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					FIBER OPTICS RESEARCH PROPOSAL




      Prepared by Andy W. Mobley, P.E.
      Chairman, ISA SP12.21, Fiber Optics




                   DRAFT
                 May 8, 1997
                        Fiber Optics Research Proposal
ISA SP12.21                                              Page 2




CONTENTS


Executive Summary                                         3

Introduction                                              4

Proposed Test Program                                     4

Test Facility                                             5

Funding                                                   5



APPENDIX A: Thermal Ignition Mechanisms                   7

APPENDIX B: Test Proposal Details                         9

References                                               11
                              Fiber Optics Research Proposal
ISA SP12.21                                                                                       Page 3




EXECUTIVE SUMMARY

Optical technologies have developed rapidly in recent years, in major applications including measurement
and sensor technology, telecommunications, data communications, and surgical and welding devices. At
this time, however, there are no guidelines for safe use of optical fiber devices in hazardous (classified)
locations. Conservative experimental tests in Europe and Australia have shown that light sources can
provide sufficient energy to cause ignition in hazardous locations. These test results are restrictive to
many industrial applications; therefore, further classification of fiber optics in hazardous locations is
required. The purpose of the research set forth in this proposal is to determine and standardize safe
power levels for optical technology applications. Failure to act now will effectively halt the advance of
this emerging technology in hazardous (classified) locations.

The purpose of ISA’s SP12.21 Fiber Optics standards subcommittee is to develop standards for the safe
use of fiber optics in hazardous locations, with a goal of receiving North American acceptance of an ISA
standard. Such a standard will provide equipment design and installation requirements for the safe use of
fiber optics in hazardous locations. However, testing must be performed for the development of safe and
practical hazardous location guidelines. As part of the former U.S. Bureau of Mines, the Pittsburgh
Research Laboratory has the experience and test equipment to test fiber optics in hazardous locations. A
proposal to the government has been submitted by the Pittsburgh Research Laboratory for hydrogen and
methane gasses; however, it is unlikely that sufficient testing will occur unless industry provides funding.
Funding for extensive testing activities can be accomplished only through support of manufacturers and
users of fiber optic devices in hazardous locations. A combined effort by government and industry will
ensure that complete and thorough testing is accomplished for acceptance within North America.

Funding support for the proposed research will be directed to and administered by the Instrumentation
Standards Foundation of ISA, the international society for measurement and control, at the following
address:


                                                   ISA
                                  Instrumentation Standards Foundation
                                          67 Alexander Drive
                                            P.O. Box 12277
                                   Research Triangle Park, NC 27709
                             Fiber Optics Research Proposal
ISA SP12.21                                                                                      Page 4



INTRODUCTION

Fiber optic systems have been shown to be an ignition source in hazardous (classified) locations. The
thermal ignition of a flammable gas by a small heated body is the most probable ignition mechanism, as
discussed in Appendix A. Many experiments under this condition have been performed through the
Optical Sensors Collaborative Association (OSCA) in Europe and BHP Research Newcastle Laboratories
in Australia. The most recent European recommendations have been based upon collaborative research
by Imperial College (U.K.), PTB (Germany), Sira Test & Certification Ltd. (U.K.), University of Leeds
(U.K.), and INERIS (France). The intent of this collaboration is to develop standardization for the safe
use of light sources within Europe. The following recommendations have been specified [2]:

       Continuous wave devices radiating in the visible and the near visible are not able to ignite a
       surrounding explosive gas atmosphere provided either:

       a) the radiated power is less than 35 mW, or
       b) the peak radiation flux is less than 5 mW/mm2.

       For pulsed or intermittent light sources, specific atmospheres (e.g., oxygen rich atmospheres),
       devices which emit radiation from an area less than 0.00003 mm2 and where sensitive
       substances are present, different values of power and flux may be appropriate.

These recommendations were intended to ensure absolute safe levels for light power sources for all
hazardous locations. These levels were obtained by focusing a carbon dioxide (CO2) laser beam on a
proprietary ceramic fiber mat in a carbon disulfide atmosphere. Additional testing using practical test
methods under conditions more representative of industrial applications can more clearly define safe light
power fiber optic levels that fit within the existing North American and IEC hazardous location
classifications.


PROPOSED TEST PROGRAM

ISA’s SP12.21 Fiber Optics standards subcommittee proposes a test program with an approach similar to
that of the intrinsic safety protection method. The proposed testing is intended to be conducted at the
Pittsburgh Research Laboratory or at another suitable facility.

Phase I:
Testing will be performed using a coal particle at the end of a 200-um fiber core using a continuous wave
800-nm semiconductor laser in a hydrogen-in-air atmosphere. Phase I testing will evaluate the diameter
variation of a single particle with respect to the required ignition energy.



Phase II:
                             Fiber Optics Research Proposal
ISA SP12.21                                                                                      Page 5

Using the optimally sized coal particle from Phase I, testing will be performed using acetylene, ethylene,
propane, diethyl ether, and heptane in air mixtures. These mixtures have been found to be the most easily
ignitable substances for Gas Group classifications A, B, C, and D (IIC, IIB, & IIA) with consideration to
the Minimum Ignition Energy (MIE) and AIT (Auto-Ignition Temperature).

Phase III:
Testing will be performed using the Phase II criteria, except using light sources with wavelengths of 1310
nm and 1550 nm.

All other variables will remain constant during the entire test program. A test report will be distributed
upon completion of the testing. A supplemental proposal for further testing funds may be distributed
based on examination of the results. See Appendix B for the detailed test set-up.


TEST FACILITY

As part of the former U.S. Bureau of Mines, the Pittsburgh Research Laboratory has a long history in
explosion prevention and protection research. The 1.2-L cylindrical Hartmann bomb development at the
Bureau during the 1930’s became a standard test apparatus that has helped scientists understand many
aspects of explosion characteristics of dusts and gases. Refinements over the years have led to the
development of a fully instrumented 20-L test chamber, which is well suited for the study of the hazards
of fiber-optic cables in explosive dust/gas atmospheres.


FUNDING

ISA’s SP12.21 Fiber Optics subcommittee is seeking corporate, government, and other organizational
sponsorship to support the proposed research, which is vital to manufacturers and users of optical fiber
equipment in hazardous (classified) locations.

All associated reports and papers, as well as the resulting ISA Standards and Practices document, will
specifically identify the sponsors of this research program, providing them with recognition as leaders in
this field.

Funding Requirements

The funding requirements for this proposed program have been identified as $100,000 for Phase I and
$100,000 for Phase II of the research and testing. Testing will begin within one calendar year of
receiving funds. Funding for Phase III will be sought prior to the completion of Phase II, provided that
additional testing is deemed necessary at that time.

ISA’s SP12.21 Fiber Optics subcommittee welcomes and appreciates all contributions to support this
vital research program. A recommended minimum contribution range for sponsorship is $1,000 to $5,000
US.
                               Fiber Optics Research Proposal
ISA SP12.21                                                                                          Page 6

Funding Administration

The escrow account and funding facility for the proposed research will be managed through ISA’s
Instrumentation Standards Foundation (ISF), which was established in 1987 to promote and expedite the
development of technically sound consensus standards in the field of instrumentation and control.
Contributions will be sent to the ISF directly and specified for use on this particular project. All funds will
be solicited as contributions and donors will be provided tax information related to their contributions via
official letters of acknowledgment and thanks.

If insufficient funds are raised for the research program, the program will be canceled and any funds that
have been raised will be returned to the contributors, who will have the option of directing the funds to
support related ISA standards activities.

Assuming sufficient funds are raised, then if research is terminated prior to the completion of the project
for any reason, any remaining funds will be transferred to a secondary fund to be administered by the ISF
to support other ISA standards activities. Similarly, upon completion of all research, any remaining funds
will be transferred to a secondary fund to be administered by the ISF to support other ISA standards
activities.

The overall scope of the project to be funded must be approved by the chairpersons of ISA’s SP12 main
standards committee, Electrical Equipment for Hazardous Locations, and the SP12.21 Fiber Optics
subcommittee, with the approval of two-thirds of the voting members of SP12.21. Verification of testing
will be performed by the SP12.21 subcommittee or its designated representative. The subcommittee will
perform verification visits to ensure that the testing is being completed to its satisfaction. If the testing
efforts are found not to meet the subcommittee’s requirements, testing will be terminated upon request of
the subcommittee.

Under the direction of the ISF and the SP12.21 Fiber Optics subcommittee, ISA staff will administer and
disburse the funds in accordance with standard accounting practices for such funds. Accordingly, ISA
staff will provide reports to the SP12.21 subcommittee at reasonable intervals on the status of the funds
received, and will maintain careful records of when funds are released to the testing organization.

Contributors to this research program are asked to direct funds to:

                                                    ISA
                                   Instrumentation Standards Foundation
                                           67 Alexander Drive
                                             P.O. Box 12277
                                    Research Triangle Park, NC 27709

APPENDIX A: Thermal Ignition Mechanisms

Existing classifications for electrical equipment in hazardous locations can be applied to fiber optic
applications. There are two characteristics of flammable substances that are critical for electrical
equipment: Minimum Ignition Energy (MIE) and Auto-ignition Temperature (AIT). Each flammable
                               Fiber Optics Research Proposal
ISA SP12.21                                                                                          Page 7

substance has a MIE for rapid ignition by point sources. There is a critical size below which the particle
will vaporize before accumulating the MIE. Flammable gasses and dusts are categorized into Groups A
through G (IEC Gas Groups IIC, IIB, & IIA) based on their MIE. Each flammable substance also has a
critical AIT characterized by the minimum temperature required to independently initiate or cause self-
sustained combustion of the heated substance. The AIT for electrical equipment classification is
categorized into Temperature Classes T1 through T6. The MIE and AIT are two independent hazardous
substance classifications since no consistent relationship exits between the ignition energy and ignition
temperature. However, recent test experiments of electrical ignitions indicate that increasing the
flammable gas temperature decreases the required electrical ignition energy [1]. This phenomena
describes the test results seen with fiber optic devices in hazardous locations. Reference Table 2 below
for further details on electrical equipment classifications.

                            Class             Group                    Gas/Dust
                                              A (IIC)                  Acetylene
                               I              B (IIC)                  Hydrogen
                                              C (IIB)                   Ethylene
                                              D (IIA)                   Propane
                                                 E                    Metal Dust
                               II                F                 Carbonaceous Dust
                                                 G                     Grain Dust
                              III                -                  Fibers & Flyings
                      Division 1: Locations in which the probability of the atmosphere being
                      hazardous is high due to flammable material being present continuously,
                      intermittently, or periodically.
                      Division 2: Locations which are presumed to be hazardous only in an abnormal
                      situation.


                             Table 2: Electrical Equipment Classifications [6]

There are two conditions under which light powered fiber optics could create an ignition of a flammable
substance: Instantaneous Light Energy or Continuous Light Power. First, direct instantaneous light
energy ignition of a flammable substance is similar to an electrical spark ignition since the focal point of a
light beam causes thermal breakdown of the flammable substance. Energy greater than or equal to the
MIE of the flammable substance must be applied in a short amount of time. An instantaneous ignition is
most efficient for a short duration pulse of energy in the microsecond range and will become less efficient
as the duration increases. Secondly, direct continuous light power ignition of a flammable substance is
similar to an electrical component temperature rise since there is a rapid increase in temperature by
absorption of radiation. The most easily ignitable gasses must be raised to temperatures of at least 100°C
throughout a volume of greater than 100cc for ignition to occur.

There are three possible light power fiber optic related ignitions within the infrared wavelengths when
considering the MIE and AIT of flammable substances:

(1)    Flammable Gas (Gas Groups A, B, C, D) {IIC, IIB, IIA}:
                                      Fiber Optics Research Proposal
ISA SP12.21                                                                                                                                                    Page 8

        The narrow absorption bands of flammable gasses and vapors in air with the wide spectral
        bandwidth of sources implies that the light power available will be absorbed in a large volume of
        gas to produce a small temperature rise.

(2)     Flammable Dust, Fibers, or Flyings (Dust Groups E, F, G):

        A thermal ignition of a particle cloud can occur when the particles are heated rapidly by absorbing
        high light power. Thermal ignitions of suspended flammable dust, fibers or flyings occur at lower
        power levels than thermal ignition of a flammable gas or liquid since particles are able to absorb
        light power more efficiently.

(3)     Flammable Gas with a Small Heated Body (Gas Groups A, B, C, D) {IIC, IIB, IIA}:

        Current literature suggests that radiation heating of a small particle or surface in a flammable gas
        atmosphere is capable of igniting the surrounding atmosphere with light power levels down to
        35mW or 5mW/mm2 [2]. However, ignition at these low power levels with particles of similar
        size to a fiber optic core are less likely to occur due to the limiting size below which the particle
        will vaporize before accumulating the minimum ignition energy. Consideration must be given to
        hazards occurring when light power fiber optics interact with a surface covered with fluffy or
        cloud dust while contained in a flammable gas environment.

The OSCA recommendations would allow a maximum input power of 35mW for hazardous location
industrial applications using common single or multimode optical fibers (e.g. diameters of 8, 50, 62.5,
100, 200, and 400 µm). An optical fiber of greater than 3mm in diameter must be used before any
relaxation is given to the light power source. Figure 1 provides a graphical representation of the existing
recommendations.                               100

                                                                    90

                                                                    80

                                                                    70
Figure 1: Maximum Allowable Power and Power Density
                                                       Power (mW)




                       Levels in Hazardous Locations                60

                                                                    50

                                                                    40
APPENDIX B: Test Proposal
                                                                    30
Details
                                                                    20
Test Chamber:                                                       10

                                                                    0
The Pittsburgh Research Laboratory
                                                                         0




                                                                                                                                   3
                                                                             0.3
                                                                                   0.6
                                                                                         0.9
                                                                                               1.2
                                                                                                     1.5
                                                                                                           1.8
                                                                                                                 2.1
                                                                                                                       2.4
                                                                                                                             2.7


                                                                                                                                       3.3
                                                                                                                                             3.6
                                                                                                                                                   3.9
                                                                                                                                                         4.2
                                                                                                                                                               4.5
                                                                                                                                                                     4.8




has designed a 20 liter test chamber for                              Fiber Diameter (mm)
explosion testing of dusts, gases, and
their mixtures [3]. It can be used to measure lean and rich limits of flammability, explosion pressures and
rates of pressure rise, minimum ignition energies, minimum oxygen concentrations for flammability, and
amounts of inhibitor necessary to prevent explosions. The 20 liter chamber can be used at initial
                              Fiber Optics Research Proposal
ISA SP12.21                                                                                        Page 9

pressures that are below, at, or above atmospheric as long as the maximum explosion pressure is less than
300psi (21 bar), which is the rated pressure of the chamber. The existing chamber instrumentation
includes a pressure transducer, optical dust probes, an oxygen sensor, and multichannel infrared
pyrometers. The chamber would be modified to include a pressure relief to ensure personnel safety.
Testing with a single dust particle or a dust cloud are possible using a variety of different gasses within
the gas/dust explosion chamber. The particles can be placed on the fiber, on a thermally insulated table,
or circulated within the chamber during ignition testing. Figure 2 shows the general test set-up
configurations available with the Pittsburgh Research Laboratory chamber.


Ignition Source:

A single coal particle varying in diameter from 10µm to 1mm is intended to be used due to the black body
energy absorption qualities. The particle heating will
be produced by means of intense light emerging from
an optical fiber. The intense light will be produced
by continuous wave Gallium Aluminum Arsenide
(GaAlAs) laser radiation having a maximum output
power of 5 Watts and a wavelength of 814nm. This
laser is capable of generating non-continuous pulses
at a maximum rate of 500 Hz for pulsed operation
testing in the future. A 200µm multimode optical
fiber with a maximum length of 1 meter will be
employed to deliver the intense light to the coal
particle since it is a common optical fiber used for
industrial applications.      A Calorimeter Model
AC2501 will be connected to the optical fiber end
for an accurate power reading by the Scientech
Vector System Model D200PC before each test.
Phase III testing will be performed using a light          2
source with a wavelength of 1320nm and 1550nm.




Flammable Substance:

A (21±1)% hydrogen in air mixture will be employed initially as the flammable atmosphere to gain
experience with the test set-up before using an acetylene in air mixture. The concentration will be varied
to find the lowest radiant powers and irradiance necessary to ignite the mixture. This mixture is known
to have a minimum ignition energy of 17µJ [4] and an auto-ignition temperature of 520°C [5]. Carbon
disulfide does NOT fit within the scope of this test proposal since it requires additional safeguards beyond
those required for the classified gas groups within the National Electrical Code (NEC) Article 500 -
                              Fiber Optics Research Proposal
ISA SP12.21                                                                                         Page 10

Hazardous (Classified) Locations. Phase II testing will be performed using acetylene, ethylene, propane,
diethyl ether, and heptane in air mixtures. These mixtures have been found to be the most easily ignitable
substances for Gas Group classifications A, B, C, and D (IIC, IIB, & IIA) with consideration to the MIE
and AIT. Reference Table 3 for further details on these substances.

        Critical            Gas         Flammable        Minimum Ignition         Auto-ignition
      Characteristic       Group        Substance         Energy [MIE]          Temperature [AIT]
                                                              (mJ)                    (°C)
                           A (IIC)       Acetylene            0.017                   305
           [MIE]            B (IIC)      Hydrogen             0.017                   520
                            C (IIB)       Ethylene            0.07                    450
                           D (IIA)        Propane             0.26                    450
                          A, B, & C     Diethyl Ether          0.20                   160
           [AIT]         (IIC & IIB)
                           D (IIA)        Heptane                0.29                    204

                   Table 3: Flammable Substance Test Recommendations [4] [5] [7] [8]


Test Duration:

Each test will be conducted until a constant or peak temperature of the particle is attained or ignition
occurs. A constant or peak temperature characteristic will be defined as three successive readings taken
at intervals of 10 seconds that indicate no change in temperature. This determination of the particle
temperature will be found by using an infrared camera through the chamber window which is capable of
calculating temperature at specified cursor locations. If the chamber window is not available after
pressure relief modifications, each test will be performed for a length of 1 minute or until ignition occurs.
The length of time selected is based upon the maximum shut-down time requirements for the associated
apparatus light source to be implemented in the ISA SP12.21 Standard.
                            Fiber Optics Research Proposal
ISA SP12.21                                                                                    Page 11


REFERENCES


[1]   Ernest C. Magison, Electrical Instruments in Hazardous Locations, Third Edition, Instrument
      Society of America, 1990.

[2]   European Commission, “Optical Techniques in Industrial Measurement: Safety in Hazardous
      Environments”, Report EUR 16011 EN, 1994

[3]   Kenneth L. Cashdollar and Martin Hertzberg, “20-L Explosibility Test Chamber for Dusts and
      Gases”, Pittsburgh Research Center, Review of Scientific Instruments, Volume 56, Pages 596-
      602, 1985.

[4]   Joseph M. Kuchta, “Investigation of Fire and Explosion Accidents in the Chemical, Mining, and
      Fuel-related Industries - A Manual”, (Bulletin / U.S. Department of the Interior, Bureau of Mines;
      680), 1985.

[5]   NFPA 497M:1991, “Classification of Gases, Vapors, and Dusts for Electrical Equipment in
      Hazardous (Classified) Locations”, 1992 Edition.

[6]   Mark W. Earley, John M. Caloggero, and Richard H. Murray, “NEC Handbook 1993”, National
      Fire Protection Association (NFPA), Chapter 5, Sixth Edition.

[7]   P. C. Hills, D. K. Zhang, P. J. Samson, and T. F. Wall, “Laser Ignition of Combustible Gases by
      Radiative Heating of Small Particles”, BHP Research Newcastle Laboratories, Combustion and
      Flame 91: 399-412, 1992.

[8]   Jon Miller, “Fiber Optics for Use in Hazardous Locations”, Instrument Society of America (ISA),
      Paper #94-023, 1994.

				
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