Compressed foam systems - Fighting fire by fixed foam producing installations on board ships

Introduction

We all know that not all types of fires can extinguished with the help of water. On the contrary, using water on few types of fires leads to more adverse conditions. For this reason, other forms of extinguishing agents such as CO2 or foam is used. Moreover, just like automatic water sprinkler system, there are systems that dispatch CO2 and foam automatically. In this article we will learn about the automatic foam induction system and how compressed foam systems are used on board a ship.

Just like a portable foam extinguisher, a foam spreading system is used on a ship to suit a particular ship’s requirement with regard to the type of fire to be extinguished, quality of foam, areas to be protected etc. In all the ships requiring foam as an extinguishing agent, mechanical foam is generally used. Mechanical foam is formed by mixing foam making material with large quantities of water. But just the ingression of this mixture in the fire affected area is not sufficient. Violent agitation of the mixture into the air is required to create large amount of air bubbles in the foam.

Automatic Foam Induction System

A foam induction system is used to monitor and control the whole foam generating process. The main parts of the system are :

• Automatic Inductor unit
• Foam Compound tank
• Fire Pumps
• Hydrants

The automatic inductor unit monitors the main function of the system and ensures that correct mixing of water and foam compound in order to generate adequate amount of foam. The mixing of the foam compound and water takes place inside a foam compound tank, which is sealed from all the sides to prevent the deteriorating of the mixture formed. This mixture is then pumped through the hydrants with the help of fire pumps. The Foam compound tank also has linked compound supply and air vent valves, which are used to control the flow of water, air and the foam mixture.

When the system is to be operated, first of all, both the linked valves are opened. The mixing of the foam producing compounds and water is carefully metered using a automatic inductor unit. Once the mixing is done, air under pressure in forced into the tank to produce foam. The foam is then pumped out using fire pumps. It is of utmost importance that both, the fire pumps and compound tanks are located away from the engine room and at a well protected area.

High Expansion Foam System

Most of the new ships are provided with “High Expansion” foam system. This foam system has special foam generators which produce large quantity of foam from foam producing compounds and sea water . The foam produced from these generators is thousand times the quantity of foam produced with a normal generator. The foam generators are provided with large ducts to spread the expanded foam quickly over a large area. The generators also have special air connections which force compressed air inside the generator.

References

Stowell, F. & Adams, B. (2003) Principles Of Foam Fire Fighting. Oklahoma: Fire Protection Publications.