Fire and Electrical Safety.ppsx

FIRE AND ELECTRICAL SAFTEY
SARK EPC PROJECTS
PVT. LTD.
3RD INTER ACTIVE SECTION ON

INDEX :
 Introduction
 Terminology
 Classification of flammable gas & liquid
 Area classification
 Standards
 Selection of equipment's
 Case studies

INTRODUCTION
 In industries many liquids, gases and vapors are
generated, processed, handled and stored are
combustible.
 When ignited these may burn with explosive
force when mixed with air in the appropriate
proportion.
 Any area where hazardous atmosphere is likely
to occur in sufficient quantity to constitute a
hazard had to be treated in a special manner.

 Three basic conditions are to be satisfied to
have Fire or Explosion.
 Presence of Flammable gases, vapor, liquid
or dust.
 Mixture of gas, vapor, liquid and dust with
oxygen in required proportion.
 Source of energy- Flame, Spark, Hot Surfaces
etc.
FIRE OR EXPLOSION

 Flammable material :
It is a gas, vapor, liquid or mist, dust which can react
continuously with atmospheric oxygen and which may
therefore sustain fire or explosion when such reaction is
initiated by a suitable spark, flame or hot surface.
 Flammable mixture :
A mixture of flammable material with air, under
atmospheric condition, in which after ignition, combustion
spreads throughout the unconsumed mixture.
TERMINOLOGY

 Hazard :
The presence, or the risk of presence, of flammable gas-air
mixture.
 Hazard area :
A area where during normal operations, a hazardous
atmosphere is likely to occur.
 Non hazardous Area :
An area no part of which has within either a hazardous
area or a remotely hazardous area.
 Flammability range:
The range of a gas or vapor mixture with air between the
flammable limits over which the gas mixtures are
continuously explosive.
TERMINOLOGY

 Explosive limits :
The extreme values for the concentration of a flammable
gas or vapor in air under atmospheric condition, which can
be ignited by an electrical are or spark. These limits are
called the ‘lower explosive limit’ (LEL) and ‘upper
explosive limit’ (UEL).
TERMINOLOGY
Explosive limits :
Gas LEL UEL
Hydrogen 4% 76%
Acetylene 1% 80%
Methane 5% 15%

 Flammable gas :
A gas at ambient temperature and pressure, forms a
flammable mixture with air at a concentration of 13% by
volume or less
 Flammable liquid :
Any liquid having a flash point below 100 deg F ( 37.8 deg C )
is considered as flammable liquid.
 Flammable Solid :
A solid, which is liable to cause fire through friction,
absorption of moisture, spontaneous chemical change, or
retained heat from manufacturing processing, or which can
be ignited readily and when ignited, burns so vigorously to
create a serious hazard.
 Flammable Mist :
Droplets of flammable liquid, dispersed in air, so as to form a
hazardous atmosphere.
TERMINOLOGY

 Flash point :
The temperature at which the liquid gives so much vapor
that this vapor, when mixed with air, forms an ignitable
mixture and gives a momentary flash on application of a
small pilot flame under specified conditions of test.
 Ignition temperature :
The lowest temperature at which ignition occurs in a mixture
at specified test condition.
 Auto Ignition temperature :
The temperature at which ignition occurs without
introduction of ignition source.
TERMINOLOGY

 Flames :
These are usually have a temperature between 1000 deg. C to
2000 deg. C. can also be able to supply energy at a high rate
and can therefore be effective source of ignition.
 Sparks :
These have very high temperature between 1000 deg. C to
3000 deg. C. can also be able to supply large amount of
energy over short period of time. It can be generated by
electricity, static electricity, by metal rubbing etc.
TERMINOLOGY

CLASSIFICATION OF
FLAMMABLE GAS & LIQUID

For ignition, it is necessary that at least a small portion of the
mixture to be raised to the ignition temperature.
Any ignition source has two essential characteristics.
 Temperature :
This must be equal to or higher than the ignition
temperature.
 Energy :
The source must supply sufficient energy at a high enough
rate, to raise enough of the gas mixture to the ignition point
to start a self sustaining explosion.
The minimum energy required to do ignition is dependent
upon the gas present and varies widely from gas to another.
IGNITION OF A MIXTURE

Gas Groups :
Gas Group No. Mini. Ignition En.
Methane I 280 Joules
Propane IIA 260 Joules
Ethylene IIB 85 Joules
Hydrogen IIC 19 Joules
GAS GROUPS
Base on Minimum Ignition Energy requirement, gases are classified
in to Four groups. i.e. I, IIA, IIB, IIC

 Electrical equipment to work safely in an explosive
atmosphere, the maximum surface temp. of the exposed
surface of the equipment must be lower than the ignition temp.
of gas or vapour mixture.
 In order to properly select electrical equipment with regard to
the ignition temperature, all gases are classified according to a
temperature.
TEMPERATURE CLASS

Surface Temperature :
Max. Surface Temp. (˚C) Class
450 ˚C T1
300 ˚C T2
200 ˚C T3
135 ˚C T4
100 ˚C T5
85 ˚C T6
TEMPERATURE CLASS

 Liquids can be classified based on Flash points.
LIQUID CLASS
Flash Point Temperature :
Flash Point Temp. (˚C) Class
23 ˚C Class A
23˚C TO 65 ˚C Class B
65˚C TO 93 ˚C Class C

 A method of analyzing and classifying the environment
 Proper selection of electrical apparatus
 Enable electrical apparatus to be operated safely
IS 5572
An area in which an explosive gas atmosphere is present, or
likely to be present, in quantities such as to require special
precautions for the construction, installation and use of
electrical apparatus.
WHAT IS HAZARDOUS AREA
CLASSIFICATION?

Petroleum Rule 1976
An area shall be deemed to be a hazardous area, where
 Petroleum liquid having flash point below 65°C or any
flammable gas or vapour in a concentration capable of
ignition is likely to be present.
 Petroleum or any flammable liquid having flash point above
65°C is likely to be refined, blended, handled or stored at or
above its flash point.
HAZARDOUS AREAS-DEFINITIONS

Potential for explosion Safety of personnel Property Damage
WHY CLASSIFY AN AREA AS
HAZARDOUS?

CLASSIFICATION OF
HAZARDOUS AREA
Hazardous areas can be determined based on
 What is the emission level of release source.
 Continuous
 First level emission: Release during normal operation
 Second level emission: release during abnormal operation.
 What type of openings available.
 Continuous opening
 Normally closed.
 Normally closed and weatherproof
 Normally closed, weatherproof, open in an emergency.

Hazardous areas can be determined based on
 What is the ventilation available.
 Very good ( Continuously available )
 Good ( Operates during operation )
 Poor ( Not reliable, may not operate )
 What level is the ventilation
 High ( Reduce concentration )
 Average ( Maintain stable situation )
 Weak ( Can’t control during release or release is over )

 All hazardous areas can be classified into 3 Zones
according to the probability of there being an explosive
gas air mixture present
 Zone 0
 Zone 1
 Zone 2

 Zone 0 :
Areas where flammable atmosphere is continuously
present or is present for long periods.
It is recommended to avoid installation of electrical
equipment's in Zone 0 areas.
 Zone 0 -typical areas
Vapour space above closed process vessels
Storage tanks
Areas containing open tanks of volatile, flammable liquid
ZONE 0 -TYPICAL AREAS

 Zone 1 :
Areas where flammable atmosphere is likely to occur
periodically or occasionally during normal operation.
 Zone 1 typical areas :
 Maintenance, repairs or leakage.
 Piping system (containing valves, meters, or screwed or
flanged fittings) is in an inadequately ventilated area.
 The area below the surrounding elevation or grade is
such vapours may accumulate therein .
 Failure of equipment is likely to cause an electrical
system failure simultaneously with the release of
flammable gas
It is recommended to installation electrical equipment's
with Ex’d enclosure with suitable temperature class.

 Zone 2 :
Areas where flammable atmosphere is not likely to occur
during normal operation and if it does it is only for short
periods.
 Zone 2 typical areas :
 Accidental release of a gasket or packing.
 The flammable vapours can be conducted to the
location as through trenches, pipes or ducts. Locations
adjacent to Zone 1 areas .
 Pressurized rooms where flammable gas /vapour can
enter in the case of failure of positive mechanical
ventilation
It is recommended to installation electrical equipment's
with Ex’e or Ex’n enclosure.

 Standards throughout the world.
 IEC – International Electro-technical commission.
 CENELEC – European Committee of Electro-technical
standards.
 NEC-National Electrical Code
 Role of IEC:
 Provides Internal definition of Zones.
 Guideline for various protection methods.
 Gas and Vapor Classification.
 Temperature classification.
STANDARDS

STATUTORY REGULATIONS
 The manufacture and use of equipment for hazardous area
is controlled by the statutory authorities for the area of
their jurisdiction
 The Director general of mines safety, Dhanbad.
 The Chief controller of Explosives, Department of
Explosive, Nagpur
 The Director general Factory advice services and labor
institute. Bombay

STATUTORY REGULATIONS
 Testing :
Equipment to be installed in hazardous area have to be
certified by a recognized testing authority. Facility is
available at Central Mining Research Station ( CMRS ),
Dhanbad
 Marking :
Marking of equipment shall conform to IS 8241-1976,
which gives method of marking for identifying electrical
equipment for explosive atmospheres.

Area Classification Div/Zone Gas Group
Temp Class Protection concept IP Codes
HOW TO SELECT EQUIPMENT FOR
VARIOUS ZONES?

 Electrical apparatus which will not ignite the surrounding
flammable atmosphere in which it is used – is known as
Electrical apparatus for hazardous areas.
ELECTRICAL APPARATUS

SELECTION OF ELECTRICAL
EQUIPMENTS FOR ZONE 0
 Selection of equipment for Zone 0 :
No electrical equipment should be allowed, when this is
not practicable, intrinsically safe electrical apparatus
categories ia, and ib and associated circuits should be
employed type of protection ’I’
 Intrinsic safe equipment (Ex-i) :
A circuit or a part of circuit is intrinsically safe when any
spark or thermal effect produced normally or accidentally
is incapable of causing ignition of a gas or mixture.

 For Zone 1 :
Flame proof equipment with ‘Ex-d’ enclosure or pressurised
enclosure type ‘Ex-p’ or sand filled apparatus type ‘Ex-q’ or
oil filled ‘Ex-o’ can be used.
 Flame/Explosion proof equipment ‘Ex-d’ :
The enclosure of electrical apparatus that will withstand an
internal explosion of the flammable gases or vapour without
suffering damage and without communicating the internal
inflammation to the external gas or vapour.
 Pressurised equipment ‘Ex-p’ :
The enclosure of electrical apparatus in which the entry of
flammable gas or vapour is prevented by maintaining the air
within the enclosure at a pressure above the external
atmosphere.

 Oil filled Flame proof equipment ‘Ex-o’ :
The electrical apparatus in which all parts on which arc may
occur in normal service are immersed in oil to a sufficient
depth to prevent ignition of an explosive gas mixture that
may be present above the surface of the oil.
 Powder filled Flame proof equipment ‘Ex-q’ :
The electrical apparatus which has all its live parts entirely
embedded in a mass of powdery material in such a way that
no arc / spark occurs in outer explosive atmosphere either
by the transmission of flame or by the overheating of the
walls of the enclosure.

 For Zone 2 :
The electrical apparatus with Non sparking ‘Ex-n’ or Increased
safety ‘Ex-e’ or hermetically sealed ‘Ex-s’ design can be used .
 Non sparking ‘Ex-n’ :
The apparatus which in normal operation is not capable of
igniting a surrounding explosive atmosphere and a fault
capable of causing ignition is not likely to occur.
 Increased safety ‘Ex-e’ :
The apparatus in which additional measures are applied to
give increased security against the possibility of excessive
temperatures and the occurrence of arcs or sparks in
electrical apparatus which does not produce arcs or sparks in
normal service.

 Increased safety ‘Ex-s’ :
The method of protection in which the equipment is so
designed and constructed that the external inflammable
gases or vapours cannot enter the enclosure and hence
prevents a source of ignition like an arc or spark from
coming into contact with the inflammable gas or vapour.

 Ingress protection :
It refer to the level of protection offered by an electrical
enclosure, against solids and liquids. In an environment
where dust or water could damage electronic components, a
sealed enclosure is used to prevent such ingress and safe
house the electronics.
IP65
First digit : SOLID INGRESS
Second digit : LIQIUD/MOISTURE INGRESS
IP TYPES AND PROTECTION
DETAILS

IP TYPE FOR INTRUSION
PROTECTION(FIRST DIGIT)
INGRESS PROTECTION
FIRST
DIGIT
INTRUSION
PROTECTION
0 No protection
1
Protected against solid objects over 50mm, e.g.
Accidental touch by hands
2
fingers.
3
Protected against solid objects over 2.5mm, e.g.
Tools & wires
4
wires & nails.
5
Protected against dust limited ingress, no harmful
deposits
6 Totally protected against dust

IP TYPE FOR INTRUSION
PROTECTION(SECOND DIGIT)
INGRESS PROTECTION
SECOND
DIGIT
LIQIUD/MOISTURE
PROTECTION
0 No protection
1
Protected against vertically falling drops of water, e.g.
condensation
2
Protected against direct sprays of water up to 15º
from the vertical.
3
Protected against direct sprays of water up to 60º
from the vertical
4
Protected against water splashed from all directions,
limited ingress permitted.
5
Protected against low pressure jets of water from all
directions, limited ingress permitted.
6
Protected against strong jets of water, e.g. on ships
deck, limited ingress permitted

MARKING
 All the apparatus for hazardous area should have
identification with special marking, applied at visible part in a
legible and durable manner.
 Marking should give following particulars :
 Manufacturer’s name or trade mark
 Type designation.
 The symbol ‘Ex’ indicates that the equipment is for
Hazardous area.
 Type of enclosure or design i.e. Ex-d, Ex-n, Ex-e
 The symbol ‘I’ for mines and ‘II’ for gases and vapours.
 Temperature class i.e. T1, T2 ..
Example : Ex d IIB T3

CONSTRUCTION OF APPARATUS
 Flame path :
This is the shortest path along a flameproof joint from the
inside to the outside of an enclosure.
 Length of flame path :
 For IIA & IIB enclosures – Min 12.5 mm
 For IIC enclosure – Min 25 mm
 Gap in a Flameproof joint :
This is the distance between the two mating surfaces of the
enclosure which form a flameproof joint when assembled.
 For given volume of enclosure Max. permissible gap varies
according to the length of the flame path.
 0.2 to 0.4 mm for IIA
 0.15 to 0.2 mm for IIB
 0.1 to 0.2 mm for IIC

PRECAUTIONS
 Cable shall be terminated through flameproof cable glands
only.
 No open cable joints allowed in hazardous area
 No site repairing is allowed in Ex d and Ex I. If repaired it is to
be certified by the authority ( Central Mining research station )
CMRS Dhanbad.

CASE-1
Freely ventilated process area-source of hazard located near ground
level (Heaver than gases or vapors )

Process area with restricted ventilation
CASE-2

Well ventilated indoor area (Heaver than air or vapors )
CASE-3

Tank with floating roof with or without protective cone roof
CASE-4

Fixed roof tank (without N2 blanketing)
CASE-5

Freely ventilated process area (lighter than air or vapor)
If the source of hazard is situated at a height less than or
equal to 4.5 m above the ground , the height the hazardous
area extends below the source of hazard up to ground level.
The entire area is Zone -2
CASE-6

Wagon/tank truck loading and unloading via closed system.
Bottom product transfer only.
CASE-7

Wagon/tank truck loading and unloading via open system.
Top or bottom product transfer.
CASE-8

Fire and Electrical Safety.ppsx

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