The document provides an introduction to explosion protection in hazardous areas. It explains that an explosion requires three elements: 1) a flammable material, 2) oxygen, and 3) an ignition source, which together form an "explosive triangle." It discusses the classification of hazardous areas into zones based on the likelihood and duration of an explosive triangle forming. Electrical equipment used in these zones must be certified to limit ignition risks from sparks or excessive temperatures. The document aims to educate about explosion hazards and promoting strategies like controlling ignition sources and ventilation to provide protection in hazardous areas.

1. Ex Basics
(An introduction to the Hazardous Area Protection )
A presentation by Asif Mirza
August 2012

2. An EXPLOSION requires following three elements
1 A flammable Material
2 Oxygen from air
3 An Ignition or fire-starter

3. 1 A flammable Material
2 Oxygen from air
3 An Ignition or fire-starter
…to form an explosive triangle or an ET
Explosive
Triangle
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4. An Explosive Triangle can exist only when (a) Flammable Material & (b) Oxygen are present with-in a
narrow range of quantities.
The Range is Between The Upper Explosive Limit & Lower Explosive Limit
Dead ET
Upper Explosive Limit
Quantity Of Explosive Material
Lower Explosive Limit
Dead ET
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5. Explosive
Triangle
Ignition
Explosive triangle is a way to harness the inherent energy by allowing its release through
oxidization. This energy was packed millions of years ago inside the crucibles of cosmos.
This happens every time we use our motor car: ETs are deliberately created inside the internal
combustion engine to get the required locomotion by TIMED and CONTROLLED explosions
ET are deliberately created inside the cylinder
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6. Explosive
Triangle
Ignition
Quantifying one side of ET as to the TYPE of flammable material
Flammable material in the form of GASES or LIQUIDS belong to CLASS 1
Flammable material in the form of DUST or POWDER belong to CLASS 2
Flammable material in the form of FIBRES or FLYINGS belong to CLASS 3
The quantity of the material is quantified indirectly by the length of the time
period an ET remains present in a location
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7. Simple Rule of Thumb is :
If an ET exists for more than 1000 Hours( >1000/ year) per year at a particular location
then it is a HIGH RISK location and WE shall call it ZONE 0 for class 1 and ZONE 20
for class 2
If an ET exists for more than 10 hours but less than 1000 Hours per year ( 10<,= TIME
<,= one year) at a particular location then it is a Moderate Risk location and WE shall
call it ZONE 1for class 1 and ZONE 21 for Class 2.
If an ET exists for 10 Hours or less per year at a particular location then it is a Low RISK
location and WE shall call it A ZONE 2 for Class 1 and ZONE 22 for Class2.
WE refers to the STANDARDS Specifying bodies, like IEC or NEC
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8. Long-life ETs create VERY HIGH RISK and short-lived ETs create LOW RISK AREA
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9. Thus presence of ETs create explosion risk areas or the Hazardous Areas
International Electro technical Commission IEC
Involvement with ET: Since 1947
National Electrical Code NEC
Indirect involvement : Since 1897
Direct involvement : 1920
There are many other authorized groups fully involved in research and
development in this and related fields
Then there is the ever present silent majority.
The dedicated & self committed engineers all across the globe
A constant source of valuable feed-back & innovation.
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10. IEC divide the Hazardous Area in to 3 REGIONS or
ZONES
RISK
D A N G E R
ZONE 2 ZONE 1 ZONE 0
ZONE22 ZONE21 ZONE20
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11. NEC divide the Hazardous Area in to 2 REGIONS or
DIVISIONS
RISK
D A E R
DIVISION 2 DIVISION 1
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12. Let us consider flammable material of Class 1 (Vapours & Gases)
The gases which form part of the ET have certain distinct and common properties which
enable us to from GAS GROUPS.
The Legendary Group Leader is
METHANE
• The explosive gas which is found in coal mines.
• The nightmare of the coal miners.
• The fuel of our industry.
Colorless, odorless but explosive. This is the material which initiated the whole PHILOSOPHY
and later the ART of explosion protection.
Its’ enormous hidden energy BUT ruthless manifestation in explosions and deaths of miners
inspired Humphrey Davy and his contemporaries like George Stephenson to develop the
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13. That was in 1815 and later, some times after 1900 when ELECTRIC lamps & fixtures
were installed in the mines, the humanitarian side of the ELECTRICAL ENGINEERING
practices formed the EXPLOSION PROTECTION SCIENCE.
The unique parameters like
• Ignition Temperature,
• minimum ignition energy
• and other properties are defined in the
GAS GROUPS.
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14. The unique parameters like Ignition Temperature, minimum ignition energy and other properties
are defined in the GAS GROUPS.
NEC A B C D Mining E F G
IEC T5
100C
Methane
I
Propane
II A T2 T3 T4
300C 200C 135C
Ethylene
II B
Carbon Acetylene Hydrogen
II C T6
Disulphide T1
85C 450C
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15. That was a brief analysis of the inflammable material; one side of the ET
Now let us look at the remaining two sides of the ET………
One of the other side is OXYGEN which manifests itself as part of AIR. Nothing remarkable about it
The remaining side is THE SOURCE OF IGNITION
The list is long and on top of the list is ………………………………..
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16. Each time when switch is operated; spark appears at the terminals specially at the time of ‘switching-off’
Lamp ‘off’
N 220 V
Switch is in ‘off position and circuit is open’
Lamp ‘on’’
N 220 V
Switch is in ‘on position and circuit is closed’
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events which takes place
inside an ordinary switch

17. Lamp ‘on’
N 220 V
Switch is in ‘on position and circuit is closed’
Lamp ‘off’’
N 220 V
At the time of the separation of the switch
contacts small arc (spark) is initiated by the
electrical inertia of the circuit .
This apparently small arc can initiate an explosion
In a hazardous area.
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18. The strategy so far has been to know the details of the requirements for the occurrence of an
explosion .
We have used the concept of The Explosive Triangle, so that we may protect ourselves and
our investments from destructive powers of ET and at the same time ,utilize the vast
resources of oil & gas
We can protect ourselves in two ways:
FIRST OR PRIMARY PROTECTION (first defense line)
BY not dealing with ETs at all-----by using substitute materials.
But this is not possible all the time-- for example there is presently no substitute for oil or gas .
Another way is to keep the ET handling area as ventilated as possible, so that the
mixture never reaches that critical concentration.
SECONDARY Protection or DEFENCE LINE
Basic strategy is to control the ignition sources, by
-Confinement
-Limiting its energy
-Quenching
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