E ach room, section and area within a facility where chemicals are processed or utilized are evaluated individually and assigned a Class I, II or III, Division 1 or 2, Group A, B, C, D, E, F or G classification based on several criteria: 1 the types of chemicals that are present; 2 the probability of their presence during normal and abnormal operation; 3 the volume being processed or utilized; and 4 the physical properties concentrations, densities, pressures, temperatures and flows that are observed during normal and abnormal plant operating conditions.
Class I Locations. A Class I location is a location where fire or explosion hazards may exist due to flammable gases, vapors or flammable liquids. NFPA reference 2 provides recommended practice for the classification of Class I hazardous classified locations. Figure 1 below is an example of an area classification diagram for a Class I area. Class I Division 1. A Class I, Division 1 location is a location in which ignitable concentrations of flammable gases, flammable liquid-produced vapors, or combustible liquid-produced vapors may exist under normal operating conditions.
Class I Division 2. A Class I, Division 2 location is a location in which ignitable concentrations of flammable gases, flammable liquid-produced vapors, or combustible liquid-produced vapors may exist under abnormal operating conditions. Class I Group Designations. C lass I flammable gases, vapors and liquids are grouped into one of four 4 groups Groups A, B, C or D based on their physical properties and the ease in which they can be ignited.
Table 4. Acetylene is an example of a Group A flammable gas. Hydrogen is an example of a Group B flammable gas. Carbon Monoxide is an example of a Group C flammable gas. Gasoline is an example of a Group D flammable liquid. Class II Locations. A Class II location is a location where fire or explosion hazards may exist due to combustible dust. Figure 2 below is an example of an area classification diagram for a Class II area.
Class II Division 1. A Class II, Division 1 location is a location in which combustible dust is in the air under normal operating conditions in quantities sufficient to produce explosive or ignitable mixtures, or where accumulations on electrical equipment are sufficient to interfere with the safe dissipation of heat generated by the equipment.
Class II Division 2. A Class II, Division 2 location is a location in which combustible dust due to abnormal operating conditions may be present in the air in quantities sufficient to produce explosive or ignitable mixtures, or where accumulations on electrical equipment may be sufficient to interfere with the safe dissipation of heat generated by the equipment.
Class II Group Designations. C lass II combustible dusts are grouped into one of three 3 groups Groups E, F or G based on their physical properties and the ease in which they can be ignited. Table 5. Titanium is an example of a Group E combustible dust.
Zone 2 is a place in which an explosive atmosphere is not likely to occur in normal operation but, if it does occur, will persist for a short period only. These areas only become hazardous in case of an accident or some unusual operating condition. To make this even easier to understand, take a look at the diagram of a typical petrol station below where we have identified the areas that are classified as Zone 0, Zone 1 and Zone 2.
Whenever you are filling up your tank you are standing in a Zone 1 hazardous area. That is why the use of mobile phones on petrol forecourts are banned. The colour of the luminaire body indicates the level of protection.
Zone 1 fittings are supplied as silver, Zone 2 as dark grey and industrial fittings as white. All emergency versions, whether Zone 1 or Zone 2 can also be easily visually identified by their red end cap, encapsulating the emergency battery back-up. You can change your settings here at any time. Your browser is out of date Internet Explorer is no longer supported.
Cookie consent s We use cookies on our website to personalize content and ads, to provide social media features and to analyze traffic to our website. Accept all Settings. Ensure safety and compliance with hazardous area classification By identifying the areas susceptible to fire or explosion, hazardous area classification HAC assists industries in reducing their chances of experiencing an incident resulting in damage to property and potential injury or loss of life.
In nine steps to your hazardous area classification. Contact Process Safety. Accept Cookies Open video external. There are varying types of equipment that can be used within these hazardous area zones to ensure that the potential for an explosion is removed or greatly reduced.
This equipment must be designed and manufactured in accordance with particular construction parameters known as protection concepts. Essentially these concepts fall under four main methods. These methods are detailed below along with a brief description of some of the concepts:. Ex i is an explosion protection concept in which the electrical energy within the equipment is restricted to a level which is below that what may cause an ignition or to limit the heating of the surface of the hazardous area equipment.
The equipment that may cause an explosion is contained within an enclosure which can withstand the force of an explosion and prevent transmission to the outside hazardous atmosphere.
The Ex d flameproof method of explosion protection also prevents the hazardous atmosphere from entering the enclosure and coming into contact with equipment. Ex m is an explosion protection concept where by equipment that could potentially cause an ignition is encapsulated within a compound or resin so as to prevent contact with the explosive atmosphere.
The concept also limits the surface temperature of the equipment under normal operating conditions. Ex e is an explosion protection concept applied to the installation to ensure increased security against the possibility of excessive temperatures and sparks from hazardous area electrical equipment.
Equipment that normally causes sparks is excluded from use within this method of protection. One process ensures that the pressure inside an Ex p enclosure is sufficient to prevent the entrance of a flammable gas, vapour, dust, or fibre and prevent a possible ignition.
Another process maintains a constant flow of air or an inert gas to dilute to take away any potentially explosive atmosphere. All equipment that has the potential to arc and potentially cause an ignition is immersed in a protective liquid or oil. The oil provides an insulating method to prevent ignition.
All equipment that has the potential to arc is contained within an enclosure filled with quartz or glass powder particles. The powder filling prevents the possibility of an ignition. A type of explosion protection where precautions are taken so that hazardous area electrical equipment that has the potential to arc is not capable of igniting a surrounding explosive atmosphere. This can be further categorised as follows:. Ex nA -Where components used in construction are non-sparking Ex nC -Where components used in construction are non-incendive Ex nR — Where components used are tightly enclosed to restrict the breathing and prevent ignition Ex nL -Where components used in construction do not contain enough energy to cause an ignition.
Ex s Special This method of explosion protection, as its name indicates, has no specific parameters or construction rules. In essence it is any method of explosion protection which can provide a pre-determined level of safety to ensure that there is no potential for an ignition.
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