8 - Hazardous Locations

7/28/2019 8 - Hazardous Locations

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Hazardous (Classified)

Locations

Presented by:



LESSON OBJECTIVESAt the conclusion of this presentation, the student should be able to:

• Discuss common controls for the arc and thermal

ignition sources of power electrical equipmentlocated within hazardous (classified) locations

• Compare the basic principles underpinning thecommon technologies used to control ignition

sources within these areas



LESSON OBJECTIVES (con’t)

• Identify hazardous classifications, groupsand divisions

• Locate relevant OSHA and National FireProtection Association (NFPA) standards



Common Controls for Arc and Thermal Ignition

Sources of Power Electrical Equipmentin/near hazardous locations

•Remote location of hazardousequipment outside plant areas

•Explosion proof equipment

•Dust ignition proof equipment



Common Controls for Arc and Thermal Ignition

Sources of Power Electrical Equipmentin/near hazardous locations

•Intrinsically safe equipment

•Non-incendive equipment

•Locating equipment withinpurged, pressurized enclosures



Explosion-proof apparatus.Apparatus enclosed in a case that is capable of

withstanding an explosion of a specified gas or vapor

which may occur within it and of preventing theignition of a specified gas or vapor surrounding the

enclosure by sparks, flashes, or explosion of the gas or

vapor within, and which operates at such an externaltemperature that it will not ignite a surrounding

flammable atmosphere.



E x p l o s i o n P

r e s s u r e

( p s i g )

Vapor/Gas Concentration in Air (%)

Propane

EthyleneHydrogen

Acetylene



Dust Ignition Proof

• …Enclosed in a manner that will excludedusts…

• Will not permit arcs, sparks or heat generated or

liberated inside the enclosure to causeignition of

– exterior accumulation or – atmospheric suspensions of specified

dusts on or in the vicinity of the

enclosure

15 micron

dust particle

http://www-curator.jsc.nasa.gov/curator/stardust/dust3.jpg


http://slidepdf.com/reader/full/8-hazardous-locations 11/66Oxygen

Confinement

IgnitionFuel

Dispersion

Dust Explosion Requirements

Adapted from CSB



Someevent

disturbs

the

settleddust into

a cloud

Dust cloud

is ignited

and

explodes

Dust Explosion Mechanism

Dust settles on

flat surfaces

Dust

Adapted from CSB



Intrinsically safe and non-incendive

• equipment limits the amount of energy available

to cause the ignition of fuel mixture

• does not have a high enough power factor for

many applications

Communicators Controllers

2876

InstrumentsDetectors


http://slidepdf.com/reader/full/8-hazardous-locations 16/66Deadly vapors

Intrisically safe circuit

…any spark or thermal effect, produced

either normally or in specified fault

conditions, is incapable…of causingignition…(of) the mixture’s most easily

ignitable concentration.

UL 913 1.4.9

Combustible

dust



Minimum Ignition Energy

FLAMMABLE GASES

Acetylene .017 millijoules

Hydrogen .017

Ethylene .08

Methane .3



Minimum Ignition Energy

COMBUSTIBLE DUSTS

Aluminum 15 millijoules

Magnesium 40Soft Coal 30

Hard Coal 60

Grain 240

Sulfur 15

Phenol Formaldehyd 15



Nonincendive

…under normal operation

conditions, any arcing or

thermal effects are not

capable of igniting the

flammable gas, vapor or

dust-in-air mixture.

NFPA 70 500 (f)

Nonincendive

controller

Drawing



Nonincendive flashlight

CSA label markTemp

T3C

Haz location

NI/I, II 2 ABCDGWarning: Approved for use with

(specified batteries and lamp)

Permissible flashlight for use in hazardous

Locations Nonincendive Model 2300

Mfg/ by… CSA

LabelMark



Purged, pressurized enclosures

Purging…supplying an enclosure with clean air or an

inert gas at sufficient flow and positive pressure to

reduce to an acceptable safe level the concentration

of any flammable gas or vapor initially present and to

maintain this safe level by positive pressure with or

without continuous flow.

NFPA 496



Purged,

pressurized

refuge area



Class III Locations

Fibers and Flyings Function at full rating without developing surfacetemperatures exceeding

165 o C. (329 o F.) for most equipment120 o C. (248 o F.) for motors and transformers andother equipment subject to overload

Do not cause excessive dehydration or

carbonization

Prevent high susceptibility to

spontaneous ignition of

fibers or flyings



Requirements differ depending on

type of equipment

Enclosed, or Dust tight, or

Minimize entrance of fibers

and flyings and prevent escape of sparks, burning material or hot

metal

See NEC Article 503

Cotton fibers

> 420 Microns

Larger

particles

Class III Locations

Fibers and Flyings



1910.307 (b) Electrical installations.

Equipment, wiring methods, and

installations of equipment inhazardous (classified) locations

shall be intrinsically safe,

approved for the hazardous

(classified) location, or safe or for

the hazardous (classified) location. OSHA

Requirement

!



NRTLs are third-party organizations

Organizations that are recognized by OSHA as

having the capability to provide product

safety testing and certification services to themanufacturers of a wide range of products for use

in the American workplace.



NRTLs are third-party organizations

The testing and certifications are based on

product safety standards developed by U.S.-based

standards developing organizations and oftenissued by the American National Standards

Institute (ANSI).



Alternatives to NRTL Certification -

Infrequent Exceptions

In certain limited circumstances,

equipment covered by

Subparts L and S may be acceptable

without NRTL certification



Alternatives to NRTL Certification

- Infrequent Exceptions (cont’d)

Subpart S - Electrical: Equipment is also “acceptable” if

it is

A kind that no NRTL will certify and it is inspected

or tested by another Federal agency, or a State,

municipal, or other local authority responsible for

enforcing and assuring compliance withoccupational safety provisions of the NEC, or



Alternatives to NRTL Certification

- Infrequent Exceptions (cont’d)

Custom-made equipment (designed, fabricatedfor, and intended for use by a particular customer)

determined to be safe by the manufacturer for its

intended use



"Occasional use of flammable or

ignitable materials."

Where flammable materials are present only occasionally,

electric equipment capable of igniting them shall not be

used unless:

• measures are taken to prevent hazardous conditions

from developing.



"Occasional use of flammable or

ignitable materials."

Such materials include, but are not limited to:

- flammable gases, vapors, or liquids;- combustible dust; and

- ignitable fibers or flyings.

Note: Electrical installation requirements for

locations where flammable materials are

present on a regular basis are contained in 1910.307.

HAZ LOC

Hot Work

Permit



8-2 Maintenance Requirements for

Hazardous (Classified) Locations.

Equipment and installations in these locations shall

be maintained so that:

(a) No energized parts are exposed.

Exception: Intrinsically safe and nonincendivecircuits.

No!





(b) There are no breaks in conduit systems,

fittings, or enclosures from damage, corrosion,

or other causes.





(c)All bonding jumpers are securely fastened and

intact.

(d)All fittings, boxes, and enclosures with bolted

covers have all boltsinstalled and bolted tight.

Closeit up!





(e) All threaded conduit shall be wrench tight and

enclosure covers shall be tightened inaccordance with the manufacturer’s instructions.

(f) There are no open entries into fittings, boxes, or enclosure that would compromise the protection

characteristics.





(g) All close-up plugs, breathers, seals, and drains

are securely in place.

(h) Marking of lighting fixtures for maximum lamp

wattage and temperature rating is legible and not

exceeded.

(i) Required markings are secure and legible.



Classification of locations

Non-classified

Division 1 = NormalDivision 2 = Abnormal



Non-classified locations

Adequate ventilation

closed piping

Not adequately ventilated closed piping - no

valves, fittings, flanges, etc.

Combustible

liquids in containers



Adequate ventilation 1910.106 (a) (31)

NFPA 30

< 25% LFL

It is considered adequate if it is sufficient to prevent

accumulation of significant quantities of vapor-air mixtures in concentration over one-fourth of the

lower flammable limit.



• Outside

• Roof plus one wall (three open sides)

• Safeguarded mechanical ventilation

• Boiler/fired heater area (Process Industry)

Locations With Adequate Ventilation



Ignitable mixture

Normal

Frequent

Equipment and electrical failure

Piping system within inadequately

ventilated space and

likely to leak

Location below grade

Class I Division 1

Hazardous Locations



Documentation on liquids should include:

•The nature of the material

TemperaturePressure

Quantity present/flowing

•Verification that the temperature of the material

exceeds its flash point



Documentation on liquids should include:

•Specific sources of leakage

Drains, bleeders, sample ports

Flanges, pump sealsRelief valves and devices

Other similar sources

•Maintenance and suitability of closed piping

systems at this plant and similar plants



Class I Division 2

Hazardous Locations

•Piping system within an inadequately

ventilated space but not likely to leak

•Process equipment within an inadequately ventilated space

and likely to leak only in abnormal situations

No ventil’n



Class I Division 2Hazardous Locations

•Adjacent and open to Division1 hazardous locations

•Failure of ventilation may permit an ignitable

mixture

No ventil’n



The chemical process industry

maintains drawings showing

classified areas



NFPA 497

Classification of

Flammable Liquids

Gases or Vapors and of

Hazardous (Classified)

Locations for Electrical

Installations in Chemical

Process Areas

NFPA497

NFPA NFPA NFPA NFPA NFPA

NFPA NFPA NFPA NFPA NFPA NFPA NFPA NFPA

GAS

VAPOR



30 inch plate and frame press



NFPA 499

Classification of

Combustible Dusts

and of Hazardous(Classified) Locations

for Electrical

Installations inChemical Process

Areas

NFPA499

NFPA NFPA NFPA NFPA NFPA

NFPA NFPA NFPA NFPA NFPA NFPA NFPA NFPA

Deadly

Dust



•Run continuously or

•Vapor detector to start ventilation and alarm at

lowest practical level andnot > than 4% by

volume or

•Machine room to conform to Class I Division

2 of NEC

Ventilation in ammonia machinery rooms



10 ft minimum 10 ft minimum



Wiring is to be arranged for Division 2 locations adjacent to, but within

10 ft vertically and 20 ft horizontally of

an UNENCLOSED spray area.

See NEC Article 511 Commercial Garages Repair And Storage



Door >18

inches above

garage floor

Class I Div. 1

Pit or de ression

Commercial

Garage(< 4 air changes/hour

or < 1ft3 min)

StockRoom(Not a

hazardouslocation)

Noopenings

(Not ahazardouslocation)

Class I Div. 218 inches

Gasoline fuel

See NEC Article 511 Commercial Garages Repair And Storage



Class I Div. 2

Commercial

Garage(Ventilated)

StockRoom(Not a

hazardouslocation)

At least 4air changesper hour

Pit or

depression

Not a

hazardous

location

Gasoline fuel

8 - Hazardous Locations

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