Halon fire extinguishers and other types use on ships: Know about their working principles.


This article is a part of a series of articles that deals with the different types of portable fire extinguishers used on board a ship. In this article we will learn about four types of fire extinguishers – Mechanical foam extinguisher, dry powder extinguisher, carbon dioxide extinguisher and halon extinguisher. Though almost similar in construction, they are used for different types of fires. Let’s take a look at the construction and working of these fire extinguishers.

Mechanical foam Extinguishers

This is a type B fire extinguisher. It is known to be a better substitute for a conventional foam type extinguisher. The construction is similar to the foam type extinguisher but the operating procedure is different.

Instead of a long container, the extinguisher contains a small metal bottle filled with liquid carbon dioxide. The bottle is surrounded by a thin plastic bag filled with foam making compound. The small carbon dioxide bottle is attached to a plunger which is attached to a pin.


When the extinguisher has to be operated, the plunger is hit sharply on the head. This pierces the seal of the CO2 bottle.The pressurized Co2 ruptures the thin plastic bag resulting in the mixture of water and foam forming compound. The pressurized Co2 ejects the mixture of foam and water out of a special nozzle which agitates the mixture and creates a mechanical foam. It is to be noted that the extinguisher should be in an upright position when operated. The extinguisher also has an internal pipe in its system.

mechanical foam type

Dry Powder Extinguisher

The construction of this extinguisher is similar to the chemical foam extinguisher but special care has been taken in order to prevent the degradation of chemicals due to external effects.

In order to prevent caking of chemicals, the extinguisher uses sodium bicarbonate power with a water proof material such as magnesium stearate added to it. The inner container contains a cartridge containing liquid carbon dioxide. The rest of the cylinder is filled with dry powder.


When the plunger is hit on the head, the pin pierces the seal of the container. The gas then passes through a tube to the bottom of the casing where it entrains the dry powder and forces it out of the discharge tube. The pressurized Co2 forces all the powder out of the discharge nozzle.

The powder forms a blanket or cloud and envelops the fire, interfering with the chemistry of combustion. Sodium bicarbonate when heated by fire, decomposes to produce carbon dioxide which helps to smother the fire efficiently. The decomposition also produces a cooling effect due to the absorption of heat from the surrounding area.

All the parts of the system are hydraulically tested at 35 bar pressure before fitting.

Dry powder type

Carbon Dioxide Extinguisher.

In carbon dioxide extinguishers, both the propellent and blanketing agents are carbon dioxide. Co2 is kept in a liquid state inside the cylinder at 6 bar pressure and at 20 degree Celsius. The shell is made of steel and the extinguisher can only be recharged ashore.

Special care is taken in order to use Co2 extinguisher in confined spaces as high concentration can become lethal.

Co2 type

Halon Fire Extinguisher

In this type, instead of CO2 gas, halon gas is used. But because of high ozone depletion potential of Halon, its usage has been discontinued. The construction and working is exactly similar to that of carbon dioxide extinguisher.


Marine Auxiliary Machinery, 7th Edition, 1995 by McGeorge

Image Credits

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.
  1. Portable Fire Fighting Equipments
  2. Portable Fire Extinguishers Types
  3. DP, Halon, Co2 & Mechanical Fire Extinguishers