ct287 - rockwell automation · pdf filethese hazardous areas is called area classification....

09/9/2014

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CT287

Hazardous Area Classifications and Protection Systems

Slide 1 Craig McIntyre

09/9/2014

CT287 - Hazardous Area Classifications and Protection Systems

Topics covered

• Types of Hazardous Area classifications with focus on North America • Types of hazardous protection systems • Overview of Recognized National Testing Laboratories (NRTL), the

National Electrical Code and OSHA • Documentation and labeling • Questions


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Types of Hazardous Area classifications with focus on North America


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What constitutes a Hazardous Location?

• In electrical engineering, a hazardous location is defined as a place where concentrations of flammable gases, vapors, or dusts occur. Electrical equipment that must be installed in such locations is especially designed and tested to ensure it does not initiate an explosion, due to arcing contacts or high surface temperature of equipment.

• In some cases the gas, ignitable vapor or dust is present all the time or for long periods; other areas would have a dangerous concentration of flammable substances only during process upsets, equipment deterioration between maintenance periods, or during an incident. These are then divided into areas of risk of release of gas, vapor or dust. The process of determining the type and size of these hazardous areas is called area classification.



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Solvent Recovery Tank



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Coal Conveyor



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Industrial Fire



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History

• Began with mine safety in the U.K.

• Low voltage concepts began early

• By 1913 a deadly explosion proved low voltage was not enough



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Ignition Triangle

• Three components are required to permit combustion, ignition, fire or explosion

Fuel

Oxygen

Energy


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Sources of Ignition


• Flame • Spark • Heat • Electrical energy


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Sources of Ignition

• Flame • Spark • Heat • Electrical energy



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Classification

• Instrumentation specifications often designate the classification of the area where instrument will be used.

• We will address the Area classification system

• The Zone classification system is in place but is not common



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Area Classification hierarchy


• Class • Division • Group


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Area Classes

• Class I - Ignitable gases or vapors • Class II - Ignitable dust • Class III - Ignitable textile fibers

NOTE: always in Roman numerals


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Three “Classes” Means Three Types of Materials



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Area Divisions


• Division 1 - Hazard constantly present, or occasionally present under normal operating conditions.

• Division 2 - Hazard present only under abnormal conditions.

NOTE: always in Arabic numerals


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Abnormal Tank Conditions



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Dike

Grade Sump or trench

Vent Hatch

Vent

Flammable Liquid

Boundaries • Division Method – Boundaries (Designated Areas)

Division 1

Division 2

Key



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Gases and Vapors



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Area Groups: Gases

• Group • A - Acetylene only • B - Hydrogen + few select gases • C - Ethylene, UDMH, etc. • D - Hydrocarbons, alcohols, etc.


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Dusts



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Area Groups: Dusts

• Group • E - Metal dusts • F - Coal dusts (carbonaceous dusts) • G - Non-conductive dusts

• Agricultural • Plastics


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Another consideration is Temperature: • Temperature Class, or T-Class

• Definition: • The temperature classes are used to

designate the maximum operating temperatures on the surface of the equipment which should not exceed the ignition temperature of the surrounding atmosphere. Ignition temperature is the minimum temperature required, at normal atmospheric pressure and in the absence of a spark or flame, to set afire or cause self-sustained combustion independently of the heating or heated element.

Typical North American Standard:



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Temperature (T) Class Values:

Typical North American Standard:



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Types of hazardous protection systems


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Achieving Safety



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Safety Approach: Terms

• Explosionproof • Dust ignitionproof • Intrinsically safe • Non-incendive • Associated apparatus • Purged


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Explosionproof

• Applies to Class I Only (Gases) • Containment Strategy - Assume gas will enter enclosure and the

contained circuitry is capable of igniting it. BUT the system is sufficiently sealed and of sufficient strength to prevent ignition of outside atmosphere.


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Explosionproof enclosures



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“Exploded” Explosion-Proof Housing



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Dust Ignitionproof

• Applies to Class II and III Only (Dusts/Fibers) • Containment Strategy - Assumes contained circuitry is capable of

igniting dust. BUT enclosure is sufficiently sealed against entry of dust, and surface temperatures are too low to ignite settled dust on enclosure.


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Intrinsically Safe

• Applies to all Division 1 Areas (i.e. in all Classes and Groups) • Circuitry Strategy - Circuits are designed to be incapable of an energy

release sufficient to ignite the specified atmosphere, even with specific instances of circuitry failures.


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Intrinsically Safe System



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How is a Circuit Made “Intrinsically Safe?”

• First must define what atmospheres will be involved • Refer to published ignition curves


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• First must define what atmospheres will be involved • Refer to published ignition curves

Max Allowable

Current

Max Operating Voltage

Group C

Group B


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• First must define what atmospheres will be involved • Refer to published ignition curves • Implement voltage and current limiting

L1

L2

device

hazardous safe


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L1

L2

device

hazardous safe


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How is a Circuit Made “Intrinsically Safe”?


• First must define what atmospheres will be involved

• Refer to published ignition curves

• Implement voltage and current limiting • What are the practical

limitations?

Max Allowable

Current

Max Operating Voltage

Group C

Group B


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How is a Circuit Made “Intrinsically Safe”?


• What are the practical limitations?

• Installation Requirements • Proper wiring connections • Proper cable routing • Attention to “entity parameters”


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Non-Incendive

• Applies to all Division 2 Areas • Circuitry Strategy - Circuits are incapable of an energy release

sufficient to ignite the specified atmosphere, under normal circuit operation. In this context “normal” includes user mis-wiring.


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Div. 2 Non-Incendive Installation



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Associated Apparatus

• Normally “safe area” equipment which affects the energy levels of intrinsically safe equipment in the hazardous area.

• Examples - Intrinsic Safety Barrier or I.S. Power Supply


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Purged

• Systems or devices are under positive pressure, to exclude hazardous atmospheres from the equipment interior. Extensive controls, interlocks may be required, depending upon specific areas involved.


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Purged

• Systems or devices are under positive pressure, to exclude hazardous atmospheres from equipment interior. Extensive controls, interlocks may be required, depending upon specific areas involved.

Type X purging: reduces classification within enclosure from Div 1 to non-hazardous Type Y purging: reduces classification within enclosure from Div 1 to Div 2 Type Z purging: reduces classification within enclosure from Div 2 to non-hazardous


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Purged

• Systems or devices are under positive pressure, to exclude hazardous atmospheres from equipment interior. Extensive controls, interlocks may be required, depending upon specific areas involved.

Type X purging: reduces classification within enclosure from Div 1 to non-hazardous Type Y purging: reduces classification within enclosure from Div 1 to Div 2 Type Z purging: reduces classification within enclosure from Div 2 to non-hazardous

Escalating Severity


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Common Purge Systems



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Overview: Safety Techniques



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NEMA Ratings

• NEMA 4 = Outdoor, Weatherproof • NEMA 4x = NEMA 4 + Corrosion Resistance • NEMA 6 and 6P: Submersible • NEMA 7 = Explosionproof • NEMA 9 = Dust Ignitionproof


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Wiring containment Techniques: NEC

Conduit Seals: Process seals:



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Overview of Recognized National Testing Laboratories (NRTL),

the National Electrical Code and OSHA


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NRTL = Nationally Recognized Testing Laboratory…

• The US Occupational Safety and Health Act (OSHA) accredits Nationally Recognized Testing Laboratories (NRTL).

• Canadian Standards Council of Canada (SCC) accredits Testing Organization and Certification Bodies (TOCB)

• Individual States are allowed to implement State Occupational Safety and Health Plans. OSHA approves and monitors State plans.

What’s an NRTL?



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NRTL = Nationally Recognized Testing Laboratory…

• A “Scope of recognition” defines the

specific safety test standards for which an NRTL applies for recognition, and that OSHA approves. OSHA does not specify which test standards an NRTL must use. Instead, when an organization applies for recognition, it submits a list of test standards for which it seeks recognition, and OSHA determines if these standards are "appropriate" as defined in 29 CFR 1910.7. An NRTL may only certify products to the specific product safety test standards included in its scope of recognition.

What’s an NRTL?



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National Electrical Code (NEC) and NRTL test standards

• The National Electrical Code (NEC) is the “bible" of the Electrical Industry, and the primary source of reference for hazardous locations. The NEC is also the basis for OSHA standard 1926.407, Hazardous (Classified) Locations.

• The NEC is approved as an American National Standard by the American National Standards Institute (ANSI) and formally identified as ANSI/NFPA 70


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National Electrical Code (NEC) and NRTL test standards

• The National Fire Protection Association NFPA 70: National Electrical Code (NEC) publishes the “Bible” with the most recent the 2011 Edition (available Sept 24 2010) which is adopted in all 50 states

• NRTLs use safety test standards that OSHA determines are "appropriate" as defined in 29 CFR 1910.7 developed to assess that a device has been designed, manufactured, tested or inspected, and marked in accordance with requirements of the listing agency as recognized by the United States Department of Labor, Occupational Safety and Health Administration (OSHA) under the requirements of 29CFR1910.7.


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Some NRTL History

• When first adopted, OSHA regulations gave two examples of approval organizations: Underwriters Laboratories (UL) and Factory Mutual Research Corporation (FMRC)

• In 1983, OSHA was ordered by a court to remove the specific references to UL and FMRC in a successful lawsuit brought by a private lab

• In 1988, OSHA revised its regulations to remove the references, and established the NRTL Program to recognize other organizations as NRTLs


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Some additional background on FM and UL • Underwriters Laboratory (UL) is not only an NRTL but a function

within the company also develops testing standards. Underwriters Laboratories is an independent, not-for-profit product safety certification organization that has been writing Standards for Safety, testing products and involved in conformity assessment for well over a century. Many of these standards are now open ANSI standards as well used by other organizations

• FM not only is an NRTL but a function within the company also develops testing standards. Many of these standards are now open ANSI standards as well used by other organizations. Another portion of FM has grown to be the largest independent insurance provider to industry.

• Each of the NRTL, standards setting and insurance portions of these organization are separate functions and are not supposed to be combined to the exclusion of others


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Documentation and labeling


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Documentation

• Certificates are issued by the cognizant NRTL • Many Labs can issue combined certifications, such as for both US and

Canada, as well as issuing separate certificates for multiple schemes simultaneously (such as ATEX and IECEx).

• Multiple certificates typically exist for any given device or model family, for multiple protection techniques as well as from multiple entities, in multiple countries.

• Copies of most certifications are available though the equipment vendor or via lifecycle management tools like the Endress+Hauser Web Asset Management (W@M) system.



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Typical Equipment Marking

• In the US, we’ll typically see a layout like this: Cl I Div 1 ABCD T4, Cl II Div1 EFG, Cl III • So, what’s it all mean? • And what can we use for a given location?



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• Let’s break it down:



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• Let’s break it down: Cl I Div 1 ABCD T4, Cl II Div 1 EFG, Cl III


NRTL (FM, for both US and Canada)

Hazard Class (Class I = Gas) Area Classification (Division 1)

Gas Groups (All)

Temperature Class (T4: 135C)

Hazard Class (Class II = Dust)

Dust Groups (All)

Hazard Class (Class III = Flyings)


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Products Solutions Services

Any questions?

Thanks very much!


ct287 - rockwell automation · pdf filethese hazardous areas is called area classification....

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