Fire Engineering - Chapter 02. Classification of Flammable Material, Explosives and Hazardous area classification, Division and Zone

A. Classification of Flammable Material

Class- A

Ordinary combustible solids.

Example: Paper, Wood, Cloth, etc

Class-B

Combustible liquids or liquefiable solids.   

Example: Oils, Paints, Chemicals, Wax, etc.

Class-C    

                   

Combustible gases.   

Examples: L.P.G., Acetylene, Hydrogen, Methane, Natural Gas, etc

Class-D 

                     

Combustible metals.                          

Examples: Magnesium, Sodium, Uranium, Thorium, etc

                                                                                               This classification is as per IS 2190

B.Classification of Explosives

Low explosives 

Low explosives are combustible materials, containing within themselves all oxygen needful for their combustion, which burn but do not explode, and function by producing gas which produces an explosion. Under normal conditions, low explosives undergo deflagration at rates that vary from a few cm/sec, to approximately 400 mtr. /sec. Examples: black powder, smokeless powder.

Primary explosives 

When they are heated or subjected to shock. They do not burn; sometimes they do not even contain the elements necessary for combustion. The materials themselves explode, and the explosion results whether they are confined or not. They differ considerably in their sensitivity to heat, in the amount of heat which they give off, and in their "brisance", that is, in the shock which they produce when they explode. Not all of them are brisant enough to initiate the explosion of a high explosive. Examples: mercury fulminate, lead aside, the lead salts of picric acid 

High explosives

High explosives detonate under the influence of the shock of the explosion of a suitable primary explosive. They do not function by burning; in fact, not all of them are combustible, but most of them can be ignited by a flame and in small amount generally burn tranquilly and can be extinguished easily. If heated to a high temperature by external heat or by their own combustion, they sometimes explode. They differ from primary explosives in not being exploded readily by heat or by shock, and generally in being more brisant and powerful. They exert a mechanical effect upon whatever is near them when they explode, whether they are confined or not.

  

C. Hazardous area classification, Division and Zone

Class I, Division 1

Ignitable concentrations of flammable gases or vapors may exist under normal operating conditions.

Ignitable concentrations of such gases or vapors may exist frequently because of repair or maintenance operations or because of leakage.

Breakdown or faulty operation of equipment or processes might release ignitable concentrations of flammable gases or vapors, and might also cause simultaneous failure of electric equipment.

Class I, Division 2

Volatile flammable liquids or flammable gases are handled, processed or used, but the hazardous liquids, vapors or gases will normally be confined within closed containers or closed systems from which they can escape only in the event of accidental rupture or breakdown of such containers or systems, or as a result of abnormal operation of equipment.

Ignitable concentrations of gases or vapors are normally prevented by positive mechanical ventilation, and which might become hazardous through failure or abnormal operations of the ventilating equipment.

Adjacent to a Class I, Division 1 location, and to which ignitable concentrations of gases or vapors might occasionally be communicated unless such communication is prevented by adequate positive-pressure ventilation from a source of clean air, and effective safeguards against ventilation failure are provided.

Class I, Zone 0

Ignitable concentrations of flammable gases or vapors are present continuously.

Ignitable concentrations of flammable gases or vapors are present for long periods of time.

Class I, Zone 1

Ignitable concentrations of flammable gases or vapors are likely to exist under normal operating conditions.

Ignitable concentrations of flammable gases or vapors may exist frequently because of repair or maintenance operations or because of leakage.

Equipment is operated or processes are carried on of such a nature that equipment breakdown or faulty operations could result in the release of ignitable concentrations of flammable gases or vapors and also cause simultaneous failure of electric equipment in a manner that would cause the electric equipment to become a source of ignition.

A location that is adjacent to a Class I, Zone 0 location from which ignitable concentrations of vapors could be communicated, unless communication is prevented by adequate positive pressure ventilation from a source of clean air and effective safeguards against ventilation failure are provided.

Class I, Zone 2

Ignitable concentrations of flammable gases or vapors are not likely to occur in normal operation and if they do occur will exist only for a short period.

Volatile flammable liquids, flammable gases or flammable vapors are handled, processed or used, but in which the liquids, gases or vapors are normally confined within closed containers or closed systems from which they can escape only as a result of accidental rupture or breakdown of the containers or system or as the result of the abnormal operation of the equipment with which the liquids or gases are handled, processed or used.

Ignitable concentrations of flammable gases or vapors normally are prevented by positive mechanical ventilation, but which may become hazardous as the result of failure or abnormal operation of the ventilation equipment.

A location that is adjacent to a Class I, Zone 1 location, from which ignitable concentrations of flammable gases or vapors could be communicated, unless such communication is prevented by adequate positive-pressure ventilation from a source of clean air, and effective safeguards against ventilation failure are provided.

Class II, Division 1

Where combustible dust is present in the air under normal operating conditions in such a quantity as to produce explosive or ignitable mixtures. This could be on a continuous, intermittent or periodic basis.

Where an ignitable and/or explosive mixture could be produced if a mechanical failure or abnormal machinery operation occurs.

Where electrically conductive dusts in hazardous concentrations are present.

Class II, Division 2

Combustible dust will not normally be in suspension in the air in quantities sufficient to produce explosive or ignitable mixtures, and dust accumulations will normally be insufficient to interfere with the normal operation of electric equipment or other apparatus, but combustible dust may be in suspension in the air as a result of infrequent malfunctioning of handling or processing equipment.

Resulting combustible dust accumulations on, in or in the vicinity of the electric equipment may be sufficient to interfere with the safe dissipation of heat from electric equipment or may be ignitable by abnormal operation or failure of electric equipment.

Class III, Division 1

Easily ignitable fibers or materials producing combustible flying are handled, manufactured or used.

Class III, Division 2

Easily ignitable fibers are stored or handled, other than in the process of manufacture.