When it co
mes to the safe installation of electrical wiring and equipment, OSHA’s National Electric Code sets the standard in the U.S. Because many businesses’ daily operations require the use of chemicals and compounds that have the potential to ignite a fire or explosion, the Code also classifies these hazardous materials into several categories according to their flammable characteristics.
Standard electrical equipment can become a source of ignition in these locations, which means that there are special regulations for seemingly innocuous items like your industrial scales. Yet even a small bench scale can ignite an atmosphere if the concentration of flammable material is high enough.
There are three categories into which these substances are classified – type, condition and nature.
Hazardous Location Types
The first category is Class, which determines the type of hazard present.
Flammable gases and vapors are Class I hazards. Any location that has high enough concentration of a flammable gas or vapor to become a risk is deemed a Class I location. Class I locations include petroleum refineries, distilleries, gasoline storage and dispensing areas and utility gas plants.
Class II includes any area that produces combustible dust, which can actually cause an explosion as powerful as one in a petroleum refinery. Class II locations include grain elevators; flour and feed mills; plants that manufacture, use or store magnesium or aluminum powders; industries that produce plastics, medicines and fireworks; starch or candy manufacturers; spice grinding, sugar and cocoa plants; and plants that prep coal and other carbon handling or processing areas.
Textile mills, cotton gins, cotton seed mills, flax processing plants and those that shape, pulverize or cut wood would all be Class III locations because their operations create sawdust or flyings, which are materials that can collect on the floor around machinery, lighting fixtures and other areas where a heat source can ignite them.
Hazardous Area Divisions
The three Class categories are subdivided into Divisions, which indicate the condition under which the hazardous substance is present.
Division I means the material is present during normal operational activities or where repair and maintenance activity is frequent.
Division II means the hazard is usually contained and will only be present during an abnormal situation such as an accidental rupture or breakage of a storage container or the unusual faulty operation of equipment.
Hazardous Substance Groups
Class I and II substances are broken down even further into one of seven groups, which are determined by the nature of the substance – or the properties of the substance (i.e. flame temperature, minimum ignition energy, upper and lower explosive limits, molecular weight) and how they will effect the likelihood and severity of an explosion. Class I is made up of groups A through D, while Groups E, F and G belong to Class II.
Sources of Ignition
The NEC highlights three unique ways in which electrical equipment can become a source of ignition in a hazardous environment.
The first is from the arcs and sparks created by everyday equipment like motor starters, contactors and switches.
The second cause is the high temperatures produced by heat-producing equipment like lamps or lighting fixtures that exceed the ignition temperature of the material. If they run above 100oC (212oF), they must be clearly marked.
The last cause is electrical failure, such as a terminal short or a blown out lamp.
Explosion Tests
Nationally recognized testing laboratories are responsible for testing equipment that’s been designed for use in the hazardous environments outlined in the NEC. Equipment must either be able to contain an explosion within the device or it must not produce sparks with sufficient energy to produce an explosion. Only when the equipment meets these rigorous standards and prevents ignition in the Class it is intended for will it pass inspection. There are often additional criteria that the equipment must meet before passing inspection.
ArlynGuard Explosion Proof Scales: Intrinsically Safe
Our line of explosion proof scales includes bench, cylinder, platform and floor models in a variety of capacities and platform sizes, which can be customized to meet your unique situation.
All of our ArlynGuard scales have one or more components that have been tested and approved to be Intrinsically Safe for use in an impressive range of hazardous locations including:
• Intrinsically safe for use in Class I, II, III; Division I; Groups A through G
• Non-incedive for use in Class I; Division II; Groups A through D
• Suitable for use in Class II; Division II; Groups F & G
• Suitable for use in Class III; Division II
Each ArlynGuard scale is equipped with one or more of:
• Model MKE-5-IS(-C) Digital Weight Indicator System
• Load Cell Models 620-300-IS, 620-100-IS, 620-50-IS, 620-25-IS, 620-10-IS, 520-10000L-IS, 520-5000L-IS, 520-5000IS, 520-2500-IS, 520-1250-IS, 320-500-IS and 320-250-IS
which are FM Approved components as per Approval Standard 3600, 3610, 3611 and 3810.
Each scale features stainless steel load cells for added stability, accuracy and protection from shock loading and overloading; durable welded construction; a large graphical display and intuitive user menu; and a display resolution of 1 part in 5,000.
And since we’re the direct manufacturer, we can also work with you on the weighing components or instrumentation of an OEM system intended for use in a hazardous environment.
We’re Committed to Safety, Quality and Our Customers
Arlyn Scales has been leading the design and development of weighing technology since 1978. Our factory direct business model ensures that you’re working with a team that can understand exactly what you need and why you need it. Whether you choose one of our standard explosion proof scales or require a custom solution, we’re here to help you find the scale that will provide you with accurate results each and every time you use it.
If you’re in the market for an explosion proof scale but aren’t sure which model meets your needs or want more information before moving forward, we urge you contact us today. We’re here to guide you through the selection process and answer any questions you may have along the way.
