Classifying Explosion Prone Areas for the Petroleum, Chemical and Related Industries

The degree of danger in the atmosphere of a hazardous location needs to be determined prior to selecting an acceptable electrical equipment installation. If maximum safety is the predominant factor in determining the type of electrical installations, the cost of electrical equipment will be extremely high. If low cost of electrical installation is the predominant factor, safety to personnel and equipment may be unacceptably low. It is, therefore, necessary to find a point of balance at which the cost and safety requirements are both satisfied and acceptable.

In nine out of ten cases, a hazardous location is classified much too conservatively. The reason for this conservative approach is a lack of knowledge and a misunderstanding of the actual concept of safety and danger. This book provides an in-depth understanding of the factors that influence the classification of a hazardous location. One factor, in combination with one or more other factors, will have an impact on the level of danger and its hazardous boundaries. These factors and their influences are explained in detail, and once their impact is understood, the classification of a hazardous location becomes a straightforward procedure.

Safety engineers, plants managers and hygiene personnel in the chemical and petrochemical industries.

Introduction Section 1. Fundamentals

1. Flammable and Combustible Principles of Hazardous Products A. General B. Flammable and Combustible Liquids C. Combustible Coke and Coal Dust D. Fire and Explosion Hazards in NEC Class I Locations
2. Classifying Sources of Hazard A. Sources of Hazard B. When a Location is Hazardous C. Safety Versus Hazard in NEC Class I Locations D. Requirements for NEC Class I, Div. 1 and Div. 2 Locations
3. The Extent of Explosion Danger for NEC Class I Locations A. General B. The Dimensional Outline of a Div. 1 and Div. 2 Zone C. Quantity of Flammable Substances Versus Extent of Explosion Danger D. Factors Influencing Quantities of Flammable Gases or Vapors E. Early and Remote Permanent Ignition Sources F. The Extent of Explosion Danger for Class II Flammable Products G. Transition Zones for NEC Class I Locations H. Additional Danger Zones I. Danger Zones Above Ground J. Classification of Sources of Hazard in Pump Stations Occupying 50, 75 or 100% Floor Space K. Fume Hoods L. Storage and Dispensing of Flammable Liquids M. Segregation
4. Spatial Considerations A. Indoor and Outdoor Locations B. Roofed Spaces in Hazardous Areas C. Nonhazardous Spaces Above or Below Hazardous Areas D. Spaces Giving Access to Hazardous Areas
5. The Degree of Explosion Danger for NEC Class H Locations A. General B. Detailed Requirements for NEC Class II, Div. 1 Locations C. Detailed Requirements for NEC Class II, Div. 2 Locations D. The Degree of Explosion Danger in Fossil Power Plants
6. Ventilation Requirements A. General B. Natural Ventilation C. Mechanical Ventilation D. Approximate Location of Mechanical Ventilation E. Demarcation Line F. Safeguards G. Wiring Diagrams for Safeguards
7. Electrical Equipment for NEC Class I Locations A. General B. Electrical Equipment Required for a Div. 1 Location C. Electrical Equipment Required for a Div. 2 Location D. Intrinsically Safe Electrical Equipment E. Marking of Electrical Equipment F. Construction of Explosion-Proof Enclosures G. Grouping of Electrical Equipment
8. Electrical Equipment for NEC Class II, Group F Locations A. General B. Class II Div. 1 Locations C. Class II, Div. 2 Locations
9. Intrinsically Safe Equipment and Wiring
10. Installation of Electrical Instruments in Hazardous Locations A. Type Z Purging B. Type Y Purging C. Type X Purging
11. Hydrogen Gas
12. Cathodic Protection
13. Static Electricity
14. Grounding of Tanks, Pipelines, and Tank Cars
15. Grounding Requirements for Electrical Equipment A. General B. Internal and External Grounding Conductors C. Supplementary Ground System
16. Application of Seals in NEC Class I Locations A. General B. Class I, Div. 1 Locations C. Class I, Div. 2 Locations
    1. Application of Seals in NEC Class II Locations Section 2. Application of Fundamentals Environmental Conditions in NEC Class I Hazardous Locations 2.1 General Requirements for Group A 2.2 General Requirements for Group B 2.3 General Requirements for Group C 2.4 General Requirements for Group D 2.5 General Requirements for Group E 2.6 General Requirements for Group F 2.7 General Requirements for Group G 2.8 General Requirements for Group H 2.9 General Requirements for Group I 2.10 General Requirements for Group J 2.11 General Requirements for Group K Section 3. Examples Application Procedure for Classifying NEC Class I Locations A. General B. Steps to be Followed for Classifying a Hazardous Location C. Examples Appendix: Properties of Flammable Liquids, Gases and Solids Definitions Bibliography Index