Motion Control Equipment: The Facts
Anywhere that is known as an explosion risk area could cause damage and injury to the environment and the people, and these areas are subject, in most places around the world, to regulations of the legal nature. IECEx is a certification scheme that creates these global frameworks for those who independently test devices or other services to protect against explosions.
The IEC, or International Electrotechnical Commission, is essentially responsible for these global standards that must be set in the electrotechnology sector. The publications from the IEC have counted for the recommendations that almost all the standards are set by, and just a few years ago, the requirements for gas explosions were in the series 60079, specified in that standard. Many of the requirements are the same for the sectors, and each series has been summarized in the series of IEC 60079. The initial step has already been taken for many of the standards, and other standards will follow soon. National regulations are allowed to deviate from these initial standards, which is why it is necessary to text the IEC standards that are applied in individual countries.
When it comes to the installation of electrical equipment, the combustible gases and vapors might be present in many locations. These locations are known as hazardous locations, and the National Electrical Code, or NEC, in the United States defines these locations. In Canada, the Canadian Electrical Code, or CEC, defines them. The installation of equipment in hazardous locations has strict requirements. These requirements include the construction of the installation which also includes the materials and design elements. There are two common methods used to protect the ignition of the flammable vapors and gasses to call them “explosion proof” or “intrinsically safe.” These methods will be discussed below.
In more general terms, explosion proof is more commonly known to describe detector or sensor assemblies for gas detection systems. The high voltages and requirements for power might be dealt with after the installation is permanent. The intrinsically safe method is used for these same permanent installations where the sensors are much lower for the power devices. Portable instruments often used the intrinsically safe method of installation. The explosion-proof method is a classification of sensors or transmitter that explains the engineering and construction of the housing to contain either flashes or explosions. These housings are often made with stainless steel or cast aluminum, and they are made with a larger strength and mass to contain the explosion should any flammable vapors or gases penetrate this housing just as an electronic inside causes an ignition. The design must be made to prevent any surface temperature from exceeding the known ignition temperature of both the gases and the vapors. A high-temperature device sensing element might be protected by something called a flame arrestor to help stop the high-temperature gases from blending with the atmosphere.
The classification of intrinsically safe is a design that prevents the electronic circuit and wiring from causing any sparking. This classification cannot store any sufficient energy to start that ignition of any flammable vapor or gas, and it cannot produce those high surface temperatures that cause ignition. This design is not explosion proof, but it doesn’t have to be. Permanent installations might have intrinsically safe barriers, located outside of the hazardous location. They also limit the energy available to the device that is located in the hazardous location.
Classifications for hazardous locations based on the flammable vapors and gases in North America:
Class I: Vapors and gases
Division 1: Vapors or gases might be present at any given time in concentrations that might be sufficient for an explosion.
Division 2: Vapors or gases are not typically present or are only present during a leak of a containment vessel or certain piping, but still resulting in concentrations that are potentially hazardous.
Groups A-D: Atmosphere groups that are categorized by the ignition temperatures. Group A is the most hazardous, while Group D is the least hazardous of all the gas and vapor groups.
Group A: Atmospheres that contain acetylene.
Group B: Atmospheres that contain hydrogen or other equivalent hazardous vapors or gases.
Group C: Atmospheres that contain ethylene, cyclo-propane, or ethyl-ether vapor.
Group D: Atmospheres that contain hexane, gasoline, naphtha, butane, benzene, alcohol, propane, natural gas (AKA methane), benzol, acetone, or lacquer solvent vapor.
Intrinsic Safety Advantages
There are several advantages to using the intrinsically safe method. It is by far the safest option, the cheapest option, and the easiest option to install for protection. The system integrity is no longer a concern because the explosions just cannot happen. These systems of intrinsic safety offer savings in labor over the traditional methods or protection because not bolted enclosures, or heavy conduits are used. The costs of materials are also less because enclosures of the standard are the only expense that incurs, and this is to mount the barriers. Intrinsic safety provides a low energy set of requirements that help eliminate the shock hazards or safety permits. Field instruments can then be calibrated and maintained all while the power stays turned on. Unlike the explosion protection methods, these systems operate in a seamless way with only the most modern technologies (Fieldbus) and retrofit applications. This newer technology mentioned is one of the major reasons why intrinsic safety is becoming the most dominant and best protection method used in hazardous locations around the world, but especially in North America.