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Part 1 Hazardous Areas
GENERAL PRINCIPLES
SOURCES OF IGNITION
Ver: 2.0
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Fire Triangle
FUEL
(GAS, VAPOUR, MISTS) OR DUSTS
AIR21% OXYGEN
79% NitrogenSOURCE OF IGNITION
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Flammable (Explosive) Limits
UPPERUPPER
EXPLOSIVEEXPLOSIVE
LIMIT (LIMIT (UELUEL) %) %
Too Rich
Insufficient
Oxygen
LOWERLOWER
EXPLOSIVEEXPLOSIVE
LIMIT (LIMIT (LELLEL) %) %
Too Weak
Insufficient
Fuel
MATERIALSMATERIALS LEL%LEL% UEL%UEL%
Propane 1.7 10.9
Ethylene 2.3 36
Hydrogen 4.0 77
Kerosene 0.7 5.0
Acetylene 2.3 100
FLAMMABLE
RANGE
(Explosive Range)
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Sources Of Ignition
EXTERNAL- Flames, Welding, Electrical Equipment
CHEMICAL REACTION
- Exothermic Runaway
PLANT OPERATIONS
- Static Electricity, Mechanical Friction, Friction Sparks
SUBJECT TO PROCEDURES AND REGULATIONS- Welding, Lightning, Electrical Equipment, Hot
Surfaces
SUBJECT TO GENERAL CONTROL IN PLANT AREA
- Mobile Phones Etc, Cigarettes, Lighters & Matches
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Ignition Sources Arising
Within Plant1. Electrostatic Sparks
2. Thermite Sparks
3. Mechanical Friction
4. Hot Surfaces
5. Smouldering Deposits
6. Ignition Temperature (Previously
Autoignition)
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Flash Point
DEFINITION:
The lowest temperature at which
sufficient vapour is given offaliquid, to form a flammablemixture withair, that can be
ignited byan arc, spark or nakedflame.
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Flash Point
Material Deg CPropane -104
Ethylene -120 (Approx)
Hydrogen -256 (Approx)
Kerosene 38
Acetylene -82 (Approx)
Amount of vapour releaseddependant on temperature
VAPOUR
Liquid1. DEPENDS ON PRESSURE
Increase with increasing pressure
Decrease with decreasing pressure
2. PRESENCE OF SOLIDS
Can raise flash point
3. PRESENCE OF VOLATILES
Can effect significant reduction
Effects to Flashpoint
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Flash Point
Ignition Source
Paraffin -
Flash Point 38 Deg C
At 0 Deg C
At 33 Deg C
At 38 Deg C
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Minimum Ignition Energy (MIE)
LIQUIDSData obtained from literature -
benzene (Approx) 200 J
hexane (Approx) 240 J
acetone (Approx) 1.15 mJ (Milli Joules)
DUSTSData normally obtained by in house measurement -
anthraquinone (Approx) 2.5 - 4 mJ
phenothiazine (Approx) 25 - 50 mJ
sulphur (Approx) < 1 mJ
GASESHydrogen (Approx) 20 J (Micro Joules)
Ethylene (Approx) 95 J
Propane (Approx) 260 J
Methane (Firedamp) (Approx ) 280 J
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Ignition Temperature
DEFINITION:
The lowest temperature at which a
material can ignite and sustain
combustion, when mixed with air at
normal pressure, without the ignition
initiated by any spark or flame. i.e.
when making contact with a hotsurface.
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Ignition Temperature
Hot Surface
MATERIAL TEMP
Propane 470 C
Ethylene 425 C
Hydrogen 560 C
Acetylene 305 C
Kerosene (Paraffin) 210 CMethane (Fire damp) 537 C
Oxygen Enrichment can occur at compressed air factories or
where there is oxygen burning equipment. It lowers the Ignition
Temperature and Widens the Flammable range
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T Rating Of Apparatus In Relation
To Ignition Temperature
Material Ignition Temp T Rating
Methane (Firedamp)
Hydrogen
Propane
595C
560C
470C
T1 450C
Ethylene
Acetylene
425C
305CT2 300C
Cyclohexane
Kerosene
259 C
210CT3 200C
Diethyl Ether 160 C T4 135C
T5 100C
Carbon Disulphide 95 C T6 85 C
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Temperature Classification
Relating To Equipment
TEMPERATURE
CLASSIFICATION
MAXIMUM SURFACE
TEMPERATURE C
T1 450
T2 300
T3 200
T4 135
T5 100
T6 85
A potential ignition surface will not exceed the temperature
related to the T rating in normal or specified fault conditions.
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Ambient Temperature Range
T6 (85C) Temperature Classification
Ta in Europe the value is:
-20 +40C
0 Deg.C
20 Deg.C
40 Deg.C
100 Deg.C
-20 Deg.C
60 Deg.C
80 Deg.C
35 Deg C
Temp rise
Correctly
Installed
Not Correctly
Installed
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Vapour Density
COMPARISON OF A GAS/VAPOUR WITH AIRPLACEMENT OF GAS DETECTORS & VENTILATION
MATERIAL VAPOUR DENSITYAIR 1.0
PROPANE 1.56
ETHYLENE 0.97
HYDROGEN 0.07
ACETYLENE 0.9KEROSENE 4.5 (Approx)
= Gas Detector
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Area Classification
ZONE 0 In This Zone, A Flammable Atmosphere IsContinuously Present, Or Present ForLong Periods.
ZONE 1 In This Zone, A Flammable Atmosphere IsLikely To OccurDuring Normal Operation.
ZONE 2 In This Zone, A Flammable Atmosphere IsNot Likely To OccurDuring Normal Operation But If It Does,Its Duration Will Be For A Short Time Only.
1000 8760 hrs per year
10 1000 hrs per year
0 10 hours per year
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Area Classification
Zones Diagrammatic Representation
Zone 0 Zone 1
Zone 2 Non Hazardous Zone
Small Circles 45 Cross Hatching
45 Slanting Lines
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Area ClassificationFixed Roof Storage Tank
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Area Classification1 2
3
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Sources of Release
Welded pipe Non-hazardous
Flanged Joint - Zone 2
300mm Diameter min standard
Pump Gland - Zone 1
Generically, a movement of a pump may
change the zone or manufacture may choose
the zone
Space above liquid in a closed tank - Zone 0
Area Classification
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Grouping
Gas or Dust
Sub Division
Representative
Material Description
IMethane
(Firedamp)Mining
II IIA Propane SurfaceIndustries
Gas
II IIB Ethylene
II IIC Hydrogen/Ace
III IIIACombustible
Flyings Surface
Industries
DustIII IIIB
Non-Conductive
dust
III IIIC Conductive Dust
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1st Figure Protection against Solids
IP Test Comment
0 No protection
1
Protected against solid bodiesgreater than 50mm diameter.(e.g. accidental contact with thehand)
2
Protected against solid bodiesgreater than 12.5mm diameter.(e.g. finger)
3Protected against solid bodies
greater than 2.5mm diameter(e.g. tools, wires)
1st Figure Protection against Solids
IP Test Comment
4
Protected against solid bodiesgreater than 1.0mm diameter(e.g. thin tools and fine wire).
5Protected against dust (noharmful deposit)
Dust Proof
6
Completely protected againstdusts
Dust Tight
INGRESS PROTECTION
IP 1st 2nd (Additional Letters)Solids
Where there is no requirement for a protection rating with
regard to one criteria the digit is replaced with an X.
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2nd Figure Protection against Liquids
IP Test Comment
0 No protection
1
Protected against vertically fallingdrops of water (condensation)
2
Protected against drops of waterfalling up to 15 from the vertical
3
Protected against water sprayed upto 60 from the vertical
4
Protected against splashing waterfrom all directions
2nd Figure Protection against Liquids
IP Test Comment
5
Protected against jets of water from alldirections
6
Protected against powerful jets ofwater from all directions
7
Protected against the effects oftemporary immersion in water
8
Protected against the continuouseffects of immersion in water havingregard to specific conditions
INGRESS PROTECTIONIP 1st 2nd (Additional Letters)
Liquids
Additionalletters that can be appended to classifyonlythe level of
protectionagainstaccesstohazardousparts bypersons:
Level Protection against access to hazardous parts with
A Back of hand
B Finger
C Tool
D Wire
Further letters can be appendedtoprovide additional information
relatedtothe protectionofthe device:
Letter Protection against access to hazardous parts with
H High voltage device
M Device moving driving water test
S Device standing still during water test
W Weather conditions