NEC Hazardous Area Classifications

explosive-environment-scale-p-1The NEC, or National Electric Code, sets the standard for the safe installation of electrical wiring and equipment in the United States. There are certain work environments that have been specifically classified as hazardous due to the nature of the materials used in that environment. For example, warehouses that work with flammable gases and liquids or textile mills that work with fibrous materials.

Standard electrical equipment in these locations can become a source of ignition, which means there are special regulations to which all equipment and employees must adhere.

Hazardous locations are classified by three different criteria type, condition, and nature.

Hazardous Location Types

  • Class I
    • Flammable gases or vapors are present in the air in such quantities that explosions are a risk
    • Includes petroleum refineries, gasoline storage and dispensing areas, aircraft hangars and fuel servicing areas, utility gas plants, spray finishing areas, and any other jobs that involve storing and/or handling of liquefied petroleum or natural gas
  • Class II
    • Operations whose work produces combustible dust, which can cause as powerful an explosion as a petroleum refinery
    • Includes plants that manufacture, use, or store magnesium or aluminum powders; grain elevators; flour and feed mills; industries that produce plastics, medicines, and fireworks; starch or candy producers; spice grinding, sugar, and cocoa plants; plants that prep coal and other carbon handling or processing areas
  • Class III
    • Ignitable materials that collect on the floor around machinery, lighting fixtures, and other areas where a source of heat can ignite them
    • Includes textile mills and cotton gins; cotton seed mills; flax processing plants; and plants that shape, pulverize, or cut wood and create sawdust or flyings

Hazardous Location Divisions

  • Division I: Normal
    • Applies to operations where hazards are a daily part of production or where repair and maintenance activity is frequent
    • For example, areas near open dome loading facilities or adjacent to relief valves in a petroleum refinery
  • Division II: Abnormal
    • Applies to operations where hazardous material is usually stored in closed containers or systems and will only be introduced to the area due to accidental rupture, breakage, or unusual faulty operation
    • For example, an operation that handles closed storage drums of flammable gas, such as hydrogen or carbon monoxide

Hazardous Substance Natures

The following Groups only apply to Class I hazardous locations

  • Group A
    • Acetylene
    • A very small percentage of Class I locations
  • Group B
    • Hydrogen and materials with similar characteristics
  • Groups C and D
    • The most common Groups for Class I Hazardous Locations
    • Group C pertains to materials like ether
    • Group D pertains to some of the more common flammable substances such as butane, gasoline, natural gas, and propane

The following Groups only apply to Class II hazardous locations:

  • Group E
    • Metal dusts that are both conductive and explosive
    • Includes aluminum, magnesium, and other metals with similar natures
  • Group F
    • Charcoal and coke dusts, carbon black, and coal
    • While only some of these materials are conductive, all are explosive
  • Group G
    • Grain dusts
    • Includes flour, starch, and cocoa
    • None of these materials are conductive, but all are explosive

Electrical Equipment as a Source of Ignition

According to the NEC, there are three different ways in which electrical equipment can become a source of ignition in a hazardous environment:

1. Arcs and sparks from everyday equipment a. Motor Starters, contractors, switches 2. High temperatures from heat-producing equipment a. Lamps, lighting fixtures that exceed the ignition temperature of the material b. If temperatures run above 100oC, the equipment must be clearly marked 3. Electrical failure a. Terminal shorts, blown out lamps

Explosion Test

Nationally recognized testing laboratories test equipment designed for use in hazardous environments to ensure that they meet the Necks rigorous standards. Only when the equipment prevents ignition in the appropriate Class will it pass inspection. Often there are additional criterion that the equipment must meet before receiving a pass.

Explosion Proof Scales

Arlyn Scales is a direct manufacturer of weighing equipment, including scales and their sub-assemblies. As such, we’re able to develop specialized equipment to meet the needs of even the most challenging work environments.

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.

ArlynGuard B is our line of intrinsically safe bench scales with capacities ranging from five to one hundred and fifty pounds. While the resolution depends on the capacity, the range is between five hundredths of a pound to one one-thousandth of a pound.

ArlynGuard C is our line of intrinsically safe cylinder scales. Capacities range from sixty to four hundred pounds, while resolution ranges from two hundredths of a pound to one tenth of a pound.

ArlynGuard P is our line of intrinsically safe platform scales. Capacities are available between five hundred and one thousand pounds. Resolutions are either one tenth or two tenths of a pound.

ArlynGuard F is our line of intrinsically safe floor scales. Capacities range from twenty-five hundred to twenty thousand pounds with resolutions from five tenths of a pound to five pounds.

Contact Us

For more information about classified hazardous locations and what kind of scales you should be using, contact Arlyn Scales today! Our customer support is available to answer all of your questions and to help guide you to the scale that exactly suits your needs.

Because we are a factory direct manufacturer, we’re able to offer competitive pricing on all of our scales. We’re also able to design and build custom solutions, so even if you don’t think our standard models will meet your needs, be sure to get in touch and ask about your options!