Committee on NFPA 51A...NFPA 51, Standard for the Design and Installation of Oxygen–Fuel Gas Systems for Welding, Cutting, and Allied Processes, 20072edition. NFPA 400, Hazardous

Committee on NFPA 51A

M E M O R A N D U M

TO: NFPA Technical Committee on Industrial and Medical Gases

FROM: Jeanne Moreau-Correia

DATE: July 31, 2009

SUBJECT: NFPA 51A ROP Letter Ballot

The ROP letter ballot for NFPA 51A is attached. The ballot is for formally voting on

whether or not you concur with the committee’s actions on the proposals. Reasons must

accompany all negative and abstention ballots.

Please do not vote negatively because of editorial errors. However, please bring such

errors to my attention for action.

Please complete and return your ballot as soon as possible but no later than Friday,

August 21, 2009. As noted on the ballot form, please submit the ballot to Jeanne

Moreau-Correia, e-mail to [email protected] or via fax to 617-984-7110.

The return of ballots is required by the Regulations Governing Committee Projects.

Attachment: Proposals

mailto:[email protected]

Report on Proposals – November 2010 NFPA 51A_______________________________________________________________________________________________51A-1 Log #CP1

_______________________________________________________________________________________________Technical Committee on Industrial and Medical Gases,

Review entire document to: 1) Update any extracted material by preparing separate proposals todo so, and 2) review and update references to other organizations documents, by preparing proposal(s) as required.

National Fire Protection Association, 1 Batterymarch Park, Quincy, MA 02169-7471.NFPA 1, Uniform Fire Code™, 20096 edition.NFPA 13, Standard for the Installation of Sprinkler Systems, 20072 edition.NFPA 30, Flammable and Combustible Liquids Code, 20083 edition.NFPA 55, Compressed Gases and Cryogenic Fluids Code Standard for the Storage, Use, and Handling of

Compressed Gases and Cryogenic Fluids in Portable and Stationary Containers, Cylinders, and Tanks, 201005 edition.NFPA 70, National Electrical Code®, 20085 edition.NFPA 72, National Fire Alarm Code®, 2007 edition.NFPA 259, Standard Test Method for Potential Heat of Building Materials, 20083 edition.NFPA 400, Hazardous Materials Code, 2010 edition.NFPA 505, Fire Safety Standard for Powered Industrial Trucks Including Type Designations,Areas of Use,

Conversions, Maintenance, and Operations, 2006 edition.NFPA 5000®, Building Construction and Safety Code®, 20096 edition.

American National Standards Institute, Inc., 25 West 43rd Street, 4th Floor, New York, NY10036.ANSI A13.1, Scheme for Identification of Piping Systems, 20071996.

American Society of Mechanical Engineers, Three Park Avenue, New York, NY 10016-5990.ASME B31.3, Process Piping, 20082 edition.

American Society for Testing and Materials, 100 Barr Harbor Drive, West Conshohocken, PA19428-2959.ASTM E 136, Standard Method of Test for Behavior of Materials in a Vertical Tube Furnace at 750°C, 20090 edition.

International Association of Plumbing and Mechanical Officials, 5001 E. Philadelphia Street,Ontario, CA 91761.20093 Uniform Mechanical Code.

Merriam-Webster’s Collegiate Dictionary, 11th edition, Merriam-Webster, Inc., Springfield, MA, 2003.

NFPA 1, Uniform Fire Code™, 20096 edition.NFPA 51, Standard for the Design and Installation of Oxygen–Fuel Gas Systems for Welding, Cutting, and Allied

Processes, 20072 edition.NFPA 400, Hazardous Materials Code, 2010 edition.NFPA 5000®, Building Construction and Safety Code®, 20096 edition.

National Fire Protection Association, 1 Batterymarch Park, Quincy, MA 02169-7471.NFPA 30, Flammable and Combustible Liquids Code, 20083 edition.NFPA 51, Standard for the Design and Installation of Oxygen–Fuel Gas Systems for Welding, Cutting, and Allied

Processes, 20072 edition.NFPA 68, Guide for Venting of Deflagrations, 20072 edition.NFPA 70, National Electrical Code®, 2008 edition.NFPA 77, Recommended Practice on Static Electricity, 2007.NFPA 497, Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous

(Classified) Locations for Electrical Installations in Chemical Process Areas, 2008 edition.

Compressed Gas Association, 4221 Walney Road, Fifth Floor, Chantilly, VA 20151-2923.CGA Pamphlet G-1.6, Recommended Practices for Mobile Acetylene Trailer Systems, 20081.CGA Pamphlet G-1.7, Standard for Storage and Handling of Calcium Carbide in Containers, 20051995.CGA Safety Bulletin SB-4, Handling Acetylene Cylinders in Fires, 20051997.

Underwriters Laboratories Inc., 333 Pfingston Rd., Northbrook, IL 60062-2096UL 2075, Standard for Safety Gas and Vapor Detectors and Sensors, 2004.

1Printed on 7/31/2009

Report on Proposals – November 2010 NFPA 51AU.S. Government Publications. U.S. Government Printing Office, Washington, DC 20402.Title 29, Code of Federal Regulations, Part 1910.38, “Emergency Action Plans.”Title 29, Code of Federal Regulations, Part 1910.165, “Employee Alarm Systems.”

CGA Pamphlet G-1, Acetylene, 20031.CGA G-1.8, Guidelines for the Operation and Closure of Lime Ponds, 20081999.UL 823, Standard for Electric Heaters for use in Hazardous (classified) Locations, 2006.

NFPA 55, Compressed Gases and Cryogenic Fluids Code, 2010 edition.NFPA 400, Hazardous Materials Code, 2010 edition.NFPA 5000, Building Construction and Safety Code®, 2009 edition.

To conform to the NFPA Regulations Governing Committee Projects.NFPA 400 is added in accordance with 51A-14 (Log #CP5).NFPA 72 is added in accordance with 51A-33 (Log #CP13).NFPA 77 is added in accordance with Committee Action on 51A-22 (Log #8).NFPA 497 is added in accordance with 51A-17 (Log #17).UL 873 is added in accordance with Committee Action on 51A-17 (Log #17).UL 2075 is added in accordance with 51A-16 (Log #4).U.S. Government publications are added in accordance with 51A- 33 (Log #CP13).References were added to section B.3 as appropriate.Extract tags for sections 3.3.1.3, 3.3.4, 3.3.5, 3.3.5.1, 3.3.5.2, 3.3.5.3, 3.3.6.2, 3.3.7, 3.3.10, 3.3.11, and 3.3.12 can be

updated as editorial changes.Updates for extracts in sections 3.3.6.1 and 3.3.8 are referred to 51A-11 (Log #CP3) and 51A-12 (Log #CP4),

respectively.All references to NFPA 55 throughout the document will be editorially updated to reflect the current title, Compressed

Gases and Cryogenic Fluids Code.

_______________________________________________________________________________________________51A-2 Log #18

_______________________________________________________________________________________________Keith Le Febvre, Sigma Engineered Systems

Revise as follows:Inspection of generator needs to be performed yearly to check for stress cracks.

Generator (Rexarc style) tends to be stressed at nopper tubes and support feed tube. Cracks canoccur over time.Note: Supporting material is available for review at NFPA Headquarters.

The TC rejected the submittal because there was no specific language proposed to modify thedocument. The submitter is encouraged to submit specific language during the comment phase.


Report on Proposals – November 2010 NFPA 51A_______________________________________________________________________________________________51A-3 Log #19


Clarification of plumbing is required.We provide solutions to customers. one of those solutions was the installation of sight glasses on

Ammonia Scrubbers built by Rexarc. This upgrade is rated at 300 psi and also has needle valves to reduce flow to theseglasses. This provides a very reliable read of what a scrubber is doing and at each hourly inspection can be observedand determined if operating properly. With original equipment—No visual indicator, the only way an operator is alerted ofa problem is on alarm.This also makes setup of the equipment and check out infinitely easier.Sight glasses are being used in the Oxweld NA7 generator as a level indicator as well as water flow indicators and

have predated the Rexarc design.Sight glasses we installed are 300 psi rated on a maximum 15 psi acetylene system. The scrubber and its gaskets will

fail before the sight glass does, particularly with needle valves reducing flow to just what is required and nothing more.It was suggested that these sight glasses violate 51A.Note: Supporting material is available for review at NFPA Headquarters.


_______________________________________________________________________________________________51A-4 Log #20


Static eliminators are required on Rexarc compressor lube systems.Static charge can build up on lube oil canister resulting in 500K volt discharges.

Note: Supporting material is available for review at NFPA Headquarters.


_______________________________________________________________________________________________51A-5 Log #21


Acetylene generator system emergency shutdown needs to be fitted with nitrogen purge and autodeluge activation.

Safety improvement.Note: Supporting material is available for review at NFPA Headquarters.





High pressure relief valves need to be located higher.Valve too low, subject to fouling.



_______________________________________________________________________________________________51A-7 Log #23


A whole new section needs to be applied for scale detection.Cylinders require active bottom inspection for leaks.



_______________________________________________________________________________________________51A-8 Log #13

_______________________________________________________________________________________________Larry L. Fluer, Fluer, Inc. / Rep. Compressed Gas Association

Update all referenced publications to the most current edition of the included documents.In addition: Update the extract text in the following sections:NFPA 1:2009 in Sections 3.3.5, 3.3.5.1, 3.3.5.2 and 3.3.5.3NFPA 51:2007 in Sections 3.3.1.3 and 3.3.7NFPA 5000:2009 in Sections 3.3.4, 3.3.6.2, 3.3.8, 3.3.10, 3.3.11 and 3.3.12.

The extract text should be updated to reflect the current text in the source documents referenced.

Update all referenced publications to the most current edition of the included documents.In addition: Update the extract text in the following sections:NFPA 1:2009 in Sections 3.3.5, 3.3.5.1, 3.3.5.2 and 3.3.5.3NFPA 51:2007 in Sections 3.3.1.3 and 3.3.7NFPA 5000:2009 in Sections 3.3.4, 3.3.6.2, 3.3.10, 3.3.11 and 3.3.12.

The TC action in the meeting was to accept the proposal as submitted. However, committeeaction on 51A-12 (Log #CP4) requires that 3.3.8 be updated as an extract from NFPA 55, not from NFPA 5000. NFPAStaff updated the committee action on this proposal accordingly.




Revise as follows:

Acetylene when compressed and packaged into cylinders is dissolved in a solvent, typicallyacetone or dimethylformamide (DMF). The solvent is absorbed into a porous material that fills the inside of an acetylenecylinder. This method of packaging is unique to acetylene and the US Department of Transportation prohibits the use ofacetylene cylinders for any other gases.

The Maximum Allowable Quantities Per Control Area (MAQ) and detached building thresholdlevels are applied based on evaluation of the applicable physical or health hazards of the material being classified. Themaximum allowable quantity per control area (MAQ) and detached building threshold quantity for each hazard class isfound in NFPA 55, Compressed Gases and Cryogenic Fluids Code. The MAQ and detached building threshold levelsmay also be specified by the applicable building code or fire prevention code adopted by local, state or federalregulations.

When acetylene is produced in a gaseous undissolved, or unstabilizedstate, it is classified as a non-liquefied flammable, unstable reactive Class 3 (non-detonable) gas in accordance with therequirements of NFPA 704, Standard System for the Identification of the Hazards of Materials for Emergency Response.

Acetylene is stabilized when it is packaged for shipment or storage bydissolving the gas in a solvent authorized by the Department of Transportation and absorbing the resultant solution in aporous filler material that fills the inside of the acetylene cylinder. Stabilized acetylene is classified as a non-liquefiedflammable gas and a Class 2 unstable reactive gas.

The TC added the informational Annex material to provide a distinction between the hazardclassification of acetylene in process versus the hazard classification of acetylene dissolved in compressed gascylinders. In addition, the material provides guidance that will assist users in identifying the proper hazard classificationand apply the proper protection level controls.

_______________________________________________________________________________________________51A-10 Log #CP6


Add new definition for building code extracted from NFPA 55-2010, Section 3.3.10:The building or construction code adopted by the jurisdiction. [55, 2010]

(Renumber subsequent)Portions of plants housing acetylene generation and charging and acetylene cylinder storage operations

classified as Protection Level 2, 3, or 4 shall be located in accordance with the requirements of NFPA 5000, BuildingConstruction and Safety Code. the building code.

When mixed-occupancy buildings are to be separated by the use of occupancyseparations, fire-resistive separations shall be provided in accordance with the building codeNFPA 5000, BuildingConstruction and Safety Code.

Exits shall be provided in accordance with the building codeNFPA 5000, Building Construction and Safety Code,as required for Protection Level 2, 3, or 4 occupancies as applicable.

Calcium carbide storage buildings shall be constructed in accordance with the building codeNFPA 5000, BuildingConstruction and Safety Code.

The TC is making the term "building code" broader to include any building code a jurisdiction mayaccept and making references throughout the document consistent with this concept. The approach is harmonized withthat used by NFPA 55.




Update definition 3.3.6.1 to extract from NFPA 5000-2009, including Annex Material:Refers to a building construction material not complying with the definition of

noncombustible material that, in the form in which it is used, has a potential heat value not exceeding 3500 Btu/lb (8141kJ/kg), where tested in accordance with NFPA 259, Standard Test Method for Potential Heat of Building Materials, andincludes either of the following: (1) materials having a structural base of noncombustible material, with a surfacing notexceeding a thickness of 1⁄8 in. (3.2 mm) that has a flame spread index not greater than 50; and (2) materials, in theform and thickness used, having neither a flame spread index greater than 25 nor evidence of continued progressivecombustion, and of such composition that surfaces that would be exposed by cutting through the material on any planewould have neither a flame spread index greater than 25 nor evidence of continued progressive combustion, whentested in accordance with ASTM E 84, Standard Test Method of Surface Burning Characteristics of Building Materials;or UL 723, Standard for Test of Surface Burning Characteristics of Building Materials. [5000, 2009]

Material subject to increase in combustibility or flame spread index beyondthe limits herein established through the effects of age, moisture, or other atmospheric condition is consideredcombustible. See NFPA 259, Standard Test Method for Potential Heat of Building Materials, and NFPA 220, Standardon Types of Building Construction. Where the term limited-combustible is used in this Code, it is also intended to includethe term noncombustible. [5000,2009]

The TC updated the extracted material to be consistent with NFPA 5000-2009.

_______________________________________________________________________________________________51A-12 Log #CP4


Revise text as follows:A temperature of 21°C (70°F) at an absolute pressure of 101.325

kPa (14.7 psia). A temperature of 70°F (21°C) at an absolute pressure of 14.7 psi (101.3 kPa). [55, 2010]The TC updated the definition to harmonize with NFPA 55-2010.




Revise text to read as follows:Construction-related controls specified for buildings, and portions thereof, where high hazard

contents are stored, used, or handled in quantities greater than the maximum allowable quantity per control area as specified in NFPA 5000. The requirements forconstruction vary with the type of hazardous materials employed.

A tier of building safety that exceeds the construction requirements for control areas toaccommodate quantities of hazardous materials in excess of those permitted using the control area concept. [2009]

NFPA uses the concept of protection levels in a manner that is analogous to Group Hoccupancies in other model codes. Although NFPA 1 and NFPA 5000 do not have unique occupancy classifications foroccupancies containing hazardous materials, Protection Levels 1 to 5 in NFPA codes and standards reflect increasedbuilding safety requirements that are applicable to occupancies containing hazardous materials, which generallycorrelate to the Group H, Division 1 to 5 occupancy classifications in other codes. [ 2009]

Delete the existing definition of Protection Levels and replace it with extract text from NFPA 50002009. The definition is also correlated with NFPA 55:2009.

_______________________________________________________________________________________________51A-14 Log #CP5


Add a definition for "Secondary Containment" extracted from NFPA 400, Section 3.3.73, includingannex note.

That level of containment that is external to and separate from primary containment.[400, 2010]

Examples of secondary containment include dikes, curbing, remote impoundment, and double-walled tanks.[400, 2010]

The TC added a definition for secondary containment because the term is used in chapter 10 andpreviously lacked a formal definition.




Revise text to read as follows:

Rooms housing acetylene operations, excluding calcium carbide storage rooms (see 5.2.7), shall be provided withmechanical exhaust or fixed natural ventilation ventilated in accordance with NFPA 55, Standard for the Storage, Use,and Handling of Compressed Gases and Cryogenic Fluids in Portable and Stationary Containers, Cylinders, andTanks.that ventilates the space at a rate of not less than 1 ft3/min/ft2 (0.03 m3/min/0.09m2) of floor area over the area ofstorage or use.

Rooms or areas where gases other than acetylene are stored or used shall be ventilated in accordance withNFPA 55 .

Calcium carbide storage rooms shall be in accordance with 5.2.7.When mechanical exhaust systems are provided the systems shall operate continuously

unless an alternate design is approved by the authority having jurisdiction.Mechanical exhaust ventilation shall be permitted to be reduced below 1

ft3/min/ft2 (0.03 m3/min/0.09 m2), provided that full ventilation is automatically restored when the acetylene concentrationexceeds 25 percent of the lower flammable limit (LFL) when measured by a gas detection system in accordance withSection 4.5.

Where powered exhaust ventilation is provided, a manual shutoff switch shall be providedoutside of the room in a position adjacent to the principal access door to the room or in an approved location.

The switch shall be of the break-glass or equivalent type and shall be labeled as follows:WARNING: VENTILATION SYSTEM EMERGENCY SHUTOFF

Inlets to exhaust systems serving rooms used for acetylene operations shall belocated within 12 in. (304.8 mm) of the highest point in the room.

Exhaust ventilation shall not be recirculated within the room or building.The point of termination for the exhaust ventilation system discharge shall be a minimum

of 15 m (50 ft) from air intakes to building ventilation systems, air-conditioning equipment, and air compressors.

Fixed natural ventilation. The movement of air into and out of a space through permanent openings that are arrangedin such a way that the required ventilation cannot be reduced by operating windows, doors, louvers or similar devices.

The use of ventilation systems varies with the location of the manufacturing facility. Facilities locatedin warmer climates traditionally use natural ventilation as a means to ventilate the space and in warmer climates it is notunusual for a facility to have one exterior wall and a roof, or simply a roof for protection from the elements. On the otherhand, facilities in colder climates are more likely to be enclosed and mechanical systems are used as a means toprovide ventilation. The reference to NFPA 55 requires the code user to interpret application, e.g., are the gasesheavier or lighter than air, etc. The revised provisions are intended to interpret the requirements of NFPA 55 as theymay be applicable to acetylene manufacturing operations. Minor modifications were made to the fundamentalprovisions found in NFPA 55 for clarification. For example, the terms “mechanical exhaust ventilation” or “exhaustventilation” were used to differentiate between mechanical and natural means.Ventilation for calcium carbide storage rooms was left under the direction of the building code as each building requires

fundamental ventilation to prevent deterioration of the building and requirements vary based on occupancy.Additional reasons as to specific changes by section are as follows:Section 4.4: Requirements for ventilation have been revised to establish the criteria applicable to acetylene operations

under the specific criteria listed in the sections that follow. Provisions have been added to recognize that naturalventilation may be used in lieu of mechanical exhaust as specified in NFPA 55. A term “fixed natural ventilation” hasbeen added to avoid a reduction in required ventilation from the area under consideration.Section 4.4.1: This section is in effect an exception to 4.4 which defers to NFPA 55 for requirements when rooms or

areas are used for gases other than acetylene.Section 4.4.2: The provisions for calcium carbide storage rooms including construction features and ventilation are

found in NFPA 5000.Section 4.4.3 and 4.4.4: Requirements based on NFPA 55. The requirements in 4.4.3.1 have been relocated from

existing Section 4.4.1 with minor edits in units of measure.Section 4.4.5 Acetylene with a molecular weight of 26 is lighter than air. The provisions for lighter than air gases have


Report on Proposals – November 2010 NFPA 51Abeen drawn from NFPA 55 with a minor clarification to indicate that the highest point in the room or area is a boundingfactor.Section 4.4.6: The exhaust air is treated as “one pass” air and recirculation is prohibited.Section 4.4.7: The point of termination for the ventilation discharge is coordinated with the requirements of NFPA 55.

Editorial revisions have been made to the SI conversions equivalent to 1cfm/sf for clarity.A new definition has been added to Chapter 3 to define “fixed natural ventilation.” Ventilation systems that can be shut

down by closing a door, window or similar devices should not be relied upon to be functional in all circumstances. Insome cases the walls of the room may be open with the area located under a roof. In other cases ventilation may beachieved through the use of natural draft or similar means. When natural ventilation is used as a means of control it isintended that the openings used for the introduction or removal of air from the space be maintained in an opencondition.

_______________________________________________________________________________________________51A-16 Log #4


Revise Section 4.5 as follows:

Rooms in which acetylene operations are conducted shall be provided with an a listed or approved flammable gasdetection system.

A listing standard for gas detection and sensing systems is published by Underwriter’s Laboratories as UL 2075.Gas detection systems shall not be required for structures equipped with fixed natural ventilation and constructed

as weather protection in accordance with the requirements of NFPA 55,.

The flammable gas detection system shall be listed or approved for use withacetylene and any other flammable gases used in the room.

Add the following informational reference to Annex B under a new section for Underwriter’s Laboratories (UL):UL 2075, UL Standard for Safety Gas and Vapor Detectors and Sensors, 2004.Add the following referenced publication to Section 2.2:NFPA 55, , 2009.

Gas detection systems specified in Section 4.5 are required to be approved, while the gas detectionsystems required in existing Section 4.5.1.1 are required to be listed. NFPA 51A is a “Standard” and gas detectionsystems should be able to be either listed or “approved.” UL 2075 provides a listing standard for application in the eventa listing is sought. By providing for the use of either a listed or “approved” gas detection system safety is maintainedwhile allowing for the development of new technology.A new Section 4.5.1 has been provided to exempt areas equipped with natural ventilation from the requirements for

gas detection systems. Gas detection in spaces that are constructed with natural ventilation do not provide an adequatemeans to collect meaningful samples of the atmosphere of the surrounding space thereby calling into question theefficacy of any installed gas detection system. For areas constructed as “weather protection (See NFPA 55:2009:6.5.2the space is considered to be an outdoor area. Areas equipped with mechanical exhaust ventilation systems whereoperation of the mechanical system is designed to meet the minimum requirements for ventilation are required to beprotected by a gas detection system as such spaces are allowed to reduce the required ventilation based on thepresence of the gas detection system.




Revise text to read as follows:Listed electric heaters shall be allowed to be used in operating areas regulated by 4.7.2 when installed and

used in accordance with the manufacturer’s instructions and the listing.The autoignition temperature for acetylene as listed in NFPA 497

is 305°C (581°F). Acetylene is the only material listed as being in Group A atthe present time. Electrical equipment is required to comply with the requirements of NFPA 70,

based on Class and Group designations determined by conditions as well as the material present.Boilers, water heaters and other heating equipment containing one or more of the following potential hazards

employing flames, or capable of creating sparks shall be located in a separate building or room not directlycommunicating with areas devoted to acetylene operations.(1) Open flames.(2) Release of sparks or spark generation during operation.(3) Exposed surface temperatures exceeding the lowest autoignition temperature of any of the materials present.

The Electrical Code (NFPA 70) establishes the requirements for the use of electrical equipment andreferences NFPA 497 for specific materials where the autoignition temperature of acetylene is published. NFPA 51A:1.5would allow the use of this equipment today, when approved by the AHJ. Section 4.7 establishes the requirements forelectrical equipment, and all electrical equipment must comply with the electrical code. A change in Section 4.6 to allowthe use of listed electrical heating systems is in accord with the electrical code, and listed equipment is available thatcan be installed in electrically classified areas. Although the use of listed equipment in itself imposes requirementsregarding the ignitability of vapors information regarding the autoignition temperature of acetylene is included in thecode change.Section 4.6.1.1 is in effect an exception to 4.6.1 to allow the use of listed equipment. A reference to 4.7.2 is included to

alert the user to the base classification for areas of this nature. Listed products can be accessed on the Underwriter’sLaboratories (UL) website at www.UL.com. There are products available that can be used in both Class I and IIlocations and are suitable for use with various Groups classifications including those in Group A, B, C, etc.The proposed revision to Section 4.6.2 is to alert users to the fact that surface temperatures are of concern as well as

active sources of ignition such as open flame and sparks. The revision to the term “create sparks” has been made todirect the user to either a release of sparks or spark generation rather than opening the potential for spark creation toinclude things like the materials of construction for equipment contained in the area or other extrinsic elements of theinstallation such as floor construction, etc..

Revise text to read as follows:4.6.1.1* Electric heaters listed for installation in hazardous locations shall be allowed to be used in operating areas

regulated by 4.7.2 when installed and used in accordance with the manufacturer’s instructions and the listing.A.4.6.1.1 The autoignition temperature for acetylene as listed in NFPA 497

is 305°C (581°F). Acetylene is the only material listed as being in Group A atthe present time. Electrical equipment is required to comply with the requirements of NFPA 70,

based on Class and Group designations determined by conditions as well as the material present.4.6.2 Boilers, water heaters and other heating equipment containing one or more of the following potential hazards

employing flames, or capable of creating sparks shall be located in a separate building or room not directlycommunicating with areas devoted to acetylene operations.(1) Open flames.(2) Release of sparks or spark generation during operation.(3) Exposed surface temperatures exceeding the lowest autoignition temperature of any of the materials present.Also add UL 823 Standard for Electric Heaters for use in Hazardous (classified) Locations to Appendix B.

The TC clarified the language to reflect that electric heaters must be listed for installation inhazardous locations to minimize confusion on the part of the user. There are several standards for listing electricheaters, and the modification to the proposal specifies that only heaters listed for use in hazardous locations shall bepermitted.


Report on Proposals – November 2010 NFPA 51A

_______________________________________________________________________________________________51A-18 Log #15


Revise text to read as follows:Calcium carbide shall be stored in packages meeting U.S. Department of Transportation or Transport Canada

regulations or in containers approved by the authority having jurisdiction.Calcium carbide may be stored or handled in containers other than original shipping containers. For

example, hoppers that are used for transfer of the material or silos used to store the material may be used. Containersused in-house are not designed for release into the transportation system; therefore having a broad requirement to meetthe requirements of the transportation system is not practical.

_______________________________________________________________________________________________51A-19 Log #5


Revise text to read as follows:The use of multiple pressure relief devices serving the same section of a gas generator shall be allowed.,

provided that the aggregate cross-sectional venting area of the individual pressure relief devices is not less than thecross-sectional area of the common vent line to which they are connected.

When multiple pressure relief devices are connected to a common vent line or manifold the cross-sectionalarea of the common vent line or manifold shall not be less than the aggregate cross-sectional venting area of theindividual pressure relief devices connected.

The aggregate cross sectional area of the connected pressure relief devices is the sum of the crosssectional areas for each of the individual relief devices connected to the manifold.

Existing Section 6.3.2.6 is in error. The cross sectional area of the common vent line serving a systemmust be not less than or larger than the cross sectional areas of the pressure relief devices served. As currently writtenone could connect a series of pressure relief devices to a common vent line thereby exceeding the carrying capacity ofthe common vent line creating a back pressure on the system in the event multiple relief devices were to operate. Theparagraph has been divided into a charging statement and a subparagraph in keeping with the Manual of Style. Aclarifying note has been added to further explain the use of the term “aggregate” within the context of the requirements.




Revise text to read as follows:When discharging to sumps, pits, or other receptacles, the point of discharge shall be located outdoors not

less than 15 ft (4.5 m) 25 ft (7.6 m) from sources of ignition and the line of adjoining property that is able to be builtupon.

The minimum required distances shall not apply when fire barriers without openings or penetrations having aminimum fire resistive rating of 2 hours interrupt the line of sight between the storage and the exposure. Theconfiguration of the fire barriers shall be designed to allow natural ventilation to prevent the accumulation of hazardousgas concentrations.

The separation distance of 25 feet has been correlated with changes proposed to Section 8.1.1.1.1.The 25 foot distance correlates the requirements for separation from ignition sources as found in 55:7.6.3.2 whichprohibits the use of open flame, smoking and ignition sources within 25 feet of the area used for the storage or use offlammable gases. It could be noted that there is an apparent inconsistency between the requirements of 55:Table 7.6.2for separation from property lines as the table uses variable distances based on quantity. On the other hand thedischarge to sumps, pits, etc. represent a circumstance where it must be assumed that the gas is always present. As aresult the required distances are conservatively based.Encroachment on sources of ignition or property lines is allowed by proposed Section 6.5.1.2.1 in a manner consistent

with that used in 55:Table 7.6.2.

6.5.1.2 When discharging to sumps, pits, or other receptacles, the point of discharge shall be located outdoors notless than 15 ft (4.5 m) 25 ft (7.6 m) from sources of ignition and the line of adjoining property that is able to be builtupon.6.5.1.2.1 The minimum required distances shall not apply when fire barriers without openings or penetrations having a

minimum fire resistive rating of 2 hours interrupt the line of sight between the point of discharge and the exposure. Theconfiguration of the fire barriers shall be designed to allow natural ventilation to prevent the accumulation of hazardousgas concentrations.

The TC clarified the reference to "storage" as specifically the "point of discharge".

_______________________________________________________________________________________________51A-21 Log #6


Revise the title to Chapter 7 as follows:

Revise the title to Section 7.3 as follows:

Purifiers and driers shall have inlet and outlet shutoff valves located and arranged so that they are able to be closed inan emergency.

By definition LOW pressure acetylene does not exceed 1 psig. MEDIUM pressure acetylene includespressures in the range >1 psig /= 15 psig to



Revise Section 8.1.1.1.1 as follows:Drain lines from high pressure [pressure above 15 psi (103 kPa)] acetylene systems, oil separators,

condensate traps, and driers shall be piped outdoors to a location away from any not less than:(1) 25 feet (7.6 m) from building openings.(2) 25 feet (7.6 m) from sources of ignition. and(3) 10 feet (3 m) from combustible material.(4) 50 feet (15.2 m) from air intakes.

The minimum required distances shall not apply when fire barriers without openings or penetrationshaving a minimum fire resistive rating of 2 hours interrupt the line of sight between the drain line discharge and theexposure. The configuration of the fire barriers shall be designed to allow natural ventilation to prevent the accumulationof hazardous gas concentrations.

Drains lines are designed to drain condensate or other fluids, they are not “vent” lines which are used tovent or exhaust gases from the system. Drain lines should be piped to the outside of the building to avoid potentialevolution of vapors that have been entrained into a liquid discharge. The location and collection of liquid drainage willbe controlled by environmental considerations depending on the nature of the discharge.Additional safeguards may be required when high pressure acetylene is vented. Protection against the potential ignitionof vented gases due to a static electric discharge should be considered. For further information see NFPA 77

The use of rapid opening valves in drain lines should be avoided in orderthat unintended ignition does not occur.

Add NFPA 77 to Annex I.1.1 as follows: NFPA 77, 2007 edition.Piping of any drain line should be to the exterior of the building, and not just those lines serving oil

separators, condensate traps and driers. As currently written the term “away from” is unenforceable as it fails to providethe designer with guidance as to specific location. Distances have been chosen to correlate with the approach used inNFPA 55. Refer to Section 7.6.2.5 for distance from building openings; Section 7.1.6.3 for separation fromcombustibles, Section 7.6.3.2 for sources of ignition and Section 7.6.2.4 for the distance from air intakes. Drain linesare not vent lines per se, rather they are designed to “drain” fluid, however, it is possible to have gases entrained intothe liquid and venting to the outside is appropriate.In older facilities the drain lines were taken to a drain pit or lime pond, in newer facilities the drain lines may be taken to

tanks where the atmosphere in the tank is vented through a vent line. Additional requirements for discharge fromsystems that may contain residual calcium carbide or waste products from the process may be found in Section 6.5.Section 8.1.1.1.1.1 has been added to provide flexibility to the user through the use of fire barriers. The concept has

been taken from footnote “a” to Table 7.6.2 in NFPA 55. The reduction in distance from air intakes is allowed with therecognition that discharge from a drain line is controlled. The discharge from system leakage or component failure suchas those anticipated by 55:Table 10.3.2.2.1 is not applicable as the discharge is controlled through the process.Informational annex notes have been provided to inform the reader as to the purpose of the drain lines and to avoidconfusion between requirements for system vents which are regulated under separate requirements. Additionalprecautionary information is provided regarding concerns for static electricity and the use of rapid opening valves (ballvalves, etc.) in discharge lines that could lead to unintended ignition in the drain line system.

8.1.1.1.1* Drain lines from high pressure [pressure above 15 psi (103 kPa)] acetylene systems, oil separators,condensate traps, and driers shall be piped outdoors to a location away from any sources of ignition and combustiblematerial not less than:(1) 25 feet (7.6 m) from building openings.(2) 25 feet (7.6 m) from sources of ignition. and(3) 10 feet (3 m) from combustible material.(4) 50 feet (15.2 m) from air intakes.8.1.1.1.1.1 The minimum required distances shall not apply when fire barriers without openings or penetrations having

a minimum fire resistive rating of 2 hours interrupt the line of sight between the drain line discharge and the exposure.The configuration of the fire barriers shall be designed to allow natural ventilation to prevent the accumulation ofhazardous gas concentrations.


Report on Proposals – November 2010 NFPA 51AA.8.1.1.1.1 Drains lines are designed to drain condensate or other fluids, they are not “vent” lines which are used to

vent or exhaust gases from the system. Drain lines should be piped to the outside of the building to avoid potentialevolution of vapors that have been entrained into a liquid discharge. The location and collection of liquid drainage willbe controlled by environmental considerations depending on the nature of the discharge.Additional safeguards may be required when high pressure acetylene is vented. Protection against the potential ignitionof vented gases due to a static electric discharge should be considered. For further information see NFPA 77

The use of rapid opening valves in drain lines should be avoided in orderthat unintended ignition does not occur.

Add NFPA 77 to Annex B.1.1 as follows: NFPA 77 2007.The TC corrected the original submittal to reflect existing text in the standard.

_______________________________________________________________________________________________51A-23 Log #7


Delete Section 8.1.1.2 and relocate it to become a new Section 7.4 with modifications to includelow pressure systems as follows (underlining and strikeouts show the modifications from 8.1.1.2):

Drain lines from low and medium gaugepressure [15 psi (103 kPa) and lower] acetylene systems shall be permitted to be piped to an indoor drain where theeffluent water drained from the system is visible to the operator from the drain valve location.

Chapter 8 is specific to acetylene compressors and high pressure driers. Section 8.1.1.2 was draftedto address requirements for low and medium pressure systems. Relocating the provision to Chapter 7 puts therequirement in the proper chapter.

_______________________________________________________________________________________________51A-24 Log #2


Revise text to read as follows:Vent lines pipes serving equipment provided with pressure relief

devices shall be in accordance with 6.3.2.Vent lines pipes serving pressure relief valves shall be in

accordance with 6.3.2.The title to Sections 8.1.1.3 and 8.1.2.2 and the terminology used in the accompanying text has been

revised to be consistent with Section 6.3.2. Section 6.3.2 consistently refers to these lines as “pipes.” Although theterm “line” is used for other services, e.g., discharge lines (Section 8.1.2.3.2), inlet lines (8.1.2.3.1), etc., the term pipe isused when vents are mentioned. The change is intended to be editorial and consistency is warranted throughout thedocument.




Revise text to read as follows:When provided, valves installed between the compressor and the pressure switch or device shall be

equipped with positive lock-open devices to ensure that the valve(s) is are maintained in a locked open position whenthe compressor is in operation.

This is an editorial change.

_______________________________________________________________________________________________51A-26 Log #CP9


Revise text to read:For Pipe of nominal size 6 in. (152 mm) and less (≤152 mm), all pipe shall be a minimum of Schedule 40, and all

pipe fittings shall have a minimum rating of a gauge pressure of 125 psi (861 kPa).All Pipe of nominal size 1 in. (25 mm) and less (≤25 mm) shall be not less than Schedule 80.All Pipe of nominal sizes 11⁄4 in. (32 mm) and 11⁄2 in. (38 mm) shall be not less than Schedule 160.All Pipe fittings shall have a minimum working pressure of a gauge pressure of 3,000 psi (20,684 kPa).

The changes are editorial.

_______________________________________________________________________________________________51A-27 Log #11


Revise text to read as follows:Cylinder charging manifolds shall be provided with a shutoff valve and a blow-down valve vented to the

outdoors or to the low pressure system.The blow-down valve shall either be arranged to vent the manifold to the outdoors in accordance with

6.3.2.4.2 or the discharge shall be returned to a low or medium pressure acetylene system with the pressure rating andcapacity to contain both the maximum pressure and volume released from the manifold.

Additional safeguards may be required when high pressure acetylene is vented. Protection against thepotential ignition of vented gases due to a static electric discharge should be considered. For further information seeNFPA 77 The use of rapid opening valves in vent lines should be avoidedin order that unintended ignition does not occur.

By definition a low pressure system is 1 psig or less. It is not uncommon for a facility to have amedium pressure system that would be available to vent the filling manifold back into. Venting of overpressure into lowor medium pressure systems is able to be done safely providing the system receiving the gas has both the capacity andthe pressure rating sufficient to handle the gas returned. A new subsection (10.1.1.1) and accompanying annex notehas been created to address the requirements of the Manual of Style.




Revise text to read as follows:Cylinder charging manifolds shall be provided with a shutoff valve and a blow-down valve vented to the

outdoors or to the low pressure system.The blow-down valve shall either be arranged to vent the manifold to the outdoors in accordance with

6.3.2.4.2 or the discharge shall be returned to a low or medium pressure acetylene system with the pressure rating andcapacity to contain both the maximum pressure and volume released from the manifold.

By definition a low pressure system is 1 psig or less. It is not uncommon for a facility to have amedium pressure system that would be available to vent the filling manifold back into. Venting of overpressure into lowor medium pressure systems is able to be done safely providing the system receiving the gas has both the capacity andthe pressure rating sufficient to handle the gas returned. A new subsection (10.1.1.1) and accompanying annex notehas been created to address the requirements of the Manual of Style.

_______________________________________________________________________________________________51A-29 Log #1


Revise text to read as follows:A check valve shall be installed in the pipeline at each cylinder charging manifold and in each cylinder charging

lead.Check valves shall not be required on charging leads used to charge individual cylinders on mobile acetylene

trailer systems equipped with manifold systems serving multiple containers.Mobile acetylene trailers contain cylinders that are manifolded in place. Cylinders are filled through

the same manifold that is connected to the user system when the trailer is used as a mobile source. A check valve is aone-way valve that allows flow in one direction and blocks the flow in the reverse direction. When individual cylindersare placed into use the gas is controlled by the user through individual pressure control and discharge systemsfurnished by the user. By contrast the gas supply cylinders on mobile acetylene trailers are filled and consumed througha fixed manifold piping system integral to the trailer where the user provides controls on the discharge from the manifoldsystem. Gas must be able to flow both into and out of the fixed cylinder manifold system, and the inclusion of checkvalves on individual cylinder leads would preclude either the filling or the use of gas through a singular piping system.Removal of the requirement for check valves allows the manifold system to function in a bidirectional manner whencylinders are filled or when the system is in use. Placement of a check valve on the cylinder manifold at the userlocation may be done, however, the check valve is not part of the mobile acetylene trailer system.

_______________________________________________________________________________________________51A-30 Log #CP11


Revise text to read as follows:Cylinder charging manifolds shall be arranged so that stress in the cylinder charging leads is limited to prevent

failure when connected for charging or transportation.The TC clarified the requirement to describe the conditions under which failure may occur.




Revise Section 10.6 to address safeguards to include fire protection requirements for MobileAcetylene Trailer Systems (MATS) for MATS charging facilities attendant to acetylene charging plants.

Mobile Acetylene Trailer Systems (MATS) are the subject of Section 10.6. At the current timereference is made to CGA G-1.6 Recommended Practices for Mobile Acetylene Trailer Systems, through the use of anannex note. There have been two recent (2007) fires involving MATS at user sites during unloading operations whichhave come to the attention of the National Transportation Safety Board (NTSB). Specific recommendations have beenmade by the NTSB regarding the G-1.6 document and CGA’s Acetylene Committee is currently in the process ofrevising the publication with revision expected to be completed at the end of 2009. Copies of the NTSB report on thefires at the unloading facilities have been added to the IMG TCs e-committee pages and the document is on file atNFPA offices. The proposed code change has been entered to allow CGA’s Acetylene Committee complete the task ofreview in order that the industry can reach consensus on the issue of fire protection for MATS at both loading as well asunloading facilities.Fire protection is the subject of Chapter 11 and perhaps a new Section 11.2.2 is the appropriate place to establish a

requirement for MATS. The proposal has been crafted to allow further consideration or clarification of the controlstrategy applicable to MATS within the context of the NFPA 51A document.The IMG TC task group on NFPA 51A is reviewing the NTSB report and potential revisions that may affect NFPA 51 arealso being discussed.

The submittal does not include specific text for modifications to the existing standard. The TCrecognizes that work continues with the IMG 51A Task Group and the CGA G-1.6 Committee and encourages thosegroups to submit specific text for the ROC phase.

_______________________________________________________________________________________________51A-32 Log #CP12


Revise text as follows:Acetylene cylinder shipping and receiving docks and plant entrances shall be posted with a sign

declaring the following or equivalent prohibition:

WARNING: NO OPEN FLAMESSMOKING STRICTLY PROHIBITED

The TC added language to the required sign to specify that all sources of ignition are prohibited.




Revise text as follows:Emergency alarms shall be provided in accordance

with NFPA 55, Standard for the Storage, Use, and Handling of CompressedGases and Cryogenic Fluids in Portable and Stationary Containers,Cylinders, and Tanks.Employee Alarm System. Where required by government regulations, an employee alarm systemshall be provided to allow warning for necessary emergency action as called for in the emergency action plan requiredby 11.2.3, or for reaction time for safe egress of employees from the workplace or the immediate work area, or both. [55,2010]

Where provided, employee alarm systems shall comply with NFPA 72, National Fire Alarm Code.Under the requirements of 29 CFR 1910.38 established by OSHA regulations, employers must establish an

employee alarm system that complies with 29 CFR 1910.165. The requirements of 29 CFR 1910.165 for the employeealarm system include, but are not limited to, systems that are capable of being perceived above ambient noise or lightlevels by all employees in the affected portions of the workplace. Tactile devices may be used to alert those employeeswho would not otherwise be able to recognize the audible or visual alarm. The alarm system can be electrically poweredor powered by pneumatic or other means. State, local, or other governmental regulations might also establishrequirements for employee alarm systems. [55, 2010]

The requirement was updated to harmonize requirements with NFPA 55 in preparation for merging ofthe NFPA 51A with NFPA 55.

_______________________________________________________________________________________________51A-34 Log #CP14


Revise text as follows:Refer to NFPA 51, Standard for the Design and Installation of Oxygen–Fuel Gas Systems for Welding, Cutting,

and Allied Processes, for of acetylene generators generating plants where the acetylene is used with oxygen forwelding, cutting, heating, and heat-treating operations.

The TC clarified the language to be consistent with NFPA 51.

_______________________________________________________________________________________________51A-35 Log #CP8


Revise text to read:

Refer to the diagram for an example of pressure relief vent piping.The TC believes that a diagram illustrating the location of the relief device discharge.

The TC rejected the proposal because no diagram was available at the time of the ROP. TheNFPA 51A Task Group will continue to work on this issue.




Add text as follows:A check valve shall be installed in the pipeline at each cylinder charging manifold and in each cylinder charging

lead.Refer to the diagram for a typical valve arrangement.

A diagram in the annex to clarify this requirement.

No diagram was provided. The NFPA 51A task group will continue to work on this issue.

_______________________________________________________________________________________________51A-37 Log #12


1. Delete the title for B.2 Informational References and combine the remaining publications withB.1.2.1.B.2 Informational References2. Revise the CGA references located in B.1.2.1 (and B.2) to the current publication and reorder as follows.CGA Pamphlet G-1, 2001 2003.CGA Pamphlet G-1.6, 2001 2008.CGA Pamphlet G-1.7, 1995 2005.CGA G-1.8, 1999 2008.CGA Safety Bulletin SB-4, 1997 2005.

Item No. 1: Strike the title for B.2 and incorporate the references to CGA G-1 and G-1.8 into B.1.2.1.All of the references to CGA Publications are informational references having a subdivision of Informational Referencesunder a list of Informational References is not needed. All of the CGA references are informational.Item No. 2: Update the list of CGA references to the current publication as indicated.

Revise the CGA references located in B.1.2.1 (and B.2) to the current publication and reorder as follows.B.1.2.1CGA Pamphlet G-1.6, 2001 2008.

CGA Pamphlet G-1.7, 1995 2005.B.2CGA Pamphlet G-1, 2001 2003.CGA G-1.8, 1999 2008.CGA Safety Bulletin SB-4, 1997 2005.

In the ROP meeting, the TC voted to accept the proposal. However, NFPA Manual of Stylesection 1.9.10.1 mandates the three sections required for Informational References: X.1 for references that are cited inAnnex A (or other informational annexes as applicable); X.2 for other informational references that are not cited in theinformational annexes; and X.3 References for Extracts in informational annexes. NFPA Staff updated the CommitteeAction to conform with the NFPA Manual of Style.


Documents

Committee on NFPA 51A...NFPA 51, Standard for the Design and Installation of Oxygen–Fuel Gas Systems for Welding, Cutting, and Allied Processes, 20072edition. NFPA 400, Hazardous