Hazardous Area Classification is a critical subject in the safety role. Most of the time it is confused with the activity and responsibility. This is a vital element that needs the EHS head's attention to ensure a safe operation in the plant premises. It is very important that both electrical and chemical expertise work together for hazardous area classification and eliminate the risk.


Lets us carefully explore different myths and challenges in the Hazardous Area Classification.


1Q.What is the guidance on the classification of hazardous areas?

During normal and abnormal operations, electrical and electronic equipment such as motors, generators, fuses, switches, relays, circuit breakers, transformers, solenoids, and resistors produce the amount of heat, arcing, and sparking that causes a fire or explosion in industries, factories, or other locations where chemicals are manufactured, processed, or used.

Because of the presence of flammable, ignitable gases, combustible or liquids, dust, fumes, or fiber’s / flying's, classified hazardous places may present fire or explosion threats under abnormal or normal conditions.

The explosion risks are different from a high current arc flash type of explosion that can be created by a line fault. Three factors combine to cause an environmental explosion: energy, fuel, and oxygen.

FUEL +OXYGEN (In right proportion) => Heated.



Hazardous area classification; The evaluation and classification of hazardous locations using scientific and engineering principles, within facilities When electrical equipment is to be installed In about a hazardous area.

It is intended for application in all industries there may be a risk due to the presence of vapor or flammable gas mixed with air under normal atmospheric  conditions.

The notional partition of a facility into zones with a high chance of the presence of an explosive gas/air mixture is one of the goals of the area categorization. Medium, low, or extremely low levels are considered inconsequential. The region categorization developed in this manner serves as a foundation for selecting electrical apparatus that is adequately protected.

Explosive Gas Atmosphere: A mixture with air, under normal atmospheric conditions, of flammable material s in the form of gas, vapor, or mist, ignition in which, after combustion spreads throughout the unconsumed mixture.

NOTES

I . This definition specifically excludes dust and fibers in suspension 10 air.

2. Although a mixture that has a concentration above the upper explosive limit (UEL) is not an explosive gas atmosphere. In certain cases, for area classification purposes it is advisable to consider it an explosive gas atmosphere.

Hazardous Area – The area in which an explosive gas atmosphere is present and likely to be present, in quantities such as to the required special precautions for the installation and construction, use of electrical apparatus.

Non-hazardous Area – The area in which an explosive gas atmosphere is not to be present in expected quantities such as to require special precautions for the installation and construction use of electrical apparatus.

Flash Point - The temperature at which a liquid produces so much vapor that the vapor, when mixed with air, creates an ignitable combination and produces a transient flash when a small pilot flame is applied under-defined test conditions.

Ignition Temperature - When the technique of measuring ignition temperatures described in the applicable Indian Standard is followed, the lowest temperature at which ignition occurs in a mixture of explosive gas and air.

Source of Release - A source of release is a point or location from which gas, vapor, mist, or liquid may be released into the atmosphere so that a hazardous atmosphere could be formed.

Zones - Hazardous areas are classified based on zones upon the frequency of the appearance and the duration of an explosive gas atmosphere follow below.

Zone 0 - an area in which place an explosive atmosphere is present continuously or for long periods or frequently.

Zone 1 – The area where an explosive atmosphere is expected to occur occasionally or at irregular intervals during normal operation.

 Zone 2 - a place where an explosive atmosphere is unlikely to arise during regular operations, but if it does, it will only last a brief time.

 

Explosive Limit:

Lower Explosive Limit (LEL) – The concentration of gases, vapor, or mist in the air. Below a lower limit which explosive gas atmosphere will not be formed.

Upper Explosive Limit (UEL) –The concentration of flammable gases, vapor, or mist in the air. Above an upper limit which explosive gas atmosphere will not be formed.

GENERAL HAC

Area classification is the method of analyzing and classifying the environment in which the explosive gas atmospheres may occur to allow the proper selection of electrical apparatus to be installed in that environment.

 


The necessary to use electrical apparatus in an environment in which there may be an explosive gas atmosphere.

a) Eliminate of explosive gas atmosphere occurring around the source of ignition:

b) Eliminate the source of ignition.

Ignition sources include heat (e.g., failed pump bearings), open flames (e.g., furnaces), faulty electrical devices, static electricity, and natural causes (e.g., lightning).

To apply this approach the first step is to assess the likelihood of an explosive gas atmosphere occurring in accordance with the definitions of Zone 0, Zone I and Zone 2.

CLASSIFICATIONOF AN HAZARDOUS AREA

As to determine the type of electrical installation are to a particular situation. the hazardous areas namely have been divided into three zones.  Zone 0. Zone I and Zone 2. to the degree of probability of the presence of a hazardous atmosphere.


Zone 0 -Areas Explosive atmosphere for more than 1000h/yr

Examples are vapor space above closed process vessels, storage tanks or closed containers, areas containing open tanks of volatile. flammable liquid.

Zone 1 -Areas in Zone 1 When any of the following conditions exist for more than 10, but fewer than 1000 hours per year, Zone I locations can be identified. The following conditions exist:

a) Flammable gas or vapor concentration is likely to exist in the air under normal

Operating conditions;

b) The Flammable atmospheric concentration is likely to occur more frequently because of maintenance and repairs or leakage;

c) Flammable liquid or vapor piping system is in an inadequately ventilated area.

d) The area below the surrounding elevation or grade is such that flammable liquids or vapors may accumulate.

This is classification typically includes:

a) Where an Imperfectly fitting peripheral seal on the floating roof of tanks;

b) The Interiors of the refrigerators and freezers in which volatile flammable materials are stored that in lightly or easily ruptured containers;

C)  LPG cylinder filling and cylinder evacuation area.

Zone 2 -Areas Explosive atmosphere for less than 10h/yr, but still sufficiently likely as to require controls over ignition sources.

Zone 2: When any of the following conditions occur, Zone 2 -locations can be distinguished:

a) The system handling flammable liquid or vapor is in an adequately ventilated area and is so designed and operated that the explosive or ignitable liquids. Vapors or gases are generally contained within closed containers or closed systems, from which they can only escape under unusual circumstances such as explosions.

Accidental failure of a gasket or packing:

b) The flammable vapors can be conducted to the location as through trenches, pipes, or ducts:

c) Locations adjacent to zone I areas: and

d) In case of use of positive mechanical ventilation, as the failure or abnormal

Operation of ventilating equipment can permit atmospheric vapor mixtures to build up to flammable concentrations.

 Areas not classified (safe installation)

The following locations are to be considered safe from the point of view of electrical installation:

a) The Areas where the piping system is without valves. fittings, flanges, or Appurtenances;

b) Areas where flammable liquids or vapors are transported only in suitable containers or vessels:

c) Areas where the permanent ignition sources are present like areas where combustion gases are present, for example, flare pits, flare tips, other open flames, and hot surfaces;

Flammable materials, such as fiberboard, wood, and foil, ignite or flame instantly when they come into touch with fire or a high the temperature in the air, and continue to burn or gently flame after they are extinguished.

These are divided into three classes, as follows,

a) Class A: Flammable liquids having flash points below 23°C

b) Class B: Flammable liquids having flash point 23°C and above but below 65°C

c) Class C: Flammable liquids with a flashpoint of 65°C or higher but less than 93°C.

At normal atmospheric temperatures, the saturated vapors of these flammable liquids have densities that are less than 1.5 times that of air.

Class A -When released in big amounts into the open, liquids can produce a lot of vapor.

 2Q.What are the characteristics of flammable liquids, vapors, and gases?

 CHARACTERISTICS OF FLAMMABLE LIQUIDS, VAPOURS, AND GASES:

The physical properties of these materials that have to be considered when the degree of risk appropriate to a particular application or installation is being assessed are defined Properties of The materials listed are for materials in their purest form; however, if there are impurities or mixes of elements, the materials listed may alter. Expert guidance should be sought in such circumstances. For descriptions of the concepts of temperature classification and apparatus, grouping refers to IS /IEC 60079-0.

 FLASHPOINT; An flash point of a material is the minimum temperature at which it gives sufficient vapor to form a flammable mixture with air near to the surface of the material or within flashpoint determination.

Materials Having High Flash Points: there are Some materials have such high flash points that they do not form flammable mixtures with air at the normal ambient temperatures, even though it when exposed to the sun in tropical locations. where should not be discounted as ignition hazards, since the exposure to a suitably hot surface or use of the material at a temperature above its flash point may create a flammable mixture normally which maybe ignited by the same hot surface or an alternative ignition source. It is necessary to consider the limitation surface temperatures even when materials are of a high flash point is being processed.

LIMITS OF FLAMMABILITY:

All combustible gases and vapors have flammable limits, which define the range in which the gas or vapor coupled with air can maintain flame propagation. The lower flammable limit (LFL) and the upper flammable limit (UFL) are the two limitations usually expressed as percentages of the material mixed with air by volume. They are also sometimes expressed as milligrams of material per liter of air. Where  appropriate, both sets of data are included in IS/IEC 60079-20.

FLAMMABILITY RANGE

The range of gas or vapor mixtures with air between the flammable limits over which the gas/air mixture is continuously flammable is called the flammability

Range. Gas/air mixtures outside this range are, therefore, non-flammable under normal atmospheric conditions. Concentrations above the UFL cannot be regulated in free atmospheric conditions, and additional dilution with air will result in combinations inside the flammability range.

The requirements for the zone classification system of an alternative to the division classification system covered in Article 500 for electronic and as electrical equipment and wiring for all voltages in Class I, Zone 0, Zone 1, and Zone 2 hazardous (classified) locations where fire or explosion hazards may exist due to flammable gases, liquids, or vapors.

3Q. what constitutes a hazardous location?

The Ignitable concentrations of flammable vapors, gases, liquids or combustible dust or fibers which may be present and that are flammable or combustible concentration or quantity is present in -NEC Article 500 NEC Hazardous Area Classifications:

Class I location: “When flammable gases or vapors are present or may be present in sufficient amounts in the air to form explosive or ignitable mixtures.”

Class I Division 1: A location at which ignitable concentrations of flammable vapors or gases can exist under normal operating conditions, or in which flammable concentrations of such vapors or gases may exist often as a result of leaks during repair or maintenance operations; or in which breakdown or faulty operation of equipment processes might release ignitable concentrations of flammable vapors or gases, and also might cause simultaneous failure of electric equipment.

 Class I Division 2: The location in which volatile flammable gases or flammable liquids are handled, or used processed,  but in which the vapors, liquids, or gases will be normally closed in containers with closed systems.it can escape only in case of the breakdown or accidental containers or systems and the abnormal Operation of the equipment that is which ignitable vapors and gases are prevented by positive mechanical ventilation, and which could become hazardous if the ventilating equipment fails or operates abnormally, and it is located near a Class I Division 1 location, Unless such communication is avoided by positive-pressure ventilation from a supply of clean air, ignitable quantities of vapors or gases may be communicated, and robust precautions against ventilation failure are provided.

Class II Locations. A Class II location is that Hazardous because of the presence of combustible dust.

Class II, Division 1; The location in which combustible dust is the air under operating conditions normally in the quantities that are sufficient to produce explosive or ignitable mixtures.

 Where abnormal operation or mechanical failure of equipment or machinery might cause explosive or ignitable mixtures are to be produced, might also provide a source of ignition through the simultaneous failure of equipment electrical through the operation of protection devices, or which the Group E combustible dust may be present in the quantities adequate to be hazardous.

Class II, Division 2:  The location In which combustible dust due to abnormal operations may be present in the air in quantities sufficient to produce explosive or ignitable mixtures; or combustible dust accumulations present, but in most cases aren't enough to cause problems with the normal flow of things. Operation of equipment or other apparatus, as a result of infrequent malfunctioning of handling processing equipment, become suspended in the air or which combustible dust accumulations on in the vicinity of the electrical equipment could be sufficient to interfere with safe dissipation of heat from electrical equipment, be ignitable by abnormal operation or failure of electrical equipment.

Class III locations

Those that are hazardous because of the presence of easily ignitable fibres or where materials creating combustible fibres are mentioned are those in which such fibres or flyings are not likely to be suspended in the air in sufficient quantities to generate ignitable mixes.

Material Groups: The purposes for testing and approval, and of area classification, air mixtures various (not oxygen-enriched) are shall be grouped accordance with from NEC 500.6(A) and (B).

Electrical Equipment identified for a specific gas, dust, vapor, or fiber/ flying. This is based on the characteristics of the materials. Facilities are available for testing and identifying electrical equipment for use in the various atmospheric groups.

The explosion of air mixtures of vapors or gases varies with the specific material involved. Class I locations, Groups A, B, C, and D, and the classification involves. 

 A Flammable Vapors and gases having flashpoint at a temperature  which a particular organic compound gives off sufficient vapor to ignite in air below 100°F

GROUP B: With a minimum igniting current ratio, flammable liquids, gases created vapor or combustible liquids mixed with air produced vapor that might explode (MIC ratio)of less than or equal to 0.40 and an MESG value of less than or equal to 0.45 mm.

GROUP C: Flammable liquids and gases that produce vapor, or combustible liquids that produce vapor mixed with air that can burn, have either a maximum experimental safe gap MESG value greater than 0.45 mm. have a minimum igniting current ratio (MIC ratio) greater than 0.40 and are less than or equal to 0.75 mm less than or equal to 0.80.

Group D: Flammable gas, flammable liquid–produced vapor, or combustible liquid–produced vapor mixed with air that may burn or explode and a minimum igniting current (MIC) ratio of 0.80 or a maximum experimental safe gap (MESG) of 0.75 mm

The Examples are:

•Group A: Acetylene,

•Group B:  Hydrogen,

•Group C: Ethylene,

•Group D: Propane.

NFPA497 Electrical Installations in Flammable Liquids, Gases, or Vapor Atmospheres.

NEC Codes for Ignition Temperatures 500.8 (C) Maximum Surface Temperature (MST) Classification



The marking must describe the particular range of ambient temperatures in degrees Celsius, from -40°C to +40°C. The symbol "Ta" or "Tamb" must be included in the marking.

For Class I, Zone 0, 1, and 2, Article 505 NEC specifies the requirements for the zone classification system as an alternative to the division classification system covered in Article 500. Flameproof [505.2] refers to keeping flames contained within the enclosure rather than whether or not something is combustible.

Encapsulation The letter "m" is encapsulated. Electrical parts that could spark or heat an explosive atmosphere are contained in a compound that prevents the explosive atmosphere from being ignited.

Note: The Encapsulation is designated as a “ma” type of protection for usage in Zone 0 environments.

For usage in Zone 1 sites, encapsulation is labeled as a kind of protection "m" or "mb."

Encapsulation is a type of protection categorized as “mc” for usage in Zone 2 environments.

The letter “d” stands for flameproof. The enclosure will withstand an internal explosion of a flammable mixture that has penetrated into the interior through any joints or structural openings in the enclosure of an external explosive gas atmosphere consisting of one or more of the gases or vapors for which it is designed, without suffering damage or causing ignition.

Intrinsic safety is categorized as a type of protection “ia” for usage in Zone 0 environments.

Intrinsic safety is a type of protection labeled as “ib” for use in Zone 1 environments.

Intrinsic safety is a type of protection labeled as “ic” for use in Zone 2 environments.

Informational Note: Intrinsically safe associated apparatus, denoted by the letters [ia], [ib], or [ic], is connected to intrinsically safe apparatus (designated by the letters “ia,” “ib,” or “ic,” respectively), but is located outside the hazardous (classified) location unless it is also protected by another type of protection (such as flameproof).

Increased Safety “e”. Additional steps are taken to provide improved security against the potential of excessive temperatures and the development of arcs and sparks in electrical equipment that does not create arcs or sparks in normal service and under specified abnormal situations.

Intrinsic Safety “i”. The letter I stands for "intrinsic safety." Under stipulated test conditions, any spark or heat effect is incapable of triggering ignition of a mixture of flammable or combustible materials in the air.

Oil Immersion “o”. “o” for oil immersion. Electrical equipment is immersed in a protective liquid to prevent an explosive environment from igniting above the liquid or outside the enclosure.

Powder Filling “q”. Filling “q” with powder To avoid the ignition of an external explosive atmosphere, electrical parts capable of igniting an explosive atmosphere are locked in position and entirely covered with filler material (glass or quartz powder).

Pressurization “p”. “p” stands for “pressurization.” The technique of guarding against the intrusion of the external atmosphere, which may be explosive, into an enclosure by maintaining a protective gas therein at a pressure above that of the external atmosphere, is used to protect electrical equipment.

Type of Protection “n”. “n” is the type of protection. Electrical equipment is not capable of igniting a surrounding explosive gas atmosphere in normal operation, and a failure capable of triggering ignition is unlikely to occur.

 4Q. what is an exhaust ventilation system?

Occupational Health and Environmental Control of ventilation

Exhaust ventilation systems: The fundamentals governing the design and operation of local exhaust systems, Z9.2–1960, and ANSI Z33.1–1961, which are incorporated by reference as spelled down in 1910. 6 must be observed when designing, installing, inspecting, and maintaining exhaust systems.

(a) When dust leaks are discovered, they must be repaired as quickly as feasible.

(b) When the installation is complete, and on a regular basis thereafter, the static pressure drop at the exhaust ducts leading from the equipment must be tested to ensure continuing satisfactory operation.

The system must be cleaned and returned to a normal working state whenever there is a significant change in the pressure drop, which signals a partial blockage.  Clean air.  Air that is so pure that it will not damage or pain a person if inhaled for long periods of time.

 Dust collector. A device (or a set of devices) that separates dust from the air that an exhaust ventilation system handles.

(ii) In installations where the abrasive is recirculated, an abrasive separator should be used instead of the blasting enclosure's exhaust ventilation system to remove particles from the wasted abrasive. For this reason, an abrasive separator must be provided.

(iii) Blast cleaning exhaust air must be collected and discharged through dust collection equipment. Dust collectors must be installed so that accumulated dust can be emptied and removed without polluting other areas of work.

 Personal protective equipment. (i) Employers are only allowed to use respirators.

 National Institute for Occupational Safety and Health To protect workers against dust, the Occupational Safety and Health Administration (NIOSH) has established 42 CFR part 84.During the abrasive-blasting process.

(ii) All abrasive-blasting operators must use abrasive-blasting respirators:

(a) When using silica sand in manual blasting operations where the nozzle and blast are not physically separated from the operator in an exhaust ventilated enclosure, or

(b) In manual blasting procedures involving silica sand, if the nozzle and blast are not physically separated from the operator in an exhaust ventilated enclosure.

(c) When the nozzle and blast are not physically separated from the operator in an exhaust-ventilated enclosure, harmful dust concentrations disseminated by abrasive blasting may exceed the limits stated in 1910.1000.

NIOSH must approve the respirators used for protection against the specific type of dust encountered under 42 CFR part 84

 (a) When non-silica abrasives are used on low-toxic materials, dust-filter respirators can be employed to protect the operator of outside abrasive-blasting activities.

(a) Where silica sand is used as the blasting abrasive or poisonous materials are blasted, dust-filter respirators should not be employed for continuous protection.

(iv)  Employers must create a respiratory protection program in compliance with 29 CFR 1910.134 for employees who wear respirators as required by this section.

(v) Heavy canvas or leather gloves and aprons, or equivalent protection, must be worn by operators to protect them from abrasives. Where large pieces of work are handled, safety shoes must be worn to safeguard against foot harm.

(a) Safety shoes must meet the standards of the Z41.1–1967 American National Standard for Men's Safety-Toe Footwear, which is incorporated by reference as required in 1910.6.

(b) Eye and face protection equipment shall be provided to the operator and any other personnel operating in the area of abrasive blasting when the respirator design does not offer such protection.

Air supply and air compressors: The air provided to abrasive-blasting respirators must be free of dangerous quantities of dusts, mists, or noxious gases, and must fulfill the requirements for supplied-air quality and use established in 29 CFR 1910.134.


There is much more to this vast subject and which needs an expert analysis and risk assessment. Keep exploring our articles for more information on safety.