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 IAEI News>Focus on the Code >CMP-14
Question 1. Could you clarify how a vehicle service area with open flame welding should be classified? As per 511-2 [NEC 1999], no open flame is allowed in these locations, so it may not be classified as a commercial garage. As a result, it seems to me that this structure should be classified as a Class 1, Division 2 location. However, this would therefore require sealed, explosionproof fittings and equipment essentially everywhere. This does not seem logical to me. The electrical equipment is explosionproof but the welding seems to be the greatest source of ignition. Please let me know if I am missing an important Code section. — D.E. Answer 1. Article 511 [NEC 1999] provides electrical requirements considered necessary for the practical safeguarding of persons and property from hazards arising from the use of electricity in both commercial repair and storage garages. Section 511-2 describes various situations that might be encountered in these repair and/or storage garages. Some of the situations will result in part of a garage being classed as a Class I, Division 1 location. In a different facility, or another area of the same facility, the situation may require a Class I, Division 2 classification. Then another situation will result in a facility or part of a facility being unclassified. Different parts of the same building will often have all three classifications. The classification of a space within a commercial garage is not a result of the ignition sources, whether code-compliant or non-code-compliant, that are in the garage but the likelihood of reaching an ignitable concentration of flammable vapor and oxygen. Section 511-3, provides guidelines for determining the area classification of a specific space within a commercial garage. This information is based on the vehicles in the garage being powered by heavier-than-air fuels, such as gasoline. The 2002 NEC provides additional requirements for commercial garages where vehicles are powered by lighter-than-air fuels, such as compressed natural gas (CNG). Ventilation provided in these facilities will have a great impact on the area classification. Extreme care should be used when reducing area classification based on ventilation. If the ventilation is not operating, because of breakdown, cold weather, or other reasons, ignitable concentrations of vapor and oxygen can accumulate. The FPN of 511-2 suggests a review of NFPA 88A—1995, Standard for Parking Structures, and NFPA 88B—1997, Standard for Repair Garages for additional information. These documents address construction limitations of the buildings, ventilation requirements, heating requirements, welding and/or open flame operations, sprinkler requirements, fire extinguisher requirements, and other operational issues for these occupancies. In the current Fire Codes, this information has been moved to NFPA 30A. Information in Articles 511, 500, 501, and 504 state that wiring and equipment might be explosionproof in the Class I, Division 1 locations but that other options are available. Wiring and equipment requirements become less severe in Division 2 areas and less severe again in unclassified areas. In most cases, much of the special electrical equipment can be avoided or minimized by careful placement of the garage equipment. The effectiveness of the requirements found in Article 511 is based on both the designer and garage occupant applying all of the applicable standards when constructing and operating a commercial garage. — Donald Cook, CMP-14 | Return to top | Question 2. Articles 500 and 504 define both intrinsically safe and nonincendive wiring methods / systems. Please explain the difference between a nonincendive and intrinsically safe wiring method? Why is one not allowed to install the nonincendive wiring method in a Class I Division I classified location? For this application Engineering has identified either system as Class 2 per NEC Article 725 (when either system is in a non-classified location). Would this be correct? What article(s) would you use to verify a nonincendive system is installed correctly? Would you use Article 504 as a guide to assure the nonincendive system is installed correctly? — E.C. Answer 2. Both intrinsically safe circuits and nonincendive circuits are permitted to use any of the wiring methods suitable for unclassified locations, including chapter 7 and chapter 8. Intrinsically safe circuits and nonincendive circuits use the same basic concept to minimize the risk of ignition of hazardous atmospheres. Both rely on energy limitation with some important differences. The major difference between the two types of equipment is that nonincendive circuits are evaluated for ignition capability under normal operating conditions, while intrinsically safe circuits are evaluated under fault conditions. During the product evaluation of an intrinsically safe circuit, up to two independent faults, per the requirements in the applicable product standard, are allowed in an attempt to increase the energy available in the circuit. With that in mind, if the wiring method fails, ignition will not occur. In 500.7 the NEC defines the protection techniques for hazardous (classified) locations and their permitted usage. Please note that 500.7(F) indicates that nonincendive circuits are permitted only in Division 2 locations. As noted in the answer above, the power supplies for nonincendive circuits are evaluated under normal operating conditions to determine that they limit the energy of the circuits to a level that is incapable through sparking or thermal conditions to ignite the surrounding atmosphere for which it was evaluated. The power supplies for intrinsically safe systems are further required to remain non-ignition capable even under fault conditions. In Class I, Division 1 locations, it is assumed that ignitible concentrations will exist under normal operating conditions. An acceptable level of safety for the electrical system has been determined to include at least two failures before the system can ignite the atmosphere. In Division 2, there has to be some abnormal condition (failure of containment of the flammable material, failure of ventilation, etc.) before an ignitible atmosphere can exist. Therefore ignition could only occur in Division 2 when the containment of the material and the nonincendive circuit failed simultaneously (two faults). Based on this, nonincendive circuits do not provide the requisite level of safety for a Division 1 location. The product standards for both intrinsically safe circuits and nonincendive systems limit the energy to a point that is not ignition capable. The values for these systems and the values for Class 2 power supplies are not identical. Many nonincendive and/or intrinsically safe supplies will also be Class 2, but it would be possible for the power supply to not be Class 2. What article(s) would you use to verify an nonincendive system is installed correctly? If you are in a Class I location and using the 2002 NEC, 500.2, 500.7, 501.4(B) (3), 501.5(A)(1) Exception (d), and the applicable chapter 3 articles for the wiring methods and materials that you are using. Would you use Article 504 as a guide to assure the nonincendive system is installed correctly? Installation requirements for intrinsically safe circuits and nonincendive systems are very similar. Both systems are required to provide control drawings, which describe how the system must be installed and not compromise the safety of the installation. — Donny Cook, CMP-14 | Return to top | Question 3. What are the hazardous areas around a gravure printing press? Normally, we use 516.3(A)(4) for division 1 and 516.3(B)(5) and (6) for division 2. Can the division 2 zone be reduced on a gravure printing press by the fact that the dryer design pulls air from the press room in such a way that the lower flammable limit (LFL) in division 1 cannot exceed 25 percent? The dimensions given for division 2 are given without considering ventilation. Thank you in advance for your assistance. — N.S. Answer 3. Thank you for the opportunity to consider your application of the NEC and comment on the application. Area classification is affected by a number of variables present at the location being considered. The extent of the classified area requires consideration of the combustible material, the vapor density of the material, the temperature of the material, the process or storage pressure, the size of the release, and the ventilation of the location. The scope of NEC 516 indicates that these rules apply to regular or frequent application of flammable liquids, combustible liquids, and combustible powders by spray operations and the application of flammable liquids, or combustible liquids at temperatures above their flashpoint, by dipping, coating, or other means. The classification information in 516 has been extracted from NFPA 33 and 34. When I look at those standards, they do not seem to apply to print press facilities. Division 2 locations can be a result of several conditions, which are located in 500.5(B)(2). NFPA 497 is a recommended practice that applies to classification of hazardous (classified) locations for electrical installations in chemical process areas. The principles provided in this document are used in many industries that include flammable liquids, gases, or vapors. Section 3-3.1(a) of 1997–NFPA 497 indicates that areas that have adequate ventilation, where combustible materials are contained within suitable, well-maintained, closed piping systems may be considered unclassified. The definition of adequate ventilation in NFPA 497 includes ventilation that prevents the accumulation of significant quantities of vapor-air concentrations from exceeding 25 percent of the lower flammable limit. Section 3-3.2(c) indicates that adequate safeguards against failure must be provided when using ventilation to reduce the classification of a location. I have not been able to find a specific recommended practice or standard that applies to printing facilities. Based on all of the information above, it may be possible to classify the space in question as unclassified. Without question, the complete package of classification documentation should be presented to the owner/operator and to the AHJ prior to selecting the electrical equipment for the space. That documentation is required by NEC 500.4(A). — Donny Cook, CMP-14 | Return to top | Question 4. I have a question regarding a new auto repair garage. In one of the car bays is a surface-mounted car lift. Below the car lift is a catchbasin for water runoff. The owner wants to put a sump pump in the basin to remove the water. They did not, however, prepare properly for a Class 1, Division 1, pump or wiring method. They are trying to avoid saw cutting the concrete floor. What they did provide is a 2" PVC sleeve into the sump to an outside wall. I have stated that if a pump is installed in the sump, the pump and wiring method must be rated for a C-1, D-1 location. I also suggested they remote the pump away and out of the classified area, which leaves the question of how to control the pump. Is there an intrinsic control apparatus that could be used inside the sump to trigger the pump when the water level is high? If so, what wiring method could be used to run through the sleeve to the float switch? Would providing six air changes per hour in the garage eliminate the need for explosionproof wiring method? I would appreciate any suggestions you may have. — M.G. Answer 4. It is possible to reduce the area classification in a commercial garage by using mechanical ventilation. It is also possible to use non-explosionproof motors in Class I, Division 2 locations if the motors do not include brushes, switches, or other arc-producing devices. That permission is provided in Article 501. It is also possible to provide a switch (simple apparatus) that is connected to an intrinsically safe circuit supplied from an associated apparatus. If the circuit to the switch is intrinsically safe, any of the wiring methods in chapter 3, chapter 7 or chapter 8 would be permitted with the limitations included within the control drawings. These answers would be the same, using either the 2002 or the 2005 NEC. The specific code sections will vary based on the edition. Article 501 and also NEC 511.3 were reconfigured during the NEC-2005 cycle. To provide more specific information related to the ventilation requirements would require some additional information related to the activities that occur within the garage. Please understand that since this has not been processed as a formal interpretation, it must be considered my personal opinion, and does not necessarily represent the official position of IAEI or NFPA or its technical committees. If you have any additional questions, please feel free to contact me, and I will do my best to provide any information that I can. — Donald Cook, CMP-14 | Return to top | Question 5. For a Class I, Division 2 area, do we need to take inlet air for microturbines from a clean area (outside the Class I Division 2 bubble)? If so, how far away can that be? —M.C. Answer 5. I would first like to clarify that I do not consider myself an authority on microturbine installations. I was interested in your question and did some research to see if I could find the answer to the question. I found the following references that might help to answer your question:
As I reviewed section 8-4.2 of NFPA 37, Standard for the Installation and Use of Stationary Combustion Engines and Gas Turbines, I see a requirement for the combustion gas turbine starting sequence to include a purge cycle that will result in a nonflammable atmosphere in the turbine and exhaust system prior to introduction of fuel. I assume that requirement might have been the genesis of your question? Although providing specific requirements for the intake air for microturbines is not the purpose of NFPA 496, it seems that the principles used in NFPA 496 might be useful in your situation. The goal in section 8-4.2 of NFPA 37 is to have a nonflammable atmosphere. Those are the same goals we have for electrical equipment enclosures in NFPA 496. If all of those assumptions are valid, it appears that the intake air for the microturbine could be taken from any unclassified location. Since a Class I, Division 2 location could have ignitible concentrations (flammable atmospheres) under abnormal conditions that would not seem to be a good place to take the inlet air. — Donny Cook, CMP-14 | Return to top | Question 6. Do soil remediation systems create Class I areas due to the nature of their process, i.e., pulling out ground contaminants (usually fuel oil) and burning them in an oxidizer chamber of some sort? Would the electrical code require that the system be listed as a unit or would individual listings on each of the components suffice?—C.H. Answer 6. I understand your concerns related to the remediation equipment described in the question. We have encountered several of these systems in our county over the past couple of years and have asked the same questions. As I have discussed the issues with the remediation system equipment manufacturers, I have gained some additional understanding of their position. I learned that these systems are used around the US to extract a variety of contaminants from soil. They are usually installed for environmental reasons. In some cases, those contaminants are flammable or combustible liquids which could result in some spaces that are classified. In those cases, the procedures outlined in NFPA 497 will provide good direction for classifying the areas around the equipment. I have found that the equipment manufacturers are aware of this, but without a clear understanding of the conditions present at the specific location, it is not possible for the manufacturer to determine the area classification. The area classification will be affected by the characteristics of the specific material that is encountered, the vapor density of the specific material, the ambient temperature and its impact on the flammable material, the process pressure, the size of the release of the material, and the ventilation of the area. These characteristics will be different at each location. In other cases, the contaminants may cause environmental problems, but may not be flammable or combustible at all. In those cases, the area would not be classified. These applications may constitute environmental or health hazards, but the special electrical equipment that is used in Articles 500, 504, and 505 is not designed to address those dangers. The NEC does not mention remediation systems and therefore does not have a specific listing requirement for that equipment. It does have a general requirement in 110.2 that all conductors and equipment required or permitted by the Code shall be acceptable only if approved. Approved is then defined as acceptable to the authority having jurisdiction. Some form of third party equipment certification is required as a basis for equipment approval in many jurisdictions across the US. However, the NEC would not prohibit a jurisdiction from evaluating the equipment in house. Most jurisdictions that I am aware do not have the resources to accomplish such a task. Many of the NRTLs now offer field evaluation services. They have copies of applicable standards, test equipment, time necessary to provide evaluations of this type equipment, and therefore may be better equipped to perform the equipment evaluation. The specific language requiring this third party certification is usually found in administrative requirements. Based on my personal experience with remediation systems, I am not aware of many jurisdictions that would be interested in evaluating the systems without some outside assistance.— Donny Cook, CMP-14 | Return to top | The views of the authors of Focus on
the Code and the editor are provided solely as a public service.
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