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Safety and HealthFact Sheet No. 28 September 2013 © 2013 American Welding Society 

Oxyfuel Safety: Check Valves and Flashback Arrestors

 

 American Welding Society8669 Doral Blvd.Doral, Florida 33166E-mail: info@aws.orghttp://www.aws.org

Fact Sheet No. 28 – 09/13 

 AWS disclaims liability for any injury to persons or to property, or other damages of any naturewhatsoever, whether special, indirect, consequential or compensatory, directly or indirectlyresulting from the publication, use of, or reliance on this information. AWS also makes noguaranty or warranty as to the accuracy or completeness of any information published herein.

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INTRODUCTION

Check Valves and Flashback Arrestors aresafety devices for protecting workers usingoxyfuel cutting and welding equipment. Acheck valve is a device that is designed toprevent the unintentional backflow ofgases. A flashback (flame) arrestor is adevice that prevents the propagation of aflame upstream. Note that these devices

reduce the volume of gases available atthe tip/nozzle.

NATURE OF THE HAZARD

 Always be sure there is enough fuel in bothcylinders to complete the operation beforestarting a job. Reverse flow of a gasgenerally happens when one cylinder goesempty during operation, creating animbalance of pressure in the system. A

clogged or blocked tip can also cause abackflow. An extremely hazardoussituation can develop when oxygen andfuel gases are mixed inside the hoses.Reverse flow check valves alone will notstop a flashback in the system. Whenconducting oxy-fuel cutting and weldingoperations, operators can experiencebackfires or flashbacks.

 A backfire is defined as the momentary

recession of the flame into the torch,potentially causing a flashback orsustained backfire. It is usually signaled bya popping sound, after which the flamemay either extinguish or reignite at the end

of the tip. The user hears a “pop” and theflame is extinguished. This can happen athigh gas exit velocities at the nozzle/tip orif the nozzle/tip gets too close to the workpiece. The flame may re-igniteautomatically or the use of an igniter maybe necessary. This is not normally a safetyconcern and, in fact, many manufacturersinduce backfires during design andproduction tests to insure flame integrity of

torches and tips.

 A sustained backfire is defined as therecession of the flame into the torch bodywith continued burning characterized by aninitial popping sound followed by asquealing or hissing sound, potentiallyburning through the torch body.

 A flashback is defined as the recession ofthe flame through the torch and into the

hose, regulator, and/or cylinder, potentiallycausing an explosion. This is a potentiallyhazardous situation, particularly if theflame reaches the hoses where anexplosion will result causing a rupture orseparation of the hose. A flashback isgenerally caused by the reverse flow ofgases upstream into the hoses or otherequipment. This reverse flow is usually theresult of 1) improper shutdown and/orstartup procedures or 2) by allowing

cylinder pressures to become too low or 3)by a check valve that is not workingproperly.

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 American Welding Society8669 Doral Blvd.Doral, Florida 33166E-mail: info@aws.orghttp://www.aws.org

Fact Sheet No. 28 – 09/13 

 AWS disclaims liability for any injury to persons or to property, or other damages of any naturewhatsoever, whether special, indirect, consequential or compensatory, directly or indirectlyresulting from the publication, use of, or reliance on this information. AWS also makes noguaranty or warranty as to the accuracy or completeness of any information published herein.

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 As with any cutting or welding operation,workers need to be aware of theirsurroundings where work is performed.

 Always have approved fire extinguishersnearby and have all personnel trained intheir proper use. Flashbacks can damage

equipment and cause injury to nearbyworkers and equipment. Proper workplaceprecautions such as barriers and otherprotections should be utilized to minimizefire hazards and injury.

HOW TO AVOID THE HAZARD

  Equipment with integrated check valvesand/or flashback arrestors is available.

  Check valves and/or flashbackarrestors can be added to existingequipment. Properly maintained andoperated systems are safe.

  Inspect the entire system before use,and repair or replace defective ordamaged parts.

  Have only qualified people make anyneeded repairs.

  Be sure that there is enough gas inboth cylinders to complete the job.

  Follow the manufacturersrecommended procedures for properstart-up and shut-down of theequipment used.

  Don’t allow the tip to touch the work.

SUMMARY

Flashback arrestors and check valves arenot intended to replace proper practices for

safe operation. They can provide anincreased level of protection in addition tothe manufacturers recommended operatingprocedures. Check valves and flashbackarrestors should be installed at the locationspecified by the manufacturer.

Manufacturers' have begun incorporatingflashback arrestors and check valves as astandard item with all of their torches sold.

INFORMATION SOURCES

 American National Standards Institute(ANSI). Safety in Welding, Cutting, and 

 Allied Processes, Z49.1, published by the American Welding Society, 8669 DoralBlvd., Doral, FL 33166; telephone 800-443-

9353; web site: www.aws.org.

National Fire Protection Association(NFPA), Standard for Fire PreventionDuring Welding, Cutting, and Other HotWork, NFPA 51B, published by theNational Fire Protection Association, 1Batterymarch Park, Quincy, MA 02269-9101; Phone: 617-770-3000; Web site:www.nfpa.org.

CGA TB-3, Hose Line Flashback Arrestors,Compressed Gas Association, Inc., 4221Walney Road, 5th Floor, Chantilly, VA20151; Phone 703-788-2700; Web site:www.cganet.com.

CGA E-5, Torch Standard, CompressedGas Association, Inc., 4221 Walney Road,5th Floor, Chantilly, VA 20151; Phone 703-788-2700; Web site: www.cganet.com.

CGA P1, Safe Handling of CompressedGases in Containers, Compressed Gas Association, Inc., 4221 Walney Road, 5th Floor, Chantilly, VA 20151; Phone 703-788-2700; Web site: www.cganet.com.

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 American Welding Society8669 Doral Blvd.Doral, Florida 33166E-mail: info@aws.orghttp://www.aws.org

Fact Sheet No. 28 – 09/13 

 AWS disclaims liability for any injury to persons or to property, or other damages of any naturewhatsoever, whether special, indirect, consequential or compensatory, directly or indirectlyresulting from the publication, use of, or reliance on this information. AWS also makes noguaranty or warranty as to the accuracy or completeness of any information published herein.

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Occupational Safety and Health Administration (OSHA). Code Of FederalRegulations,Title 29 Labor, Chapter XVII,Parts 1901.1 to 1910.1450, Order No. 869-019-00111-5, U.S. Government Printing

Office, 732 North Capitol Street NW,Washington, DC 20401; Phone: 800-321-6742; Web site: www.osha.gov.