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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
A Pa ssion for S a f et y
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
A Pa ssion for S a f et y
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
A Pa ssion for S a f et y
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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A Pa ssion for S a f et y
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
A Pa ssion for S a f et y
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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A Pa ssion for S a f et y
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
A Pa ssion for S a f et y
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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A Pa ssion for S a f et y
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!
A Pa ssion for S a f et y
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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A Pa ssion for S a f et y
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
A Pa ssion for S a f et y
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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A Pa ssion for S a f et y
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
A Pa ssion for S a f et y
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
A Pa ssion for S a f et y
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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A Pa ssion for S a f et y
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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A Pa ssion for S a f et y
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)
A Pa ssion for S a f et y
EQUIPMENT MARKING
1180 II 2 G D
Ex d II C T4 IPXX
ATEX Marking
BS‐EN Marking

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A Pa ssion for S a f et y
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