This presentation explains the Hazardous gas Classification and area Classification, and the responsibility of Electrical, Instrument and Process Engineer Responsibility.

1. HAZARDOUS AREA
CLASSIFICATION
By
Kathiresan Nadar
Process Engineer-II

2. 2
Hazardous Area Failure Case Study
 On October 23 2009 Massive explosion at Caribbean Petroleum (CAPECO)
 Gasoline Storage area
 Gasoline Storage operation done without a Level Transmitter. Thus required Manual Operation and Manual
Checking for predicting tank Level
 Error in Predicting the Level of the tank thus The Gasoline Overflow and come out of the storage tank
 Gasoline Vapor Covered area of 104 Acre and the atmosphere is windless (Low Ventilation)
 Gasoline Liquid Drained from the Containment tank to the waste water area and reached Electrical Equipment
 Electrical Equipment Ignited the area.
 The Accident Cause the Death of 2 Employee and 1 was Critically Injured.

3. 3
??
And Who are
Responsible ??
1. Poor Ventilation (Natural Cause)
2. Improper Instrumentation
3. Poor Process Design to flow the containment liquid to Waste water area
4. Waste water area’s Hazardous area Classification.
1. Since Waste water has the Low or negligible source of Flammable material. The area is
classified for the Zone 2.
2. The Corresponding Instrumentation and Electrical Equipment is designed for the Zone 2
3. Process Safety Calculation Mistake.

4. 4
Safety Characteristics of Gas and Vapor
 Flash Point
 Auto Ignition Temperature
 Explosion Limit
• Lower Explosion Limit
• Higher Explosion Limit
 Maximum Oxygen Concentration
 Vapor Density

5. 5
Explosion Group
 The explosive characteristics of the air mixtures of gases, vapors, or dusts
vary with the specific material involved.
 Group I: Electrical apparatus for mines susceptible to firedamp (for use
underground).
 Group II: Electrical apparatus for places with a potentially explosive
atmosphere other than mines susceptible to firedamp.
 Group III: Electrical apparatus for places with a potentially explosive
atmosphere other than mines susceptible to firedamp. For Dust.

6. 6
Grouping and Classification of Area
 Grouping is based on
• maximum experimental safe gap (MESG)
• minimum igniting current (MIC) ratio
 Groups for Gases are IIA, IIB, IIC
Gas Groups Chemical/Component MESG MIC Ratio
IIC Acetylene, Hydrogen, Flammable Liquid produced Vapor, Flammable Gas,
Combustible Liquid Produced Vapor
<0.5 mm < 0.45
IIB acetaldehyde, ethylene, Flammable Liquid produced Vapor, Flammable Gas,
Combustible Liquid Produced Vapor
>0.5
<0.9
>0.45
<0.8
IIA acetone, ammonia, ethyl alcohol,
gasoline, methane, propane, or fammable gas, fammable liquid-produced
vapor, or combustible liquid-produced vapor
>0.9 >0.8

7. 7
Temperature Classification
 Minimum temperature required to cause the fire without spark or flame to set a
fire.
 T1 - 4500C
 T2 - 3000C
 T3 - 2000C
 T4 - 1350C
 T5 - 1000C
 T6 – 850C
• For intrinsically safe it is inside temperature whereas for flame proof it is outside
temperature.

8. 8

9. 9
What is Hazardous Area Classification ??
 Area classification is a method of analyzing and classifying the
environment. where explosive gas atmosphere may occur to allow the
proper selection of electrical apparatus to be installed in that environment.
 Objective - The object of the classification procedure is to enable electrical
apparatus to be operated safely in that environment.

10. 1 0
In Situations When Explosive Gas are
Present
 Eliminate the likelihood of an explosive gas atmosphere occurring around the source of ignition
or eliminate the source of ignition
► Raising the flash point by substitution for e.g Adding Water
► Lower process temperature by cooling (water spray jet)
► Limiting concentration below LEL by Proper Ventilation
 Limit the range of explosion fames and explosion pressures to a sufficient level of safety.
► Explosion Proof Design Containment.
In practice however, it is very difficult to ensure that an
explosive gas atmosphere will never occur. In this case,
apparatus with special protective measures should be used.
And for proper
selection we need
area classification

11. 11
Explosion Protection Avoiding fammable substances (replacement technologies) or by inerting
with N2
This is done by proper venting or removing one component from the fire
Triangle.
For e.g
1. Avoiding Hot Surface
2. Avoiding Static Electricity
3. Lightining etc
provision such that the fire or explosion occurred is not transferred to
the bulk system. For E.G
1. Explosion pressure resistant construction.

12. 1 2
Hazardous area Defined by
1. The type of hazard (groups).
2. The AIT of the hazardous material (temperature or T rating).
3. The likelihood of the hazard being present in flammable
concentrations(zones/ Class and Division)
Type of Hazard
Group I, II, III and its subdivision.
NFPA Publication 70, National Electrical Code (NEC) defnes the type of
hazardous substance
Class and Division – Followed in North America
Zones – Followed in the Rest of the World

13. 1 3
What are Classes, Division and Zones
 Class I – Flammable Gases and Vapor may present.
 Class II – Location in which combustible dust may be present.
 Class II – Location in which Ignitable fibre may be present.
► Division Defines the probability of the hazardous materials being able to produce the hazardous
mixture
► Division 1 – The mixture has the high probability of forming the explosive atmosphere at normal
operating conditions.
► Division 2 – The Mixture has low probability of forming the explosive mixture at normal operating
conditions.
 Zone 0, 1, 2 – Zones where hazardous vapor and Gas will be present
 Zone 20, 21, 22 – Zones where hazardous dust or fibers will be present.

14. 1 4

15. 1 5
Sources of Release
 Identify the Source of Release
 Process Item such as Tank, Pump, Pipeline, Vessels etc are the source of
release
 Welded pipeline are not considered as the source of release.

16. 1 6
Next Important thing is the Grade of
Release
 The Release is Continuous, Primary or Secondary
 Grade should be estimated based on operating conditions (T and P) at Normal or Abnormal
situations.
 Continuous – A Release that is expected to occur for longer period of the time
 For E.g Surface of a flammable liquid in a fixed roof tank
 Surface of an open reservoir (e.g., oil/water separator)
 Primary – A Release that occur Periodically or Occasionally during normal operation
 Seal of Pump, Compressor, Valves, Water draining point, Sample Collecting Point, Relief Valve, Vent during normal operation. Also
changing filter cloth.
 Secondary – A Release that occur infrequently or if it occur the duration is low
 Seal of Pump, Compressor, Valves, Water draining point, Sample Collecting Point, Relief Valve, Vent during abnormal condition

17. 1 7
Extent of Zone
 Extent of Zone Depend on the following factor
• Release Velocity or Release Rate
• Concentration of flammable gas in the released mixture
• Ventilation
• Obstacles
• Boiling Point of the flammable liquid
• LEL
• Flash Point
• Relative Density
• Liquid Temperature

18. 1 8
Ventilation

19. 1 9
Why Ventilation effect the Zone type and
Zone Extent ?
 Ventilation Promote Dispersion thus Hazardous material fall below LEL.
 Availability of Ventilation
► Good – Ventilation is present continuously (Wind speed 0.5 m/s)
► Fair – Ventilation that occur during normal operation and interruption is permissible
► Poor – Ventilation that did not meet standard and interruption is not expected.
 Ventilation Degree
► High Ventilation – Reduce the Source of release below LEL Instantaneously.
► Medium Ventilation – Ventilation that provide stable Zone Extent once the Hazard Release and
reduce concentration below LEL when Release is stopped.
► Low Ventilation – Cannot control the concentration when release is in progress

20. 2 0
Who are responsible for Area Classification
??
 Process Engineer (Process Safety Engineer )
 For Extent of Zones, Type of Zones and Hazard Group
 Electrical Engineer and Instrumentation Engineer
 Proper selection of instrument or electrical Equipment based on Zone selected.

21. 2 1
What effects ??
 Locations of Vessels or potential release point location may change
 Guide the location of Flare, LPG connection etc.
 Location of Motors or other electrical and Electronic instrument changes. Thus
effect the cost of wiring and Electrical Tray.
 Type of Electrical and Electronic Equipment Changes. This add the cost
variations.
 Defines the number of Fire and Gas Detectors, type and Locations
 Defines the type and safety requirements of Fire water.
 Safety and Operational Manuals and Procedures.

22. 2 2
Process Engineer Responsibility
 Plant and Installation at which hazardous material being handled such a
way that Zone 0 and Zone 1 are kept to minimum and mainly area should
be Zone 2
 Try mostly to make the secondary source of release. If primary source is
unavoidable than try to minimize the quantum of release
 Process Equipment relocation is needed to fit the requirements. Most Area
classifications are generated in the FEED stage itself.

23. 2 3
Electrical and Instrument Engineer
Responsibility
 Engineers work on the principle that Hazard as defined by the Process is
always present
 Select the Equipment to avoid the Explosion or Fire Hazard
 Choose Explosion Proof Housing when Process is not critical.
 Choose Intrinsically safe or Increased Protection When the Process is SIL
Critical.

24. 2 4

25. 2 5
 Instrument for Different Zones.
 Equipment Protection Level
► The EPL is a level of protection assigned to equipment based on its likelihood of becoming a source of ignition
 EPL Ga – Equipment with Very high level of protection that is not the source of ignition during normal operation
 EPL Gb - Equipment with high level of protection that is not the source of ignition during normal operation
 EPL Gc - Equipment for explosive gas atmospheres having an enhanced level of protection that is not a source of ignition in
normal operation
Zone 0 Category 1
Zone 1 Category 2
Zone 2 Category 3

26. 2 6

27. 2 7
THANKS