Keeping the “Ex” out of explosive atmospheres and equipment

By Jeanne Erdmann

While you may not think of the sugar for your morning coffee or the aspirin for your headache as explosive items, the dusty atmospheres in creating in the manufacturing process of many items including paint and flour pose an explosion hazard under the right circumstances. In fact, nearly everything that touches our daily lives, from the printing and textile industries, to grain silos, to oil refineries, to filling our cars at the petrol station, involves use of equipment, especially electrical, in hazardous areas that need to be operated safely. While all electrical products need to achieve the minimal requirements of electrical safety, and the risk of fire, electric shock, and personal injury, safety standards for explosive (Ex) atmospheres and equipment reach well beyond basic certification.

These qualifications make safety certification more complicated and thus more costly because, from day one, manufacturers need to choose Ex concepts for the product. Often, an entire building, such as a petrochemical plant, needs to be designed and constructed with explosion safety in mind. Over the past decade or so, certification has become easier with a strategy provided by the IECEx that certifies and monitors Ex equipment and work areas where concentrations of gases and vapours or combustible dusts are present . The system is based on standards developed by the International Electrotechnical Commission.

To date, 25 countries are members of IECEx, but others may use the scheme without membership, which helps developing countries who may not have the technical infrastructure to develop standards. “While it might cost USD 50 or 60 to purchase a light fitting in a non-Ex environment, the same device purchased for use in an Ex area or environment would cost 10 times that amount because the device itself, the light fitting switch or motor, needs to be designed so that it will not have faults in the course of its normal operations that can result in an ignition source, from a spark, arc, or a hot surface,” explains Chris Agius, IECEx Secretary.

Spirit of cooperation
A piece of Ex equipment takes 12 months on average and tens of thousands of dollars to certify, says Agius. Before the 1990s, an Ex product had to be approved in each country before it could be sold there. Since then, IECEx has developed an internationally accepted system of testing and certification so when a product is tested and a certificate of compliance is issued, it is accepted where the standards are accepted. Today, IECEx provides a single certification process and a single operations manual supported by operational procedures and documents. “We have created an IECEx way of Ex testing and certification and any bodies that want to join must demonstrate they can do work this way. This has gained support from industry and regulators because they know what they’re up against everywhere,” comments Agius.

Agius has been involved with IECEx from its inception. The strength of the scheme, he says, lies in the participation of all stakeholders: manufacturers, regulators, testing and certification agencies, chemical and mechanical engineers, and consumers. This spirit of cooperation helps foster trade because the manufacture of hazardous location equipment is truly global in nature. Often, equipment for petrochemical plants or for agribusiness are manufactured in one country and sold around the world. This means that products need to be suitable for each country’s regulatory systems. Experts also participate in yearly meetings of the management and technical committee meetings. “We bring together a majority of like minded people who all desire to make sure things are done correctly. That’s why I view IECEx members and stakeholders as a huge extended family,” says Agius. “This spirit of cooperation among 150 or so of the best experts in the field has helped create an environment in which certification experts and industry work together instead of against one another, which in turn has helped make Ex certification accessible and affordable on a global basis.”

The aim of the system is for all countries to make IEC standards their national standard. As the system and what it can offer becomes more widely known and understood, more manufacturers around the globe are signing on. That has certainly held true in the United States where 52 certificates were issued to U.S. manufacturers in 2005. Kerry McManama, chairman of the U.S. national committee for IECEx and also chairman of the IECEx Technical Group, ExTAG, expects that number to double in 2006.

Quenching the fire triangle
McManama has global responsibility for all offices related to testing and certification of hazardous location equipment for Underwriter’s Laboratory (UL). This certification helps manufacturers obtain market access through the IECEx scheme. UL tests Ex equipment in one of four locations: the USA, Denmark, Brazil, and Germany. Some countries have national differences in their certification requirements, explains McManama, so the regulatory system in that country may require an in-country certification body to issue certificate for use. By this time, however, the testing and the review of documentation have been completed so all of the work required to bring the product into that marketplace has been completed.

UL tests the type of industrial equipment (pressure transducers, gas monitors, pumps, valves), for use in mining, agri-business or an oil refinery. Size ranges from very small, high tech equipment used to formulate processes in a chemical plant, or large apparatus used in large enclosures containing motor control equipment, such as what might be found on an oil platform in Prudhoe Bay, Alaska. Preventing explosions in hazardous locations or in Ex equipment goes back to the fire triangle: You need a heat source, combustible material, and oxygen to cause a fire. Protecting equipment against explosion requires removing at least one element in this triangle. The two most commonly used methods are flameproof or explosion proof enclosures and a technique called intrinsically safe, says McManama.

Flameproof enclosures remove the heat source from the fire triangle by channeling gas through a designated flame path. This design assumes gas is going to migrate into a given enclosure. If you have other electrical equipment in that enclosure such as little switches that can cause even a tiny arc when the switches are turned on or off, that arc could cause an explosion if the gas has migrated into the overall enclosure. Flamepaths are manufactured to quench any flame and thus prevent a fire from escaping out of the equipment. “If that area goes, the whole facility blows up,” says McManama.

That’s why testing and certifying this equipment is critical. Testers at UL will actually introduc gas into an enclosure and use a sparkplug as an ignition source to see if the equipment can withstand the explosion. Failures happen quickly and it’s hard to see the gas exploding as it leaks out of the enclosure. A high-speed camera shows where the failure occurred and UL can notify the customer where the gas comes out so the apparatus can be redesigned. “This is a mature industry so few pieces of apparatus fail. Most players have been around for a while and have a pretty good understanding of what’s necessary to make equipment right,” remarks McManama.

The intrinsically safe technique removes both heat and energy from the fire triangle. This technique represents the high tech end in the Ex field. The idea is to work at very low energy levels so that if equipment fails there is not enough energy in that spark to cause the gas to explode. The intrinsically safe technique follows the trend found in the high tech industry in which electronic equipment is getting lighter and more reliable; the same goes for equipment used in the Ex industry. “But the evaluation and testing of this equipment is very complex. It is essentially called a two-fault method because when we do our evaluation we can take any two components and fault them to generate a spark,” says McManama. “It’s difficult to design a circuit and a complete piece of equipment such that two faults will not cause an explosion. So when a test finds failures, we give the manufacturers options as to what the standard will allow in terms of construction and hopefully help them get their product to market.”

If manufacturers don’t want to use intrinsically safe or flameproof technology, they can purge and pressurize an entire building so a hazardous gas is prevented from entering a building or an enclosure by pumping an inert gas into the enclosure, which is then kept at a higher pressure. All Ex equipment is kept inside the purged and pressurized area. “You’ll often find, perhaps in Alaska at Prudhoe Bay, entire buildings will be pressurized to keep hazardous gases out of buildings, and have controlled buildings where people work,” says McManama.

Serving its customers
As part of the IECEx certification process of Ex equipment, the scheme provides ongoing audits to ensure that safety standards are upheld. Local IECEx certification bodies can inspect a plant in the manufacturer’s home country and also inspect a plant on other side of world.

The website (www.iecex.com), also serves as a meeting ground for manufacturers and certification bodies. Rules and operational documents are available freely to public. Industry representatives can scan the site for standardized report forms and to find other much needed information. The site has recently added one unusual feature: certificates of conformity are applied for and issued online. Once issued, certificates move immediately to the public area for full access. Since the site is searchable by keyword, manufactures can use it as a buyer’s guide for Ex certified products, says Agius.

Because Ex equipment is a large capital investment it has to last. Agius says it’s common for Ex equipment to be in service for 20 years or more. All of the work put into design, manufacturing, and certification can go out the window during repair or overhaul if the workshop can’t maintain Ex parameters. To address this concern, IECEx launched a program in February 2006 to certify service facilities that repair and overhaul Ex equipment.

Agius says that comprehensive services and a central forum for conformity assessment issues have helped spark global growth of IECEx at a much higher level than initially expected. “We’re going back to basics in terms of customer service. We know the system so we can respond to technical concerns. I do not believe that the system would be the success it is today if we didn’t include provisions for stakeholders in industry in the overall day to day management. At end of the day test and certification bodies are a business and they respond to the needs and demands of their customers or their clients.