Concluding Remarks
Today most companies are thinking globally. In 1996 the NEC allowed zones to be used and Canada quickly followed in
its 1998 code. Understanding of the rules governing hazardous area classification and how they differ around the world is
an important part of ensuring safety of the operation, loss prevention, and participation in global economy.
References
1. National Electrical Code-NFPA 70-2011, National Fire Protection Association
2. NFPA 497-2012, Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of
Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas
3. NFPA 499-2013, Recommended Practice for the Classification of Combustible Dusts And of Hazardous (Classified)
Locations for Electrical Installations in Chemical Process Areas
4. API RP 500-2012, Recommended Practice for Classification of Locations for Electrical Installations at Petroleum
Facilities Classified as Class I, Division 1 and Division 2;
5. API RP 505-1997, Recommended Practice for Classification of Locations for Electrical Installations at Petroleum
Facilities Classified as Class I, Zone 0, Zone 1, and Zone 2;
6. IEC 60079-10-1-2008 Explosive atmospheres - Part 10-1: Classification of areas - Explosive gas atmospheres
7. IEC 60079-10-2-2009 Explosive atmospheres - Part 10-2: Classification of areas - Combustible dust atmospheres
HAZARDOUS
AREA
Hazards Control
& AssessCLASSIFICATION IN
US (NFPA/NEC) AND
EUROPE (ATEX/IEC)
Vladimir Stetsovsky
Vladimir Stetsovsky, M.S., is a Senior Process Safety Specialist with over 19 years experience in the
manufacturing industry and utilities, and 7 years specializing as an Electrostatic Safety Engineer. His career
involved converting and specialty chemical manufacturing with numerous hazardous chemicals in both batch
and continuous operations. He has participated in the design and construction of several large chemical and
converting processing facilities and provided support and training in all areas of Process Electrostatic Safety
Management. As an Electrical Engineer he has led process hazard analysis, risk assessments and facility
siting reviews. At the corporate level he has created installation specifications and taught courses in ESD
and hazard recognition methods and provided technical safety support to manufacturing sites producing
adhesives and pressure sensitive products.
Mr. Stetsovsky has led or provided technical assistance to many fire and explosion incident investigations
including incidents involving thermal heat transfer fluids, spontaneous combustion, dust explosions and
thermal oxidizer and incinerator operations. In these investigations he has provided valuable insight into the
root cause and made practical suggestions for eliminating or controlling the identified hazards.
CHILWORTH TECHNOLOGY, INC.
Chilworth Technology, a DEKRA company, helps its clients achieve enabling and sustainable Process Safety Management
programs, Process Safety Proficiency (competency, know-how, and experience), and a culture that encourages excellence
in process safety. Our full range of services includes:
Process Safety Management (PSM) Programs
•
Design and creation of relevant PSM programs
•
Support the implementation, monitoring, and sustainability of PSM programs
•
Audit existing PSM programs, comparing with best practices around the world
•
Correct and improve deficient programs
Process Safety Information (Laboratory Testing)
•
Flammability/combustibility properties of dusts, gases, vapors, mists, and hybrid atmospheres
•
Chemical reaction hazards and chemical process optimization (reaction and adiabatic calorimetry RC1, ARC, VSP, Dewar)
•
Thermal instability (DSC, DTA, and powder specific tests)
•
Energetic materials, explosives, propellants, pyrotechnics to Dot, UN, etc. protocols
•
Regulatory testing: REACH, UN, CLP, ADR, OSHA, DoT
•
Electrostatic testing for powders, liquids, process equipment, liners, shoes, FIBCs
Specialist Consulting (technical/engineering)
•
Dust, gas, and vapor flash fire and explosion hazards
•
Electrostatic hazards, problems, and applications
•
Reactive chemical, self-heating, and thermal instability hazards
•
Hazardous area classification
•
Mechanical equipment ignition risk assessment
•
Transport & classification of dangerous goods
PS - US - WP - 045 -01
Chilworth serves clients throughout the agrochemical, chemical, engineering, food processing, government, insurance/legal, metals, oil/gas, pharmaceutical, plastics, rubber and other industries. Chilworth has offices throughout North America,
Europe, and Asia. For more information about Chilworth, visit www.chilworth.com.
To contact us:
> France:
info-fr@chilworthglobal.com
>Spain : info-es@chilworthglobal.com
> Netherlands: process-safety@dekra.com
>UK
> India:
info-in@chilworthglobal.com
>USA : safety-usa@chilworthglobal.com
>Italy
: info-it@chilworthglobal.com
: info-uk@chilworthglobal.com
HAZARDOUS AREA CLASSIFICATION IN US
(NFPA/NEC) AND EUROPE (ATEX/IEC)
Vladimir Stetsovsky, Senior Process Safety Specialist
Many gases, vapors and dusts can form flammable (explosive) atmospheres when mixed in appropriate concentrations
with air. As part of the management of ignition sources for ensuring safety of an operation, a hazardous area
classification (HAC) is performed to identify places where, because of the potential for the presence of a flammable
atmosphere, special precautions are needed to prevent electrical devices from causing an ignition source. For many
years HAC procedures have been carried out strictly to determine the need to select and install electrical equipment
in flammable atmospheres that would not become an ignition source. These same procedures and methodologies
can be used to evaluate hazardous areas in regards to any other sources of ignition – electrostatic, mechanical,
and thermal. Hazardous area classification is carried out as an integral part of the risk assessment to identify areas
where controls over ignition sources are needed (hazardous locations) and also those places where they are not (non
hazardous locations).
A large number of variables must be considered in order to correctly determine HAC. These variables include properties
and behaviors of the materials, volumes, pressures, temperatures, flows, piping and equipment, construction, weather,
building arrangements, adequacy of mechanical ventilation and gas detection systems, operator interfaces, and, of
course, experience. Careful evaluation of all data in accordance with established techniques, along with the application
of sound engineering judgment, should result in a consistent and safe classification scheme. A hazardous area extent
and classification study involves due consideration and documentation of the following:
•
•
•
•
•
•
The flammable materials that may be present;
The physical properties and characteristics of each of the flammable materials;
The source of potential releases of the materials and how they can form explosive atmospheres or accumulate
on equipment allowing heat to build up;
Prevailing operating temperatures and pressures;
Presence, degree and availability of ventilation (forced and natural) to maintain the
concentration of released vapors and dusts to below flammable limits;
The likelihood of each release scenario.
Hazardous Areas Regulatory Information
IEC/ATEX Zone System
The evolution of hazardous location electrical codes and standards throughout the world has taken two distinct paths.
In North America, a “Class-Division” System has been used for decades as the basis for classification of hazardous
(classified) locations. Because the hazards associated with flammable and combustible materials and methods of
selecting appropriate electrical equipment differ for different materials, hazardous locations are divided into three
Classes, and two Divisions.
The Class and Group designations are based on the explosibility and ignitibility characteristics of the material with
the Division designation being based on the likelihood of fire or explosion that the material presents. While the United
States and Canada have some differences in HAC of new installations and acceptable wiring methods and product
standards, their systems are very similar. In other parts of the world, areas containing potentially explosive atmospheres
are dealt with using a “Zone System”.
Zones are based predominantly on the International Electrotechnical Commission (IEC) and European Committee for
Electrotechnical Standardization (CENELEC) and ATEX standards. Whereas North American Class/Division system
deals with multiple types of hazardous atmospheres through the guidance given in National Fire Protection Association
(NFPA) 497 and NFPA 499, the US Zone System presently addresses, in detail (through NFPA 497), only flammable
gases and vapors which is the equivalent to North America’s Class I locations. The current NFPA 499 does not provide
guidance on how to classify areas containing combustible dusts using Zone system.
The most significant difference in the Zone system is that the likelihood of presence of a flammable atmosphere
is divided into three Zones as opposed to two Divisions. While specific requirements differ, the United States and
Canada have incorporated the Zone System for Class I, hazardous locations into their recent electrical code updates.
Both systems provide effective solutions for electrical equipment used in hazardous locations.
The abnormal conditions of occurrence, or lower risk areas, in the Zone and Division system are basically identical.
However, in areas where a hazard is expected to exist in normal operation, the Zone system deals with highest risk
areas separately, and risk associated with the remaining location is considered lower. The Division system tends to be
less specific in its consideration of Division 1. The Division system treats all areas where a hazard is expected to occur
in normal operation the same. Additionally, the Division system requires that locations, where breakdown or faulty
operation of equipment or processes might release ignitable concentrations of flammable gases or vapors and might
also cause simultaneous failure of electrical equipment to become a source of ignition, be also classified as Division 1.
In North America, hazardous locations are separated into three “Classes” or types based on the physical characteristics
of the materials. The Classes or type of material is further separated into “Divisions” or “Zones” based on the risk of
fire or explosion that the material poses. The Zone system has three levels of hazard versus the Division System’s
two levels.
Additionally, unlike NFPA/NEC system, IEC and ATEX do not differentiate between different groups of combustible
dusts for the purpose of classification. It is used only for the selection of equipment in hazardous areas.
Table 1: Hazardous Areas and Relationship between Divisions and Zones
Class I – Gas
or Vapor
Class II Dust
Class
III - Fiber
or Flying
(No Group
Designation)
NFPA 70/NEC
(North America)
IEC /ATEX
(Europe and some other countries)
Class-Division
Zones
Division 1: Explosive
atmosphere is present or
likely to be present in normal
operation
Zone 0 (Gas)
Zone 20 (Dust)
An area in which an explosive atmosphere is
continually present or present for long periods
or frequently
Zone 1 (Gas)
Zone 21 (Dust)
An area in which an explosive atmosphere is
likely to occur in normal operation
Division 2: Explosive
An area in which an explosive atmosphere is
Zone 2 (Gas)
atmosphere is not present in
not likely to occur in normal operations and, if
normal operation, could be
Zone 22 (Dust) it does occur, will exist for only a short time
present in abnormal operation
Note: The United States has adopted guidance for Zones for Gasses and Vapors per NFPA 497. Similar guidance
for Zones for Dust are not yet developed for North America.
Table 2: Gas and Dust Groups
NFPA/NEC Class/Division System1
IEC /ATEX
NFPA 70/NEC
(Europe and some
(North America)
other countries)
Group A
Non-quantitative probability of flammable atmosphere presence
IIC
Examples of Hazardous Material in Surrounding Atmosphere
Acetylene
Hydrogen, fuel and combustible process gases containing more than 30%
Group B
IIB+H2
hydrogen by volume or gases of equivalent hazard such as butadiene,
ethylene oxide, propylene oxide, and acrolein.
Group C
IIB
Ethyl ether and ethylene, or gases of equivalent hazard.
Gasoline, acetone, ammonia, benzene, butane, cyclopropane, ethanol,
Group D
IIA*
hexane, methanol, methane*, natural gas, naphtha, propane or gases of
equivalent hazard.
-I
Methane
Metal conductive dusts, including aluminum, magnesium and their
commercial alloys or other combustible dusts whose particle size,
Group E
-abrasiveness and conductivity present similar hazards in connection with
electrical equipment.
Carbonaceous dusts, coal black, charcoal, coal or coke dusts that have
Group F
-more than 8% total entrapped volatiles or dusts that have been sensitized
by other material so they present an explosion hazard.
Group G
-Flour, sugar, starch, grain, wood, and plastic dusts and chemicals
* Under IEC/ATEX classification Methane is designated as Group I