product approval for explosion-
proof (flameproof) enclosures based on compliance with the IEC 
standards provided MSHA's specified list of modifications is also 
addressed in the submitted design.

DATES: Effective Date: This final rule is effective May 17, 2006. The 
incorporation by reference of certain publications listed in the rule 
is approved by the Director of the Federal Register as of May 17, 2006.

FOR FURTHER INFORMATION CONTACT: For information concerning the 
technical content of the rule, contact David C. Chirdon, Chief 
Electrical Safety Division, Approval and Certification Center, MSHA, 
R.R. 1, Box 251 Industrial Park Road, Triadelphia, West Virginia 26059. 
Mr. Chirdon can be reached at [email protected] (e-mail), 304-547-
2026 (voice), or 304-547-2044 (facsimile). For information concerning 
the rulemaking process, contact Patricia W. Silvey, Acting Director, 
Office of Standards, Regulations, and Variances, MSHA, 1100 Wilson 
Blvd., Arlington, Virginia 22209-3939. Ms. Silvey can be reached at 
(202) 693-9440.
    MSHA maintains a listserve on the Agency's Web site that enables 
subscribers to receive e-mail notification when MSHA publishes 
rulemaking documents in the Federal Register.

[[Page 28582]]

    To subscribe to the listserve, visit MSHA's Web site at http://www.msha.gov/subscriptions/subscribe.aspx. You may obtain copies of 
this final rule in an alternative format by accessing the Internet at 
http://www.msha.gov/REGSINFO.HTM. The document is also available by 
calling 202-693-9440.

SUPPLEMENTARY INFORMATION:

I. Background

    On June 17, 2003, MSHA published a final rule, Testing and 
Evaluation by Independent Laboratories and Non-MSHA Product Safety 
Standards (68 FR 36407). The final rule established alternate 
requirements for testing and evaluation of products that MSHA approve 
for use in gassy underground mines under 30 CFR parts 18, 19, 20, 22, 
23, 27, 33, 35, and 36. The final rule permitted manufacturers seeking 
MSHA approval of their products to use an independent laboratory to 
test their products in accordance with Agency standards. The final rule 
also allowed manufacturers to test their products in accordance with 
non-MSHA standards once the Agency had determined that the non-MSHA 
standards were equivalent to MSHA's applicable product approval 
requirements or could be modified to provide at least the same level of 
protection. The final rule requires that MSHA publish in the Federal 
Register a listing of all equivalency determinations in 30 CFR part 6 
and in the applicable approval parts of 30 CFR.
    At the time the final rule was promulgated, 30 CFR part 7 already 
allowed an applicant or third party to test certain products to MSHA 
standards. Specifically, part 7 specified requirements for MSHA 
approval of applicant or third party testing and evaluation of 
equipment and materials for use in underground mines that do not 
involve subjective testing. Paragraph 7.10(b) required MSHA to publish 
our intent to review any non-MSHA product safety standard for 
equivalency in the Federal Register for the purpose of soliciting 
public input. In addition, paragraph 7.10(c) required MSHA to list our 
equivalency determinations in 30 CFR part 7.
    On December 1, 2003, MSHA announced in the Federal Register (68 FR 
67216) our intent to review the International Electrotechnical 
Commission's (IEC) standards for Electrical Apparatus for Explosive Gas 
Atmospheres, Part 0, General Requirements (IEC 60079-0); Part 1, 
Electrical Apparatus for Explosive Gas Atmospheres, Flameproof 
Enclosures ``d'' (IEC 60079-1); and Part 11, Intrinsic Safety (IEC 
60079-11). The Federal Register notice solicited comments concerning 
the Agency's intent to review the IEC standards.
    MSHA has not yet completed a review of the IEC standard for 
Electrical Apparatus for Explosive Gas Atmospheres, Part 11, Intrinsic 
Safety (IEC 60079-11). Those results will be published separately at a 
later date.
    The IEC is a worldwide organization for standardization comprising 
all national electrotechnical committees. The IEC promotes 
international cooperation concerning standardization in the electrical 
and electronic fields. To this end, the IEC publishes international 
standards in the fields of electricity, electronics, and related 
technologies. The IEC standards referenced in this notice are subparts 
of the IEC standards for hazardous location equipment.
    A 60-day comment period was provided which closed on January 30, 
2004. Comments were received from four (4) commenters. Two commenters 
suggested that MSHA should deem the IEC standards equivalent in their 
unmodified form and urged us to pursue participation in the 
international agreement between countries relative to the IEC standards 
known as the ``IECEx Scheme.'' The goal of the IECEx Scheme is to 
facilitate international trade in electrical equipment intended for use 
in explosive atmospheres (Ex equipment) by eliminating the need for 
multiple national certifications while preserving an appropriate level 
of safety. Two commenters suggested additional standards for MSHA to 
consider reviewing for equivalency in the future. Because these 
comments are beyond the scope of this equivalency determination, the 
Agency will not address them here.
    One commenter expressed concern over what it characterized as 
MSHA's intent to accept international approval standards as equivalent 
to U.S. standards for products used in coal mines. The commenter 
further expressed concern regarding the manner in which the standards 
would be tested and approved.
    As we explained in the preamble to the 2003 final rule, Testing and 
Evaluation by Independent Laboratories and Non-MSHA Product Safety 
Standards (68 FR 36408), MSHA will only accept standards as equivalent 
after carefully evaluating the standards to ensure that they provide at 
least the same degree of protection as existing 30 CFR requirements. 
With respect to part 7 equivalency determinations, MSHA will also 
determine whether the testing and evaluation of the non-MSHA standard 
involves subjective analysis, because the requirements in part 7 apply 
to certain equipment and materials whose product testing and evaluation 
does not involve subjective analysis. Where deficiencies are noted in 
the subject standards, MSHA will add additional requirements to ensure 
that at least the same degree of protection is provided as in existing 
requirements.
    Further, MSHA will review all test and evaluation results submitted 
by independent laboratories to ensure that all applicable requirements 
of the standard and any additional requirements that MSHA specifies 
have been met. If the testing methodology or evaluation results do not 
clearly demonstrate that a product meets the applicable requirements, 
MSHA will conduct an independent evaluation including additional or 
repeat testing. MSHA will also continue the post-approval product audit 
program to ensure compliance with the approved design.
    In the December 1, 2003, Federal Register notice MSHA stipulated 
that at the conclusion of the evaluation, the Agency would publish the 
final determination in the Federal Register. The determination would be 
accompanied by a list of modifications, if they are deemed necessary to 
achieve equivalency. This notice contains MSHA's final determination 
after evaluating the IEC standards.

II. Discussion

    MSHA's review of the International Electrotechnical Commission's 
(IEC) standards for Electrical Apparatus for Explosive Gas Atmospheres, 
Part 0, General Requirements (IEC 60079-0, Fourth Edition, 2004-01); 
and Part 1, Electrical Apparatus for Explosive Gas Atmospheres, 
Flameproof Enclosures ``d'' (IEC 60079-1, Fifth Edition, 2003-11) is 
completed. These two IEC standards together describe the overall 
requirements for design of flameproof enclosures. The IEC 60079-1, 
Flameproof Enclosures ``d'' document provides the specific technical 
design and testing requirements for explosion-proof enclosures while 
the IEC 60079-0, General Requirements document provides the general 
application and use specifications for all IEC Electrical Apparatus for 
Explosive Gas Atmosphere standards. Applicants may request that MSHA 
grant product approval for explosion-proof (flameproof) enclosures 
based on compliance with these IEC standards provided our specified 
list of modifications is also addressed in the submitted design.

[[Page 28583]]

Equivalency Review Results for IEC 60079-0 and IEC 60079-1

    The equivalency review for the IEC standards concerning Electrical 
Apparatus for Explosive Gas Atmospheres, Part 0, General Requirements 
and Part 1, Electrical Apparatus for Explosive Gas Atmospheres, 
Flameproof Enclosures ``d'' involved comparing them with MSHA's 
corresponding requirements for explosion-proof enclosures found in 30 
CFR part 7--Testing by applicant or third party and part 18--Electric 
motor-driven mine equipment and accessories.
    MSHA's technical review consisted of a detailed comparison of the 
IEC requirements for Group I (mining) enclosures to MSHA's requirements 
for explosion-proof enclosures. MSHA's requirements for explosion-proof 
enclosures are based on three principles. First, an enclosure shall be 
rugged in construction and suitable for use in mining applications. 
Second, it shall have a minimum structural yield pressure of at least 
150 psig, without significant permanent distortion, and third, there 
shall be no visible luminous flames or ignitions of a combustible 
methane-air atmosphere surrounding the enclosure during explosion 
testing.
    Part 7 specifies requirements for MSHA-approval of applicant or 
third party testing and evaluation of equipment and materials for use 
in underground mines that do not involve subjective testing. In 
addition to our review for equivalency, MSHA reviewed the IEC 
requirements for testing and evaluation of Group I (mining) enclosures 
to determine that they do not involve subjective analyses. We 
determined that the testing and evaluation of equipment using the 
applicable IEC standards, including MSHA's specified list of 
modifications, does not involve subjective analyses.
    For the purpose of the equivalency review, MSHA organized the 
technical requirements for both the IEC standards being evaluated and 
MSHA's requirements according to certain features that were considered 
common to the design, construction, testing and evaluation of all 
explosion-proof enclosures. Technical requirements for features such as 
mechanical strength, flamepaths, lead entrances, and performance 
testing (including explosion tests and static pressure tests) were used 
as the basis for comparing the standards. Other factors such as 
insulating materials, electrical clearances, voltage limitations, and 
grounding methods were not addressed because these items are not 
considered part of the enclosure certification activities we currently 
perform.
    Specific details of MSHA's findings of the Agency's equivalency 
review can be obtained from http://www.msha.gov/Part6SingleSource/Part6SingleSource.asp or by contacting the Electrical Safety Division, 
Approval and Certification Center, MSHA, R.R. 1, Box 251, Industrial 
Park Road, Triadelphia, West Virginia 26059, [email protected] (e-
mail), 304-547-2026 (voice), or 304-547-2044 (facsimile).
    Based on MSHA's review, the Agency determined that the IEC 
standards could be modified to provide at least the same degree of 
protection as existing requirements. Thus explosion-proof enclosures 
that are designed and tested according to IEC Standards IEC 60079-0 
(Fourth Edition, 2004-01) and IEC 60079-1 (Fifth Edition, 2003-11) may 
be submitted for MSHA product approval subject to the modification set 
out in the regulatory text below.

Section-by-Section Discussion

    This final rule adds Sec.  6.30, MSHA listing of equivalent non-
MSHA product safety standards, which lists non-MSHA product safety 
standards MSHA have evaluated and determined to provide at least the 
same degree of protection with or without modifications. Subparagraph 
6.30(a) specifies the IEC product safety standards reviewed for 
equivalency to MSHA's explosion-proof enclosure standards and 
references sections 7.10(c)(1) and 18.6(a)(3)(i) for a list of the 
required modifications.
    Section 7.10, MSHA acceptance of equivalent non-MSHA product safety 
standards, is amended by revising paragraph (c) to include subparagraph 
(1) listing the specific product safety standard and (1)(i) through 
(1)(ix) specifying required modifications to provide the same degree of 
protection as MSHA requirements.
    Subparagraph (a)(3) of Sec.  18.6, Applications, is amended to 
include subparagraph (i) and subparagraphs (i)(A) through (i)(I). 
Subparagraph (i) lists the specific IEC product safety standards and 
subparagraphs (i)(A) through (i)(I) specify the modifications to the 
IEC standards required to provide the same degree of protection as MSHA 
requirements.

List of Subjects in 30 CFR Parts 6, 7, and 18

    Incorporation by Reference, Mine Safety and Health, Reporting and 
Recordkeeping Requirements, Research.

    Dated: May 3, 2006.
David G. Dye,
Acting Assistant Secretary for Mine Safety and Health.

0
For the reasons set out in the preamble, chapter I of title 30 of the 
Code of Federal Regulations is amended as follows:

PART 6--TESTING AND EVALUATION BY INDEPENDENT LABORATORIES AND NON-
MSHA PRODUCT SAFETY STANDARDS

0
1. The authority for part 6 continues to read as follows:

    Authority: 30 U.S.C. 957.



0
2. Add Sec.  6.30 to read as follows:


Sec.  6.30  MSHA listing of equivalent non-MSHA product safety 
standards.

    MSHA evaluated the following non-MSHA product safety standards and 
determined that they provide at least the same degree of protection as 
current MSHA requirements with or without modifications as indicated:
    (a) The International Electrotechnical Commission's (IEC) standards 
for Electrical Apparatus for Explosive Gas Atmospheres, Part 0, General 
Requirements (IEC 60079-0, Fourth Edition, 2004-01) and Part 1, 
Electrical Apparatus for Explosive Gas Atmospheres, Flameproof 
Enclosures ``d'' (IEC 60079-1, Fifth Edition, 2003-11) must be modified 
in order to provide at least the same degree of protection as MSHA 
explosion-proof enclosure requirements included in parts 7 and 18 of 
this chapter. Refer to Sec. Sec.  7.10(c)(1) and 18.6(a)(3)(i) for a 
list of the required modifications. The IEC standards may be inspected 
at MSHA's Electrical Safety Division, Approval and Certification 
Center, R.R. 1, Box 251, Industrial Park Road, Triadelphia, West 
Virginia 26059 and may be purchased from International Electrical 
Commission, Central Office 3, rue de Varemb[eacute], P.O. Box 131, CH-
1211 GENEVA 20, Switzerland.
    (b) [Reserved].

PART 7--TESTING BY APPLICANT OR THIRD PARTY

0
3. The authority for part 7 continues to read as follows:

    Authority: U.S.C. 957.


0
4. Amend Sec.  7.10 by revising paragraph (c) to read as follows:


Sec.  7.10  MSHA acceptance of equivalent non-MSHA product safety 
standards.

* * * * *
    (c) A listing of all equivalency determinations will be published 
in this

[[Page 28584]]

part 7. The listing will state whether MSHA accepts the non-MSHA 
product safety standards in their original form, or whether MSHA will 
require modifications to demonstrate equivalency. If modifications are 
required, they will be provided in the listing. MSHA will notify the 
public of each equivalency determination and will publish a summary of 
the basis for its determination. MSHA will provide equivalency 
determination reports to the public upon request to the Approval and 
Certification Center. MSHA has made the following equivalency 
determinations applicable to this part 7.
    (1) MSHA will accept applications for motors under Subpart J 
designed and tested to the International Electrotechnical Commission's 
(IEC) standards for Electrical Apparatus for Explosive Gas Atmospheres, 
Part 0, General Requirements (IEC 60079-0, Fourth Edition, 2004-01) and 
Part 1, Electrical Apparatus for Explosive Gas Atmospheres, Flameproof 
Enclosures ``d'' (IEC 60079-1, Fifth Edition, 2003-11) (which are 
hereby incorporated by reference and made a part hereof) provided the 
modifications to the IEC standards specified in Sec.  7.10(c)(1)(i) 
through (ix) are met. The Director of the Federal Register approves 
this incorporation by reference in accordance with 5 U.S.C. 552(a) and 
1 CFR part 51. The IEC standards may be inspected at MSHA's Electrical 
Safety Division, Approval and Certification Center, R.R. 1, Box 251, 
Industrial Park Road, Triadelphia, West Virginia 26059 or at the 
National Archives and Records Administration (NARA). For information on 
the availability of this material at NARA, call 202-741-6030, or go to: 
http://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.html. These IEC standards may be obtained 
from International Electrical Commission, Central Office 3, rue de 
Varemb[eacute], P.O. Box 131, CH-1211 GENEVA 20, Switzerland.
    (i) Enclosures associated with an electric motor assembly shall be 
made of metal and not have a compartment exceeding ten (10) feet in 
length. External surfaces of enclosures shall not exceed 150 [deg]C 
(302 [deg]F) in normal operation.
    (ii) Enclosures shall be rugged in construction and should meet 
existing requirements for minimum bolt size and spacing and for minimum 
wall, cover, and flange thicknesses specified in paragraph(g)(19) of 
Sec.  7.304 Technical requirements. Enclosure fasteners should be 
uniform in size and length, be provided at all corners, and be secured 
from loosening by lockwashers or equivalent. An engineering analysis 
shall be provided for enclosure designs that deviate from the existing 
requirements. The analysis shall show that the proposed enclosure 
design meets or exceeds the mechanical strength of a comparable 
enclosure designed to 150 psig according to existing requirements, and 
that flamepath clearances in excess of existing requirements will not 
be produced at an internal pressure of 150 psig. This shall be verified 
by explosion testing the enclosure at a minimum of 150 psig.
    (iii) Enclosures shall be designed to withstand a minimum pressure 
of at least 150 psig without leakage through any welds or castings, 
rupture of any part that affects explosion-proof integrity, clearances 
exceeding those permitted under existing requirements along flame-
arresting paths, or permanent distortion exceeding 0.040-inch per 
linear foot.
    (iv) Flamepath clearances, including clearances between fasteners 
and the holes through which they pass, shall not exceed those specified 
in existing requirements. No intentional gaps in flamepaths are 
permitted.
    (v) The minimum lengths of the flame arresting paths, based on 
enclosure volume, shall conform to those specified in existing 
requirements to the nearest metric equivalent value (e.g., 12.5 mm, 19 
mm, and 25 mm are considered equivalent to \1/2\ inch, \3/4\ inch and 1 
inch respectively for plane and cylindrical joints). The widths of any 
grooves for o-rings shall be deducted in measuring the widths of flame-
arresting paths.
    (vi) Gaskets shall not be used to form any part of a flame-
arresting path. If o-rings are installed within a flamepath, the 
location of the o-rings shall meet existing requirements.
    (vii) Cable entries into enclosures shall be of a type that 
utilizes either flame-resistant rope packing material or sealing rings 
(grommets). If plugs and mating receptacles are mounted to an enclosure 
wall, they shall be of explosion-proof construction. Insulated bushings 
or studs shall not be installed in the outside walls of enclosures. 
Lead entrances utilizing sealing compounds and flexible or rigid 
metallic conduit are not permitted.
    (viii) Unused lead entrances shall be closed with a metal plug that 
is secured by spot welding, brazing, or equivalent.
    (ix) Special explosion tests are required for electric motor 
assemblies that share leads (electric conductors) through a common wall 
with another explosion-proof enclosure, such as a motor winding 
compartment and a conduit box. These tests are required to determine 
the presence of any pressure piling conditions in either enclosure when 
one or more of the insulating barriers, sectionalizing terminals, or 
other isolating parts are sequentially removed from the common wall 
between the enclosures. Enclosures that exhibit pressures during these 
tests that exceed those specified in existing requirements must be 
provided with a warning tag. The durable warning tag must indicate that 
the insulating barriers, sectionalizing terminals, or other isolating 
parts be maintained in order to insure the explosion-proof integrity 
for either enclosure sharing a common wall. A warning tag is not 
required if the enclosures withstand a static pressure of twice the 
maximum value observed in the explosion tests.
    (2) [Reserved]
* * * * *

PART 18---ELECTRIC MOTOR-DRIVEN MINE EQUIPMENT AND ACCESSORIES

0
5. The authority for part 18 continues to read as follows:

    Authority: 30 U.S.C. 957, 961.


0
6. Amend Sec.  18.6 by revising paragraph (a)(3) to read as follows:


Sec.  18.6  Applications.

    (a) * * *
    (3) An applicant may request testing and evaluation to non-MSHA 
product safety standards which have been determined by MSHA to be 
equivalent, under Sec.  6.20 of this chapter, to MSHA's product 
approval requirements under this part. A listing of all equivalency 
determinations will be published in 30 CFR part 6 and the applicable 
approval parts. The listing will state whether MSHA accepts the non-
MSHA product safety standards in their original form, or whether MSHA 
will require modifications to demonstrate equivalency. If modifications 
are required, they will be provided in the listing. MSHA will notify 
the public of each equivalency determination and will publish a summary 
of the basis for its determination. MSHA will provide equivalency 
determination reports to the public upon request to the Approval and 
Certification Center. MSHA has made the following equivalency 
determinations applicable to this part 18.
    (i) MSHA will accept applications for explosion-proof enclosures 
under part 18 designed and tested to the International Electrotechnical 
Commission's (IEC) standards for Electrical Apparatus for Explosive Gas

[[Page 28585]]

Atmospheres, Part 0, General Requirements (IEC 60079-0, Fourth Edition, 
2004-01); and Part 1, Electrical Apparatus for Explosive Gas 
Atmospheres, Flameproof Enclosures ``d'' (IEC 60079-1, Fifth Edition, 
2003-11) (which are hereby incorporated by reference and made a part 
hereof) provided the modifications to the IEC standards specified in 
Sec.  18.6(a)(3)(i)(A) through (I) are met. The Director of the Federal 
Register approves this incorporation by reference in accordance with 5 
U.S.C. 552(a) and 1 CFR part 51. The IEC standards may be inspected at 
MSHA's Electrical Safety Division, Approval and Certification Center, 
R.R. 1, Box 251, Industrial Park Road, Triadelphia, West Virginia 26059 
or at the National Archives and Records Administration (NARA). For 
information on the availability of this material at NARA, call 202-741-
6030, or go to: http://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.html. These IEC standards may be 
obtained from International Electrical Commission, Central Office 3, 
rue de Varemb[eacute], P.O. Box 131, CH-1211 GENEVA 20, Switzerland.
    (A) Enclosures shall be made of metal and not have a compartment 
exceeding ten (10) feet in length. Glass or polycarbonate materials 
shall be the only materials utilized in the construction of windows and 
lenses. External surfaces of enclosures shall not exceed 150 [deg]C 
(302 [deg]F) and internal surface temperatures of enclosures with 
polycarbonate windows and lenses shall not exceed 115 [deg]C (240 
[deg]F), in normal operation. Other non-metallic materials for 
enclosures or parts of enclosures will be evaluated, on a case-by-case 
basis, under the new technology provisions in Sec.  18.20(b) of this 
part.
    (B) Enclosures shall be rugged in construction and should meet 
existing requirements for minimum bolt size and spacing and for minimum 
wall, cover, and flange thicknesses specified in paragraph (g)(19) of 
Sec.  7.304 Technical requirements. Enclosure fasteners should be 
uniform in size and length, be provided at all corners, and be secured 
from loosening by lockwashers or equivalent. An engineering analysis 
shall be provided for enclosure designs that deviate from the existing 
requirements. The analysis shall show that the proposed enclosure 
design meets or exceeds the mechanical strength of a comparable 
enclosure designed to 150 psig according to existing requirements, and 
that flamepath clearances in excess of existing requirements will not 
be produced at an internal pressure of 150 psig. This shall be verified 
by explosion testing the enclosure at a minimum of 150 psig.
    (C) Enclosures shall be designed to withstand a minimum pressure of 
at least 150 psig without leakage through any welds or castings, 
rupture of any part that affects explosion-proof integrity, clearances 
exceeding those permitted under existing requirements along flame-
arresting paths, or permanent distortion exceeding 0.040-inch per 
linear foot.
    (D) Flamepath clearances, including clearances between fasteners 
and the holes through which they pass, shall not exceed those specified 
in existing requirements. No intentional gaps in flamepaths are 
permitted.
    (E) The minimum lengths of the flame arresting paths, based on 
enclosure volume, shall conform to those specified in existing 
requirements to the nearest metric equivalent value (e.g., 12.5 mm, 19 
mm, and 25 mm are considered equivalent to \1/2\ inch, \3/4\ inch and 1 
inch respectively for plane and cylindrical joints). The widths of any 
grooves for o-rings shall be deducted in measuring the widths of flame-
arresting paths.
    (F) Gaskets shall not be used to form any part of a flame-arresting 
path. If o-rings are installed within a flamepath, the location of the 
o-rings shall meet existing requirements.
    (G) Cable entries into enclosures shall be of a type that utilizes 
either flame-resistant rope packing material or sealing rings 
(grommets). If plugs and mating receptacles are mounted to an enclosure 
wall, they shall be of explosion-proof construction. Insulated bushings 
or studs shall not be installed in the outside walls of enclosures. 
Lead entrances utilizing sealing compounds and flexible or rigid 
metallic conduit are not permitted.
    (H) Unused lead entrances shall be closed with a metal plug that is 
secured by spot welding, brazing, or equivalent.
    (I) Special explosion tests are required for explosion-proof 
enclosures that share leads (electric conductors) through a common wall 
with another explosion-proof enclosure. These tests are required to 
determine the presence of pressure piling conditions in either 
enclosure when one or more of the insulating barriers, sectionalizing 
terminals, or other isolating parts are sequentially removed from the 
common wall between the enclosures. Enclosures that exhibit pressures 
during these tests that exceed those specified in existing requirements 
must be provided with a warning tag. The durable warning tag must 
indicate that the insulating barriers, sectionalizing terminals, or 
other isolating parts be maintained in order to insure the explosion-
proof integrity for either enclosure sharing a common wall. A warning 
tag is not required if the enclosures withstand a static pressure of 
twice the maximum value observed in the explosion tests.
    (ii) [Reserved]
* * * * *
[FR Doc. 06-4391 Filed 5-16-06; 8:45 am]
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