Ignition Risk of Hydrocarbon Liquids and Vapors by Hot Surfaces in the Open Air

API RECOMMENDED PRACTICE 2216 THIRD EDITION, DECEMBER 2003

REAFFIRMED, OCTOBER 2015

Ignition Risk of Hydrocarbon Liquids and Vapors by Hot Surfaces in the Open Air

Downstream Segment

API RECOMMENDED PRACTICE 2216 THIRD EDITION, DECEMBER 2003

REAFFIRMED, OCTOBER 2015

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Copyright © 2003 American Petroleum Institute

FOREWORD

Recommended Practice 2216 Ignition Risk of Hydrocarbon Liquids and Vapors by Hot Surfaces in the Open Air was prepared under the auspices of the API Safety and Fire Protec- tion Subcommittee. It is intended to provide information concerning the technical basis for auto-ignition of hydrocarbon vapors by hot surfaces in the open air. This information may be used to determine whether or not hot surfaces are potential sources of ignition should a release of hydrocarbon vapors or liquids occur and to develop safe practices for controlling or preventing such ignition. Other documents referenced in this publication provide supple- mental information applicable to this subject.

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, DC 20005.

iii

CONTENTS

Page

1. GENERAL 1

   1. Scope 1

   2. Applicability 1

   3. Non-applicability 1

2. DEFINITIONS 1

3. AUTO-IGNITION TEMPERATURE TESTING 1

   1. General 1

   2. Auto-ignition Temperature Testing Criteria 1

   3. Standard ASTM Auto-ignition Test Methods 2

   4. Open Air Auto-ignition Tests 2

   5. Gasoline and Oxygenate Blends 3

4. IGNITION BY HOT SURFACES 3

   1. Equipment Surfaces 3

   2. Sides of Storage Tanks 4

   3. Ignition of Heavy Oils by Hot Surfaces 4

5. SUMMARY 4

   1. General 4

   2. Conclusion 4

6. REFERENCES 4

Tables

1. Auto-ignition Temperatures of Hydrocarbon Liquids at Two Different

   Pressures 2

2. Open Air Auto-ignition Tests under Normal Wind and Convection Current Conditions 3

3. Effect of Ignition Lag Time on Auto-ignition Temperature 3

4. Effect of Wind Velocity in Auto-ignition Tests Using Kerosene 3

5. Auto-ignition Temperatures of Motor Fuels (NFPA 325) 3

v

Ignition Risk of Hydrocarbon Liquids and Vapors by Hot Surfaces in the Open Air

1. GENERAL

   1. SCOPE

      This recommended practice provides information concern- ing the potential for ignition of hydrocarbons that are exposed to hot surfaces in the open air. Hydrocarbon liquids, when heated sufficiently, can ignite without the application of a flame or spark. The ignition of hydrocarbons by hot surfaces may occur when oil is released under pressure and sprays on a hot surface or is spilled and lies on a hot surface for a period of time. Understanding the mechanism and dynamics of auto- ignition is an important step in preventing or controlling the ignition of hydrocarbons by hot surfaces in the open air. In addition to the information provided herein, appropriate industry standards and other information may assist users to understand the potential hazards of hydrocarbon auto-ignition (such as spontaneous combustion) not specifically covered by this publication and implement appropriate prevention and control measures.

      
      

   2. APPLICABILITY

      Hot surfaces, in areas where hydrocarbon liquids or vapors are present and may be released, are often presumed to be the sources of ignition should fires occur. However, it is generally recognized by the petroleum industry that hot surfaces, even at temperatures considerably above the auto-ignition temper- atures (AIT) of the hydrocarbons involved, are not always capable of igniting flammable vapor-in-air mixtures. This publication provides information applicable to the better understanding and controlling of hot surface ignition hazards.

      
      

   3. NON-APPLICABILITY

      This recommended practice does not cover every possible hazard or situation that may involve ignition of hydrocarbon liquids and vapors from hot surfaces. This publication does not apply to the ignition of hydrocarbons when certain condi- tions occur, such as spontaneous combustion (see 2.2). The mechanism for spontaneous combustion is entirely different from that required for ignition of hydrocarbon vapors from contact with hot surfaces in open air. This publication also does not apply to the ignition of hydrocarbon vapors when contacted by heated or glowing metal such as welding slag or by direct impact of super-hot exhaust fumes or gases. In addi- tion, this publication does not cover ignitions arising from hydrocarbon liquids trapped behind rust or oil soaked or satu- rated insulation or rust covering hot surfaces.

      
      

2. DEFINITIONS

   1. Auto-ignition: The ignition of a material (commonly in air) as the result of heat liberation due to an exothermic

      1

      oxidation reaction in the absence of an external ignition source such as a spark or flame.

   2. Auto-ignition Temperature (AIT): The AIT of a substance is the minimum temperature required to initiate or cause self-sustained combustion (exothermic reaction) inde- pendent of an external ignition source. As used in this publica- tion, it is the minimum temperature at which auto-ignition occurs under the specified conditions of the ASTM E 659 test1 (see Section 6). The terms, “auto-ignition temperature,” “igni- tion temperature,” “self ignition temperature,” “autogenous ignition temperature,” and “spontaneous ignition temperature,” are used synonymously in this publication. ASTM E 659.

      
      

3. AUTO-IGNITION TEMPERATURE TESTING

   1. GENERAL

      This recommended practice covers the technical basis for the risk of ignition of hydrocarbons by hot surfaces based on AIT and the practical implications thereof. An understanding of AIT is important when hydrocarbon vapors or liquids are exposed to hot surfaces or when handling very hot hydrocar- bon liquids. It should be understood that ignition of flamma- ble hydrocarbon vapors by a hot surface at the minimum ignition temperatures (for the specific hydrocarbon) is not likely. Experimental studies, testing and practical experience have shown that hot surfaces must typically be hundreds of degrees above published minimum ignition temperatures to ignite freely moving hydrocarbon vapor in the open air. Even properly operating automotive vehicle catalytic exhaust sys- tems, in most instances, do not create a surface temperature sufficiently high enough to ignite hydrocarbon vapors in the open air2. Whether or not flames will develop when a hydro- carbon contacts a hot surface depends not only on the surface temperature, but also on the extent (size) of the hot surface, its geometry and the ambient conditions3.

      The following information, covering AIT research, is intended to assist in understanding why the ignition of hydro- carbon vapors by hot surfaces (at published minimum AITs), is highly improbable.

      
      

   2. AUTO-IGNITION TEMPERATURE TESTING CRITERIA

Although the definition for “auto-ignition temperature” is specific, the values observed when testing specific hydrocar- bons will be different depending on the conditions at the time of testing and the test method used. AITs observed under one set of conditions may be changed substantially by different conditions4. Some of the variables that affect AITs are the molecular structure of the hydrocarbon mixture (i.e., gaso-