Ex Basics(An introduction to the Hazardous Area Protection )

A presentation by Asif Mirza

August 2012

An EXPLOSION requires following three elements

1 A flammable Material

2 Oxygen from air

3 An Ignition or fire-starter

Explosive Triangle

expeltec.com

1 A flammable Material

2 Oxygen from air

3 An Ignition or fire-starter

…to form an explosive triangle or an ET

expeltec.com

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

Upper Explosive Limit

Lower Explosive Limit

Dead ET

Dead ET

Qua

ntity

Of E

xplo

sive

Mat

eria

l

Explosive Triangle

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

expeltec.com

ET are deliberately created inside the cylinder

Explosive TriangleO

xyge

n fro

m a

ir

Flamm

able material

Ignition

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

expeltec.com

Quantifying one side of ET as to the TYPE of flammable material

Explosive TriangleO

xyge

n fro

m a

ir

Flamm

able material

Ignition

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.

expeltec.com

WE refers to the STANDARDS Specifying bodies, like IEC or NEC

expeltec.com

Long-life ETs create VERY HIGH RISK and short-lived ETs create LOW RISK AREA

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.

expeltec.com

Thus presence of ETs create explosion risk areas or the Hazardous Areas

D A GN E R

ZONE 2

ZONE22

ZONE 1

ZONE21

ZONE 0

ZONE20

IEC divide the Hazardous Area in to 3 REGIONS or ZONES

RISK

expeltec.com

D A E R

DIVISION 2 DIVISION 1

NEC divide the Hazardous Area in to 2 REGIONS or DIVISIONS

RISK

expeltec.com

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

expeltec.com

Let us consider flammable material of Class 1 (Vapours & Gases)

MINERS’ SAFETY LAMP

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.

expeltec.com

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

I Methane

II A Propane

II B Ethylene

II C Carbon Disulphide

Acetylene HydrogenT1

450C

T2300C

T3200C

T4135C

T5100C

T685C

expeltec.com

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………

The remaining side is THE SOURCE OF IGNITION

One of the other side is OXYGEN which manifests itself as part of AIR. Nothing remarkable about it

The list is long and on top of the list is ………………………………..

expeltec.com

THE FIRE STARTER

Each time when switch is operated; spark appears at the terminals specially at the time of ‘switching-off’

220 V

220 V

N

N

This is the account of the events which takes place inside an ordinary switch

expeltec.com

THE ELECTRIC SWITCH

Lamp ‘off’

Switch is in ‘off position and circuit is open’

Lamp ‘on’’

Switch is in ‘on position and circuit is closed’

expeltec.com

220 V

220 V

N

N

Lamp ‘on’

Switch is in ‘on position and circuit is closed’

Lamp ‘off’’

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.

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

expeltec.com