Module 02_ Explosive Atmospheres September 2007

7/28/2019 Module 02_ Explosive Atmospheres September 2007

1/33

September 2007 copyright Epsilon Compliance 2007 Compex module 2 Explosive atmospheres 1

ExplosiveAtmospheres

Overview


2/33


Two types of explosions

Deflagration: Burns with great heat and light.

Flame front speed 1 m/sec

Speed of sound 330 m/sec

Detonation: A violent explosion

Flame front speed 2000-8000 m/sec

Speed of sound 330 m/sec

Deflagration and Detonation


3/33


Explosion Properties

Fuel

Oxygen

Ignition source


4/33



5/33



All flammable gases, vapours and mists require to be

mixed with oxygen to make them burn. There is about20-21% of oxygen in the air we breath. Mixtures of aflammable gas and certain percentages of air will burn ifignited.

Too much or too little oxygen, the mixture will not ignite.The upper and lower concentrations of gas in

atmospheric air, by volume, are known as theirflammability or explosive limit.


6/33


Flammable Range All dangerous substances have a flammable

range


7/33


Flammable Range


8/33


Examples of Flammable Range(PD IEC 60079-20)

774Hydrogen1002.3Acetylene

362.3Ethylene111.7Propane

174.4Methane

UEL (%)LEL (%)Substance


9/33



For any mixture of a

combustible gas orvapour with an oxidizer(air) there is a criticalignition energy.

Release less than thecritical amount ofenergy into the mixture

and there will not be anexplosion.


10/33


At a critical concentration called the mosteasily ignited concentration (MEIC), theamount of energy required to cause ignition isminimal.

The critical energy at the MEIC is calledminimum ignition energy (MIE).


MEIC

MIE


11/33


477


12/33



The LEL (LFL) and UEL (UFL) are not inherent

properties of a combustible mixture. Theirvalues depend on the nature of the experimentby which they are determined.


13/33


Historical Background

The first hazardous area was discovered in the

coal mines.

This area held a double hazard: methane gas

(firedamp) and coal dust.


14/33




15/33




16/33


In 1815 Sir HumphreyDavy invented theDavy lamp, whichwas a kerosene lamp

with a fine brassmesh. This was usedto indicate methane

concentration in themine atmosphere.



17/33


Electrical Equipment


18/33


This method of

protection lead tothe development ofthe Flameproof

(FLP) concept ofprotection

Ex d.



19/33


Historical BackgroundHistorical BackgroundMine explosion in South Wales 1912.

Cause- a spark generated by the signalling system


20/33


Historical BackgroundHistorical Background


21/33


Research at the Mines Research Establishment,Buxton, England that these low voltage circuitswere capable of igniting mine gases, it also ledto new circuit designs in which the stored energywas reduced to a non ignition capable level.



22/33


This technique was labelled intrinsic safety Ex

i and it was the beginning of a new era insafety methods for explosive hazardous areas.

More on the Ex i concept later.



23/33


Gas Group 1(I)

Explosive Atmosphere

Gas Group 2 (II)


24/33


Group I is for mining and not covered further in

this presentation.

Group II is for surface industries

Group II gases is further divided into 3 sub-divisions.



25/33


IIA, for atmospheres containing propane orgases of an equivalent hazard.

IIB, for atmospheres containing ethylene orgases of an equivalent hazard.

IIC, for atmospheres containing hydrogen orgases of an equivalent hazard.



26/33


Examples of Flammable Range(PD IEC 60079-20*)

77 IIC4Hydrogen

100 IIC2.3Acetylene

36 IIB2.3Ethylene11 IIA1.7Propane

17 IIA4.4Methane

UEL (%) GGLEL (%)Substance

* There are 299 substances listed in PD IEC 60079-20 (Flammable Gas Data).


27/33


Temperature class

Equipment is identified with a temperature class

Identified by a T rating (or by a temperature indegrees C).

The temperature class identifies the hottest

temperature that the equipment can obtain innormal operation.

This can be either the inside or the outside of the

equipment depending on the protection concept.


28/33



29/33


Temperature ClassThe full list of temperature codes are

85T6

100T5

135T4

200T3

300T2

450T1

Max Temp limit

(C)

Temperature

Class


30/33


The temperature codes for the substanceslisted previously (temperature

classification) are shown below:

T1Hydrogen

T2Acetylene

T2Ethylene

T1Propane

T1Methane

Temp ClassSubstance

Temperature Class


31/33


T1 IICHydrogen

T2 IICAcetylene

T2 IIBEthylene

T1 IIAPropane

T1 IIAMethane

Temp Class Gas GroupSubstance


32/33


Equipment Marking

Example


33/33


Any Questions

Documents

Module 02_ Explosive Atmospheres September 2007