Hazardous classified locations

Hazardous (Classified) Locations1910.307

INTRODUCTION

• A hazardous location is any location where a potential hazard, either a fire or an explosion can exist due to the presence of flammable, combustible, or ignitable materials.

• These materials can consist of gases, vapors, liquids, dusts, fibers, etc.

HAZARDOUS LOCATION TYPES

• Class I Locations:

An area where flammable gases or vapors are or can be present in the air in quantities sufficient to produce explosive or ignitable mixtures. For Example

* Petroleum Refineries, Gasoline storage and dispensing areas, Dry cleaning plants, Spray Finishing areas, utility gas plants.

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• Class II Locations:

An area where presence of combustible dust present a fire or explosion hazard. For example:

Grain elevators, flour and feed mills, Use or store of magnesium or aluminum powders, producers of plastics, fireworks.

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• Class III LocationsClass III Locations::

An area made hazardous due to the An area made hazardous due to the presence of easily ignitable fibers or presence of easily ignitable fibers or flyings. For example:flyings. For example:

Textile mills, cotton gins, cotton seed Textile mills, cotton gins, cotton seed mills, plants that shape or cut wood and mills, plants that shape or cut wood and create sawdust or flyings.create sawdust or flyings.

Hazardous Location Conditions

• In addition to the types of hazardous locations, the kind of conditions under which these hazards are present are very important : Normal Conditions, Abnormal Conditions.

• Division 1: Normal Conditions

• Division 2 : Abnormal Conditions

Continued• Class I, Class II, and Class III hazardous

locations can be either Division 1 or Division 2

• Good examples of Class I, Division 1 locations: areas near open dome loading facilities or adjacent to relief valves in a petroleum refinery, because the hazardous material would be present during normal plant operations.

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• Closed storage drums containing flammable liquids in an inside storage room would not normally allow hazardous vapors to escape into the atmosphere but, what happens if one of the containers is leaking? You have got a Division 2 – Abnormal – condition … A Class I, Division 2 hazardous location.

Class I, Division 1• Where ignitable concentration of flammable gases,

vapors or liquids can exist all of the time or some of the time under normal operating conditions.

• Where ignitable concentrations of such gases or vapors may exist frequently because of repair or maintenance operations or because of leakage.

• Faulty operations of equipment or processes might release ignitable concentrations of flammable gases or vapors and might cause simultaneous failure of electrical equipment in such a way as to directly cause the electrical equipment to become a source of ignition.

Class I, Division 2

• Is a location in which volatile flammable liquids or flammable gases are handled, processed, or used, but in which the liquids, vapors, or gases will normally be confined within closed containers or closed systems from which they can escape only in case of accidental rupture or breakdown of such containers or systems or in case of abnormal operation of equipment.

Class I, Division 1 & Class I, Division 2

Class II, Division 1 & Class II, Division 2

Class III, Division 1 & Class III Division 2

Nature of Hazardous Substances

• The gases and vapors of class I locations are broken into four groups : A, B, C, and D. These materials are grouped according to the ignition temperature of the substance, its explosion pressure, and other flammable characteristics.

Group A

• Group A is an atmosphere containing acetylene.

• Equipment with rating up to 536º F (280ºC) can be utilized.

Group B

• Group B is an atmosphere containing hydrogen, or gases or vapors with a hazard equal to hydrogen. Butadiene, and ethylene and propylene oxide are included in this group.

Group C

• Group C is an atmosphere containing cyclo-propane, ethyl ether, or gases or vapors with hazard equal to these gases.

Group D

• Group D is an atmosphere containing acetone, alcohol, benzene, butane, gasoline, propane, natural gases or gases with vapors with a hazard equal to these gases.

Nature of Hazardous Substances

• In Class II - dust locations – we find the hazardous materials in Groups: E, F, G. These groups are classified according to the ignition temperature and the conductivity of the hazardous substance.

• Conductivity is an important consideration in Class II locations, especially with metal dusts.

Group E

• Group E is an atmosphere containing metallic dusts or other dusts with a similar hazard that is equivalent, such as Aluminum and Magnesium dusts.

Group F

• Group F is an atmosphere containing Carbon Black, Charcoal Coal, or Coke dusts with 8% or less total volatile material.

Group G

• Group G is an atmosphere containing grain dusts, flour , starch, cocoa, and similar types of materials.

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• Class III locations are not broken into groups.

North America Optional Area Classification

Class I, Zone 0, 1, and 2

Class I, Zone 0 is a Locations in which:

• Ignitable concentration of flammable gases or vapors are present continuously; or

• Ignitable concentrations of flammable gases or vapors are present for long periods of time.

Class I, Zone 1 is a location:• In which ignitable concentrations of flammable gases

or vapors are likely to exist under normal operating conditions; or

• May exist frequently because of repair or maintenance operations or because of leakage;

• In which equipment is operated or processes are carried on, of such a nature that equipment breaking down or faulty operations could result in the release of ignitable concentrations of flammable gases or vapors and also cause simultaneous failure of electrical equipment in a mode to cause the electrical equipment to become a source of ignition.

Class I, Zone 2 is a location

• In which ignitable concentrations of flammable gases or vapors are not likely to occur in normal operation and, if they do occur, will exist only for a short period.

• Ignitable gases and liquids are confined within closed containers from which they can escape, only as a result of accidental rupture or breaking of the containers or system, or as a result of abnormal operation of the equipment.

Elements of Hazardous Area Classification

• Sparks can occur by electrical or mechanical activity.

• Electrically the sparks are usually made by:

• Switching contacts

• Loose contacts in circuit carrying current

• Poorly mating metallic faces that are carrying current

• Static discharge.

Mixtures of Gases, Vapors and Air

• Ignition can only lead to a fire or explosion if three necessary components occur simultaneously, these are:

1. Flammable gas or vapor is present in sufficient quantities. (leakage)

2. Sufficient air (oxygen)3. Source of ignition (this could be spark having

sufficient energy or hot surface that will cause spontaneous or auto-ignition.

Gases and Vapors

• Imagine a flammable gas or vapor slowly leaking into confined volume of air that is not replenished.

• The concentration of gas or vapor in the mixture will be too low to support combustion

• As concentration increases until we reach LEL.• More increase we reach UEL.• LEL is very important in case of hazardous areas

to dilute it by air to low and safe levels

Temperature Class

• It is important to know how hot equipment gets, so that hot surfaces cannot be ignition sources.

• Six temperature classes are used T1 – T6• The lower the number the higher the maximum

allowable surface temperature• Temperature classification is based on fault

conditions.• T-class must be below Auto-ignition Temperature

of the gas.

Example of AIT

• Material AIT (°C)• Carbon Disulfate 102• Diethyl Ether 170• Kerosene 210• Ethylene 450• Propane 466• Methane 538• Hydrogen 560

Apparatus Group

• All flammable gases are sub-grouped into IIA, IIB or IIC on the bases of:

1. How easily the burning gas will burn through a narrow gap (measured as the maximum experimental safe gap (MESG)

2. The maximum spark ignition energy (MIE)

Apparatus Group

• A group IIA gas or vapor is the hardest of these sub-groups to ignite by a spark.

• Conversely a group IIC gas or vapor is the easiest to ignite.

Explosion Groups• The maximum experimental safe gap is determined

using a test apparatus.• Each gas or vapor/air mixture in its most volatile form,

under normal temp. and pressure is filled into the interior and exterior chambers of the test apparatus.

• The circumferential gap between the two chambers is accurately adjusted to the desired value.

• The explosive mixture in the interior chamber is ignited and the flame propagation, if any is observed through the windows in the exterior chamber.

• To find the maximum value of gap which prevents ignition of the explosive mixture in the exterior chamber.

MESG (Maximum Experimental Safe Gap)

• The maximum clearance between two parallel metal surfaces that has been found, under specified test conditions, to prevent an explosion in a test chamber from being propagated to a secondary chamber containing the same gas or vapor at the same concentration.

MIC (Minimum Igniting Current) Ratio

• The ratio of the minimum current required from an inductive spark discharge to ignite the most easily ignitable mixture of a gas or vapor, divided by the minimum current required from an inductive spark discharged to ignite methane under the same test conditions.

Explosion ClassesApparatus group for flameproof enclosure “d” Limiting Gap

Width

Minimum Ignition Current for Intrinsically

Safe Circuits “i”

Ratio in relation to Methane

A > 0.9 mm > 0.8

B > Or = 0.5 to 0.9 mm

> Or = 0.45 to 0.8

C < 0.5 mm < 0.45

Example of MIE

• Material Ignition Energy µJ

• Hydrogen 40

• Ethylene 120

• Propane 320

• Methane 525

Explosion Groups & Temp. ClassesExp.

Groups

T1 T2 T3 T4 T5 T6

I Methane

IIA Acetone

Ethane

Propane

Ammonia

Ethane

Ethyl Alcohol

N-Butane

N-Hexane

Petrol

Diesel Fuel

Heating oil

Acetaldehyde

Ethyl-ether

IIB Town Gas Ethylene

Diethyl ether

CO

IIC Hydrogen Carbon Disulfide

Equipment for Hazardous Locations

• Equipment for Class I locations:The equipment used in Class I locations are housed in enclosures designed to contain any explosion that might occur if hazardous vapors were to enter the enclosure and ignite.Also it is designed to cool and vent the products of this explosion.

Equipment for Class II Locations

• Class II locations make use of equipment designed to seal out dust. The enclosures are not intended to contain an internal explosion, but rather to eliminate the source of ignition so no explosion can occur within the enclosure.

Equipment for Class III Locations

• Equipment used in class III locations need to be designed to prevent fibers and flyings from entering the housing. It also needs to be constructed in such a way as to prevent the escape of sparks or burning materials.

• It must also operate below the point of combustion.

Types of Protection

1. Flameproof Enclosures “d”2. Intrinsic Safety “i”3. Increased Safety “e”4. Powder/Sand Filled “q”5. Pressurized Apparatus “p”6. Oil Immersion “o”7. Special Protection “s”8. Encapsulation “m”9. Type of protection N “N”

Flameproof Enclosures “d”

Type of protection, for which the parts which can ignite an explosive atmosphere are inside an enclosure which willWithstand the pressure of theExplosion within the enclosure.

Prevent the transmission of theExplosion to an explosiveAtmosphere surrounding theEnclosure.

Intrinsic Safety “i”

• Type of protection, for which the energy in the electrical circuit is held so low that sparks, arcs or temperatures capable of causing ignition cannot occur.

• Includes sub-division into the categories ia & ib

• Ia must not produce any ignition when any combination of two faults is present.

• Ib must not produce any ignition, in normal operation, when one fault is present.

Increased Safety “e”

• Type of protection, for which measures are taken to prevent the possibility of non-permissible high temperatures and the formation of sparks or arcs on inner or outer parts of electrical apparatus, on which these do not occur in normal operation, with an increased level of safety.

Powder/Sand Filled “q”

• The electrical apparatus enclosure is filled with powder or sand.

• An arc occurring in the enclosure does not ignite an explosive atmospheres surrounding the enclosure.

Pressurized Apparatus “p”

• Preventing the entry of surrounding atmosphere into the enclosure by holding an ignition-protection gas (air, inert gas) under over-pressure in relation to the surrounding atmosphere

Oil Immersion “o”

• Electrical apparatus or parts thereof are made safe by immersion in oil such that potentially explosive atmosphere above the surface of the oil or outside the enclosure will not be ignited.

European System

Hazardous Zones

• Zone 0

• Zone 1

• Zone 2

• Non-Hazardous area

• Area that was deemed to be completely free of potential hazards.

Area (Zone) Classification

• In order to evaluate and stipulate the necessary protective measures, hazardous areas have been classified into different zones in respect to the probable occurrence of an explosive atmosphere.

• Hazardous area is defined as three-dimensional space in which a flammable atmosphere may be expected to be present at such frequencies as to require special precautions for the construction and use of electrical apparatus.

• The European classification: Hazardous areas are divided into three zones:

• Zone 0 , Zone 1, and Zone 2

Zone 0

• Is a zone in which an explosive gas/air mixture is continually present for long periods of time.

Zone 1

• Is a zone in which an explosive gas/air mixture is likely to occur under normal operating conditions.

Zone 2

• Is a zone in which an explosive gas/air mixture is unlikely to occur under normal operating conditions, and if it does it will exist only for a short period of time.

Extend of zone

• The distance in any direction, vertical and horizontal, from the source of release to the point where the flammable atmosphere has been diluted by air to a sufficiently low level

• For a given release the extend will vary with the vaporizing potential of the fluid release, the ventilation state and the bouyancy factor of the vapor.

Area Classification

Oil Water Separator

Floating-Roof Tank

Fixed Roof Tank

Selection of apparatusZone Type of Protection

0 Intrinsically safe Ex ia

Special protection Ex s

1 Any type of protection suitable for zone 0

Flameproof Ex d

Intrinsically safe Ex ib

Pressurized Ex p

Increased safety Ex e

Special protection Ex s

2 Any type of protection suitable for Zone 0 or Zone 1

Ex N or Ex n

Oil immersion Ex o

Quartz Filled Ex q

Types of Protection for Ingress of Water and Solid Particles

European Practice

Enclosure (IP) Protection

• The measures required to be applied to the enclosure to provide a chosen degree of protection to:

1. Persons against contact with internal live or rotating parts inside the enclosure, and to the apparatus against ingress of solid objects, dusts, etc.

2. The apparatus against the ingress of water, spray, jets, heavy seas and even total immersion.

Ingress Protection against Particles3rd Digit Degree of Protection

0 No mechanical protection

1 Protection against large-sized foreign bodies (hands)

2 Protection against 12.5 mm diameter foreign bodies (finger)

3 Protection against the ingress of foreign bodies greater than 2.5 mm thick.

4 Protection against the ingress of foreign bodies greater than 1 mm thick

5 Protection against the ingress of dust, whereby dust shall not enter the enclosure in sufficient quantities to cause equipment malfunction.

6 Complete protection from ingress of dust.

Ingress Protection against Liquids

3rd Digit Degree of Protection

0 No protection

1 Protection against drops of condensed water

2 Protection against drops of liquid with the equipment tilted at any angle up to 15 degree from the vertical

3 Protection against rain falling at an angle of 60 degree or less from vertical

4 Protection against water splashed from any direction

5 Protection against jets of water

6 Protection against water from heavy seas

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7 Protection against immersion in water under stated conditions of pressure and time

8 Protection against immersion in water under specified pressure, for an indefinite period of time.

Ingress Protection

• The degree of protection depend upon whether the equipment will be installed outdoors and exposed to the extremes of the weather, or indoors and exposed (or not) to dust or liquid ingress.

• If the location is outdoors, then the IP code will typically vary between IP54 and IP66

• For indoor equipment in a hazardous area not exposed to particles or water, the minimum IP code would be typically IP44

Commonly Used IP Codes

0 1 2 3 4 5 6 7 8

0

1 IP11 IP12

2 IP21 IP22 IP23

3 IP31 IP32 IP33 IP34

4 IP41 IP42 IP43 IP44

5 IP54 IP55

6 IP65 IP66 IP67 IP68

Marking

• Applicable national or international standard (BS5501 Part 5, IEC60079 Part 2

• Name or abbreviation of the testing lab (BASEEFA)

• Approved symbol for the certifying authority EEX hexagonal symbol

• Type of protection EEX “d” EEX “e”• Gas Group IIA IIB IIC• Temperature Class T6• Serial or certificate number

Example

•EEx de IIC T6

EEx ib IIB T4• E: European Standards• Ex ib: Intrinsically safe to category ib• II: Certification for use in apparatus group II

(in other industries) (I is for mines)

• B: Explosion classes

• T4: The ignition temperature of any gas or vapor with which this device will be used is not less than 135 degree C