Final answer:
An AFFF portable extinguisher is intended for use on Class B fires, which involve flammable liquids like fuels and oils. The extinguishing agent creates a barrier between the oxygen and the fuel, effectively extinguishing the fire.
Step-by-step explanation:
An AFFF portable extinguisher is specifically designed to tackle fires involving organic liquids, such as fuels and oils, which are classified as Class B fires. The AFFF, which stands for Aqueous Film Forming Foam, creates a barrier between the fuel and the fire, effectively cutting off the oxygen supply and helping to prevent re-ignition by cooling the fuel. This fluorinated solution is able to spread across the burning surface to smother and extinguish the fire.
These extinguishers are particularly effective on fires involving materials like dry-cleaning solvents and waste oils, which have flash points below 60°C. However, despite their effectiveness, some older fire extinguishing agents, like those containing certain fluorinated compounds, are no longer recommended due to environmental considerations. Instead, fire extinguisher systems may include foaming agents that are more environmentally friendly.
It's important to note that while AFFF extinguishers are suitable for Class B fires, they are not the right choice for all types of fires. They should not be used on Class A fires (ordinary combustibles like wood and paper) without the foam having a rating for this class as well, or on Class C fires (electrical equipment) as the water content can conduct electricity, nor Class D fires (combustible metals) or Class K fires (cooking oils and fats).