the practical guide to hazardous area classification ebook

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The Practical Guide to Hazardous Area Classification

By Abhisam Software

© Copyright 2009-2010 Abhisam Software. All rights reserved.

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Copyright InformationCopyright InformationCopyright InformationCopyright Information © 2009-2010 Abhisam Software. All Rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, mechanical or electronic, including photocopying or recording, or by any information storage and retrieval system, or transmitted by email without permission in writing from the author and publisher. Published ByPublished ByPublished ByPublished By Abhisam Software, First Edition -2009 Second Edition -2010 www.abhisam.com

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Disclaimer: Nothing that is stated or construed by reading the contents of this book can be claimed to be safety advice in the legal sense. You are urged to refer to your own local

regulations, national and international standards for the exact regulations that may apply to

you. This guide book is to make the task of understanding the various codes and standards,

much easier and to give you broad guidelines and a roadmap to help your plant or facility

become a better and safer place. While all attempts have been made to verify the information

provided in this publication, neither the author nor the publisher assumes any responsibility

for errors, omissions, or contrary interpretations of the subject matter herein. The publisher

wants to stress that the information contained herein may be subject to varying international,

federal, state, and/or local laws or regulations. The purchaser or reader of this publication

assumes responsibility for the use of these materials and information. Adherence to all

applicable laws and regulations, including international, federal, state and local governing

professional licensing, business practices, advertising, and all other aspects of doing

business in the EU, US, Canada or any other jurisdiction is the sole responsibility of the

purchaser or reader. Neither the author nor the publisher assume any responsibility or liability

whatsoever on the behalf of the purchaser or reader of these materials. While due care has

been taken to review and verify the accuracy, reliability and correctness of the contents of this

ebook, the publishers are not liable for any direct or indirect or consequential or any other

kind of damage, which may result from using this ebook and the contents therein.

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TABLE OF CONTENTS

Chapter 1 Introduction

Introduction to Hazardous Areas Why do we classify Hazardous Areas? Chapter 2 Basic Concepts

What is a Hazard? What is Risk? Can we avoid risk altogether? Area Classification - A measure of risk Area Classification Benefits How does Area Classification work? How can Area Classification reduce costs? Chapter 3 Fire & Explosion Fundamentals

Fire Flammable or Hazardous Material Fire Triangle What is an Explosion? Properties of Hazardous Materials LEL & UEL

Flash Point Fire Point

Auto-ignition Combustible dusts Dust Explosions - Five necessary Factors Chapter 4 Fundamental Ideas about Area Classification

Chapter 5 Standards for Area Classification

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European System / IEC System Zones Groups

American System (NEC) Classes

Divisions Chapter 6 Standards for Classification of Explosive Dusts

IEC System North American System Chapter 7 Material Classification

IEC System North American System Chapter 8 Temperature Classification

IEC System Example of Temperature Classification North American System Chapter 9 Some other important Standard Guidelines

ATEX Guidelines ATEX Marking System Equipment Group Equipment Category Substance Group Chapter 10 IEC Ex-Unification of the two Systems

Chapter 11 How to carry out Area Classification

Area Classification Myths Myth 1 Myth 2

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Myth 3 Myth 4 Sources of release Relations of Grade with Zones Ventilation Considerations Step by step guide to Area Classification Chapter 12 Practical Study of an Area Classification Exercise

Chapter 13 Consequences of poor Area Classification

Over Classification - A white elephant Under Classification - Playing with Fire So now, what do we do? Example 1 Example 2 Example 3 Example 4 Example 5

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Introduction to hazardous areas

Many industrial work places produce, process, handle and store materials which are potentially explosive and thus hazardous in nature. The risk of fire or explosion while handling these materials is high. But it is not just the chemical or petrochemical industries that we are talking about here. Surprised? You should not be really. Grain storage silos, processing plants that handle large amounts of powders (including flour milling units), coal mining and handling plants, large oil supertankers, all handle materials, that could possibly lead to fires and explosions. Other typical examples, include offshore and onshore oil & gas production platforms, oil refineries, ships carrying chemical containers, storage terminals at ports, large tank farms, pulp & paper industries, industrial warehouses, gas based power plants and even gasoline filling stations. Potentially explosive atmospheres, need not be generated in only these obviously hazardous areas. A location which looks innocuous enough, like a grain silo can also be classified as a hazardous area, because grain dust can also be explosive. In fact, dust explosions can sometimes be more severe than even gas or vapor explosions. Therefore grain elevators & associated equipment like bucket elevators and conveyors carrying grain, which have a large amount of grain dust are also classified as hazardous areas. Similar powder processing plants like those handling coal dust, flour or cotton fibers can also be classified as hazardous (dust) locations. These areas are prone to risk of fires and explosions due to the nature of the materials handled and hence need a different approach than other “normal” areas. If proper area classification and safety engineering practices are followed while working in these areas, we can greatly reduce the risk of fire and explosion hazards in these places. This “practical” guide book is meant to be used as the name suggests-to get a working idea of how hazardous area classification works,

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how you can use it to your advantage, by reducing the costs of compliance-but without compromising in any way, on the actual safety of your plant. It is intended for all those people who are involved in working in hazardous areas, whether as a plant engineer, or instrument technician or a safety supervisor. It should be noted that this book does not contain complicated math or partial differential equations (that may induce sleep in the best of practising engineers).

Why do we classify hazardous areas?

This is the first fundamental question that begs an answer. Why do we classify areas and the materials present in these areas and call them “hazardous”? The reason is, that general purpose electrical equipment, like motors or lamps, cannot be used in these areas without having some kind of protection against accidental ignition. Nor can we use general purpose electrical or electronic instruments like transmitters or local indicators. This is because all electrical equipment can produce energy in the form of sparks, which can ignite these hazardous materials and /or cause explosions, thereby causing catastrophic damage. Hence, in hazardous areas we use special purpose, “explosion protected” electrical equipment and instruments. Note that the mere presence of flammable materials or explosive dusts in an area, does not immediately mean that the risk of fire or explosion is high. The flammable vapor or gas, has to be a part of a mixture with air, which can then easily ignite or explode, if some more conditions are met. Since these conditions are not uniformly present throughout a place that handles these materials, we have the concept of classification. It is to be noted that “hazardous area classification” is to be done for areas of the plant that would have instances of flammable mixtures of vapors, gases or dusts

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in the day to daythe day to daythe day to daythe day to day operations. Under unusual conditions like a catastrophic accidental release of a large quantity of inflammable vapors for example, this is not applicable, as such situations are not easily predictable. Under the usual day to day operational conditions in a plant or facility, there are some areas, which would have the presence of flammable mixtures of vapors, gases or dusts. Thus, the vapor space in a storage tank, the area around a mechanical seal of a pump or agitator, the area surrounding a breather valve on a storage tank (that contains flammable liquids), are all hazardous areas, which need to be classified. We classify some areas as “more prone” to the risk of fire and or explosion and others as “less prone”. We may find some areas, that are not at all prone to any kind of fire or explosion, except in the rarest of circumstances. For example, if an industrial facility has large open spaces and the office building is located several hundred meters away from the plant that actually processes the hazardous materials, then the chance of an explosion occurring in the office block, is very less (assuming some other conditions that will be explained later). How we do this segregation and classification in a structured manner, will be the main subject of this book, area classification. Before we jump headlong into area classification, let us understand some basic concepts first.

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Basic Concepts

What is a hazard?

A hazard is an inherent attribute or feature of a material, that can cause harm to equipment, people or the environment. An example of a hazard is a large quantity of flammable gas stored at a high pressure in a tank. Thus a plant having a large quantity of a flammable gas stored in a tank, as shown in the picture below, is an example of a hazard.

Fig 1: A HazardFig 1: A HazardFig 1: A HazardFig 1: A Hazard

What is Risk?

Risk is the measure of the likelihood, that the undesired event or accident will actually occur. Thus if a plant stores a large quantity of flammable gas as described above, but has a lot of safety systems in place to ensure that the gas does not leak, ignite or explode, or cause an accident in other ways, then the likelihood of an accident happening, is very less, therefore, one can say that the risk is low. Risk is also dependent on the severity of the consequences. The severity of the consequence means in simple words “how bad”. For example how bad will it be if a large storage tank of Acetone, a highly volatile and inflammable

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liquid explodes? The extent of the damage is what we mean by the words “severity of the consequence” Thus Risk= (Probability of Occurrence) X (Severity of Consequence)Risk= (Probability of Occurrence) X (Severity of Consequence)Risk= (Probability of Occurrence) X (Severity of Consequence)Risk= (Probability of Occurrence) X (Severity of Consequence). The severity of consequences, for fires and explosions in hazardous areas is very high, as all of us know. Therefore in the above equation, if we want to reduce the risk, we can only reduce the probability of occurrence, since we have almost no control over the severity of the occurrence. By classifying hazardous areas, we intend to reduce the probability of occurrence and thus reduce the risk.

Can we avoid risk altogether?

It is not possible to exist in a world without some amount of risk. Many people know that driving a car is riskier than flying in an airplane, however, do you know that staying at home also entails a risk? It is certainly not zero. Since we cannot avoid risk, we then manage it in a logical way. We do this unconsciously in our day-to-day activities, without realizing it. For example, to reduce the risk of getting knocked down by a car, while crossing a busy street, we reduce the risk by crossing it only at a pedestrian crossing, when the traffic signal turns green (for pedestrians) and also by watching out for speeding cars. Notice that here also, we cannot reduce the severity of the consequence. The severity of the consequence of getting knocked down by a speeding car could entail death, or disability or at least a severe injury. Since we have no control over the severity of the consequence, we reduce the other factor in the risk equation, which is the probability of the occurrence. In the same way, we manage the risk of handling and storing large amounts of flammable and explosive materials by area classification, which reduces the probability of the materials catching fire or exploding.

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Hazardous Area Classification- A measure of risk

Hazardous Area classification tries to give a profile of the risk of explosion in these areas. It cannot predict definitively, that an explosion will or will not take place in that area. It only segregates areas into areas where the likelihoodlikelihoodlikelihoodlikelihood of an explosion is more and areas where the likelihood is low or improbable. The classification provides us a tool to mitigate the risk of explosion in such areas.

Area Classification-What are the benefits?

If properly carried out, an area classification can

a) Give us a risk profile of the plant or facility, to enable us to operate it safer. This enables top management to really understand the real risk of the facility and then come up with appropriate strategies to mitigate this risk.

b) Enable us to design and install electrical, instrumentation and control system equipment that will not cause fires or explosions, at an optimum cost.

c) Reduce the costs of compliance to regulations and standards without compromising on the safety.

d) Make the overall operations safer and more profitable.

How does Area Classification work?

By properly and judiciously designating certain areas of the plant or facility, as hazardous (with its subdivisions of Zone 0,1 and 2 or Division 1 and Division 2) we can know which areas of the plant are more hazardous (and need special attention or equipment) and which are less hazardous. We can also know which areas are safe (well, almost). This gives a proper risk profile to the top management

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