How fire pumps work in firefighting systems

A fire pump is the component responsible for supplying the adequate water pressure to fire sprinklers and hose standpipes in order to control or contain a fire.

Fire pumps play a vital role as the first response to a fire situation, saving countless lives and property from destruction. They are usually found in manufacturing and industrial facilities, housing complexes, power plants, schools, hospitals, airports, commercial buildings and offshore oil platforms.

A firefighting system is, therefore, the most important of the various industries services, as its aim is to protect human life and property, strictly in that order.

But what does a firefighting system consists?

There are 3 parts to it: a large store of water in tanks, either underground or on top of the building, called fire storage tanks, a specialized pumping system and a large network of pipes ending in either hydrants or sprinklers (nearly all buildings require both of these systems).

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Fire pumps
Fire pumps are usually housed in a pump room very close to the fire tanks. The key thing is that the pumps should be located at a level just below the bottom of the fire tank, so that all the water in the tanks can flow into the pumps by gravity.

Like all important systems, there must be backup pumps in case the main pump fails. There is a main pump that is electric, a backup pump that is electric, and a second backup pump that is diesel-powered, in case the electricity fails, which is common. Each of these pumps is capable of pumping the required amount of water individually – they are identical in capacity.

There is also a fourth type of pump called a jockey pump. This is a small pump attached to the system that continually switches on to maintain the correct pressure in the distribution systems, which is normally 7 Kg/cm2 or 100 psi. If there is a small leakage somewhere in the system, the jockey pump will switch on to compensate for it. Each jockey pump will also have a backup.

The pumps are controlled by pressure sensors. When a fire fighter opens a hydrant, or when a sprinkler comes on, water gushes out of the system and the pressure drops. The pressure sensors will detect this drop and switch the fire pumps on. But the only way to switch off a fire pump is for a fire fighter to do this manually in the pump room. This is an international code of practice that is designed to avoid the pumps switching off due to any malfunction in the control system.

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The capacity of the pumps is decided by considering a number of factors, some of which are:

• the area covered by hydrants / standpipes and sprinklers
• the number of hydrants and sprinklers
• the assumed area of operation of the sprinklers
• the type and layout of the building

The distribution system consists of steel or galvanized steel pipes that are painted red.  These can be welded together to make secure joints, or attached with special clamps.  When running underground, they are wrapped with a special coating that prevents corrosion and protects the pipe.

Types of distribution systems
There are basically two types of distribution systems.

Automatic Wet systems: These are networks of pipes filled with water connected to the pumps and storage tanks. The networks of pipes are filled with pressurized air instead of water. When a fire fighter opens a hydrant, the pressurized air will first rush out.

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The pressure sensors in the pump room will detect a drop-in pressure, and start the water pumps, which will pump water to the system, reaching the hydrant that the fire fighter is holding after a gap of some seconds. This is done wherever there is a risk of the fire pipes freezing if filled with water, which would make them useless in a fire.

Manual distribution systems: These systems have an inlet for fire engines to pump water into the system. Once the fire engines are pumping water into the distribution system, fire fighters can then open hydrants at the right locations and start to direct water to the fire. The inlet that allows water from the fire engine into the distribution system is called a Siamese connection.

In high-rise buildings it is mandatory that each staircase have a wet riser, a vertical firefighting pipe with a hydrant at every floor.  It is important that the distribution system be designed with a ring main, a primary loop that is connected to the pumps so that there are two routes for water to flow in case one side gets blocked.

In more complex and dangerous installations, high and medium velocity water-spray systems and foam systems (for hazardous chemicals) are used.  The foam acts like an insulating blanket over the top of a burning liquid, cutting off its oxygen.  Special areas such as server rooms, the contents of which would be damaged by water, use gas suppression systems.  In these an inert gas is pumped into the room to cut off the oxygen supply of the fire.

It is a legal duty of building owners and/or employers  to ensure that suitable fire prevention and fire-fighting equipment is in place and functional. An annual inspection by a third party who meets the relevant fire management qualifications and guidelines is required. In between annual inspections, it is recommended that the pump is run for a short period once a week to check performance. Regular visual checks are also recommended, in order that early signs of wear can be detected.