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UL Standards for Hazardous Location Industrial Instrumentation

UL Standards for Hazardous Location Industrial Instrumentation

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  • UL Standards are used to classify industrial instrumentation by giving it a safety rating, based on which hazardous locations in which using the instrument is safe.
  • Area Classifications can either be listed as in the Division System or the Zone System.
  • These classifications are used to identify instrumentation that is suitable for such things as areas with combustible gases or dust, specific types of gases that may be present, while some classifications offer dust ingress ratings similar to IP Ratings, etc.

For the automation and manufacturing industry, hazardous location industrial instrumentation may be required to ensure safety and compliance. UL Standards help classify instrumentation and designate its suitability for use in certain areas. A hazardous location, or HazLoc, is described as an area where explosion or fire hazards exists. The presented hazard is due to the presence of flammable gases, flammable or combustible liquid-produced vapors, combustible dusts, or ignitable fibers or flyings.

UL Standards create uniform coding for identifying potentially hazardous areas and material to improve safety across many industries. These standards are written and governed by UL Solutions and include a large number of standards including: TC31 (IECEx), UL STP (North America), NFPA, API, BSEE, and CFR committees. Various components and materials will have different Area Classifications depending on the type and degree of potential hazard that may be presented.

Area Classification for the UL Standards Division System

For the Division System, an Area Classification describes multiple aspects about a given area that can make it potentially hazardous. Each area classification will identify a material type, or Class, along with a Division. The Division indicates the “likelihood of presence” such as material stored in containers, being processes, transported, etc. Also included in an Area Classification is the Group, which describes the material’s properties along with the Temperature Class.

UL-Listing-example-division-markings-Process-Solutions-Corp

For example, Class II, Division 2, Groups F and G. T100°C may be used to classify a particular area and the products suitable for use in that area. Class II indicates that combustible dust may be present. Division 2 indicates that the dust may accumulate, causing nearby equipment to overheat and ignite the combustible dust.

Class I Locations

Class I locations include areas where inflammable gases or vapors are or may be present in sufficient quantities to produce explosive or flammable mixtures.

Class I, Division 1

Class 1, Div 1 include locations where hazardous atmosphere may be present during normal operations. It may be present continuously, intermittently, periodically, or during normal repair or maintenance operations. Or those areas where a breakdown in processing equipment releases hazardous vapors with the simultaneous failure of electrical equipment.

Class I, Division 2

Class 1, Div 2 locations are those in which volatile flammable liquids or gases are handled, processed, or used. Normally, they will be confined within closed containers or in closed systems from which they can only escape in the case of rupture or deterioration of the containers or systems.

Class II Locations

Class II locations are classified as hazardous due to the presence of combustible dust.

Class II, Division 1

Class 2, Div 1 includes locations where combustible dust may be in suspension in the air, under normal conditions, in sufficient quantities to produce explosive or ignitable mixtures. Dust may be emptied into the air continuously, intermittently, or periodically. Or where failure or malfunction of equipment might cause a hazardous location to exist and provide an ignition source with the simultaneous failure of electrical equipment. Also included are locations in which combustible dust of an electrically conductive nature may be present.

Class II, Division 2

Class 2, Div 2 designates locations where combustible dust will not normally be in suspension nor will normal operations put dust in suspension, but where accumulation of dust may interfere with heat dissipation from electrical equipment or where accumulations near electrical equipment may be ignited.

Class III Locations

Class III locations are those considered hazardous due to the presence of easily ignitable fibers of flyings, which are in quantities sufficient to produce ignitable mixtures.

Class III, Division 1

Class 3, Div 1 includes locations in which easily ignitable fibers or materials producing combustible flyings are handled, manufactured, or used.

Class III, Division 2

Class 3, Div 2 includes locations where easily ignitable fibers are stored or handled.

Area Classification for the UL Standards Zone System

With the Zone System, an Area Classification will identify the Explosion Protection, Protection Type, Group, Temperature Class, and Equipment Protection Level that’s required in a particular zone.

Zone Classifications

UL-Listing-Example-zone-markings-Process-Solutions-Corp
Zone 0

Ignitable concentrations of flammable gases, flammable liquid-produced vapors, or combustible liquid-produced vapors are present continuously or for long periods of time under normal operating conditions.

Zone 1

Ignitable concentrations of flammable gases, flammable liquid-produced vapors, or combustible liquid-produced vapors are likely to exist under normal operating conditions.

Zone 2

Ignitable concentrations of flammable gases, flammable liquid-produced vapors, or combustible liquid-produced vapors are not likely to exist under normal operating conditions.

Zone 20

Ignitable concentrations of combustible dust or ignitable fibers/flyings are present continuously or for long periods of time under normal operating conditions.

Zone 21

Ignitable concentrations of combustible dust or ignitable fibers/flyings are likely to exist occasionally under normal operating conditions.

Zone 22

Ignitable concentrations of combustible dust or ignitable fibers/flyings are not likely to occur under normal operating conditions.

Groups – Class I, Zone 0, 1, 2, 20, 21, and 22

IIC

Acetylene and Hydrogen

IIB + H2

Hydrogen

IIB

Ethylene

IIA

Propane

IIIC

Conductive Dust

IIIB

Non-Conductive Dust

IIIA

Combustible Flyings

UL Standards for Electrical Protection Types – Gas Atmospheres

d

flameproof (for EPL Gb or Mb)

e

increased safety (for EPL Gb or Mb)

ia

intrinsic safety (for EPL Ga or Ma)

ib

intrinsic safety (for EPL Gb or Mb)

ic

intrinsic safety (for EPL Gc)

ma

encapsulation (for EPL Ga or Ma)

mb

encapsulation (for EPL Gb or Mb)

mc

encapsulation (for EPL Gc)

nA

non-sparking (for EPL Gc)

nC

protected sparking (for EPL Gc)

nR

restricted breathing (for EPL Gc)

o

il immersion (for EPL Gb)

op is

inherently safe optical radiation (for EPL Ga, Gb or Gc)

op pr

protected optical radiation (for EPL Gb or Gc)

op sh

optical system with interlock (for EPL Ga, Gb or Gc)

pv

pressurization (for EPL Gb or Gc)

px

pressurization (for EPL Gb or Mb)

py

pressurization (for EPL Gb)

pz

pressurization (for EPL Gc)

q

powder filling (for EPL Gb or Mb)

Electrical Protection Types – Dust Atmospheres

ta

protection by enclosure (for EPL Da)

tb

protection by enclosure (for EPL Db)

tc

protection by enclosure (for EPL Dc)

ia

intrinsic safety (for EPL Da)

ib

intrinsic safety (for EPL Db)

ma

encapsulation (for EPL Da)

mb

encapsulation (for EPL Db)

mc

encapsulation (for EPL Dc)

p

pressurization (for EPL Db or Dc)

UL Standards for Equipment Protection Level (EPL)

Level of protection assigned to equipment based on its likelihood of becoming a source of ignition and distinguishing the differences between explosive gas atmospheres, explosive dust atmospheres and the explosive atmospheres in mines susceptible to fire damp.

EPL Ma

Equipment for installation in a mine susceptible to firedamp, having a high level of protection, which has sufficient security that it is unlikely to become an ignition source in normal operation, during expected malfunctions or during rare malfunctions, even when left energized in the presence of an outbreak of gas.

EPL Mb

Equipment for installation in a mine susceptible to firedamp, having a high level of protection, which has sufficient security that it is unlikely to become a source of ignition in normal operation or during expected malfunctions in the time span between there being an outbreak of gas and the equipment being de-energized.

EPL Ga

Equipment for explosive gas atmospheres, having a high level of protection, which is not a source of ignition in normal operation, during expected malfunctions or during rare malfunctions.

EPL Gb

Equipment for explosive gas atmospheres, having a high level of protection, which is not a source of ignition in normal operation or during expected malfunctions.

EPL Gc

Equipment for explosive gas atmospheres, having an enhanced level of protection, which is not a source of ignition in normal operation and which may have some additional protection to ensure that it remains inactive as an ignition source in the case of regular expected occurrences, for example, failure of a lamp.

EPL Da

Equipment for explosive dust atmospheres, having a high level of protection, which is not a source of ignition in normal operation, during expected malfunctions, or during rare malfunctions.

EPL Db

Equipment for explosive dust atmospheres, having a high level of protection, which is not a source of ignition in normal operation or during expected malfunctions.

EPL Dc

Equipment for explosive dust atmospheres, having an enhanced level of protection, which is not a source of ignition in normal operation and which may have some additional protection to ensure that it remains inactive as an ignition source in the case of regular expected occurrences, for example, failure of a lamp.

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