API RP 2210-2000

Flame Arresters forVents of Tanks StoringPetroleum Products

API RECOMMENDED PRACTICE 2210THIRD EDITION, MAY 2000

COPYRIGHT 2003; American Petroleum Institute

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Flame Arresters forVents of Tanks StoringPetroleum Products

Downstream Segment

API RECOMMENDED PRACTICE 2210THIRD EDITION, MAY 2000



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SPECIAL NOTES

API publications necessarily address problems of a general nature. With respect to partic-ular circumstances, local, state, and federal laws and regulations should be reviewed.

API is not undertaking to meet the duties of employers, manufacturers, or suppliers towarn and properly train and equip their employees, and others exposed, concerning healthand safety risks and precautions, nor undertaking their obligations under local, state, or fed-eral laws.

Information concerning safety and health risks and proper precautions with respect to par-ticular materials and conditions should be obtained from the employer, the manufacturer orsupplier of that material, or the material safety data sheet.

Nothing contained in any API publication is to be construed as granting any right, byimplication or otherwise, for the manufacture, sale, or use of any method, apparatus, or prod-uct covered by letters patent. Neither should anything contained in the publication be con-strued as insuring anyone against liability for infringement of letters patent.

Generally, API recommended practices are reviewed and revised, reafÞrmed, or with-drawn at least every Þve years. Sometimes a one-time extension of up to two years will beadded to this review cycle. This publication will no longer be in effect Þve years after itspublication date as an operative API recommended practice or, where an extension has beengranted, upon republication. Status of the publication can be ascertained from the APIDownstream Segment [telephone (202) 682-8000]. A catalog of API publications and mate-rials is published annually and updated quarterly by API, 1220 L Street, N.W., Washington,D.C. 20005.

This document was produced under API standardization procedures that ensure appropri-ate notiÞcation and participation in the developmental process and is designated as an APIstandard. Questions concerning the interpretation of the content of this recommended prac-tice or comments and questions concerning the procedures under which this standard wasdeveloped should be directed in writing to the director of the Downstream Segment, Ameri-can Petroleum Institute, 1220 L Street, N.W., Washington, D.C. 20005. Requests for permis-sion to reproduce or translate all or any part of the material published herein should also beaddressed to the general manager.

API recommended practices are published to facilitate the broad availability of proven,sound engineering and operating practices. These recommended practices are not intendedto obviate the need for applying sound engineering judgment regarding when and wherethese standards should be utilized. The formulation and publication of API recommendedpractices is not intended in any way to inhibit anyone from using any other practices.

Any manufacturer marking equipment or materials in conformance with the markingrequirements of an API recommended practice is solely responsible for complying with allthe applicable requirements of that recommended practice. API does not represent, warrant,or guarantee that such products do in fact conform to the applicable API standard.

All rights reserved. No part of this work may be reproduced, stored in a retrieval system, or transmitted by any means, electronic, mechanical, photocopying, recording, or otherwise,

without prior written permission from the publisher. Contact the Publisher, API Publishing Services, 1220 L Street, N.W., Washington, D.C. 20005.

Copyright © 2000 American Petroleum Institute



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FOREWORD

This publication is intended to provide guidelines for evaluating the need for the use ofßame arresters on the vents of tanks storing petroleum products.

API publications may be used by anyone desiring to do so. Every effort has been made bythe Institute to assure the accuracy and reliability of the data contained in them; however, theInstitute makes no representation, warranty, or guarantee in connection with this publicationand hereby expressly disclaims any liability or responsibility for loss or damage resultingfrom its use or for the violation of any federal, state, or municipal regulation with which thispublication may conßict.

Suggested revisions are invited and should be submitted to the director of the DownstreamSegment, American Petroleum Institute, 1220 L Street, N.W., Washington, D.C. 20005.

iii



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CONTENTS

Page

1 INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2 SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

3 BACKGROUND. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

4 FLAME ARRESTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

5 PRESSURE-VACUUM VALVES AS A SUBSTITUTE FOR FLAME ARRESTERS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

6 SUMMARY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

7 CONCLUSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

v



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1

Flame Arresters for Vents of Tanks StoringPetroleum Products

1 Introduction

1.1

In addition to connections for liquid entry and with-drawal, every atmospheric Þxed-roof tank requires a vent thatallows escape or entry of air and/or vapors to avoid develop-ment of pressure or vacuum conditions sufÞcient to damagethe tank during liquid transfer or changes in ambient condi-tions. This publication discusses the beneÞts and detrimentsassociated with the use of ßame arresters on these vents.

1.1.1

The provisions of this publication are intended foruse when designing new facilities or when considering majorexpansions. It is not intended that the recommendations inthis publication be applied retroactively to existing facilities.This publication also can be used as guidance when there is aneed or desire to review existing facilities.

1.2

NFPA 30,

Flammable and Combustible Liquids

Code,

lists requirements for tank vents in which ßammable andcombustible liquids are stored. API Standard 2000,

VentingAtmospheric and Low-Pressure Storage

Tanks,

and NFPA 30cover the size and venting capacity to accommodate normaland emergency conditions of the tanks. Devices that are nor-mally closed, except when operating under pressure or vac-uum conditions, are often called pressure-vacuum valves.Such valves are normally required for ßammable liquids (seeNFPA 30). Additional information on vents and pressure-vac-uum valves can be found in API Standard 620,

Design andConstruction of Large, Welded Low-Pressure Storage Tanks,

and API Standard 650,

Welded Steel Tanks for Oil Storage.

Under certain circumstances, ßame arresters listed by theUnderwritersÕ Laboratories or approved by the FactoryMutual Engineering and Research Corporation are used inconjunction with, or in lieu of, a pressure-vacuum valve. Thepublications cited are considered standards for good practice,and may be incorporated in mandatory codes or ordinances insome jurisdictions.

1.3

The most recent edition or revision of each of the fol-lowing standards, codes, and publications are referenced inthis Publication as useful sources of additional informationsupplementary to the text. Additional information may beavailable from the cited Internet World Wide Web sites.

API

www.api.org

Std 620

Design and Construction of Large, WeldedLow-Pressure Storage Tanks

Std 650

Welded Steel Tanks for Oil Storage

Std 2000

Venting Atmospheric and Low-PressureStorage Tanks

Publ 2028

Flame Arresters in Piping Systems

RP12N

Recommended Practice for the Operation,Maintenance and Testing of Firebox FlameArresters

AIChE

1

(CCPS)

www.aiche.org/docs/ccps

Guidelines for Engineering Design for Process Safety

FM

2

www.factorymutual.com

Approval GuideÑA Guide to Equipment, Materials & Ser-vices Approved by Factory MutualResearch Corporation for PropertyConservation

Class 6061 Flame Arresters for Vent Pipes of StorageTanks

NFPA

3

www.nfpa.org

30

Flammable & Combustible Liquids Code

69

Standard on Explosion Prevention Systems

OSHA

4

www.osha.gov

1910.106

Subpart HÑHazardous Materials

UL

5

www.ul.com

Gas and Oil Equipment Directory

525

Flame Arresters

2 Scope

2.1

This publication covers ßame arresters on vents forabove-ground steel petroleum tanks operating essentially atatmospheric pressure as deÞned in API Standard 650,

WeldedSteel Tanks for Oil

Storage.

1

American Institute of Chemical Engineers, Center for ChemicalProcess Safety, 345 East 47th Street, New York, New York 10017.

2

Factory Mutual Insurance Company, 1151 Boston ProvidenceTurnpike, P.O. Box 9102, Norwood, Massachusetts 02062.

3

National Fire Protection Association, 1 Batterymarch Park, Quincy,Massachusetts 02269.

4

U.S. Department of Labor, Occupational Safety and Health Admin-istration, 200 Constitution Ave. NW, Washington, D.C. 20210.

5

Underwriters Laboratories, 333 PÞngsten Road, Northbrook, Illi-nois 60062.



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2 API P

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2210

2.2

SpeciÞcally excluded from the scope of this publicationare all in-line ßame arresters such as

Flame Arresters in Pip-ing Systems

which are addressed in API Publication 2028 orßame arresters for marine vapor control systems (which haverequirements regulated by the Federal Government, Title 33

CFR

Part 154).

Operation, Maintenance and Testing of Fire-box Flame Arresters

is the subject of API RecommendedPractice RP12N. API Publication 2028 discusses the inßu-ence of ßame speed on ßame arrester performance for deßa-grations (subsonic ßame speed) and detonations (ßamepropagation at speeds greater than the speed of sound). Tankvent ßame arresters are not intended for protection againstdetonation.

3 Background

3.1

In the early history of the petroleum industry, whenstorage tanks were constructed of wood or wrought iron withwooden roofs, there were spectacular losses from tank Þres.Lightning or other ignition sources that ignited vapors in (orescaping from) the tank usually caused the tank Þres. Thepermeability and combustible nature of wooden roofs con-tributed to the start and magnitude of the Þres.

3.2

The losses caused by Þres and the evaporation of crudeoil and gasoline in wooden-roof tanks contributed to thedevelopment and use of riveted steel-roof tanks. The tightnessof the riveted steel-roof tanks led to the need for controlledtank venting. The use of a valve that remains tightly closedduring periods when the tank internal pressure is within spec-iÞed limits but that promptly opens when pressure or vacuumexceeds those limits can prevent tank damage and reduce Þrelosses. This valve, initially known as a breather valve, is nowmore commonly known as a conservation vent or a pressure-vacuum (PV) valve.

3.3

As steel-roof tanks began to replace wooden ones, itwas noted that lightning-caused Þres continued to occur intanks with wooden roofs, but tanks with steel roofs were vir-tually immune to lightning-caused Þres. Based on this experi-ence, steel-roof tanks were selected for the storage of volatilestocks. Such tanks were usually equipped with pressure-vac-uum valves as a measure to reduce evaporation loss. A 1925API committee report documented the fact that the combina-tion of a tight steel roof and a pressure-vacuum valve gavevirtually complete protection against lightning-caused Þres;the use of this combination in the ensuing years has con-Þrmed this report.

4 Flame Arresters

4.1

The term

ßame arrester

describes a device or form ofconstruction that will allow free passage of a gas or gaseousmixture but will interrupt or prevent the passage of ßame. Itprevents the transmission of ßame through a ßammable gas/

air mixture by quenching the ßame on the high surface areaprovided by an array of small passages through which theßame must pass. The emerging gases are cooled enough toprevent ignition on the protected side. Effective and reliablearresting devices are designed for many speciÞc situations.The metal screen in the coal minersÕ Davy safety lamp andthe tiny passages in the sintered metal powder device in acombustible gas indicator are examples of ßame-arrestingdevices.

4.2

Arresters have been made incorporating wire screens,small metal tubes, drilled holes, or passages between inter-leaved corrugated and ßat sheets of metal for use on tanksstoring gasoline and similar ßammable liquids. Such deviceshave been tested and listed as acceptable by the UnderwritersLaboratories or approved by the Factory Mutual InsuranceCompany. The listing is based on tests made with mixtures ofhydrocarbon vapor and air of maximum explosiveness, withprescribed limitations on the manner of installation. Forexample, a pipe extension on the atmospheric side of thearrester that is longer than the extension used in the test inval-idates the listing (see UnderwritersÕ Laboratories

Gas and OilEquipment Directory

and the

Factory Mutual ApprovalGuide).

For other vapors or gases and for installations that donot conform to the arrangement described in the listing, thereis no assurance that the arrester will be effective.

4.3

Problems in the application and maintenance of tankßame arresters occur from a number of causes such as:

1. The tank vapor must pass through the arresterÕs narrowpassages causing a friction loss that may reduce the ßowcapacity below that of an open pipe or a vent pipe with apressure-vacuum valve of comparable size. Thus, thepressure drop must be considered when a ßame arrester isselected.

2. Narrow passages can clog with dust, scale, polymers orairborne debris. A rigorous maintenance program is nec-essary to avoid vent plugging and the possibility ofpressure or vacuum-related damage to the tank roof.

3. The water bottoms of certain petroleum tanks producehigh-humidity in the vapor space. Ice can accumulate andclog the arrester in freezing weather and jeopardize thetank. External environmental icing conditions can alsocause arrester plugging. To remedy an icing situation, thearrester must be heated or removed. Since removal wouldnullify the protection for which the arrester was installed,heat tracing may be required.

4. The need for periodic inspecting and cleaning affordopportunities for errors in reassembly, possibly makingthe arrester incapable of stopping ßame.

5. A listed ßame arrester is not reliable indeÞnitely, evenin perfect conditions. Although the mixture of hydrocar-



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F

LAME

A

RRESTERS

FOR

V

ENTS

OF

T

ANKS

S

TORING

P

ETROLEUM

P

RODUCTS

3

bon vapor and air employed in the UnderwritersÕLaboratories tests is the mixture most likely to ßashthrough a narrow passage, evidence exists that a richermixture could burn at the inlet of the ßame arrester andproduce heat damage which may render the device inca-pable of preventing ßame propagation. UL 525 includesan

Endurance Burn Test

and a

Continuous Flame Test

totest ßashback potential. Arresters categorized as Type I aretested using the

Endurance Burn Test

which requires a Þreto burn from the ßame arresterÕs exit for at least two hoursafter which time ßashback should not occur. Type IIarresters are designed to resist ßashback in the UL 525

Continuous Flame Test

which requires a ßame to burnfrom the exit of the ßame arrester during ten minute inter-vals for at least one hour.

6. Flame arrester maintenance requires safe access toavoid placing personnel at risk and to facilitate efÞciency.

4.4

The above limitations are recognized in NFPA 30 (seeparagraph 2Ð3.5.7) and in the paragraphs introducing theproducts in the UnderwritersÕ Laboratory

Gas and Oil

Equip-ment Directory

and the

Factory Mutual Approval

Guide.

5 Pressure-Vacuum Valves As a Substitute For Flame Arresters

5.1

NFPA 30 and OSHA 1910.106(b)(2)(iv)(f) recognizethat a pressure-vacuum valve is an acceptable alternative to aßame arrester under certain circumstances. This recognitionis based on tests started in 1920, supplemented by many yearsof experience.

5.2

Even in mixtures of maximum ßammability, ßame can-not pass back through an opening if the efßux velocityexceeds a critical value. Tests by the Bureau of Mines andothers made with mixtures of gasoline components and airßowing through openings typical of tank vents have demon-strated that this critical velocity is approximately 10 feet persecond. In a valve set to close when the upstream pressurefalls below approximately

3

/

4

inch of water, the velocity ofßow across the pallet-seat area exceeds twice this criticalvelocity. The ßame propagation cannot overcome the gasßow to pass from the low-pressure to the high-pressure side.In these tests, ßame was snuffed out when the valve closed asthe upstream pressure was deliberately reduced to test andconÞrm this condition. Chapter 13 of the AIChE CCPS book,

Guidelines for Engineering Design for Process Safety,

dis-cusses ßame arresters and cites test work done which sub-stantiates velocity ßame stopping.

5.3

Tests have also shown that under some circumstancesa long-burning ßame at the valve outlet could damage thevalve sufÞciently to interfere with its closing. Under suchcircumstances, ßashback may occur when the ßow rate falls

below the critical velocity, if a ßammable mixture existsinside the tank.

6 Summary

6.1

The desire to protect a tank vent from ßashback is basedon the

theoretical

potential for a simultaneous occurrence ofan ignition source in the vicinity of the vent and the releasefrom the vent of a mixture capable of transmitting ßame.

6.2

Ignition sources such as open ßames usually are, andcertainly can be, excluded from the vicinity of tank vents.Falling embers, unless actually ßaming, are not an ignitionsource for petroleum vapors. Lightning is a potential ignitionsource, as demonstrated by the occasional ignition of ventstacks that release vapor continuously. However, such stacksare usually taller and thus a much more attractive target forlightning than a tank vent.

6.3

The availability of a mixture capable of producingßashback must be considered. Stocks stored at temperaturesbelow their ßash points do not produce ignitable mixtures inthe vapor space. Crude oil and gasoline generally producemixtures too rich to transmit ßame. Expelled vapor, if ignited,will burn as a torch until its ßow ceases, at which time the Þrewill go out. If a tank containing crude oil, gasoline or similarhydrocarbon materials with volatile fractions were to breathein a substantial volume of air, it is possible that the dilutedmixture within the vapor space in the tank could fall withinthe ßammable range. Such a condition. however, is likely tobe brief. There are, of course, a few stocks that produce amixture within the ßammable range under normal atmo-spheric conditions. These stocks are the exceptions and maywarrant special consideration.

6.4

The conditions under which a tank can exhale must beexamined. Whether because of Þlling or ambient conditionchange, this exhaling period is unlikely to exist more thanhalf the time.

6.5

Flashback through an open tank vent can only resultfrom the coincidental occurrence of two unlikely eventsÑefßux of a ßammable mixture and the presence of an ignitionsource (such as lightning) at the right time and place. Therecords support the belief that the probability of this coinci-dence is very low.

6.6

Most companies have accepted the premise that a tightsteel roof and a pressure-vacuum valve provide appropriateprotection and that any potential additional protectionafforded by ßame arresters does not warrant their installationin addition to a pressure-vacuum valve. API Standard 2000(4.4.1.2) and NFPA 30 (paragraph 2Ð3.5.6) state that a ßamearrester is not considered necessary for use in conjunctionwith a pressure-vacuum valve where the tank is normallyclosed except when venting. This is consistent with OSHArequirements in 1910.106(b)(2)(iv)(f).



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4 API P

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7 Conclusion

A systematic evaluation based on engineering analysis andtests, supported by experience, show that there is no technicalor experiential basis for requiring that an outdoor above-ground petroleum tank provided with a pressure-vacuumvalve must also be equipped with a ßame arrester.

For practical safety considerations the use of ßame arrest-ers for these vents is discouraged to avoid tank damage result-ing from the introduction of a new failure mode, unless theuser is able to institute the ßame arrester maintenance neces-sary to ensure that the required venting capacity is main-tained.



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05/00—6C



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Additional copies available from API Publications and Distribution:(202) 682-8375

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Documents

API RP 2210-2000