Protection Against Ignitions Arising Out of Static, Lightning, and Stray Currents

API RECOMMENDED PRACTICE 2003 SEVENTH EDITION, JANUARY 2008

Protection Against Ignitions Arising Out of Static, Lightning, and Stray Currents

Downstream Segment

API RECOMMENDED PRACTICE 2003 SEVENTH EDITION, JANUARY 2008

Special Notes

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

Neither API nor any of API's employees, subcontractors, consultants, committees, or other assignees make any warranty or representation, either express or implied, with respect to the accuracy, completeness, or usefulness of the information contained herein, or assume any liability or responsibility for any use, or the results of such use, of any information or process disclosed in this publication. Neither API nor any of API's employees, subcontractors, consultants, or other assignees represent that use of this publication would not infringe upon privately owned rights.

API publications may be used by anyone desiring to do so. Every effort has been made by the Institute to assure the accuracy and reliability of the data contained in them; however, the Institute makes no representation, warranty, or guarantee in connection with this publication and hereby expressly disclaims any liability or responsibility for loss or damage resulting from its use or for the violation of any authorities having jurisdiction with which this publication may conflict.

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

Any manufacturer marking equipment or materials in conformance with the marking requirements of an API standard is solely responsible for complying with all the applicable requirements of that standard. 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 © 2008 American Petroleum Institute

Foreword

This updated publication was prepared under the direction of the API Safety and Fire Protection Subcommittee. The first edition was published in 1956 with subsequent editions in 1967, 1974, 1982, 1991 and 1998. This seventh edition builds on the technically sound work presented in prior editions. It emphasizes the need to maintain awareness and the continuing need to develop and use sound procedures for controlling hazards and minimizing the possible static ignition risks associated with handling hydrocarbons.

Producing fuel with low sulfur content typically requires increased processing. One example of a low sulfur specification is the regulatory requirements for reduced sulfur content of Diesel fuel (15 ppm max effective in mid- 2006 in the USA). Similar regulations exist in the European Community. Severe hydroprocessing can remove natural constituents of the fuel and result in very much lower conductivity, often below 2 C.U. at field conditions This in turn enhances the ability of the fuel to generate and accumulate static charges while simply flowing through pipes. While there is not a direct correlation between sulfur level and conductivity, current data shows that most highly processed low sulfur hydrocarbons fuels have low conductivity. (European experience suggests that some highly processed fuels may also have a greater charging tendency than fuels subjected to less severe processing.) This edition of API Standard 2003 defines a new third “ultra-low conductivity” classification for hydrocarbons. This is included in the definitions and used when discussing residence times in Section 4.

The advent of “Ultra-low Sulfur Diesel” ULSD fuel into the marketplace reinforces the need to understand and use good operating procedures with regards to “switch loading.” The precautionary advice provided in this seventh edition of API Std 2003 is essentially the same as in prior editions. Further, the safe operations challenge increases to the extent that ULSD products have lower conductivities than conventional diesel fuels. Inclusion of the third “ultra-low conductivity” classification should help those handling bulk products safely meet that challenge.

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

This document was produced under API standardization procedures that ensure appropriate notification and participation in the developmental process and is designated as an API standard. Questions concerning the interpretation of the content of this publication or comments and questions concerning the procedures under which this publication was developed should be directed in writing to the Director of Standards, American Petroleum Institute, 1220 L Street, N.W., Washington, D.C. 20005. Requests for permission to reproduce or translate all or any part of the material published herein should also be addressed to the director.

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

Suggested revisions are invited and should be submitted to API, Standards Department, 1220 L Street, NW,

Washington, D.C., 20005

iii

1. Scope 1

   1. Concept of Hazard vs. Risk 1

   2. Units of Measurement 1

2. References 2

3. Definitions 3

4. Static Electricity Hazards 6

   1. General 6

   2. Tank Truck Loading 13

   3. Tank Car Loading. 25

   4. Marine Operations 26

   5. Storage Tanks 29

   6. Miscellaneous Electrostatic Hazards 36

5. Lightning. 46

   1. General 46

   2. Direct-stroke Lightning 46

   3. Indirect Lightning Currents 46

   4. Protection of Specific Equipment Against Lightning 47

   5. Protection Against Direct-stroke Lightning 50

6. Stray Currents 50

   1. General 50

   2. Sources and Limitations 50

   3. Protection of Specific Operations Against Stray Currents 51

Annex A Fundamentals of Static Electricity 55

Annex B Measurement and Detection of Static Electricity 67

Annex C Direct-stroke Lightning Protection Systems 71

Annex D Units of Measurement 73

Annex E Bibliography 75

Figure

1a Fixed Spark Promoter 8

1b Floating Spark Promoter 9

1. Approximate Relationship Between Temperature, Reid Vapor Pressure, and the Flammability Limits of Petroleum Products at Sea Level 11

2. Tank Truck Bonding for Top Loading 17

3. Loading and Unloading of Tank Trucks Through Closed Connections 17

4. Conversion Chart for Flow Rates and Velocities for Selected Pipe Sizes 21

5. Tank Car Bonding 25

6. Electrostatic Charge Generation During Tank Truck Loading 37

7. Charge Separation in a Filter 38

8. Bonding during Container Filling 40

9. Stray Current Bypass 51

10. Isolating Spur Tracks from Main-line Stray Current Sources. 52

11. Bonding, Grounding, and Insulating at Marine Wharves 53

v

1. Static Procedures 55

2. Charge Separation in a Pipe 56

3. Charge Movement Through a Liquid 57

4. Charged and Uncharged Bodies Insulated from Ground 62

5. Both Insulated Bodies Share the Same Charge 62

6. Both Bodies are Grounded and Have No Charge 63

Tables

1a Summary of Precautions for Tank Truck Loading 14

1b Charge Relaxation Precautions for Tank Truck Loading with Micropore Filters 15

2 Velocities and Flow Rates for Schedule 40 Pipe 20

A.1 Conductivity and Relaxation Time Constant of Typical Liquids 59

B.1 Effect of Temperature on Hydrocarbon Conductivity 68

G.1 Conventional (English) to Metric (SI) Units of Measure 73

Protection Against Ignitions Arising Out of Static, Lightning, and Stray Currents

1 Scope

This recommended practice presents the current state of knowledge and technology in the fields of static electricity, lightning, and stray currents applicable to the prevention of hydrocarbon ignition in the petroleum industry and is based on both scientific research and practical experience. Furthermore, the principles discussed in this recommended practice are applicable to other operations where ignitable liquids and gases are handled. Their use should lead to improved safety practices and evaluations of existing installations and procedures. When the narrow limits of static electricity ignition are properly understood, fire investigators should be encouraged to search more diligently for the true ignition sources in instances where static ignition is unlikely or impossible.

This recommended practice is not required under the following conditions:

1. Static discharges may occur, but flammable vapors are always excluded by gas freeing or inerting the atmosphere in the area of discharge.

   
   

2. Product handling occurs in a closed system, and oxygen in that system is always below the minimum concentration required to support combustion, such as in the handling of liquefied petroleum gas (LPG).

   
   

3. The flammable concentration is always above the upper flammable limit (UFL).

This document does not address electrostatic hazards relating to solids handling. (See [4], [5], and [15] in the bibliography.) Vehicle fueling (truck or passenger car) is also outside the scope of this document.

1. Concept of Hazard vs. Risk

   
   

   Hazards are situations or properties of materials with the inherent ability to cause harm. Flammability, toxicity, corrosivity, stored electrical, chemical or mechanical energy all are hazards associated with various industrial materials or situations. Charge separation and the accumulation of a static charge are inherent properties of low conductivity hydrocarbon fluids.

   
   

   Risk requires exposure. A hot surface or material can cause thermal skin burns or a corrosive acid can cause chemical skin burns, but these can occur only if there is contact exposure to skin. An accumulated static charge can be a source of ignition only if exposed to a flammable fuel-air mixture under conditions where a discharge is possible. There is no risk when there is no potential for exposure to all the required elements of charge accumulation, flammable mixture and spark discharge.

   
   

   Determining the level of risk involves estimating the probability and severity of exposure events that could lead to harm, and the resulting consequences. While the preceding examples relate hazards to the risk to people, the same principles are valid for evaluating risks to people, property or the environment. For instance, hydrocarbon vapors in a flammable mixture with air can ignite if exposed to a source of ignition (such as a static discharge) resulting in a fire which could injure people or damage property.

   
   

2. Units of Measurement

Values for measurements used in this document are generally provided in both U.S. customary and SI (metric) units. To avoid implying a level of precision greater than intended, the second cited value may be rounded to a more appropriate number. Where specific code or test criteria are involved, an exact mathematical conversion is used. Some conversions are included in Annex D.

1