Fire hazardous area classification in O&GC

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.