Explosion protection refers to the techniques used to reduce the possibility of electrical and electronic equipment igniting in a hazardous environment (HAZLOC). HAZLOCs are environments containing flammable gases, vapors, or dusts. The Mine Safety and Health Administration has approved specific equipment for use in U.S. coal and gassy mines, where methane and dust are present, to minimize the risk of ignition or thermal ignition.
Three basic methods are employed for explosion protection: preventing the gas (explosive mix) from reaching the equipment, limiting the power of the equipment to prevent ignition, and containing the explosion in the immediate vicinity of the equipment to prevent it from spreading. NIOSH-sponsored research refers to these methods as “techniques,” and the details are documented in explosion safety standards. According to OSHA and the International Electrotechnical Commission, techniques allowed in a particular location are typically identified by four zones. These zones are determined by factors such as the relative danger of an explosive atmosphere. They range from Zone 0, where an explosive atmosphere may be expected to occur frequently or continuously, up to NRZ (No Requirements Zone), where there is a negligible risk of the atmosphere being explosive during equipment operation. The IEC recognizes thirteen different techniques.
MSHA’s explosion protection regulations generally recognize two techniques: the use of explosion-proof enclosures (XP box) and 2-fault Intrinsic Safety for electrical and electronic equipment. U.S. regulations also consider only two categories of hazardous locations (equivalents to zones): the “inby the last cross-cut” (as well as several other specified areas) where the atmosphere is considered to always be potentially explosive, and the “outby areas,” which are similar to the NRZ. The alignment between U.S. designated areas and IEC zones in the table is solely based on the aligning of the techniques allowed between the two approaches. The terms “Inby,” “Outby,” and “Outside” are not defined by the IEC in terms of probability or likelihood of an explosive atmosphere occurring but rather based on the location of the mine.
Recent NIOSH-sponsored efforts in the field of explosion protection research
NIOSH’s research program in the mining sector has a mission to eliminate occupational illnesses, injuries, and fatalities from the industry. NIOSH’s explosion protection research focuses on improving safety for miners. The U.S. coal industry cannot use certain explosion-protected mining equipment that is used by other countries to improve safety and health due to a lack of certification (explosion protection) required by U.S. law. To better understand the technical differences, research was conducted to compare the explosion protection requirements of US mining criteria and equipment that meets IEC standards. NIOSH evaluated an explosion protection method recognized by both MSHA (Mining Safety Administration) and the IEC: Two-fault Intrinsic Safety (IS). Both the IEC standard for IS equipment and the MSHA approval criteria evolved from the original document (UL 911 4th Edition 1988). The assumption was made that because the technique is similar, this evaluation would be easier than evaluating the relative safety of completely different techniques not recognized by MSHA. The analysis was further reduced in scope and complexity by limiting it to portable (stand-alone) equipment, eliminating the need to resolve distinctly different approaches taken by MSHA and IEC to approve IS interconnected equipment and components.
This post was written by Justin Tidd, Director at https://beckersmcusa.com/. For nearly a half a century, Becker Mining has been at the forefront of industry safety. Becker/SMC is the industry’s leader in increasingly more sophisticated electrical control systems. Most of the major innovations, design features and specialized electrical components have been developed by Becker/SMC.
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