The need for weights and measures is pervasive in the U.S., which is why it is sometimes necessary for a regulatory body to create and enforce standards for the safe and fair use of weighing equipment in a variety of situations. So while not all weighing equipment must adhere to these legal standards, there are two particular circumstances where it must. The first is in commercial transactions that rely on weight. The second is in classified hazardous locations where the use of electrical equipment creates a fire or explosion hazard.
Legal for Trade / Commercial Scales and Pre-Pack Lines
Many commercial transactions are based on weight, volume, length, or count of products bought and sold. The commercial measurement system is regulated by the National Institute of Standards and Technology so that consumers are protected from deceptive and misleading practices, to promote fair competition among companies, and ensure an orderly marketplace without the regulations becoming a huge burden to businesses.
In the U.S., requirements for trade weighing equipment are outlined in Handbook 44: Specific Tolerances and Other Technical Requirements for Weighing and Measuring Devices. NTEP (National Type Evaluation Program) is the process used to test and evaluate weighing equipment and critical components to check for compliance with Handbook 44.
The most common example is retail price computing, where a container of food is sold to a consumer by its price per weight measurement (i.e. price per pound). This is common in supermarkets, delis, butcher shops and famer’s markets. These scales can either stand alone or be part of a larger system, such as a checkout scanner. No matter what situation, these scales must be tested and certified by a testing lab then calibrated, tested, and seal by an inspector from the regulatory agency.
Explosion Proof Scales for Classified Hazardous Locations
There are many normal manufacturing processes that involve the measurement or use of flammable or explosive materials. However, when these substances are introduced to the atmosphere, electrical equipment can become a source of ignition and cause fires or explosions.
The U.S. Department of Labor’s Occupational Safety and Health Administration has created a system that classifies the different types of hazardous environments and set forth guidelines for the installation and operation of electrical wiring and equipment used therein to mitigate the risks involved. The National Electric Code (NEC) classifies hazardous locations in three ways: by the type of substance being handled, the condition under which the hazard is present, and the nature of the particular substance being handled.
Types of Hazardous Locations
There are three types of hazardous locations. Class I locations handle flammable gases and liquids. A petroleum refinery, distillery, paint manufacturing plant, or gas service station would all be Class I hazardous locations. Class II locations handle combustible dusts. Class II locations would include grain elevators, flour and feed mills, candy factories and other plants that handle sugary or starchy products as well as those that produce plastics, medicines, or fireworks. Class III locations handle ignitable fibers and flyings, for example, textile mills, cotton gins, and plants that shape, pulverize, or cut wood.
Hazardous Location Conditions
There are two conditions under which a hazardous material will be present. Each of the three types of hazardous location will also be classified according to the conditions under which that material is present.
Normal conditions are considered Division I. Normal conditions means that the hazard is expected to be present in the everyday operation of the facility or during frequent repair and maintenance activity.
Abnormal conditions, or those where the hazard is only present in the event of an accident (accidental rupture, breakage, unusual faulty operation), are considered Division II.
So a Class I location can either be Division I or Division II, as can Class II and III.
The Nature of Hazardous Substances
The types of material found in Class I and Class II locations are further broken down into groups based on the nature of individual substances. The nature of a substance is determined by its flammable properties and characteristics including ignition temperature, explosion pressure and/or conductivity.
Testing and Certification of Scales for Classified Hazardous Locations
While the NEC has set rigorous standards for the installation and use of equipment in hazardous locations, it’s also necessary to ensure that these standards are being met. This is why all scales and weighing devices must be tested by a nationally recognized testing laboratory to ensure that they are safe to use in the hazardous location they’re intended for.
For example, an explosion test for a Class I environment would mean that the lab tests the device in a variety of mixtures of gas and air until the lab finds the mixture that creates the greatest explosion pressure.
To pass inspection, the weighing device must prevent the ignition of the surrounding atmosphere and withstand a hydrostatic test of its strength. It will not pass unless it can resist rupture at four times the maximum pressure found in the explosion tests.
Explosion Proof Scales from Arlyn
Our ArlynGuard B, C, F, and P 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.
We offer a variety of bench, cylinder, platform and floor scales at many maximum capacities and with a variety of platform sizes to ensure that finding a safe, accurate, and useful scale is a quick and easy process for you.
Have a Question?
We can answer any questions you may have about our explosion proof scales and help you choose the model that will best suit your needs. Our factory direct business model means you’ll find superior quality products at competitive prices. It also allows us to custom design and develop weighing solutions for those situations where a standard model may not suit. Contact us today!