Application Notes


Installation of Electrical Equipment in Hazardous Areas


Introduction
 This Applications Note is intended to provide general information about hazardous areas and how to correctly apply Bently Nevada machinery information systems. Recommendations listed within this document are based on definitions and guidelines established by the North American Electrical Codes, IEC, European, and other agencies throughout the world. Since most field installations vary depending upon the type of hazardous area and the category of equipment to be placed in the area, a careful examination must be made of which equipment is suitable for the area prior to equipment protection. The system design work is completed first, thus allowing proper selection of transducers and electrical equipment with appropriate agency approvals before hardware installation begins.

When practical, electrical systems and instruments should be installed in areas having non-hazardous atmospheres to avoid the possibility of electrical ignition of a hazardous atmosphere. However, these systems must frequently be installed in locations where flammable or explosive atmospheres exist. Such environments are found in chemical plants, petroleum refineries and other industries where combustible liquids, gases, or vapors exist.

In explosive atmospheres, the instrumentation system must be configured to prevent or control system-caused ignition of the atmosphere. This Applications Note outlines typical hazardous environments in which machinery protection instruments may be installed, ignition-related characteristics of the instrumentation and various safety measures that may be employed to prevent or control ignition.

The material in this discussion is intended to familiarize the reader with types of hazardous area problems and solutions but does not present specific instructions and safety code requirements necessary to install a complete instrument system. For additional data required designing and installing an instrument system in such areas, you may refer to publications listed in the appendix of this paper, the instrument manufacturer and/or the local safety or code enforcement agency. The final authority on what is and is not a safe equipment installation rests with the "Safety Enforcement Authority" for that area. This authority may be a representative of the insurance underwriters, a local government inspector or a member of the corporate safety organization.

Prior to instrumentation system installation, the user must determine whether system components will be located in atmospheres that can burn or explode. The degree of hazard must be classified for various areas. These tasks generally fall to the local plant authority. The instruments and wiring to be installed in the area must be evaluated as to their ignition capability. Then, with respect to instrument location, necessary protection measures must be determined for the installation. In all cases, the user must specify the Zone, Group or Class, Division, Group, where the transducers, and where the monitors are to be located.

Hazardous Areas
 An area classified as "hazardous" is an area in which the atmosphere contains, or may contain, flammable or explosive gases, dusts, or fibers. In this type of area, fire or explosion could occur when all three basic conditions are fulfilled:
  1. Flammable gas, vapor, dust or fibers must be present.
  2. The combustible material must be mixed with air in the proportions required to produce a flammable mixture.
  3. A source of ignition must act to ignite the mixture. The source under consideration is any portion of the instrumentation system that could release sufficient energy to cause ignition. A spark or hot surface may release the incendiary energy.

In the United States, the National Electrical Code, Article 500 for both Zones and Divisions, Canada, Canadian Electrical Code, Section 18 for Zones, defines a hazardous area by applying a three-part classification. In Europe the classification is in type of industry and degree of hazard. See the following tables, for relationship of North America, European definitions and comparisons.

Applying safety barriers requires some knowledge of intrinsic safety principles and terminology. The two main systems in international use are summarized below.

IEC COUNTRIES
(Countries accepting International Electrotechnical Commission Standards, e.g. Australia, Europe, S. Africa)
USA and CANADA
(Are adopting IEC terminology )
Intrinsic safety Technique that achieves safety by limiting the ignition energy and surface temperature that can arise in normal operation, or under certain foreseeable fault conditions, to levels that are insufficient to ignite an explosive atmosphere.
Intrinsic safety standards Exia: safety maintained with up to two component faults: hazardous area equipment may be used in Zones 0, 1 and 2.

Exib: safety maintained with up to one component fault: hazardous area equipment may be used in Zones 1 and 2.		 Exia: safety maintained with up to two component faults: hazardous area equipment may be used in Zones 0, 1 and 2.

Exib: safety maintained with up to one component fault: hazardous area equipment may be used in Zones 1 and 2.
Or
Standards for Divisions
Safety maintained with up to two component faults: hazardous area equipment may be used in Divisions 1 and 2.
Type n Non arcing/Non incendive Note Type N equipment (safe in normal operation) may be used in Zone 2. Type N equipment (safe in normal operation) may be used in Zone 2.
Or
Non-incendive equipment (safe in normal operation) may be used in Division 2.
Type of industry I: underground mining -- Group I

II: surface -- Group II		 No classification, but mining and surface industries dealt with by different authorities.
Type of fuel Explosive mixtures of air with flammable gases or vapors and dust.

Note: See Ignition by spark.		 Explosive mixtures of air with:
Class I: gases or vapors
Class II: dusts
Class III: fibers or filings

Note: See Ignition by spark.
Degree of hazard Zone 0: explosive gas-air mixture continuously present, or present for long periods.

Zone 1: explosive gas-air mixture is likely to occur in normal operation.

Zone 2: explosive gas-air mixture not likely to occur and, if it occurs, it will exist only a short time.		 Zone 0/1 or Class I, Division 1: hazardous concentrations of flammable gases or vapors continuously, intermittently or periodically present under normal operating conditions.

Zone 2 or Class I, Division 2: volatile flammable liquids or flammable gases present, but normally confined within closed containers or systems, from which they can escape only under abnormal operating or fault conditions.
Ignition by spark Apparatus is grouped according to the ignition energy produced under fault conditions, in terms of the gas-air mixture that it will not ignite

Representative gases are:
Group IIC: hydrogen, acetylene
Group IIB: ethylene
Group IIA: propane

Group I: methane		 Explosive atmospheres are grouped according to their ignition energy.
Representative atmospheres are:
Standard version IEC
Group A: acetylene Class I IIC Class I
Group B: hydrogen Class I IIC Class I
Group C: ethylene Class I IIB Class I
Group D: propane Class I IIA Class I
Group E: metal dust Class II
Group F: carbon dust Class II
Group G: flour, starch,and grain Class II
Ignition by hot surface Hazardous area apparatus is classified according to the maximum surface temperature produced under fault conditions at an ambient temperature of 40°C (or as otherwise specified).
T1: 450°C T2: 300°C T3: 200°C
T4: 135°C T5: 100°C T6: 85°C
For North America there are sub Temperature codes. e.g. T4A-120C
Gas characteristics Details of gas grouping by ignition energy and of gas ignition temperatures are contained in:

British Standard Code of Practice for Electrical Apparatus and Associated Equipment for use in Explosive Atmospheres (other than Mining Applications), BS5345: Part 1 - Basic requirements for all parts of the code.

NFPA, Vol. 5 Electrical, Article 500, Table 500-2(c) (ignition energy)

CSA No. C22-1 (ignition energy) Section 18
Approval National certifying authority issue Apparatus and/or System Certificates for approved equipment, or Listings of approved equipment, defining all or most of the following:
IS standard
Apparatus (gas) group		 Temperature Class
Installation conditions		 Cable parameter limits
Zone division classification
In Europe, all CE national authorities have adopted the CENELEC standards. In the USA, OSHA, under NRTL, requires CSA, FM, UL or other NRTL approved agency approval.
In Canada, CSA is required.
Note: North America has adopted the IEC standards. This means there are two types of certifications: Zones and Divisions.



Non-hazardous
(Safe) Area
 An area classified as non-hazardous has a small probability of a flammable mixture being present. It is also called a "safe area" and includes most control rooms.

The Instrumentation
System
 An electrical system generally contains potential sources of ignition that are of concern in a hazardous area installation. Therefore, the types of ignition sources and applicable methods of preventing ignition must be considered by an instrument manufacturer and user. Systems that are designed to meet certain safety criteria may receive certification from a safety standards approval agency such as Canadian Standards Association (CSA), BASEEFA, SIRA or LCIE. ATEX can be obtain from these same agencies.

Sources of Ignition
 Generally, a potential source of ignition from an electrical system is any spark or hot component that release energy sufficient to ignite a combustible mixture surrounding it. The ignition source may occur in any of four mechanisms: a) discharge of capacitive circuits, b) interrupting (opening) of inductive circuits, c) opening or closing of resistive circuits with slow intermittent interruption increasing the ignition capability (hazard), and d) high temperature sources. The ignition mechanisms may occur in relay contacts, switch contacts, fuses, short circuits (from damage or component failure), and arc-over between components or conductors. The components or circuits that present a potential ignition source may be designed in a variety of ways in order to prevent ignition of a hazardous atmosphere.

Methods of Preventing
Ignition
 Three basic approaches are used individually or in combination to prevent ignition of hazardous atmospheres by Bently Nevada machinery information systems:
  1. Intrinsically Safe/Non-incendive Equipment: Eliminates the ignition source by designing equipment that cannot cause ignition when in contact with flammable or explosive atmospheres.
  2. Gas Purge/Hermetic Sealing: Controls the atmosphere surrounding the potential ignition source so those components are enveloped within a non-hazardous atmosphere.
  3. Flameproof/Explosion-proof Housing: Contains the explosion within a housing, preventing the ignition of the surrounding atmosphere.

Instrument System
Certification
 Safety enforcement authority's job is made easier if the proposed equipment is certified for use in the hazardous area by a private or government-testing agency. The testing agency subjects the equipment to rigorous electrical tests varying in difficulty depending on the Class, Zone, Division, and Group of hazard for which the equipment is being certified.

Over the years several testing agencies have earned the confidence of safety enforcement authorities in their respective countries. A partial listing, by country, of several major-testing agencies includes the following:
    USA CSA/NRTL, Factory Mutual System (FM), or UL
    Canada Canadian Standards Association (CSA) or UL
    Europe British Approvals Service for Electrical Equipment in Flammable Atmospheres (BASEEFA), or SIRA, or Laboratoire Central Des Industries Electriques(LCIE)
    Japan Safety Standard (RIIS)
    Australia Standards Association of Australia (SAA)
    International Electrotechnical Commission IEC International Standards for other countries.

Safety enforcement authorities within that country generally accept certification by one of these agencies. Safety enforcement authorities in other countries may also accept this certification as valid for their own applications.

Since Bently Nevada monitors are powered by voltages up to 230 Vac or 120 Vdc, the possibility exists that sufficient energy to cause ignition could be released from the monitor under abnormal conditions. In extreme conditions, a Proximity transducer (without safety barriers) could be affected. Because of this, the Proximity, transducer power outputs from Bently Nevada monitors cannot be economically rendered intrinsically safe due to the stringent approvals required. However, the monitor outputs are designed to be non-incendive, a factor that has led to Division 2/ Zone 2 certification of many monitors.

For intrinsic safety barrier and galvanic isolators installations, the maximum allowable barrier-to-Proximity transducer cable length will vary depending upon the type of cable and its inherent capacitance and inductance values. For this reason, the design of all proposed intrinsically safe systems must be studied to assure that energy stored in the cables does not exceed intrinsic safety limits outlined in the barrier certificate.

An important aspect of an intrinsically safe installation is application of measures to prevent any cross-connections between intrinsically safe and other wiring. Wiring of the two types should be positively separated by use of separated conduits or other methods to maintain separation. Wiring must also be secured to prevent possible cross-connections in the event that any wires come loose. This is good general instrumentation practice and is mandatory to achieve and maintain a working instrumentation system.

Because many safety enforcement authorities accept CSA, BASEEFA, LCIE and SIRA certification, Bently Nevada continues to submit much of its standard product line (and standard modifications) to these agencies for certification.

The certification process for new equipment requires a considerable period of time. The testing agency conducts many tests on the equipment, testing its safety for use in the area for which it will be certified. Certifications are for specific to Class, Zone, Division and Group. Equipment certified for use in a particular Class, Zone, Division and Group might not be certified when used in a different classified area.

Determine Necessary
Safety Measures
 Instrument System Location and Hazard Reduction Requirements
Establishing the location of system equipment is based upon many considerations.
Items to consider are:
    a) equipment that must be mounted at specific machine locations
    b) cable length limits between units
    c) accessibility for maintenance and operation
    d) hazard reduction measures required for a proposed area, and
    e) objectionable instrument environmental factors (temperature extremes, corrosive pH, etc.)

In order to determine the hazard reduction measures required, the area classification must be known. Although plant engineers are generally able to determine area classification, the final authority rests with the local code or safety enforcement authority. Once the area has been classified (Zone and Group or Class, Division, and Group) Bently Nevada can recommend instrumentation and protective equipment suitable for installation. (But remember BENTLY NEVADA CORPORATION does not classify areas)

Several typical installations are shown in the block diagrams. The equipment is shown in different areas with varying types of certifications, and the minimum protective measures that could be used for such installations. Before a system could be installed as diagrammed, however, approval from the local code enforcement authority must be obtained.

System Approval by Local Enforcement Authority
 As previously mentioned, the local safety enforcement authority makes the final determination of the, Zone and Group or Class, Division, and Group, of hazard that exists in a specific area. Once the area is classified, the instrument manufacturer must show that the proposed installation will be safe for the area and is approved by a recognized agency.

If all the equipment being installed in a hazardous area is not certified and cannot be made intrinsically safe using safety barriers, negotiation with the safety enforcement authority will result in a suitable approach to hazard reduction. Of the basic hazard reduction methods available (explosion-proof housings, purging, and non-incendive equipment), the safety enforcement authority will require one or a combination of these methods to insure a safe installation. Enforcement authorities do not have common rules that govern all installations. In granting approval on a particular installation, they may exercise personal judgment, accept certification of the equipment by a testing agency (such as CSA, BASEEFA, SIRA or LCIE) or use any other approach they deem suitable.

Summary
 Installation of Electrical Equipment in Hazardous Areas has covered some basic levels of applying Bently Nevada equipment. This Applications Note does not cover all aspects of the hazardous area environment nor does it discuss all of the equipment that is permitted in these areas.

When specifying a monitoring system to be placed in a Hazardous Area, the area must be fully defined before selecting electrical equipment. Once the area is defined, the location of the transducers and the location of the monitors can then be determined. Transducers may be placed into the Zone 1/ Division 1 areas when used with safety barriers or galvanic isolators. Monitoring systems are different. They require approved weatherproof housings for Division 1 having a Type X or Type Y purge set-up as defined by the National Electrical Code, Article 500 or Canadian Electrical Code. Primarily, this promotes use of monitors in Division 2 or Safe areas.

In most European countries, monitors are preferably installed in safe areas except in the UK where they are certified for Zone 2.

In Europe, if a monitor has to go in a Zone 1 area, it has to be certified to a purge system (EExp).

Once the area is defined and the equipment locations are chosen, equipment and approval agency selection can then take place. Generally, the approval agency is determined based on geographic location of the job site and which approvals Bently Nevada has received for various products which are being considered. It is important to be sure that all equipment being placed into the hazardous area is certified and approved by a recognized approval agency such as BASEEFA, SIRA, LCIE, or CSA. These approved products will carry the agency's sticker and logo on them.

Next, the method of preventing ignition should be decided. Flameproof/Explosion-proof housings, air-purged housings, and intrinsic safety barriers or galvanic isolators are all acceptable ways of containing or limiting the source of ignition. Bently Nevada recommends using intrinsic safety barriers or galvanic isolators over explosion-proof housings whenever possible to limit the energy going into the Division 1/ Zone 1 hazardous area. The use of safety barriers or galvanic isolators has proven to be universally accepted throughout the world because of ease of installation, cost-effectiveness, and the high standard of safety attained by using them. With the arrival of internal safety barriers found in recent Bently Nevada monitoring systems, even more safety, convenience, and cost reduction are realized.

Should your specification call for Bently Nevada electrical equipment in hazardous areas, prepare a worksheet of the installation requirements and then contact your nearest Bently Nevada Sales and Service Office for detailed information and assistance.

Bibliography
 Comins, Carlton C., "Guide to Intrinsic Safety," Oil, Gas, Petrochem Equipment, February 1975.

Magison, Ernest C., Electrical Instruments in Hazardous Locations, Instrument Society of America, Pittsburgh, 1972.

"Hazardous Locations," Section 18, Canadian Electrical Code, Part 1, Rexdale, Ontario, Canada.

Intrinsically Safe and Non-incendive Electrical Instruments, Recommended Practice 12.2, Instrument Society of America, 1995.

Purged and Pressurized Enclosures for Electrical Equipment, No. 496, National Fire Protection Association, Boston.

National Electrical Code, Article 500. 1999 Edition.

Canadian Electrical Code, Section 18. 1998 Edition.

Intrinsically Safe Apparatus for use in Division 1, Hazardous Locations, NFPA#493.

Factory Mutual Research Approval Standard: "Intrinsically Safe Apparatus and Associated Apparatus for Use in Class I, II, and III Division 1 Hazardous Locations;" Class Number 3610.

Canadian Standards Association Standard C22.2 No. 157-M1992, "Intrinsically Safe and Non-incendive Equipment for Use in Hazardous Locations."

C22.2 No. 30-1970 "Explosion-Proof Enclosures for Use in Class I Hazardous Locations"

British Standards Institution, BS EN50 020 1995, EN50 021, EN50 014, EN61010.1

IEC 60079 series Explosive Atmosphere standards

UL913 and 1604 for Explosive Atmosphere

"The Intrinsic Safety Training Program", R. Stahl, Inc., Woburn, Massachusetts.



Figure 1: An example of a major failure and how Barriers protect the area.   Return to article




Figure 2: Another example of a fault to earth and still the equipment is protected forms the fault.   Return to article




Figure 3: Typical hook up scheme for the internal Barriers.   Return to article




Figure 4: The Monitor system is shown in a Safe Area.
The Prox must be in a IP54 / Type 4 enclosure.
The Probes must be in an IP54 / Type 4 enclosure if mounted on the machine.   Return to article




Figure 5: The entire system is in a Zone 2 / Div 2 area
The Monitor must be in a IP54 / Type 4 enclosure.
The Probes must be in an IP54 / Type 4 enclosure if mounted on the machine.   Return to article




Figure 6: This employs the external Barrier between the Monitor and Transducer.
The Monitor and Barrier are located in the Safe Area. For the wiring to meet non-incendive requirements the whole system must be certified to CSA.
The Proximitor / Probe and Cable are Intrinsically Safe with the Barriers installed.
The Cable parameters must be considered for the total capacitance of the system in the hazardous area.
The Monitor and Barriers may be installed in a cabinet.   Return to article




Figure 7: This employs a "Y" purge.
A "Y" purge reduces the area around the Monitor from a Class I Div 1 GR. C, D to a Class I Div 2 GR. C, D.
The Monitor must be Class I Div 2 certified.
The purge system is approved on site by the local authority.   Return to article




Figure 8: Explosion Proof system, all the potential ignitions are contained in the enclosure. The enclosure is not perfectly sealed and small openings quench the flames and cool the escaping gases.   Return to article




Figure 9: The Monitor System with internal Barriers. This makes the Prox / Probe and Cable Intrinsically Safe.   Return to article




Figure 10: This employs an external Barrier between the Monitor and the Transducer.
The Monitor and Barriers are located in a Safe Area, but for use in Canada the Monitor must be certified for non-incendive wiring.
Co must be equal or less than the Ci plus the C of the cable to meet the Intrinsically Safe max Cable parameters.
The Monitor and Barriers can be installed in a cabinet.
* Check with tech support for the proper Barrier and polarity.   Return to article




Figure 11: This figure employs an external Barrier between the Monitor and the Transducer.
The Monitor and Barriers are located in a Safe Area, but for use in Canada the Monitor must be certified for non-incendive wiring.
Co must be equal or less than the Ci plus the C of the Cable to meet the Intrinsically Safe max Cable parameters.
The Monitor and Barriers can be installed in a cabinet.
* Check with tech support for the proper Barrier and polarity.   Return to article




Figure 12: This employs an external Barrier between the Monitor and the Transducer.
The Monitor and Barriers are located in a Safe Area, but for use in Canada the Monitor must be certified for non-incendive wiring.
Co must be equal or less than the Ci plus the C of the Cable to meet the Intrinsically Safe max Cable parameters.
The Monitor and Barriers can be installed in a cabinet.   Return to article




Figure 13: This employs an external Barrier between the Monitor and the Transducer.
The Monitor and Barriers are located in a Safe Area, but for use in Canada the Monitor must be certified for non-incendive wiring.
Co must be equal or less than the Ci plus the C of the Cable to meet the Intrinsically Safe max Cable parameters.
The Monitor and Barriers can be installed in a cabinet.   Return to article




Figure 14: Galvanic isolation approach for systems having grounding problems.
Notice: The system has no critical grounding system as in a passive barrier system. This application still meets Intrinsically Safe requirements.   Return to article




Figure 15: The I.S. grounding for passive Barriers. Grounding is very critical for the I.S. passive barrier system. The impedance for grounding must be less than or equal to 1 ohm.   Return to article




Figure 16: Typical layout of Intrinsically Safe (I.S.) wiring to the back of a Monitor with internal Barriers. The spacing between the I.S. and non-I.S. is a minimum of 50 mm.   Return to article


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