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A Pa ssion for S a f et y
UNDERSTANDING
HAZARDOUS AREA
CLASSIFICATION
Consultancy
Training
Testing
A Pa ssion for S a f et y
COURSE OBJECTIVES
On completion of the course you will learn:
What are the Flammability Characteristics that are required to
carry out Hazardous Area Classification (HAC);
How to conduct Hazardous Area Classification (HAC) & classify
workplace into various hazardous and non hazardous zones for
both vapors and dusts
What equipment to select for identified hazardous zones.
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A Pa ssion for S a f et y
INTRODUCTION
SIGMA‐HSE (INDIA) PVT. LTD.
A Pa ssion for S a f et y
AREAS OF EXPERTISE
We bring together our Indian and UK experts to provide our clients
with EHS services and appropriate engineering solutions.
We undertake Laboratory testing in our UK laboratories to ISO, BSI
ASTM and VDI individual test standards.
Consultancy Testing Training
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A Pa ssion for S a f et y
OUR PRESENCE
Technical Offices
New Delhi, India
Mumbai, India
Hyderabad, India
Winchester, UK
Abu Dhabi, UAE
Laboratories
Process Safety Lab, Winchester, UK
The Environmental Laboratory (ELAB), UK
A Pa ssion for S a f et y
CONSULTANCY SERVICES
Our Consultancy team provides a wide range of specialist technical knowledge
covering the following sectors:
Process Safety Management (PSM) Implementation
Industrial Fire & Explosion Hazards
Electrostatic Hazard Assessment
Process Hazard Analysis (PHA)
Functional Safety
Chemical Reaction Hazards
Training Workshops
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A Pa ssion for S a f et y
LABORATORY TESTING
Powder Fire & Explosion Properties
Gas and Vapor Properties
Electrostatic Properties
Chemical Reaction Hazard Testing
A Pa ssion for S a f et y
PIPER ALPHA DISASTER
An explosion and the resulting oil and gas fires destroyed Piper Alpha Platform on 6 July
1988, killing 167 men, with only 61 survivor. The total insured loss was about £1.7
billion.
As per the investigation, deluge system was activated by gas leak. This resulted in
ingress of deluge water into a light fitting, which was no longer explosion proof. This
resulted in short circuiting and spark generation.
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A Pa ssion for S a f et y
DANVERS CHEMICAL PLANT EXPLOSION,
NOVEMBER 2006
CAI / Arnel Chemical Plant Explosion
Steam supply left on during night.
Overheating in the reactor led to
vaporization of reactor content,
forming confined vapor cloud.
No personnel on site during night.
Confined Vapor Cloud ignited by
non‐rated consumer‐type box fan.
10 Injured, and 24 Houses and Six
Businesses Destroyed
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IMPERIAL SUGAR EXPLOSION, FEBRUARY
2008
Sugar Plant in Georgia USA
Dust explosion occurred in sugar silo
8 people dead in the workplace,
6 more died in hospital
42 people injured
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A Pa ssion for S a f et y
WHAT CONSTITUTES AN EXPLOSION
Oxidant
Confinement
Mixing
Fuel Ignition source
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CONDITIONS FOR VAPOUR EXPLOSION
The liquid must be above its Flash Point temperature.
Concentration must be within flammability limits.
Flammable atmosphere need to support combustion.
Energy related to the ignition source must be sufficient.
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A Pa ssion for S a f et y
CONDITIONS FOR A DUST EXPLOSION
Dust must be flammable/ combustible and airborne to form a cloud.
Concentration must be within explosible limits.
Particle size distribution should be capable of propagating flame.
The atmosphere need to support combustion.
Energy related to the ignition source must be sufficient.
A Pa ssion for S a f et y
FLAMMABILITY DATA – HAC (VAPORS
AND GASES)
For HAC the following data
are relevant
Flash Point
Flammability Limits
Auto‐Ignition Temperature
Gas Group
Vapour Density *
* not flammability data
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A Pa ssion for S a f et y
FLAMMABILITY DATA – HAC (DUSTS)
For HAC the following data are
relevant
A/B Classification
Minimum Explosible Concentration
Particle Size
Minimum Ignition Temperatures
⁻ MIT (cloud)
⁻ LIT (layer)
Electrical Resistivity *
* not flammability data
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SOME OF THE GUIDES FOR GAS/VAPOR
EN 60079‐10
essential but no guidance on zone extents
identical to IEC 60079‐10
Energy Institute; Model code of safe practice ‐ Part 15
4th edition, 2015
applies mainly to installations handling flammable liquids
IS 5571 and IS 5572
Mainly used for gases and vapors only
And others
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A Pa ssion for S a f et y
PHILOSOPHY OF HAZARDOUS AREA
CLASSIFICATION
Area classification assesses the probability of flammable atmospheres
occurring
Once the probability is established, ignition sources can be prevented to
match this
area classification does not specify the equipment
Area classification does not take account of consequences
these are covered as part of the general safety considerations
A Pa ssion for S a f et y
AREA CLASSIFICATION PROCEDURE
Identify sources of release
Consider ventilation and review
standard of housekeeping
Determine the duration &
grade of release.
Estimate zone size
Assign zone numbers
Report !
Where can it get out
Is there
ventilation
Housekeeping
Continuous Normal
Operation
Infrequently
Continuous
Zone 0/20
Primary Zone
1/21
Secondary
Zone 2/22
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ZONES DEFINITION
Zone 0/20
An area in which an explosive gas/vapor/dust atmosphere is continuously
present, or present for long periods
Zone 1/21
An area in which an explosive gas/vapor/dust atmosphere is likely to occur
during normal operation
Zone 2/22
An area in which an explosive gas/vapor/dust atmosphere is not likely to
occur in normal operation, and if it occurs it will only exist for a short time
Note: Normal operation includes expected abnormal events, but not catastrophic failures
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SOURCE OF RELEASE
Continuous grade
continuously, or for long periods, or frequently
Primary grade
periodically or occasionally during normal operation
Secondary grade
not in normal operation
only infrequently and for short periods
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GRADES OF RELEASE AND ZONES
Grade Duration Zone
Continuous
Primary
Secondary
>1000 hr/year
> 1 hr/shift
<1000 hr/year
> 10 hr/year
<10 hr/year
< 1 min/shift
0/20
1/21
2/22
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EXTENT OF ZONES
Use Example Approach.
Use examples offered in guidance to develop own “rule of thumb”
guidance
Or if not applicable then calculate individual zones
Adjust size and shape
But do not significantly reduce the size
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EXTENTS OF ZONES – DUSTS
Depends upon the environment
creating the dusty atmosphere
Can be affected by
working procedures
Ventilation, forced or natural
Housekeeping (good or bad)
Maintenance of equipment
HAS TO BE DETERMINED, CANNOT BE
CALCULATED!
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VENTILATION
Poor ventilation can lead to larger or more strict zone designation
Also, high ventilation rates can be used to relax the classification,
sometimes even as far as “non‐hazardous” because zone is of “negligible
extent”
Such high degree of ventilation is virtually only applicable to local artificial
ventilation
Availability of ventilation is crucial
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EXAMPLES – GASES & VAPORS
Continuous
Surface of flammable liquid (e.g. in vessel)
Exhaust from continuously emitting vent stack
Primary
Pump, valve seals or fittings where release normally expected
Open handling of flammable liquids
Sample points used as part of normal operation
Open manway additions to vessels
Secondary
Pump or valve seals, release not normally expected
Sample points not used in normal operation
Relief valves, vents not normally active
Flanges, connections, pipe fittings
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EXAMPLES ‐ DUSTS
Zone 20
Normally inside dust handling equipment. For Eg. Mill, Silo, Dust Collector (Dirty
Side)
Zone 21
Inside some equipment
Area outside equipment. For Example Around Dumping station, Vessel Charging
point
Zone 22
Wherever dust layers occur and where the powder can release because of any
leakages. For Ex. Clean Side of Dust Collector, Around Flange Joints in conveying
line.
Around a non‐confined Zone 21 due to fine dust or dust layers
Note : Practical considerations can make it necessary to classify a whole area
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RECOMMENDED ZONE MARKINGS
Show zones on a site plan
Make side views as required
If possible include the gas
group and temperature class
Report contains all data used
and assumptions made for the
classification
Heights and shapes of zones to
be mentioned in report
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DRAWINGS AND REPORT
Show zones on a site plan
Make side views as required
If possible include the relevant
dust data
Report contains all data used
and assumptions made for the
classification
Heights and shapes of zones to
be mentioned in report
Recommended zone markings
Zone 20
Zone 21
Zone 22
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A Pa ssion for S a f et y A Pa ssion for S a f et y
AREA CLASSIFICATION REVIEWS
Responsibility for area classification rests with project manager or site
manager
New plant
review during design
review during start up
review in use
General reviews
when changes are made
at least every two years
results may indicate the frequency needed
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A Pa ssion for S a f et y
TYPES OF PROTECTION ‐ ELECTRICAL
APPARATUS
Flameproof Ex d
Increased safety Ex e
Purged or
pressurised Ex p
Oil filled Ex o
Sand or powder
(quartz) filled Ex q
Encapsulated Ex m
Intrinsically safe Ex ia/ Ex ib
Non‐incendive Ex n
Special protection Ex s
Protection by EX t
Enclosure
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SELECTION OF ELECTRICAL APPARATUS
Zone 0
Ex ia
Ex s (specially certified)
Zone 1
any suitable for Zone 0
Ex d ‐ Ex p
Ex q ‐ Ex o
Ex e ‐ Ex ib
Ex m
Zone 2
any suitable for Zone 0 or 1
Ex n (Ex N)
Zone 20
Ex ta
Zone 21
Ex tb
Zone 21
Ex tc
In addition the maximum surface
temperature must be considered
determined by AIT
usually as temperature classes
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INGRESS PROTECTION
A Pa ssion for S a f et y
INGRESS PROTECTION
Zone 20
Use Dust tight enclosure (IP 6X)
Zone 21
Use Dust tight enclosure (IP 6X)
Zone 22
Use Dust tight enclosures (IP 6X) ‐ Zone 22 (If powder is conductive)
Use Dust protected enclosures (IP 5X) ‐ Zone 22 (If powder is non‐
conductive)
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TEMPERATURE CLASS FOR VAPOURS
AND GASES
Maximum surface
temperature
(°C)
AIT
(°C)
T1 450 °C >450 °C
T2 300 °C >300 °C (450 °C)
T3 200 °C >200 °C (300 °C)
T4 135 °C >135 °C (200 °C)
T5 100 °C >100 °C (135 °C)
T6 85 °C >85 °C (100 °C)
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EQUIPMENT MARKING
1180 II 2 G D
Ex d II C T4 IPXX
ATEX Marking
BS‐EN Marking
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HAZARDOUS AREAS EXAMPLE
A Pa ssion for S a f et y
THANK YOU!
For Queries, contact our Process Safety Expert on +91 9599 024327
or write to him on hchichra@sigma‐hse.com
CONSULTANCY
Hazardous Area Classification
Electrostatic Hazard Assessment
Process Safety Assessment
Dust Explosion Risk Assessment
ATEX assessment
And OTHERS
PROCESS SAFETY TESTING
Electrostatic Properties
Powder Fire & Explosion Properties
Gas and Vapor Properties
Chemical Reaction Hazard Testing
DETAILED TRAININGS