1、 AMERICAN NATIONAL STANDARD ANSI/ISA-61241-2 (12.10.06)-2006 (R2011) Electrical Apparatus for Use in Zone 21 and Zone 22 Hazardous (Classified) Locations Protection by Pressurization “pD” Approved 19 May 2011 ANSI/ISA-61241-2 (12.10.06)-2006 (R2011) Electrical Apparatus for Use in Zone 21 and Zone 2
2、2 Hazardous (Classified) Locations Protection by Pressurization “pD” ISBN: 978-1-936007-94-3 Copyright 2011 by IEC and 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
3、 form or by any means (electronic mechanical, photocopying, 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-61241-2 (12.10.06)-2006 (R2011) Preface This preface, as well
4、 as all footnotes and annexes, is included for information purposes and is not part of ANSI/ISA-61241-2 (12.10.06)-2006 (R2011). This document has been prepared as part of the service of ISA towards a goal of uniformity in the field of instrumentation. To be of real value, this document should not b
5、e static but should be subject to periodic review. Toward this end, the Society welcomes all comments and criticisms and asks that they be addressed to the Secretary, Standards and Practices Board; ISA; 67 Alexander Drive; P. O. Box 12277; Research Triangle Park, NC 27709; Telephone (919) 549-8411;
6、Fax (919) 549-8288; E-mail: standardsisa.org. The ISA Standards and Practices Department is aware of the growing need for attention to the metric system of units in general, and the International System of Units (SI) in particular, in the preparation of instrumentation standards. The Department is f
7、urther aware of the benefits to USA users of ISA standards of incorporating suitable references to the SI (and the metric system) in their business and professional dealings with other countries. Toward this end, this Department will endeavor to introduce SI-acceptable metric units in all new and re
8、vised standards, recommended practices, and technical reports to the greatest extent possible. Standard for Use of the International System of Units (SI): The Modern Metric System, published by the American Society for Testing b) the maximum surface temperatures of internal parts that are protected
9、by a type of protection in accordance with IEC 61241-1-2.ANSI/ISA-61241-0 and which remain energized when the supply of protective gas for pressurization is removed or fails, for example electric heaters. If, during normal service, the temperatures of internal surfaces which may be exposed to an exp
10、losive dust atmosphere exceed the maximum values permitted in IEC 61241-1-1 ANSI/ISA-61241-0, for the temperature class of the equipment, appropriate measures shall be taken to ensure that, if pressurization ceases, any explosive dust atmosphere which may exist is ANSI/ISA-61241-2 (12.10.06)-2006 (R
11、2011) - 20 - prevented from making contact with that surface before it has cooled below the permitted maximum value. This may be achieved either by design and construction of the joints of the pressurized enclosure and ducts by other means, for example, by bringing alternative (or auxiliary) sources
12、 of protective gas into operation, or by arranging that the hot surface within the enclosure is in a dust-tight or encapsulated housing. When determining the temperature for rotating electrical machines, the duty type according to IEC 60034-1 as specified by the manufacturer shall also be considered
13、. 7 Safety provisions and safety devices (except for static pressurization) 7.1 General Protective measures shall be adopted to prevent the electrical apparatus installed in a pressurized enclosure from being energized before pressurization is established. All safety devices shall either be a) prote
14、cted by an appropriate type of explosion-protection in accordance with IEC 61241-1-2 ANSI/ISA-61241-0, or b) non-electrical and not capable of causing ignition, or c) located in a non-hazardous area. The safety devices required by this standard form safety-related parts of a control system. It is th
15、e responsibility of the manufacturer and the user to assess that the safety and integrity of the control system is appropriate. The safety devices shall be provided by the manufacturer of the apparatus or by the user. In the latter case, the apparatus shall be marked “X“ in accordance with 29.2 of A
16、NSI/ISA-61241-0 and the description documents shall contain all the necessary information required by the user to ensure conformity with the requirements of the standard. The enclosure shall be cleaned before the electrical supply to the system is connected or restored in order to remove any accumul
17、ated combustible dust left in the enclosure, either accidentally following failure of the pressurization system, or following normal shutdown. The manufacturer shall provide the necessary instructions to the user detailing the requirements for cleaning the enclosure. The manufacturer shall specify t
18、he maximum and minimum action levels and tolerances of the safety devices. The safety devices shall be used within the normal operational limits as specified by the manufacturer taking due account of the most onerous conditions specified for normal service. 7.2 Pressure- or flow-activated devices Pr
19、essure-activated devices provided for the operation of alarm and electrical trip devices shall operate when the pressure within the enclosure falls below the permitted minimum value or exceeds the permitted maximum pressure. Flow-monitoring devices provided for the operation of alarm and electrical
20、trip devices shall operate when the pressure within the enclosure falls below the permitted minimum value, or exceeds the permitted maximum pressure, and shall be located at the outlet. - 21 - ANSI/ISA-61241-2 (12.10.06)-2006 (R2011) An electrical interlock on the fan motors or controls is not suita
21、ble to indicate failure of pressurization. It does not give an indication in the event of the fan belt slipping, the fan becoming loose on the shaft or reverse rotation of the fan. 7.3 Electrical supply Where protection is not provided to prevent the ingress of dust following the shutdown or failure
22、 of the pressurization system, a warning label shall be fixed stating that dust shall be removed from the interior prior to switching on the electrical supply. 7.4 Switching off electrical supply When required by this standard, the switching-off of the electrical supply shall require the isolation o
23、f all live conductors, including the neutral, in accordance with IEC 61241-1-2ANSI/ISA-61241-0. 7.5 Failure of pressurization The design of a pressurization system relies on the principle that a failure of the pressurization automatically disconnects the system from the electricity supply and/or ini
24、tiates alarms. To guard against the possibility that electrical apparatus protected by pressurization may cause an explosion in the case of the protective gas supply failure, the following measures shall be incorporated. They take into account the characteristics of the apparatus, prevailing environ
25、-mental conditions, and the use of devices for monitoring and warning purposes. 7.5.1 Protection requirements Requirements applicable to apparatus protected by pressurization vary according to the level of hazard, being dependent on the type of apparatus used, and the classification of the area, and
26、 specific installation and process requirements. These factors require either switching off the electrical supply and giving an alarm, or giving an alarm only. Whatever protective measures are adopted, the following provisions shall also be made. a) All electrical apparatus which is to be energized
27、in the absence of pressurization shall be suitable for use in the explosive dust atmosphere corresponding to its position. b) Visible or audible alarms shall be located where they will immediately be seen or heard by the responsible personnel who will take the necessary action. c) Either a pressure-
28、monitoring device, flow-monitoring device, or both, shall be used to monitor the satisfactory functioning of the pressurization. ANSI/ISA-61241-2 (12.10.06)-2006 (R2011) - 22 - Table 1 Requirements on failure of pressurization Type of apparatus in the enclosure Area classification Ignition-capable a
29、pparatus Apparatus with no sources of ignition in normal operation Zone 20 Not applicable aNot applicable aZone 21 7.5.1.1 7.5.1.2 Zone 22 7.5.1.2 Internal pressurization not required aRequirements for ALL apparatus for use in zone 20 have not yet been finalized. 7.5.1.1 Switching off electrical sup
30、ply The following requirements apply. a) An automatic device shall be provided to switch off all electrical supplies to the equipment protected by the apparatus, unless it is protected by one or more of the concepts described in the IEC ISA-61241 series, and initiates an audible and/or visible alarm
31、 when the overpressure and/or protective gas flow fall below the minimum prescribed value. In special cases, when the apparatus is intended for use in an installation where the switching-off may jeopardize the safety of the installation or persons, this requirement may be rearranged to provide a con
32、tinuous audible or visible alarm until pressurization is restored or other appropriate measures are taken. b) Doors and covers, which can be opened without the use of a tool, shall be interlocked so that, on opening any door or cover, the electrical supplies are switched off from all parts not prote
33、cted by one or more of the concepts of the IEC ISA-61241 series. This includes all phases and the neutral if available. The supply must be prevented from being switched on again until all doors and covers have been re-closed. c) A warning shall be prominently mounted on the apparatus stating the fol
34、lowing or equivalent: WARNING: REMOVE ALL DUST FROM THIS ENCLOSURE BEFORE CONNECTING OR RESTORING THE ELECTRICAL SUPPLY 7.5.1.2 Alarm only The following requirements apply. a) An automatic device shall be provided to either audibly and/or visibly warn the operator when the overpressure and/or protec
35、tive gas flow fall below the minimum prescribed value to enable him to take appropriate measures. b) All doors and covers which can be opened without the use of a tool shall be marked carry the following warning: WARNING: DO NOT OPEN WHILE ENERGIZED UNLESS IT IS OBVIOUS THAT NO COMBUSTIBLE DUST IS P
36、RESENT c) A warning shall be prominently mounted on the apparatus stating the following or equivalent: WARNING: REMOVE ALL DUST FROM THE INSIDE OF THE ENCLOSURE BEFORE CONNECTING OR RESTORING THE ELECTRICAL SUPPLY - 23 - ANSI/ISA-61241-2 (12.10.06)-2006 (R2011) 7.6 Level of overpressure A minimum ov
37、erpressure of 50 Pa (0,5 mbar) shall be maintained relative to the external atmosphere at every point within the enclosure and its associated ducts where leakage can occur. Examples of the distribution of pressure in different systems of enclosures and ducts are illustrated in figures A.1 and A.2. N
38、OTE Rotating machines should be of the enclosed type. Consideration should be given in the application of pressurized apparatus having an internally enclosed cooling circuit in which circulation is assisted by an internal fan, since the effect of such fans may be to produce a negative pressure in pa
39、rts of the casing with consequent risk of ingress of dust if pressurization ceases (see figure A.2). 7.7 Possible sources of ignition When the protected apparatus incorporates components such as batteries, which remain sources of ignition, suitable precautions shall be taken in the design of the app
40、aratus to prevent the accidental production of sparks, by ensuring that these components are designed with a type of protection appropriate to the characteristics of the prevailing external and internal atmospheres. Such components shall be clearly identified. 7.8 Enclosed components Any components
41、inside the enclosure which remain in operation in the absence of the protective gas, for example devices for heating the equipment when it is not in operation, shall be protected by one of the types of protection for electrical equipment in combustible dust atmospheres in accordance with IEC 61241-1
42、-2ANSI/ISA-61241-0, with the type of protection suitable for the particular hazardous area. 7.9 Separate enclosures Where the apparatus is intended to form part of a multi-enclosure installation with a common protective gas supply, the resulting design shall take into account the most unfavourable c
43、onditions of the whole installation. If the protective safety devices are intended to be common, the opening of a door or cover need not necessarily switch off the whole electrical supply or initiate the alarm provided that a) the opening of a door or cover is preceded by switching off the supplies
44、to the apparatus located in that particular enclosure that is not protected by a suitable concept of dust ignition protection, or the door is interlocked with the supplies to achieve the same end; and b) the common protective safety device continues to monitor the rest of the installation. 8 Safety
45、provisions and safety devices for static pressurization Additional requirements for static pressurization. The pressurized enclosure shall be filled with an inert gas in a non-hazardous area using the procedure specified by the manufacturer. Automatic device(s) shall be provided to operate when the
46、overpressure falls below the minimum value specified by the manufacturer. It shall be possible to check the correct operation ANSI/ISA-61241-2 (12.10.06)-2006 (R2011) - 24 - of the device(s) when the apparatus is in service. The automatic device(s) shall only be capable of being reset by the use of
47、a tool or a key. NOTE 1 The purpose for which the automatic device(s) is (are) used (i.e. to disconnect power or to sound an alarm or otherwise ensure the safety of the installation) is the responsibility of the user. The minimum level of overpressure shall be greater than the maximum pressure loss
48、in normal service, measured over a period not less than 100 times the time necessary for the cooling of the enclosed components below the maximum permissible surface temperature for the dust concerned, with a minimum of 1 h. The minimum level of overpressure shall not be less than 50 Pa above the ex
49、ternal pressure under the most onerous conditions specified for normal service. NOTE 2 If the overpressure falls below the minimum specified, it is the users responsibility to ensure that the pressurized enclosure is removed to a non-hazardous area before refilling. 9 Supply of protective gas 9.1 Type of gas A protective gas shall be used for maintaining pressurization in the enclosure. The gas shall be non-flammable and shall not, by reason of its chemical characteristics or the impurities that it may contain, reduce the level of protection below that sought, or affect the sa
