|By Nailen, Richard L|
A look at the international standards governing apparatus for hazardous areas
"EX"- SHORT FOR "EXPLOSION" OR "EXPLOsive." Throughout most of the world, it refers to either an atmosphere containing a flammable gas, vapor, or dust, or to construction of equipment (primarily electrical, such as motors and control) that must operate safely within such an environment. "IEC," of course, refers to the
After several years of discussion, an IECEx Management Committee held its first meeting in 1 996. Three years later Publication 01, the Basic Rules of the system, was published. Other major developments in hazardous area equipment safety are shown in the time line of Figure 1.
The IECEx System has grown rapidly. At least 30 countries have now joined the program. Among those outside
Although the IEC standards system now involves nearly 100 nations, some national differences with local standards are unavoidable. For example, electrical system voltages, some circuit breaker ratings, and conductor sizes aren't interchangeable between the U.S. and many other countries. Some U.S. organizations, including UL, have made "national adoptions" of some IEC standards only by incorporating variations. Hence, the U.S. has become an IECEx member only with the proviso that full inclusion in the system will come only after resolution of national differences that may take 10-15 years.
How IEC and U.S. standards differ
One such difference is in the nature of the National Electrical Code, which is legally enforceable throughout much of the country. Code enforcement is not within U.S. government control. The NEC retains the Division system of classifying hazardous areas (more about this later) as well as protection against fire and electrical shock - conditions not dealt with in IECEx.
An essential feature of the IECEx program is acceptance by any member country of product evaluation or facility assessment by recognized authorities in other member countries. Full U.S. participation in IECEx suffered a setback when in
Scheme tends to imply something shady, underhanded, perhaps even illegal. In electrical technology, however, the word simply denotes a plan - a way of doing something. For example, a control scheme is an arrangement of circuits and devices to carry out a desired sequence of operations. The IECEx "Scheme" is more properly termed the IECEx "System," consisting of these four components:
1. Certified Equipment Scheme
2. Certified Service Facilities Scheme
3. Scheme for Certification of Personnel Competencies
4. Conformity Mark Licensing System
Together they form a comprehensive method for ensuring that electrical apparatus in an explosive environment is initially, and will remain, compliant with international safety standards. Quoting from the IECEx Basic Rules, 'The objective of the IECEx System is to facilitate international trade in equipment and services for use in explosive atmospheres, while maintaining the required level of safety." The goal is one test procedure, one record of compliance, one product marking recognized worldwide.
As stated in IECEx documentation, "While technically rigorous, the process of achieving an IECEx Certificate of Conformity is rather straightforward." That documentation is voluminous and precise (see Figure 2). The basic publications and guides take up 200 pages. The Operational Documents total nearly 600 more (some of the on-line versions are password-protected). Many authorities have produced summaries.
The adoption procedureHere is how the system works: First, a country must choose to apply for IECEx membership. If the country is already an IEC member, that's done through that country's
Figures 3 and 4 illustrate the subsequent steps leading up to issuance of a Certification of Compliance allowing one manufacturer's products to be recognized by all IECEx participating nations. Such certificates are issued by Certification Bodies, relying on reports by product
Assessment of the quality management system leads to a Quality Audit Report of "limited duration" (three years). The Facility Audit Report on which the eventual certificate is based is also good for three years, subject to annual intermediate assessments of the manufacturing operation (to be scheduled at least every 12 months, which can be extended to 18 months if no deficiencies appear).
Test laboratories that determine IECEx product compliance are subject to ISO/IEC standard 17025 (first published in 1999), setting forth the "general requirements" for competency of laboratories involved in certification system operation.
Although the most comprehensive program of its kind, IECEx was not first in the field. Within the European Community, the first multi-national attempt at a simplified approach to apparatus explosion protection was the ATEX system.
What is ATEX? The name is a French acronym for "ATmospheres EXplosibles," or explosive atmospheres. Such an environment is defined as "a mixture with air, under atmospheric conditions, of flammable substances in the form of gases, vapours, mists or dusts." ATEX describes a pair of European Union Directives, one (Directive 94/9/EC, known also as ATEX 95) dealing with "equipment and protective systems intended for use in potentially explosive atmospheres," and the other (ATEX 99/92/EC, or ATEX 137) a "workplace directive" giving minimum requirements for "improving the safety and health protection of workers potentially at risk from explosive atmospheres." The aim of ATEX 95 is to allow free trade of suitable electrical or mechanical apparatus within the European Community, without requiring each member nation to provide its own testing or documentation.
In a general way, the 29-page ATEX 95 (which took effect in mid-2003, superseding all previous European legislation) is analogous to a combination of NEC and UL requirements, except that the ATEX Directives have the force of law within all EU member nations. ATEX 137 can be compared to
Old and new international standards
ATEX or IECEx - why two different approaches? One
As IECEx management acknowledged in 2008, "Since the introduction of the IECEx On-Line Certificate of Conformity, late 2003, there has been a constant flow of inquiries seeking an explanation of the differences between the IECEx System and the European ATEX System." An accompanying table (top of page) highlights the more important ones.
The most recent addition (2008) to the IECEx System, unmatched by any U.S. certification program, is "personnel competency." This program, charted in Figure 7, is the subject of Publication 05. (When that was issued in 2009, IECEx management stated that a guide, Publication 05A, would follow; it was finally published in
Publication 05 does not prescribe any training requirements. A certificate of competency is issued only on the basis of an ExCB assessment, under the "general requirements" of 1SO/IEC standard 17024. Such certificates are subject to periodic re-assessment and testing as determined by the Certifying Body.
How that's done is outlined in other IECEx publications: OD 502, 503, and 504. An applicant for certification chooses the training or demonstration modules ("Units of Competency") on which to be assessed. Among the 10 such units are "Apply basic principles of protection in explosive atmospheres," "Perform area classification," "Design electrical installations," "Test electrical installations," and "Perform detailed inspections." Within each unit, OD 503 describes "Knowledge assessment instruments" ("tests" in plainer English) from which to judge the applicant's expertise.
Both multiple-choice and essay-type questions are suggested, with expected answering times. For example, for Unit Ex 004, "Maintain equipment," the OD proposes 80 test questions, three-fourths of them multiple-choice, with expected test time of two minutes each for multiple-choice and three to five minutes each for the others. Total test time for that one unit would therefore be at least three hours. The first IECEx personnel competence certificate was issued in 2010 to an individual assessed for Unit Ex 001 ("Apply basic principles of protection in explosive atmospheres"). Several other certificates have since been issued in two countries.
One authority describes this procedure as "a judging of the competence of workmen." However, personnel competence is not limited to equipment operators or repairers. Also included aré those who determine the nature and extent of such areas, design electrical installations in those areas, and carry out tests and inspections of the equipment. Not everyone employed in a repair shop, for example, is expected to be competent in all such matters. But for a given installation, some responsible party must be qualified to interpret and apply the standards involved.
Of particular concern is area classification. Design of a motor or other apparatus to suit a specific atmosphere is not that difficult. The challenge lies in determining when and for how long the hazard will be present, and exactly where. Defining the area boundaries can be highly subjective and dependent upon conditions not readily controllable. Likewise, weather conditions, process operations, and equipment failures can cause wide variation in the risk of an ignitible atmosphere being present regardless of the location.
In the U.S., the National Electrical Code divides hazardous areas into two Divisions. For flammable gases or vapors, NEC Section 500.5 defines Division 1 as one where the ignitible concentration can exist "under normal operating conditions" or "frequently," or when some process abnormality "might release" such a concentration. ("Normal operation" has been ruled to exclude motor starting.) The terms frequently and might release are obviously subject to broad interpretation.
In the less hazardous Division 2 location, combustible gases or vapors are normally confined and can escape only through accident or "occasionally" (another undefined term). Similar NEC descriptions of various possibly hazardous atmospheres apply terms such as "can," "might," "may," or "easily ignitible."
What, then, is the relative degree of risk between Divisions 1 and 2? No quantitative answer exists. Just where to draw the line between the two Divisions has been debated for many years. As one engineer wrote in a 1978 article, "A major problem is defining the limits of the hazardous location." (
At least one book, numerous technical papers, handout guides, magazine articles, and university courses have dealt with area classification. The
A further complexity appeared with the more recent European approach to hazardous area definition: the Zone concept. Engineers recognized that the risk of explosion was quite low in what had been considered Division 1 , represented by a small percentage of installations. That category was therefore subdivided into a Zone 0, in which no spark or flame-producing apparatus is allowed; a Zone 1, where traditional explosion-proof ("flameproof ' in
In 1995, following years of acrimonious debate among the NEC Code Panels, the IEEE, and the petrochemical industry, that Zone structure was incorporated into the NEC as an alternate classification system. However, the same subjective terms like "frequently" or "likely" also appear in the Zone definitions.
Consider also the issue of motor surface temperature in an explosive atmosphere. "Normal operating conditions" in the NEC has always been interpreted as excluding motor starting. An IEEE standard (1349) deals with surface temperature limits only for a running motor. The incongruity is obvious, inasmuch as no motor can run without first being started. In contrast, IEC practice does consider motor starting to be "normal." Locked-rotor or stall testing is needed to evaluate motor capability.
That applies to motor protection category "Ex e" or "increased safety." Design of such machines, usable in either Division 1 or Zone 1 locations, must "prevent sparks and overheating which could cause ignition." "Sparks" would be of little concern inside a totally enclosed motor. In the far less costly open machine, however, they can occur under several conditions. For many years, attention has been paid to "rotor sparking" originating in a squirrel cage rotor. Sparking at the joints of steel enclosures in large machines had become a recognized hazard by 1 990. And in
For most hazardous-area apparatus, economics dictates repair rather than replacement following failure. For motors, concern eventually arose about the effect of repairs on the integrity of explosion-proof enclosures. In 1974, UL initiated a "Rebuilt Hazardous Location Motor Program," including a "Rebuilt Listing Mark," governing such repair. The program provided technical information to participating shops on motor construction, assembly, and testing, with periodic inspection of work by UL representatives.
Ten years later in
In the U.S., the two industry standards dealing with motor repairs in general are ANS1/
Motor manufacture had already been the subject of IEC 60079 (first published in 1957 as IEC 79, then containing only "recommendations" dealing with equipment in hazardous areas). A more recent standard, IEC 61241, covers equipment exposed to flammable dust.
The current edition of IEC 60079 is divided into dozens of separate sections, concerning the several types of explosion protection, maintenance and inspection, and explosion test apparatus. In 1993, a new section ofthat standard - IEC 60079-19 - was titled "Equipment repair, overhaul, and reclamation." Compliance with those requirements is now covered by the IECEx Certified Service Facilities Scheme, per Publications 03 and 03A. Here, too, quality management requirements are based on ISO 9001. The process leading to certification is shown in Figure 9.
The scope of IECEx Publication 03 includes "repair, overhaul, and or modification," as well as "reclamation." What's meant by "reclamation" isn't clearly defined there. "Modification," however, can include a variety of changes to suit different equipment applications. Figure 10 illustrates a possible example, in which a motor not originally suitable for a hazardous area is converted to "Ex p" construction.
Who judges repair shop capability? "Assessors approved by ExMC," says Publication 03, all of whom "will have a working knowledge of repair or other service facilities." A compliant facility is to be inspected and re-assessed annually; a good initial report allows extension to 18 months.
Eleven agencies in seven countries are now authorized to certify service center compliance. The first repair facility certificate was issued in 2008 to a shop in
As harmonization continues between U.S. and IEC standard practices, designers and manufacturers will see more of the IECEx requirements. Whether that applies to the service industry as well remains to be seen.
Although the IEC standards system now involves nearly 100 nations, some national differences with local standards are unavoidable
Weather conditions, process operations, and equipment failures can cause wide variation in the risk of an ignitible atmosphere being present regardless of the location
For motors, concern eventually arose about the effect of repairs on the integrity of explosion-proof enclosures
Acronyms that are frequently encountered in ATEX/IECEx documents
ACB Accepted Certification Body
CAB Conformity Assessment Board
CA Conformity Assessment
CB Certification Body (or Council Board)
CoC Certificate of Conformity
CoPC Certificate of Personnel Competencies
CRF Compliance Report Form
DOC Declaration of Conformity
DSEAR Dangerous Substances and Explosive Atmospheres Regulations
EDR Essential Differences in Requirements
ExCo IEC Executive Committee
FAR Facility Audit Report
HAZLOC Hazardous Location
HOTL Heads of
MC Management Committee
NB Notified Bodies
NCR Non-Conformance Report
OD Operational Document
PCAR Personnel Competencies Audit Report
QAN Quality Assessment Notification
QAR Quality Assessment Report
QMS Quality Management System
TGD Technical Guidance Document
TR Test Report
Note: many of these terms are preceded in various documents by "Ex" (e.g.. ExMC or ExCB).
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