Module 04_Ignition Sources_September 2007

7/28/2019 Module 04_Ignition Sources_September 2007

1/26

September 2007 copyright Epsilon Compliance 2007 Compex module 4 Ignition sources 1

Ignition Sources


2/26


Fire triangle

Heat = Ignition source

Fuel = Gas, Vapours ,Mists and Dust

Oxygen = Air, etc

Mix all together and .


3/26


By eliminating any one of

the sides of the firetriangle, the dangers of afire or an explosion can

be removed. The following slides

identify the ignition

source, (heat).

IGNITION SOURCES


4/26


Eliminate ignition sources


5/26


Ignition sources can be broken down into two

groups.a) Produced by work or maintenance

b) Produced by the process

IGNITION SOURCES


6/26


Those which are caused by general work in the

plant are:SmokingOpen flamesOpen light (bulbs)WeldingCuttingGrinding

The above sources can be eliminated by stafftraining and enforcing adequate working routines,(permits, procedures, etc)

IGNITION SOURCES


7/26


The ignition sources presented by the processitself:

Open flames

Hot surfaces

Self heating, Smouldering and Exothermic

decomposition Heat from mechanical impacts

Exothermic decomposition of dust via

mechanical impacts Electric sparks and electrostatic discharges

IGNITION SOURCES


8/26


Five most common Ignition sources


9/26


If ignition sources cannot be eliminated then all

possible ignition sources that could arise must beconsidered.

Two documents that can be used as references:

BS EN 1127-1, Identifies thirteen ignition sources

L136 DSEAR ACOPS


10/26


Hot Surfaces

Hot bearings on a motor


11/26


If an explosive atmosphere comes into contactwith a heated surface, ignition can occur. Notonly can a hot surface itself act as an ignitionsource.

Ignition also depends on the size and shape of

the heated body. Where an explosiveatmosphere flows past heated surfaces, a highersurface temperature could be required to causeignition.

Examples of ignition sources are: Surfaces of motors, pumps, gearboxes, bearing

housing, pipes, cables etc

Hot Surfaces


12/26


Flames


13/26


FlamesFlames from welding or cutting operations areeasily sufficient to trigger a dust explosion. Oxy-acetylene torches are particularly dangerous asthey supply oxygen to the area, and the moreoxygen present, the less heat is required totrigger an explosion. Therefore there should beno use of cutting or welding torches inhazardous areas.

Smoking should be prohibited anywhere in the

plant as a match flame generates 100W of heatenergy, which is more than sufficient to ignite anexplosive atmosphere.


14/26


Mechanically Generated Sparks

Grinding produces sparks


15/26


Often referred to as friction sparks, mechanical

impacts can cause ignition. This is not to beconfused with friction burning (i.e. where a beltslips and slowly heats) which is much less likelyto cause an ignition source. Friction sparks can

be particularly dangerous if they are betweentwo metals (combinations of aluminium and rustcan cause thermite reactions). These can often

be caused by falling objects (such as nuts orbolts) or by moving equipment contacting plantitems.

Mechanically Generated Sparks


16/26


Electrical Apparatus

Opening and closing of contactors

arcs, sparks.

Loose connections

Hot surfaces


17/26


Stray electric currents

WeldingElectrical short circuit


18/26


Static Electricity

Pouring dusts

Agitator/stirring

liquids

Air/steam leaks

Moving ConveyorsWalking

Flowing liquids


19/26


Lightning

If lightning strikes in anexplosive atmosphere,

ignition will always occur


20/26


21/26


Ionizing RadiationIonizing radiation is givenoff by the sun (cosmic

rays), radioactivematerials, and high energyelectronic devices (X-ray

machines).


22/26


Ultrasonics

Large proportion of the

energy emitted by thetransducer is absorbed bysolids or liquids


23/26


Adiabatic compression and

shock waves


24/26


Exothermic reactions, including self

ignition of dusts

StrawChemical


25/26


Controls

Control methods for ignition sources include:

Procedures

Permit-to-work

Area classification


26/26


End of Section

Module 04_Ignition Sources_September 2007

Documents