In the previous article we learned about the various types of fires and their dedicated fire extinguishers.Using a wrong fire extinguisher for a particular fire might make the situation worse or won’t produce any results. Also, neither all the portable fire extinguishers have the same construction nor the method to operate them is the same. In this article, we will learn about the construction and working of the two types of fire extinguishers - carbon dioxide and water extinguisher and chemical foam extinguisher. Both these types are just variations of soda-acid extinguisher, having different constituents. Though both the extinguishers are similar in many ways, they are used for different types of fires.
Carbon Dioxide and Water Extinguisher
This is also a Type A fire extinguisher. It is similar to soda-acid extinguisher as it also uses carbon dioxide to push the water out of the cylinder.The only difference is that there is no usage of chemicals. The main advantage of this type of extinguisher is that the discharge water does not contain any chemical residue.
The construction is almost similar to soda-acid extinguisher. The cylindrical body is made of steel. The striker pin is connected to a container inside the cylinder, which contains pressurized carbon dioxide gas. The container or CO2 cartridge is suspended from the center. Rest of the cylinder is filled with water .
When the extinguisher has to be operated, the striker pin is pushed. The sudden force pierces the carbon dioxide cartridge seal and releases the gas into the cylinder. The pressurized gas expels the water out of the nozzle or hose connection.
Chemical foam Extinguisher
This is a type B fire extinguisher whose construction is similar to that of soda-acid extinguisher. The internal construction is also similar with two different containers filled with different chemicals. The shell along with the containers are hydraulically tested before fitting.
The cylinder contains a long inner container which is suspended from the neck ring and is filled with aluminum sulphate solution. This long container is contained in an outer container filled with sodium bicarbonate solution. A lead disc, fixed on the top of the inner container acts like a stopping pin. This eradicates the need for internal pipe.
The initiating system of this extinguisher is different than those of the other types.In order to activate the extinguisher, it has be to inverted and shaken. The movement loosens and dislodges the disk, facilitating the mixing of both the chemicals. The chemical reaction takes place in a much similar way to that of soda-acid extinguisher, but the action is much slower. The extinguisher initiates with bubble formation which later gets converted to foam. The nature of the foam depends on the foam making substances added to sodium carbonate.
The only drawback of this extinguisher is that the action is rather slow and non-continuous. Also , the results become unreliable if the quality of chemicals gets deteriorated due to extreme weather condition or adverse storage facilities.
Marine Auxiliary Machinery, 7th Edition, 1995 by McGeorge
This post is part of the series: Portable Fire Extinguishers
This series deals with the different types of portable fire extinguishers used on ships. It also contains their construction and working, including the reason why a particular type of extinguisher should be used for a specific type of fire.