The National Fire Protection Association (NFPA) categorizes fires by class.
The relevant graphics and letter designations that accompany these classes are specified by NFPA 10, the standard for portable fire extinguishers.
CLASS A FIRES
Class A fires (designation symbol is a green triangle) involve ordinary combustible materials like paper, wood and fabrics, rubber. Most of the times, this type of fire is effectively quenched by water or insulating by other suitable chemical agent
CLASS B FIRES
Class B fires (designation symbol is a red square) mostly involve flammable liquids (like gasoline, oils, greases, tars, paints etc) and flammable gases. Dry chemicals and carbon dioxide are typically used to extinguish these fires.
CLASS C FIRES
Class C fires (designation symbol is a blue circle) involve live electrical equipment like motors, generators and other appliances. For safety reasons, nonconducting extinguishing agents such as dry chemicals or carbon dioxide are usually used to put out these fire.
CLASS D FIRES
Class D fires (designation symbol is a yellow decagon) involve combustible metals such as magnesium, sodium, lithium potassium etc. Sodium carbonate, graphite, bicarbonate, sodium chloride, and salt-based chemicals extinguish these fires.
CLASS K FIRES
Class K fires are fires in cooking appliances that involve combustible cooking media (vegetable, animal oils or fats).
SYMBOLS FOR FIRE CLASSES DESIGNATION
Picture 1 - Fire classes designation
CLASSIFICATIONS OF HAZARDS
In accordance with NFPA, areas are typically classified as being light (low) hazard, ordinary (moderate) hazard, or extra (high) hazard.
Light (low) hazard areas are locations where the quantity and combustibility of Class A combustibles and Class B flammables is low. In these areas, expected fires have relatively low rates of heat release. Light hazard areas may include offices, classrooms, meeting rooms etc.
Ordinary (moderate) hazard areas are locations where the quantity and combustibility of Class A combustible materials and Class B flammables is moderate. Fires with moderate rates of heat release are expected in these areas. Ordinary hazard locations could be offices, malls, light manufacturing or research operations, parking garages, workshops, or maintenance/service areas.
Extra (high) hazard areas are locations where the quantity and combustibility of Class A combustible material is high or where high amounts of Class B flammables are present. Quickly developing fires with high rates of heat release are expected. These locations could be sites for cars repair, aircraft and boat servicing, painting, dipping, and coating, storage areas (tanks, containers etc).