|Understanding Fire Extinguisher Ratings|
The ratings assigned to different fire extinguishers have a purpose of communicating the effectiveness of an individual fire extinguisher in putting out a fire. The rating itself have a reference to the type of fire in which they can be used and a numerical evaluation on the effectiveness against that type of fire. The combination of the letters and numbers associated with those letters are the indicator of the size/intensity of the fire it can be effective against.
Different types of fires are classified by different letters primarily relating to the fuel associated with each fire. Most fire extinguishers are effective against multiple classifications of fires and have separate rating associated with each type of fire. As a rule of thumb, the larger the number, the more effective that fire extinguisher can be against a given fire and the larger fire it can handle.
The number associated with the classification rating on the fire extinguishers is a direct relationship in the overall effectiveness of that fire extinguisher against that particular class of fire. There is said to be a relationship in the area of a fire that a fire extinguisher can extinguish and it rating. That relationship is 0.1 meters of fire per rating for class A fires. In other words a 30-A rating would typically test out to handle a fire of 3 square meters. The ratings in class B and C fires are more related to the square footage and a different type of fire. Therefore, there is no good comparison between class A and class B or C fires. The rule of thumb still applies to both in the larger the number, the more effective.
The rating of a fire extinguisher is a tested objective evaluation done by Underwriters Laboratories. The things that directly affect the ratings of the fire extinguisher are primarily the size or mass of the agent which is expelled, the speed of agent expulsion, and the agent effectiveness itself.
Fire Classification Desriptions
Class A - Solid materials such as wood, card, paper, fabric, etc.
Class B - Flammable liquids including kerosene, oils, petrol, paints, diesel, etc.
Class C - Electrical fires
Class D - Combustible metals or alloys, such as potassium, magnesium or titanium.
Fire Extinguisher Ratings - Commentary
While understanding fire classes and potential fuels for fires which you are at risk is very important, it is also good to consider the cleanup or damage that any agent can cause. The quality choice of a fire extinguisher considers both effectiveness and the end result of cleanup and damage to the materials affected.