A fire extinguisher, as covered in Basic Fire Fighting under the STCW 95 guidelines, is a crucial safety device designed to control or extinguish small fires in emergency situations. It is composed of a handheld cylindrical pressure vessel containing a substance that can be discharged to suppress a fire. The materials contained inside may vary based on the type of fire the extinguisher is designed to combat. For instance, common substances include pressurized water, carbon dioxide, dry chemical, or foam. Fire extinguishers are classified into multiple classes, such as A, B, C, D, and K, each designed to suppress specific types of fires. Training under the STCW 95 codes ensures seafarers are familiar with the operation of different types of fire extinguishers, their applications, and maintenance procedures ensuring the safety and integrity of the vessel and crew onboard.

1. Cartridge Operated Dry Chemical Fire Extinguisher: This fire extinguisher uses monoammonium phosphate as an extinguishing agent and is suitable for class A, B, and C fires, such as those started by solid materials, flammable liquids or gases, and electrical appliances. 2. Water and Foam Fire Extinguishers: These types of extinguishers remove heat from the fire and separate the oxygen, which stops the chemical reactions responsible for the fire. They're typically used for class A and class B fires, which involve solid materials and liquids, respectively. 3. Carbon Dioxide Fire Extinguishers: These extinguishers are filled with non-flammable carbon dioxide gas under extreme pressure. They're suitable for class B fires and fires involving electrical equipments (class C), as they starve the fire of oxygen. 4. Wet Chemical Fire Extinguishers: These extinguishers are particularly designed for Class F fires, which are fires fueled by cooking oils or fats. In basic fire fighting STCW 95, you learn how to handle these extinguishers to eliminate a fire without causing it to spread or restart. 5. Halotron Fire Extinguishers: These are clean agent extinguishers which discharge a yellow-colored liquid that leaves no residue. They're commonly used on class B and C fires. They are also safe for use on class A or common combustible fires. In basic fire fighting STCW 95, learners are taught how to use these extinguishers safely and effectively.

One interesting fun fact about fire extinguishers that is covered in the Basic Fire Fighting STCW 95 training is that not all fire extinguishers are created equal or intended to be used on all types of fires. Different fires often require different types of extinguishing agents. For example, while a water-based extinguisher may be effective against a fire fuelled by ordinary combustible materials like wood or paper (Class A fire), it could be incredibly dangerous to use on a fire caused by flammable liquids like gasoline or cooking oil (Class B fire) or an electrical fire (Class C fire). This is because water can spread the flammable liquid and increase the fire's intensity, or potentially conduct electricity in the case of an electrical fire. Understanding the specific purposes and appropriate usage of various types of fire extinguishers is crucial in effectively fighting and controlling fires, and this knowledge could potentially save lives and property.