ANSI ISA TR12.21.01-2004 Use of Fiber Optic Systems in Class I Hazardous (Classified) Locations.pdf

1、 TECHNICAL REPORT ANSI/ISATR12.21.012004 (R2013) Use of Fiber Optic Systems in Class I Hazardous (Classified) Locations ANSI Technical Report prepared by ISA Approved 1 September 2013 ANSI/ISA-TR12.21.01-2004 (R2013) Use of Fiber Optic Systems in Class I Hazardous (Classified) Locations ISBN: 978-0-

2、876640-30-2 Copyright 2013 by the International Society of Automation (ISA). All rights reserved. Not for resale. Printed in the United States of America. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means (electronic mechanical, p

3、hotocopying, recording, or otherwise), without the prior written permission of the Publisher. ISA 67 Alexander Drive P.O. Box 12277 Research Triangle Park, North Carolina 27709 3 ANSI/ISA-TR12.21.01-2004 (R2013) Copyright 2013 ISA. All rights reserved. Preface This preface, as well as all footnotes

4、and annexes, is included for information purposes and is not part of ANSI/ISA-TR12.21.01-2004 (R2013). This document has been prepared as part of the service of ISA toward a goal of uniformity in the field of instrumentation. To be of real value, this document should not be static but should be subj

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18、E HAS NOT YET ADDRESSED THE POTENTIAL ISSUES IN THIS VERSION. The following people served as members of ISA Subcommittee ISA12.21 which prepared this technical report: NAME COMPANY P. Kelly, ISA12.21 Chair UL LLC M. Coppler, Managing Director Det Norske Veritas Certification Inc. D. Baker P b) photo

19、chemical ignition due to photodissociation of oxygen molecules by radiation in the ultraviolet region; and c) direct laser induced breakdown of the gas at the focus of a strong beam, producing plasma and a shock wave, both of which acting as ignition sources. These three mechanisms require either re

20、latively high peak powers or ultraviolet radiation n ot commonly found in current practice. Although one should be aware of these other mechanisms, they are not addressed in this technical report. Explosive targets or targets that contain their own oxidizer are also outside the scope of this technic

21、al report. 5.4 Optical beam spatial and temporal characteristics greatly influence ignitability of explosive gas atmospheres. Table 1 summarizes the limiting beam strength parameters for igniting explosive gas atmospheres as a function of beam spatial and temporal characteristics. For a short durati

22、on optical pulse with a small beam diameter, the energy required to cause ignition reaches a minimum. For such a beam, limiting the pulse energy to levels below the minimum optical ignition energy will prevent ignitions, regardless of the peak power, peak power density, or energy density. Similar re

23、lationships apply to the other combinations of beam diameter and duration. As long as the optical beam does not exceed the limiting beam strength parameter for its particular temporal and spatial domain, the other beam strength parameters need not be considered. Table 1 Limiting beam strength parame

24、ters for igniting explosive gas atmospheres based on beam spatial and temporal characteristics. Short duration (pulsewidth 1 cm) Energy density Power density 19 ANSI/ISA-TR12.21.01-2004 (R2013) Copyright 2013 ISA. All rights reserved. 5.5 Optical ignition powers generally reach a minimum for beam di

25、ameters of about 50 m or less. Ignition of a carbon disulfide-air mixture has been reported using 24 mW optical power, which is significantly less than igniting powers observed to date for other explosive gas atmospheres. These explosive gas atmospheres generally ignite at power levels above 50 mW.

26、Explosive gas atmospheres that fall within Material Group D or Material Group IIA, and have an AIT above 200 C (T Codes T1-T3), generally ignite at power levels above 200 mW. 5.6 For large beam diameters incident on inert target layers, optical ignition power d ensities generally reach a minimum for

27、 beam diameters of about 1 cm or larger. Explosive gas atmospheres with no combustible solid targets present generally ignite at power densities above 10 mW/mm2. In one study of large beam areas ( 400 mm 2) incident on combustible coal dust layers, it was shown that combustible solids may pose a smo

28、ldering ignition hazard at relatively low beam power densities compared to power densities needed to ignite explosive gas atmospheres by laserheated inert targets. 5.7 Optical beams of intermediate dimensions can exceed the minimum optical ignition criteria without causing ignition. In the range of

29、large core diameter optical fibers (100 to 1000 m), studies indicate ignition threshold powers are above the absolute minimum opt ical igniting powers for explosive gas atmospheres. Threshold igniting powers observed to date for some explosive gas atmospheres were approximately proportional to beam

30、diameter over this range of beam diameters. Ignitions may be prevented for relatively powerful beams by controlling the beam diameter, such as with large core diameter ( 100 m) optical fiber. 5.8 Optical ignition energies for explosive gas atmospheres generally reach a minimum for pulse durations of

31、 about 100 s or less and beam diameters of about 100 m or less. The minimum optical ignition energies observed to date were about twice the corresponding electrical spark ignition energies. 5.9 Optical pulses of intermediate duration can exceed the minimum optical ignition criteria without causing i

32、gnition. In one study, optical pulse durations in the millisecond range required over 10 times as much energy to ignite explosive gas atmospheres as a 70 s optical pulse. Ignitions may be prevented even for relatively high-energy optical pulses by extending the duration and thus decreasing the peak

33、power of the pulse. 5.10 Periodic optical pulses (pulse trains) in explosive gas atmospheres are safe if the individual pulses and the average power over the period of transmission meet the safe criteria for pulses and continuous wave, respectively. 6 Protection concepts 6.1 Three protection concept

34、s are suggested to prevent ignitions by fiber optic terminal devices and cables in Class I hazardous (classified) locations. a) inherently safe optical radiation; b) protected optical fiber cables; and c) optical radiation interlock with optical fiber breakage. This list is not all-inclusive, other

35、protection concepts should be considered where appropriate such as ensuring an adequate target or an explosive gas atmosphere is not present. The classification of an area as a Division or Zone implies the frequency and duration that an explosive gas atmosphere may be present. Divisions are defined

36、in Article 500 of the NEC and Zones are defined in Article 505 of the NEC. ANSI/ISA-TR12.21.01-2004 (R2013) 20 Copyright 2013 ISA. All rights reserved. Protection concepts should be developed through an appropriate process hazard analysis (PHA), where potential failure modes leading to, and effects

37、of, ignition events are analyzed (AIChE 1992). PHAs include (but are not limited to) a) electrical area classification (source of hazard method); b) hazards and operability studies (HAZOPS); c) failure modes and effects analysis (FMEA) (IEC 60812); d) fault tree analysis; e) event tree analysis; and

38、 f) layers of protection analysis (LOPA). 6.2 Inherently safe optical radiation Visible, near infrared, or mid infrared radiation that is incapable of producing sufficient thermal energy under normal or specified fault conditions to ignite a specific hazardous atmospheric mixture is inherently safe.

39、 6.2.1 The inherently safe concept applies to unconfined radiation and does not require maintaining a target-free environment. Secondly, the concept is an energy limitation approach to safety, and studies indicate ignition of explosive gas atmospheres by an optically heated target requires the least

40、 amount of energy, power, or power density of the identified ignition mechanisms in the visible through mid infrared spectrum. 6.2.2 Research to date has concluded the values of visible, near infrared, and mid infrared beam strength, as called out in this clause, are safe. The safe values incorporat

41、e a modest safety factor on observed ignition values obtained under severe test conditions. a) an optical pulse energy equal to or less than the minimum spark ignition energy of the explosive gas atmosphere. A higher energy level is safe under the following conditions: 1. For an optical pulse durati

42、on greater than 1 ms and less than 1 s, an optical pulse energy equal to or less than 10 times the minimum spark ignition energy of the explosive gas atmosphere 2. For an optical pulse duration greater than 1 s, a peak power or peak power density equal to or less than the applicable value listed in

43、Table 2 b) optical powers or optical power densities equal to or less than the values listed in Table 2 c) an optical pulse train is safe if the individual pulses meet the safe energy criteria of 6.2.2 a) and either the average power or average power density meets the applicable value listed in Tabl

44、e 2 Table 2 Safe optical powers or safe optical power densities for Class I locations by Material Group and Temperature Class (T Code) Material Group A B C D D IIA IIA IIB IIC T Code T1-T6 T1-T6 T1-T6 T1-T3 T4-T6 T1-T3 T4-T6 T1-T6 T1-T6 Power (mW) 35 35 35 150 35 150 35 35 35 a Power Density b (mW/m

45、m2) 5 5 5 20 c 5 20 c 5 5 5 a A 15 mW power applies to carbon disulfide atmospheres. b Lower values for power density may apply for irradiated areas greater than 400 mm 2. c For irradiated areas greater than 30 mm2 and less than 400 mm2 where combustible solids may intercept the beam, the 5 mW/mm2 p

46、ower density limit applies. 21 ANSI/ISA-TR12.21.01-2004 (R2013) Copyright 2013 ISA. All rights reserved. 6.2.3 Ignition tests to demonstrate inherent safety may be advantageous under certain cases such as a) beams of intermediate dimensions or durations that may exceed the minimum optical ignition c

47、riteria but are still incapable of causing ignition; b) beams with complex time waveforms such that pulse energies, average power, or average power density are not easily resolved; or c) specific atmospheres, targets, or other test conditions that reflect specific applications that are demonstrably

48、less severe than test conditions studied to date. 6.2.4 Fiber optic terminal devices incorporating the inherently safe concept should provide over -power fault protection to prevent excessive beam strengths in Class I locations. Optical sources such as laser diodes or light-emitting diodes will fail

49、 if over-heated under over-power fault conditions. The thermal failure characteristic of certain optical sources may provide the necessary over-power fault protection. Electrical circuits such as intrinsically safe barriers placed between the optical source and the electrical power source can provide over-power fault protection. Fiber optic terminal devices may incorporate shutters or other automatic beam strength reduction devices (interlocks) when fault conditions are detected, also provi ding over-power fault protection. All forms of over-power