Weighing in Hazardous Areas

Safe & Easy Solutions for Weighing in Hazardous Areas

Weighing equipment used in areas where there may be explosive concentrations of vapors or dust must be equipped with special wiring and other intrinsically safe electrical components. Hazardous (classified) locations might exist in any manufacturing location with vapors, dust or flyings, but are common in large bakeries (flour), plastics manufacturing plants (vapors or dust), chemical plants (vapors), paint-finishing locations (vapors), and grain silos (dust or flyings), to name just a few.  Other examples include locations where vehicles are fueled or any transfer mechanisms for inherently hazardous materials.

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Reducing Risk in Hazardous Areas Definitions of Hazardous Areas

Class I Locations:

Class I locations are those in which flammable gases or vapors are present in the air in quantities sufficient to produce explosive or ignitable mixtures. Class I locations are further subdivided into two Divisions and three Zones.

Class I, Division 1: There are three different situations that could exist to classify an area as a Class I, Division 1 location:

  1. Ignitable concentrations of flammable gases or vapors under normal operating conditions.
  2. Ignitable concentrations of such gases or vapors may exist frequently because of repair or maintenance operations or because of leakage.
  3. Breakdown or faulty operation of equipment or processes might release ignitable concentrations of flammable gases or vapors, and might also cause simultaneous failure of electric equipment.

Note:  These classifications are designated by regulatory agencies. Hardy doesn’t classify, but does deliver solutions that comply with regulatory requirements.

Class I, Division 2: One of the following three situations must exist for an area to be considered a Class I, Division 2 location:

  1. Volatile flammable liquids vapors or flammable gases are handled, processed or used, but the hazardous materials will normally be confined within closed containers or closed systems from which they can escape only in the event of accidental rupture, breakdown of containers or systems, or from abnormal operation of equipment.
  2. Ignitable concentrations of gases or vapors are normally prevented by positive mechanical ventilation, which might become hazardous through failure or abnormal operations of the ventilating equipment.
  3. Adjacent to a Class I, Division 1 location, where ignitable concentrations of gases or vapors might occasionally be transmitted unless prevented by adequate positive-pressure ventilation with safeguards against ventilation failure.

Zone Definitions:  Zones take into account different dangers from potentially explosive atmospheres.  Zone 0 is the most hazardous, and Zone 2 is the least hazardous. 

Zone 0: Everywhere that ignitable concentrations of flammable gases or vapors are:
Present continuously and/or Present for long periods of time
Zone 1: Everywhere that ignitable concentrations of flammable gases or vapors are:

  1. Likely to exist under normal operating conditions
  2. May exist frequently because of repair, maintenance operations, or leakage

Zone 2 Everywhere that ignitable concentrations of flammable gases or vapors are:

a. Not likely to occur in normal operation

b. Occur for only a short period of time

c. Become hazardous only in case of an accident or some unusual operating condition

Class II Locations:

Class II hazardous locations are areas where combustible dust, rather than gases or liquids, may be present in varying hazardous concentrations. Class II locations are further subdivided into two divisions.

Class II, Division 1: One of the following three situations must exist:

  1. Where combustible dust is present in the air under normal operating conditions in such a quantity as to produce explosive or ignitable mixtures. This could be on a continuous, intermittent or periodic basis.
  2. Where an ignitable and/or explosive mixture could be produced if a mechanical failure or abnormal machinery operation occurs.
  3. Where electrically conductive dusts in hazardous concentrations are present.

Class II, Division 2: One of following two situations must exist:

  1. Combustible dust will not normally be in suspension in the air in quantities sufficient to produce explosive or ignitable mixtures, and dust accumulations will normally be insufficient to interfere with the normal operation of electric equipment or other apparatus, but combustible dust may be in suspension in the air as a result of infrequent malfunctioning of handling or processing equipment.
  2. Resulting combustible dust accumulations on, in or in the vicinity of the electric equipment may be sufficient to interfere with the safe dissipation of heat from electric equipment or may be ignitable by abnormal operation or failure of electric equipment.

Class III Locations:

Class III hazardous locations contain easily ignitable fibers or flyings, but Asbestos Fibresthe concentration of these fibers or flyings are not suspended in the air in such quantities that would produce ignitable mixtures. Class III locations are further subdivided into two divisions.

Class III, Division 1: Easily ignitable fibers or materials producing combustible flyings are handled, manufactured or used.

Class III, Division 2: Easily ignitable fibers are stored or handled, other than in the process of manufacturing.

 

Regulatory Agencies

In North America, the most widely used hazardous location classification system is defined by the National Fire Protection Association (NFPA) Publication 70, National Electric Code® (NEC) in Articles 500 to 506. These regulations specify the type of hazardous substances that are or may be present in the air in quantities sufficient to produce explosive or ignitable mixtures.

The NFPA establishes area classifications based on Classes, Divisions and Zones that when combined delineate the hazardous conditions of a specific area. This classification method provides a description of the hazardous material, and the probability that it is present, so that the appropriate equipment is safely installed and operated. The Occupational Safety and Health Administration (OSHA) has adopted these hazardous classifications from the NEC and they are defined in the 29 Code of Federal Register (CFR) 1910.399.

Almost all developed countries are members of the International Electrotechnical Commission (IEC). Positive pressure enclosures, or “welding habitats” work on the principle of overpressure. This protection principle is regulated by IEC standard 60079-13:2017.  The IECEx certification scheme is regulated by the IECEx 02 IEC System for Certification to Standards relating to equipment for use in Explosive Atmospheres (IECEx System) IECEx certification is compulsory to operate electrical equipment in explosive atmosphere in most Countries outside Europe. Australia, New Zealand, UAE, Malaysia, and the Philippines accept IECEx certification directly.

ATEX Certification is the national certification standard of the European Union, and mandatory to operate equipment in explosive atmospheres in Europe. Certification is based on the ATEX directive 2014/34/EU with all equipment requiring a proper manufacturer’s EU Declaration of Conformity. For Zone 1 welding habitats this EU Declaration of Conformity must be based on a Notified Body issued EU–Type Examination Certificate for pressurized habitats (rooms) EN 60079-13.

Download the Free Guide:  Safe, Easy Weighing Solutions for Hazardous Areas

Hardy Weighing Solutions for Hazardous Areas

Designing Safety into a Weighing System

Intrinsic safety (IS) is a protection technique for safe operation of electrical equipment in hazardous areas by limiting electrical and thermal energy, available for ignition to safe levels. 

Download the Free Guide:  Safe, Easy Solutions for Weighing in Hazardous Areas

For potentially hazardous Class I, Div. 1 environments, Hardy Process Solutions has designed safety into its components with an appropriate level of protection for different applications.  Hardy recommends using intrinsically safe low-energy components in hazardous areas (including load cells, scales, and summing boxes) and limit power and current to them through intrinsic barriers that prevent energy from crossing over from the safe area.

For Tanks, Vessels, Mixers or Reactors, a Typical Weighing System  Configuration for a Hazardous Area: Use Intrinsically Safe Barriers to prevent energy and current from instruments in the safe area from crossing over to low energy equipment in the hazardous area.

Hardy Weight Processors and Weight & Rate Controllers use proprietary technologies that have great value for Hazardous Area applications and confined spaces. Our C2® Electronic Calibration allows calibration of the weighing system without ever entering the environment. Conversely, Integrated Technician® is used for system diagnostics and troubleshooting from the safety of the safe area thereby reducing risk to operators. Other features such as WAVERSAVER® is used to eliminate the effects of vibration on the weight signal so only Stable Weight is communicated to the Control System.  

Hardy’s single-slot Rockwell® PLC/PAC modules read and condition data from strain gage load cells and communicate it over the I/O chassis backplane to the processor. They provide basic weight data or are loaded with sophisticated algorithms to perform application-specific industrial weighing processes from simple batch weighing to loss-in-weight control, filling or dispensing. Modules are available for Allen-Bradley® ControlLogix®, CompactLogix®,  Micro800® or POINT I/O chassis.

Floor & Bench Scale Weighing System Configuration For a Hazardous Area: Use Intrinsically Safe Floor or Bench Scales with built in summing cards and IS Barriers to prevent energy from instruments in the safe area from crossing over to low energy IS scales in the hazardous area.

Intrinsically Safe Barriers