25 Years of the Zone System in the USA

Impact, evolution, and future of Zone Classifications through Article 505

Author: J.M. McIntyre und B.J. Zimmermann

In the area of explosion protection, the publication of Article 505 in the 1996 National Electrical Code (NEC^®) was seen as a giant step toward global harmonization. It allowed for the implementation of the Zone system for explosive gas atmospheres (gases, flammable liquid-produced vapors, and combustible liquid-produced vapors) in the United States to co-exist with the traditional North American Class/Division system. Since then, many more products and engineering solutions have become available to the many industries with hazardous locations, permitting different Types of Protection and explosion-protected equipment. Standards development committee acceptance and review, training, field installation, and product testing/certification were and continue to be main areas of hazardous location development. To mark the twenty-fifth anniversary of the adoption of Article 505, this article will explore these areas through the lens of experts who themselves were key players in its adoption and implementation. Each expert was separately interviewed with a set of similar questions prior to the composition of this article.

NEC Standards Committee and Article 505

The National Electrical Code (NEC^®) is the requirement for the safe installation of electrical wiring and equipment in the United States. It is part of the National Fire Code series published by the National Fire Protection Association (NFPA) and adopted by the American National Standards Institute (ANSI). The NEC^® is updated every three years and published officially as document ANSI/NFPA 70. The NFPA’s National Electrical Code Committee reviews and edits the NEC^®. Various code-making panels oversee and update the different NEC^® Articles. These panels consist of appointed volunteer members from industry representatives, electrical contractors, insurance carriers, testing labs, and government agencies. Code Making Panel 14 is the panel that oversees the classification of and requirements for equipment in hazardous (classified) locations. The Code Making Panel meets typically twice to discuss revisions and to vote on any major changes to be included in the next publication.

Table 1: Comparison of Divisions and Zones

“In reality, the first proposal to harmonize the NEC^® requirements with International Electrotechnical Commission (IEC) requirements had been submitted in 1969 for the 1971 NEC^®but was voted down by entrenched industry roadblocks.” Mac Criswell commented.

Mac Criswell is currently the General Manager of R. STAHL, Inc. the North American branch of R. STAHL Schaltgeräte GmbH.
In 1992, Mac Criswell became the Managing Director of Killark-STAHL, the joint venture of R. STAHL and Hubbell Incorporated.

The strategic objective of the joint venture was then to encourage the US adoption of a Class, Zone system. This objective was enabled when in 1989, Joe Kuzcka, Hubbell’s codes and standards representative, was confirmed as the NEMA (National Electrical Manufacturer’s Association) principal representative on the NFPA 70 – Code Making Panel 14.

Joe Kuzcka’s new role enabled him and his colleagues to have increased dialogue with other industry leaders. While some industry leaders were interested in the Zone system for global applications, many users in the U.S. had already transitioned to primarily Class I, Division 2 area classifications. This reality meant that some of the most significant benefits of the Zone system such as increased safety equipment had similar approaches in Class I, Division 2 applications. The real synergy was created when key Gulf of Mexico offshore operators sought to expand the utilization of Metal Clad (MC) cable into Class I, Division 1 Wellhead area applications instead of using conduit. This need led to the desire by these operators to work with the cable manufacturers to develop Metal Clad – Hazardous Location (MC-HL) cable and implement it in the NEC^®. Many of these same operators saw the benefits of the additional Types of Protection for instrumentation applications and began to push for additional harmonization including the Zone system.

In October of 1989, Mac Criswell introduced Joe Kuzcka to David Bishop of Chevron USA - Gulf of Mexico Operations. Mr. Bishop was at the time very active in the International Society of Automation (ISA), known at the time as the Instrument Society of America. The ISA had begun the development of US adoptions of the IEC 60079 Series of standards. These equipment standards were used to drive the NEC^®change. David Bishop led the ISA efforts to propel the movement of adopting the Zone system forward.

While there was strong select user interest, most users were not active in the standards development process. Through continued discussions with the core users and expansion out to select other influential users, a quorum supporting the harmonization began to form. In spite of this user interest, key industry factions blocked the proposals in the 1990 NEC^® cycle. Progress was made in the 1993 NEC^® cycle in that the proposal for the 1996 NEC^® cycle was submitted. In January 1995, Article 505 passed the Code Making Panel 14 straw ballot, but in the formal vote in February, the panel voted against it. The only way to contest the results of that ballot was to orchestrate a “floor fight” debate in May at the 1995 NFPA conference in Denver where the 1996 NEC^®adoption would be voted on by the NFPA members. Key users participated in the floor fight debate and were successful in the getting the proposal returned to the Code Making Panel for another vote. After passing again, it went to the NFPA NEC^®correlating committee for approval in July of 1995. The correlating committee rejected the proposal. The decision was then appealed to the standards council of the NFPA. The Standards Council approved the proposal later that July. Following the approval, the International Brotherhood of Electrical Workers (IBEW), a trade union, filed another appeal in August. Finally in October of 1995, this appeal too was denied, and Article 505 became part of the 1996 NEC^®.

Zones and Divisions Training

The evolution of hazardous location installation codes and product standards throughout the world has taken two distinct paths. In North America, a “Class, Division” System has been used since 1949 as the basis for area classification of hazardous (classified) locations. In this system, hazardous locations are separated into three “Classes” (originally four, later reduced to three) or types based on the explosive characteristics of the materials. The Classes or type of material is further separated into two “Divisions” based on the risk of release of the flammable material. With the adoption of Article 505, the Classes can also be separated into three “Zones” based on the release of the flammable material. Note that the Zone system has three levels of “risk of release” versus the Division System’s two levels.

The Class/Zone system in Article 505 is based the US implementation of International Electrotechnical Commission (IEC) Standards 60079 series. Additionally, the Zone-based system introduced new Types of Protection. These new Types of Protection provided an increased flexibility in designing and installing electrical equipment for hazardous (classified) locations. The Zone classification system intended to be a parallel area classification system for Class I, which would serve as an alternate to the Division system. Many division-classified areas can be reclassified to Zone-defined areas, but only by a qualified “Registered Professional Engineer,” according to NEC^®wording. The NEC^® has also given provisions to allow equipment listed using Zone Types of Protection in Division applications and vice versa. To make sure that the ordinary location requirements of the equipment are met as required by the NEC^®, a unique separate marking for the Zone system in the United States (AEx) was derived and is required.

Even before the 1996 NEC^®, the need to educate people in the IEC Zone system had compelled Heinz Bockle to move from Künzelsau, Germany to Houston, Texas. Heinz worked over forty years with R. Stahl, Inc. educating, marketing, overseeing the development and certification of products, and creating engineering solutions using both the Division and Zone systems for the U.S. market. According to Heinz, “After the 1982 oil crisis, many manufacturers were looking to sell oil equipment overseas. These companies needed consultation and product.” Heinz recalled a four hour meeting with members of the U.S. Coast Guard to explain the Zone system for Zone equipment coming into the Port of Houston on foreign vessels. Table 1 is one of the main slides that Heinz used in his presentations to compare Divisions and Zones. Another concept that Heinz explained a lot over the years was the method of protection, “Increased Safety” (Ex e – IEC Explosion Protection designation; AEx e – United States Explosion Protection designation). This Type of Protection was originally developed in Germany around 1951 as “erhöherste Sicherheit” (Ex e). Heinz remarked, “I always thought that “elevated safety” should have been the English translation instead of increased safety. Then the “e” would make more sense to English speakers.” This Type of Protection elevates the safety of electrical equipment against the possibility of excessively high temperatures and of the occurrence of arcs and sparks by applying additional measures to the device. Heinz added, “By increasing the robustness of a terminal by applying additional measures to ensure connection security, we can make electrical connections without using explosionproof terminal boxes. Article 500, which details the Class/Division system, considers all terminals as arcing devices, thus requiring Division 1 protection. Article 505 permits terminals that are designed and approved to be non-arcing. This is a major advantage as cast enclosures are no longer needed for terminal boxes. Using increased safety terminal boxes, lighter enclosures made of sheet steel or non-metallic materials can be used.”

Field Installation

“To be new and innovative enough to think “outside the box,” replied Will McBride to the question of why the Alpine Project utilized the Zone method of area classification. The lead engineering consultant for the ARCO Alaska Alpine Project, also added, “Not having to use heavy and large flameproof / explosionproof enclosures coupled with the cost of hauling them up to the site, was definitely going to cut costs. It bears mentioning that a mix of Zone and Division products was used since at that time there was not a full range of fully certified Zone classified products available for the United States”. Will McBride (the former ARCO Alaska Electrical Technical Authority) is currently one of the foremost authorities of the Zone system in Alaska and is considered the most knowledgeable engineer for the selection and installation of conductors in the oil field.

The ARCO Alaska Alpine Project on the North Slope of Alaska is distinguished as the first major complete oil production facility in North America to use NEC^® Article 505.

There were many successes and many lessons learned on this project. Before this project, oil refineries were required to use heavy explosionproof enclosures to house all of the electrical equipment in Class I, Division 1 and often in Class I, Division 2 hazardous (classified) locations.

Using the Zone method, the project saved on the weight of air lifting heavy equipment up the North Slope (referring to the portion of Alaska North of the Brooks Mountain Range).

Another advantage of not using the cast enclosures is reduced maintenance. These enclosures corrode thus degrading their explosion protection ability. Additionally, cast enclosures require explosionproof conduit / cable seals. Pouring these water-based seals in extremely low temperatures is not always possible and heaters need to be used to keep the material warm enough to properly cure. These seals also have to be maintained. One of the main advantages was that terminals did not have to be in cast enclosures. This saved lots of physical space considering the required indoor installation of this equipment. More physical space was saved by not having to run as much conduit in between the equipment. Even more space could have been conserved by using TC-ER-HL cable. As pointed out by Will McBride, “There was not the cable allowance that there is now in the code. The allowance of the TC-ER-HL cable and the elimination of the gland plate for grounding was a huge step forward, but did not occur until the 2017 NEC^®.” This meant MC-HL cable, which is more likely to be damaged due to kinking for small diameter instrument cables, had to be used. The MC-HL is more rigid, and in order to meet the bending requirements STAHL developed swiveling adaptors.

One of the biggest challenges of using the Zone method on this project was training. There was a large learning curve for the designers and installers, especially given the limited product selection. Joe Kuzcka and Heinz Bockle conducted many training sessions and did their best to provide information and product solutions.

Since Article 505 had recently been adopted, Zone equipment had to be tested and certified in order to receive the new U.S. Zone marking. Certifying products in time for installation was a challenge. As a result, there were a mix of Class I, Division 1 and Class I, Zone 1 equipment used and none of the Zone lighting products were available. Because of the MC-HL wiring method selected, a junction box was required with every light fitting. The lesson learned was that individual circuits should have been run to that device. As Will McBride noted, “This was part of the big learning curve even after the project was completed.”

Figure 2: Zone 1 Junction Boxes at Alpine Facility using MC-HL cable

Figure 3: Zone 1 Junction Box utilizing TC cable installation

Figure 4: Zone 1 Emergency Shut Down Control Box at Alpine Facility

Product Testing/Certification

Products rated for use in Zone system by the IEC or other nationally recognized certification agencies do not automatically receive the US marking. These products have to be tested against the AEx standards. Fortunately, the US Nationally Recognized Testing Laboratories had and continue to have interlaboratory agreements with other Certification Bodies throughout the world. Test data from other national Certification Bodies can be used as the basis for approval testing for the U.S. This serves to reduce approval test cost and the time-to-market. Many U.S-based manufacturers partnered with foreign manufactures to support the Zone product market.

As mentioned previously, the Zone system refined the practice of area classification further within the Class I area. For area classifications for gas and vapors, what the US calls Class I, the IEC divides into three Zones: Zone 0, 1 and 2 – one more area than the North American division classifications. ”It is important to note that the first proposal to create a third area of higher risk in the Class, Division system, Class I, Division 0, was made for the 1971 NEC^®by the Foxboro Company. The proposal did not go anywhere.” noted Bill Lawrence, FM Approvals Operations Vice President and Principal Engineer. Later in 1991, there was a formal paper entitled, “R. Stahl, Inc. Supports the Division 0 Proposals Submitted by the Instrumentation Society of America (ISA), written by the Alexander B. Anselmo, Technical Director, R. Stahl, Inc. at that time. Alex, who called himself Mr. Division 0, was part of the ISA SP12 Committee that developed the product standards to help support the 1996 NEC^® Code change. It must be noted the ISA SP12 Committee has now transitioned to a UL Standards Technical Panel, STP60079. This is the committee is responsible for the development and maintenance of hazardous location equipment standards for the United States. Brad Zimmermann, current Design and Development Manager for R. STAHL, Inc. currently serves as the Chairman of STP60079. He is also the Vice Chairman of the IEC standards committee, Technical Committee 31 (TC 31).

The approval process for changes to the NEC^® with all of the various stakeholders including manufacturers, inspectors, certification agencies, is complex. It takes a super majority of two-thirds of the voting members of Code Making Panel 14 to change the code. There was much debate over the Article 505 proposal. At one point, it even looked like it would not be approved. The sticking point was over the installation of Zone equipment. The resolution was a provision written into Article 505 stating that Zone installation had to be overseen only by a qualified registered Professional Engineer.

The inclusion of Article 505 in the 1996 NEC^® helped move towards the global harmonization in the area of explosion protection and opened the market for more methods of protection and more products than an addition of Class I, Division 0 would have given. Over the years, there have been many changes to Article 505. Bill Lawrence added, “The Article 505 revision of the original provision requiring all Zone installations to been overseen by registered Professional Engineer to a “qualified person,” according to NEC^® wording, as published in the 1999 NEC^® was one of the biggest changes to foster the use of the Zone system in the U.S.” Bill is currently still on Code Making Panel 14. Updates are constantly being made, and the latest ones are being discussed for the NEC^®, 2023 edition.

Present and Future of the Zone System

Despite all the advancements over the past twenty-five years including the addition of Article 506 for explosive dust atmospheres in the 2005 NEC^®, the Zone-system is not as prevalent in the United States as one would expect. However, in the future, worker safety and environmental considerations might drive more Zone-system utilization. As there is an expected presence of a flammable material under normal circumstances in Division 1, separating out the areas where there is regular release of a flammable material, Zone 0, where no workers are present, and not having regular release of the flammable material, Zone 1, helps to isolate the hazard from the worker. When a large explosionproof enclosure provides the explosion protection to a number of standard industrial contactors, circuit breakers, and the like; an open cover of maintenance work exposes normally arcing devices to an explosive gas mixture and exposes accessible electrical contacts to workers creating a potential shock hazard. Alternatively, the explosion protection can be applied to individual flameproof devices located in an increased safety enclosure. In that case, even when a cover is open for maintenance, the explosion protection of the normally arcing devices is still in place, and additional electrical shock protection for exposed terminals is practical to provide. Since the Zone-system is still not widely known or understood, Will McBride pointed out that “Without a champion, most projects will not go forward with using the Zone system.” Each one of interviewed experts (who all have different experiences in dealing with the development and evolution of the Zone system in the United States,) said there is still a great need for training. With more information and education, the Zone system can become a powerful tool for facility owners and operators across many industries. R. STAHL, Inc. will continue to be a major player in educating, marketing, and developing products and solutions for hazardous locations.