Zone 0/ 20 An area in which an explosive gas/ dust atmosphere is continuously present, or present for long periods Zone 1/ 21 An area in which an explosive gas/ dust atmosphere is likely to occur during normal operation Zone 2/ 22 An area in which an explosive gas/ dust atmosphere is not likely to occur in normal operation, and if it occurs it will only exist for a short time

1. BASICS
OF
HAZARDOUS AREA
CLASSIFICATION
Slide 1 © 2011 DEKRA

2. What is an Hazardous Area?
Hazardous areas are defined as "any place in which an
explosive/flammable atmosphere may occur in quantities such as to
require special precautions to protect the safety of workers". In this
context, 'special precautions' is best taken as relating to the construction,
installation and use of apparats in this areas.
Slide 2 © 2011 DEKRA

3. Type Of Hazards In Plant?
• General hazards: tripping, etc.
• Health hazards, toxicity
• Hazards of specific equipment: electrical equipment, welding, inert atmosphere,
etc.
• Environmental hazards
• Process safety issues:
 Explosive properties
 Flammable atmospheres (“operational hazards”)
­ gas, (solvent) vapour, dust, mist, hybrid
 Chemical reaction hazards

4. Basic Terminology
Explosive Limit:
Fuel - air mixtures are only flammable within the flammable range i.e. between
LEL and UEL

5. Basic Terminology
Flash Point:
Temperature at which liquid gives so much vapor, which forms an ignitable
mixture when mixed with air.
Explosive Atmosphere:
A mixture of flammable material (in form of gas, vapor, mist, dust) with air (under
normal atmospheric conditions), in which ignition spreads throughout the
unconsumed mixture after ignition.
Hazardous Area:
Area in which explosive gas/ dust atmosphere is present or likely to be present,
in such quantities that we require special precautions for construction,
installation and use of electrical equipments.

6. Basic Terminology
Non Hazardous Area:
Area in which explosive gas/ dust atmosphere is not expected to be
present, in such quantities that we require special precautions for
construction, installation and use of electrical equipments.
Adequate Ventilation:
It is considered adequate if it is sufficient to prevent accumulation of
significant quantities of vapor-air mixtures in concentration over one-
fourth of the lower flammable limit.

7. How Explosion Can Occur?
Oxidant
Confinement
Mixing
Fuel Ignition source

8. Why HAC is Required?
• Explosion can be prevented in many ways like reduction of explosive concentration
below LEL or above UEL, Removal of Oxidant (Inerting), minimizing ignition sources,
etc.
• Unsuitable electrical equipments in past have been major contributors towards ignition
of flammable atmosphere.
• To reduce the ignition probability due to ignition sources, it is necessary to use rated
equipments.
• Electrical Equipments are rated based on different hazardous zones, which are
classified in a facility based on HAC study.
• In HAC, we assess the probability of existence of Explosive atmosphere, based on
which type of electrical equipments can be selected.

9. Find sources of release
Identify the duration
(grade of release)
Consider ventilation
Assign zone numbers
Estimate zone size
Report
What Is The Procedure For Area Classification
CONTINUOUS
(ZONE 0)
PRIMARY
(ZONE 1)
SECONDARY
(ZONE 2)
RARELY
A LOT OF
THE TIME
MOST OF
THE TIME
HOW OFTEN?
WHERE CAN
IT
GET OUT?

10. What Are Different Zones For Gases And Dusts?
Zone 0/ 20
An area in which an explosive gas/ dust atmosphere is continuously present, or
present for long periods
Zone 1/ 21
An area in which an explosive gas/ dust atmosphere is likely to occur during
normal operation
Zone 2/ 22
An area in which an explosive gas/ 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

11. What Are Different Grades Of Release?
Continuous grade of release:
Release which is continuous or is expected to occur frequently or for long
periods.
Primary grade of release:
Release which is expected to occur periodically or occasionally during normal
operation
Secondary grade of release:
Release which is not expected to occur in normal operation and, if it does
occur, is likely to do so only infrequently and for short periods.

12. How To Quantify Grades Of Release?
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

13. Effect Of Ventilation?

14. THINK FIRST ...
• Are there any sources of release ?
• Can sources of release be eliminated ?
• Is there enough flammable material to produce a
dangerous volume of explosive gas atmosphere ?
• Can continuous sources be changed to primary ones
and primary sources to secondary ?
• Can poor ventilation be improved ?
• Can availability of ventilation be improved ?

15. Which Electrical Equipments Are Suitable?
Type of protection Marking
Zone 0
Intrinsic safety “ia”
Zone 1
Equipments suitable for Zone 0
Flameproof enclosure “d”
Pressurised apparatus “p”
Powder filling “q”
Oil immersion “o”
Intrinsic safety “i”
Encapsulation “m”
Zone 2
Equipment suitable for Zone 0 or 1
Non-sparking “n”
Increased safety “e”

16. What Should Be The Temperature Class Of
Electrical Equipment
Maximum surface
temperature
(°C)
AIT
of the material
(°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)

17. References for HAC
• BS EN 60079-10 - Electrical Apparatus for Explosive Gas Atmospheres, Part
10: Classification of hazardous areas.
• BS EN 61241-10 - Electrical Apparatus for Use in the Presence of Combustible
Dust. Part 10: Classification of areas where combustible dusts are or may be
present
• BS EN 60079-10:2003 – Electrical apparatus for explosive gas atmosphere –
Part 20: Data for flammable gases and vapors, relating to the use of electrical
apparatus
• ATEX 95 equipment directive 94/9/EC, Equipment and protective systems
intended for use in potentially explosive atmospheres;
• ATEX 137 workplace directive 99/92/EC, Minimum requirements for improving
the safety and health protection of workers potentially at risk from explosive
atmospheres
• NFPA 30 - Flammable and Combustible Liquid Code.

18. • NFPA 499 - Recommended Practice for the Classification of Combustible
Dusts and of Hazardous (Classified) Locations for Electrical Installations in
Chemical Process Areas.
• Institute of Petroleum, (2005), Area Classification Code for Installations
Handling Flammable Fluids, Part 15 of the Institute of Petroleum Model of Safe
Practice in the Petroleum Industry, the Institute of Petroleum.
• IS 5572 : 2009 : Classification of Hazardous areas (other than mines) having
flammable gases and vapor for electrical installation (Third Revision)
• NFPA 497 - Recommended Practice for the Classification of Flammable
Liquids, Gases, or vapors and of Hazardous (Classified) Locations for
Electrical Installations in Chemical Process Areas.
References for HAC

19. Thank You
CHILWORTH TECHNOLOGY PVT. LTD., INDIA