Fire
hazardous area classification in O&GC
A
hazardous area classification chart
is a graphical representation of the classification of hazardous areas
according to the types of hazardous materials present and their potential for
ignition. The chart typically includes a legend that describes the various
types of hazardous materials and the criteria used to classify them.
The
hazardous area classification chart is used to identify and evaluate the risks
associated with the presence of flammable or explosive materials in a
particular area. The chart provides a visual reference for the classification
of the area and the associated safety measures that must be implemented.
The
chart typically includes several zones, which are defined by the probability of
the presence of flammable materials and the duration of their presence. The
zones are used to determine the type of equipment and safety measures that must
be used in each area. For example, Zone 0 is an area where flammable materials
are present continuously or for long periods of time, while Zone 2 is an area
where flammable materials are present only intermittently or in small
quantities.
The
hazardous area classification chart is an important tool in the design,
construction, and maintenance of facilities where flammable or explosive
materials are present. It helps to ensure that appropriate safety measures are
implemented to protect personnel and equipment from potential hazards.
The oil and gas
industry involves the handling and processing of flammable and explosive
materials, which can create hazardous areas. Some examples of hazardous areas
in the oil and gas industry are:
·
Drilling platforms: Drilling
platforms are offshore structures where oil and gas exploration and extraction
take place. These platforms have several areas that are classified as
hazardous, such as drilling areas, storage areas, and processing equipment.
·
Refineries: Refineries are facilities that
process crude oil into various petroleum products. The processing equipment,
storage tanks, and pipelines in refineries are all potentially hazardous areas.
·
Oil and gas pipelines: Pipelines are
used to transport crude oil, natural gas, and petroleum products over long
distances. The pipelines and their associated equipment, such as pumps, valves,
and compressors, can be classified as hazardous areas.
·
Gas processing plants: Gas
processing plants are facilities that separate natural gas into its component
gases and remove impurities. The processing equipment, storage tanks, and
pipelines in gas processing plants can all be classified as hazardous areas.
·
LNG facilities: LNG facilities are used to
liquefy natural gas for transportation and storage. The liquefaction process,
storage tanks, and associated equipment in LNG facilities are all potentially
hazardous areas.
These are just a
few examples of hazardous areas in the oil and gas industry. It’s important to
identify and classify these areas properly to ensure the safety of personnel
and equipment.
The three classes of hazardous
locations are defined by the National Electric Code (NEC) in the United States.
They are:
·
Class I: Locations where flammable gases
or vapors are present in the air in sufficient quantities to produce explosive
or ignitable mixtures. Class I locations are further divided into Division 1
and Division 2, depending on the likelihood and duration of the presence of
these materials.
·
Class II: Locations where combustible
dust is present in sufficient quantities to produce explosive or ignitable
mixtures. Class II locations are also divided into Division 1 and Division 2.
·
Class III: Locations where easily
ignitable fibers or materials producing combustible flyings are handled,
stored, or processed. Class III locations are not divided into divisions.
The classification of a hazardous location is
important for determining the appropriate electrical equipment and wiring
methods that can be used in that location. This helps to reduce the risk of
ignition and explosion caused by electrical equipment.
Hazardous area classification has
several advantages in ensuring the safety of personnel and equipment in areas where
flammable or explosive materials are present. Some of the advantages are:
·
Increased safety: Hazardous area classification
helps to identify and evaluate the risks associated with the presence of
flammable or explosive materials. By identifying the hazards, appropriate
safety measures can be implemented to prevent accidents and protect personnel
and equipment.
·
Compliance with regulations: Many
countries have regulations and standards that require hazardous area
classification in certain industries, such as oil and gas or chemical
manufacturing. Compliance with these regulations can help to avoid fines and
legal issues.
·
Cost-effective design: Hazardous
area classification can help to optimize the design of facilities and equipment
by identifying areas that require special protection measures. This can help to
reduce costs associated with over-design or unnecessary safety measures.
·
Effective emergency response: Hazardous
area classification helps to ensure that emergency response plans are
appropriate for the risks present in the area. This can help to minimize the
impact of accidents and improve the effectiveness of response efforts.
·
Improved communication: Hazardous
area classification provides a common language for communication between
designers, engineers, and safety professionals. This can help to ensure that
all parties have a clear understanding of the hazards and appropriate safety
measures.
Overall, hazardous
area classification is a critical process in ensuring the safety of personnel
and equipment in areas where flammable or explosive materials are present. By
properly identifying and evaluating the risks, appropriate safety measures can
be implemented to minimize the risk of accidents and protect personnel and
equipment.
Following
are the general steps for hazardous area classification:
·
All potential leak sources in the area under review are determined like
vents, pump seals, flanges, sample points, instruments, etc.
·
For each potential leak source the grade of release is determined (that
is no. of hours per annum that the leak of flammable material can be expected
to occur.
·
The degree of ventilation in the area around the potential leak source
is established (whether there is adequate ventilation or not).
·
Together it is the grade of release and the degree of ventilation near
the potential leak source that determine the type of hazardous zone around the
leak source.
·
The hazard radius around the potential leak source is determined from
the category of fluid leaking. The hazard radius forms a horizontal circle
around the potential leak and is valid at the elevation of the leak.
·
From the hazard radius and based on whether the release is lighter or
heavier than air and the presence/absence of platforms – the extent of the
three-dimensional hazardous zone around the potential leak source is determined.
·
In a similar way, the hazardous zones from all potential leak sources
are determined and superimposed. This gives contours of hazardous areas for the
concerned facility both in the horizontal and vertical planes.
Hazardous Area Zone Classification
The Zone system
of hazardous area classification, defines the probability of the hazardous
material, gas, or dust, being present in sufficient quantities that can
generate explosive or ignitable mixtures. Refer to Fig.1 which shows the
hazardous area zone classification based on hazardous gas release grade. There
are three zones, Zone 0, Zone 1, and Zone 2..
The grade of
release determines the designation of hazardous zones in the immediate vicinity
of the release. In open-air situations with adequate ventilation, a secondary
grade release will lead to Zone 2, a primary grade release will lead to Zone 1
and a continuous grade release will lead to Zone 0.
 |
Fig. 1:
Hazardous area zones |
Zone
classification will be influenced by ventilation also. IEC 60079-10 categorizes
ventilation degrees as High, medium, and low. Poor ventilation may push the
zone higher by one level. Poor ventilation may result in a more stringent zone
while with high ventilation, the converse will be true. A secondary grade
source of release may give rise to Zone 1 if local ventilation is restricted.
(Example in a sump).
Adequate
Ventilation is defined as ventilation sufficient to avoid a flammable
atmosphere within a sheltered or enclosed area. This will normally be achieved
by a uniform ventilation rate of 12 air changes per hour with no stagnant
areas.
Depending on
the presence of combustible dust or ignitable fibers and flyings, the hazardous
area is classified into three zones: Zone 20, Zone 21, and Zone 22.
In both the
above zone classification, the probability of explosion severity reduces when
we move from zone 0 (or zone 20) to zone 2 (zone 22).
The extent of the Hazardous area
zone
Distance in any
direction from the source of release to the point where the gas/air mixture has
been diluted by air to a value below the lower explosive limit. Refer to Fig. 1
above that shows a typical example of a hazardous area zone extent.
·
Pressure breathing valve (Fig. 1) in the open air, from the
process vessel.
·
A fixed process mixing vessel (Fig. 1); liquids are piped into and out
of the vessel through all-welded pipework flanged at the vessel.
For a given
release the extent of the zone will vary with the vaporizing potential of the
fluid release, the ventilation rate, and the buoyancy of the vapor. The 3rd
edition of IP 15 provides three methods for determining the extent of hazardous
zones:
·
Direct Example Approach– limited to common
facilities in open areas
·
Point Source Approach– release rates are
dependent on process conditions
·
Risk-based Approach– an optional
rigorous methodology that may reduce the hazardous area determined by the point
source approach
Fluid Category of Petroleum Products
The hazard
radius for each point of release is a function of fluid characteristics (vapor forming
potential) under the circumstances of the release, the release rate, and the
rate of vaporization. Hydrocarbon fluids are classified into four fluid
categories based on their vaporizing potential.
|
Fluid Category
|
Description
|
|
A
|
A flammable
liquid that on release would vaporize rapidly and substantially. This
category includes:
(a)Any LPG or lighter flammable liquid;
(b)Any flammable liquid at a temperature sufficient to produce, on release,
more than 40% vol. vaporization with no heat input other than from
surrounding.
|
|
B
|
A flammable
liquid, not in category A, but at a temperature sufficient for boiling to
occur on release.
|
|
C
|
A flammable
liquid, not in Category A and B, but which can on release be at a temperature
above its flash point or form a flammable mist or spray.
|
|
D
|
Flammable gas
or vapor (Natural Gas, Hydrogen, etc)
|
Table:
Fluid Category of Petroleum Products
With the fluid
category leaking from the particular leak source established, now
the extent of vapor travel (radii) around the leak source can be
determined.
Hazardous Area Classification Drawing
The hazardous
area classification drawings are of sufficient scale to show all the main items
of equipment and all the buildings in both plan and elevation. The boundaries
of all hazardous areas and zones present shall be clearly marked using the
clear shading convention for Zone 0, Zone 1, and Zone 2.
It has to be
recognized that however, well-protected electrical equipment may be, there will
always be a residual risk if it is placed in areas where explosive atmospheres
may occur.
Electrical Equipment Selection in Hazardous Area
Classification
Once the
Hazardous Area classification of a facility is determined, it is used as a
basis for selecting suitable electrical equipment. To reach the intended level
of safety, equipment must then be installed correctly, operated within its
design envelope, and maintained adequately.
As a general
policy, electrical equipment should not be located in a hazardous area if it is
possible to place it in a non-hazardous area, nor should be placed in Zone 1 if
it can be placed in Zone 2. The installation and maintenance requirements for
electrical equipment in Zone 1 locations are more stringent than for Zone 2
locations and Zone 0 are more stringent than Zone 1 locations.
ATEX directives
for electrical apparatus for hazardous areas distinguish between two equipment
groups as listed below:
·
Group I – For use in mines (Methane)
·
Group II – Other than mines
Sub-divisions
in group II based on ignition energy requirement
·
IIA – Atmospheres containing acetone, ammonia, ethyl, alcohol, gasoline,
methane, propane, or similar gases
·
IIB – Atmospheres containing ethylene, acetaldehyde, or similar gases
·
IIC – Atmospheres containing acetylene, hydrogen, or similar gases
Standards for Hazardous Area Classification
Codes and standards
define minimum electrical design and installation requirements for electrical
equipment to be used in hazardous areas. The following are some of the codes
and standards that are commonly used for hazardous area classification
·
National Fire Protection Association (NFPA) 70,
National Electric Code (NEC): This standard provides
guidelines for electrical installations in hazardous locations, including
classification of hazardous areas, selection, and installation of electrical
equipment, and wiring methods.
·
American Petroleum Institute (API) RP 500 and RP
505: These standards provide guidance for the classification of
hazardous locations in petroleum facilities, including refineries,
petrochemical plants, and onshore and offshore production facilities.
·
International Electrotechnical Commission (IEC)
60079 series: This series of standards provide guidelines for the design,
installation, and maintenance of electrical equipment in hazardous areas. The
standards cover equipment protection methods, zone classification, and
explosion prevention.
·
Occupational Safety and Health Administration
(OSHA) 29 CFR 1910.307: This regulation provides requirements for
electrical installations in hazardous locations, including classification of
hazardous areas, equipment selection and installation, and wiring methods.
·
Canadian Standards Association (CSA) C22.1,
Canadian Electrical Code: This standard provides requirements for
electrical installations in hazardous locations in Canada, including
classification of hazardous areas, selection, and installation of electrical
equipment, and wiring methods.
·
IECEx Scheme: This is an international
certification scheme for equipment used in explosive atmospheres. The scheme
provides a framework for conformity assessment of equipment and systems,
including testing, certification, and ongoing surveillance.
·
IP 15
·
DEP 80.00.10.10
·
ATEX – EU Directives
The hazardous area
classification and location of equipment must be ascertained before
the choice of appropriately certified electrical equipment is made.
References and Further Reading
·
https://www.emerson.com/documents/automation/product-bulletin-hazardous-area-classifications-protections-en-123358.pdf
·
Mr. Anup Kumar Dey Guidance.
