Fire water pumps requirement for hazardous Industries

The provision of fire water pumps is exclusively for firefighting purposes. These pumps may be horizontal centrifugal type or vertical turbine submersible pumps. It includes Main pumps, Standby pumps and jockey pumps. While selecting the numbers of fire pumps, there should be combination of electrically driven and diesel operated pumps to manage the black out or failure of electrical power supply. Only centrifugal type pumps are suitable for firefighting purpose. 

Fire water pumps requirement for hazardous Industries

Fire water pumps requirement for hazardous Industries

According to standards, the fire water system must be designed for a minimum residual pressure of 7.0 kg/cm2 at the hydraulically remotest point of application at the designed flow rate at that point. To meet this requirement, fire water network must be kept pressurized by jockey pumps higher than 7 Kg/cm2. Actual network pressure to maintain all time, depends on total fire water demand, piping design and length of piping network.

 

Requirement for main and standby Fire pumps

While deciding the numbers of main and standby fire pumps, combination of electric motor driven centrifugal pumps and Diesel engine driven centrifugal pumps should be considered.

Including standby pumps, the number of diesel driven pumps must be minimum 50% of the total calculated number of pumps requirement based on total fire water demand. Minimum 50% of total flow requirement should be available through diesel driven pumps all the time. All such pumps should be identical in capacity.

With reference to total water demand calculation and capacity selection of fire pumps, if the total number of working pumps derived as one or two then 100% standby pumps must be considered. If the total numbers of working pumps derived more than two, then 50% standby pumps must be provided. In major industries where two fire water pump houses or two sets of firewater storage and pumps are provided, then the number of fire pumps at each location will be decided according to hydraulic analysis of piping network.

For Example:

As per total fire water demand calculation and capacity selection of pumps, if the required fire main pumps are four numbers then there should two more pumps as standby pumps.

So, the total fire pumps will be 6 numbers (04 Nos Main + 02 Nos Standby).

Out of above six pumps, there should three diesel driven and three electrical driven. All these six pumps must be identical in capacity.

While selecting the sequence of operation, out of four main pumps, there should be two electrical and two diesel driven. Similarly, for two standby pumps, there should be one electrical and one diesel driven.

 

Requirement for Jockey pumps

The jockey pump maintains the designed pressure in the fire water network to compensate the minor leakages and to avoid non-emergency starting of the main fire pump.

There should be two jockey pumps (main + standby) and must be maintained in auto mode. Both the pumps should be electrically driven.

The capacity of the jockey pumps must be enough to compensate the desired fire water system pressure in the event of any minor leakages from valves, piping or operation of single hydrant etc. to avoid non-emergency starting of the main fire pump.

The capacity of jockey pumps should not be less than 5% and should not be more than 10% of the design fire water rate. As these pumps maintains the header pressure in non-emergency situation and therefore it’s head shall be higher than the main fire water pumps.

Know more about requirement of jockey pumps

 

Capacity of Fire water main and standby pumps

To deal with fire and explosion hazards in hazardous industries such as chemicals, fertilisers and oil & gas including refineries and petrochemicals, robust firefighting system must be designed. Fire water system is very crucial and therefore selection of adequate numbers of fire pumps with suitable capacity must be decided according to national and international standards.

While deciding the capacity of fire water pumps,  each selected pumps must be designed in such a way that it should capable to discharge 150% of its rated capacity at a minimum of 65% of the rated head. The shut-off head should not exceed 120% of rated head, for horizontal fire pumps and 140% in case of vertical turbine type fire pumps.

Based on the total fire water demand calculation and designed fire water rate, the capacity and number of main fire water pumps should be considered. While deciding the capacity of each pump, it should not be less than 400 m3/hr or more than 1000 m3/hr. Whatever the capacity calculated for fire pumps, all pumps should be identical with respect to capacity and head characteristics.

For Example:

Suppose the total fire water demand is calculated as 2400 m3/hr then the numbers of main pumps may be four numbers of capacity 610 m3/hr each.

Standby pumps will be two numbers of identical capacity and in head characteristic. So, total pumps will be six numbers. Out of these six numbers, there will three electrically driven and three diesel driven.

Other than above six pumps, there will two jockey pumps (one main and one standby) of capacity 120 m3/hrs each (5% of total water demand).

 

Sequence of operation of fire main pumps

All the fire water pumps should be maintained in auto mode and operation philosophy should be as per designed pressure. Pumps must start automatically and sequentially with PT/ PLC on fire water mains. The system shall ensure auto start of the standby pump in case a pump in sequence failed to take start.

Main pump will be started automatically but stop will be manual.

For example:

Suppose, the designed header pressure is calculated as 10.5 kg/cm2 to be maintained in the fire water network at all time then the jockey pump operational sequence may be set as; auto start at 10 kg/cm2 and auto stop at 10.5kg /cm2.

Whereas for Main fire pumps, below auto start sequence may be considered;

1^st pump – start at 9.5 kg/cm2

2^nd pump – start at 9 kg/cm2

3^rd pump – start at 8.5 kg/cm2

4^th pump – start at 8 kg/cm2

5^th pump – start at 7.5 kg/cm2

6^th pump – start at 7 kg/cm2

All above main pumps shall be stopped manually.

 

Power Supply to Fire water pumps

Power supply to the electric driven pumps should be from two separate feeders and dedicated only to fire pumps from the sub-station to ensure reliable power supply. Emergency power supply must be provided for jockey pumps to deal with black out event. The direct feeder line from electrical substation should not run along with other HT cables.

All the pump should be provided with local manual ON/OFF switches and remote selection switch on controller. Push button should be provided near the diesel pumps and all the diesel engines must be quick starting type with the help of these push buttons or can be operated from remote location

Fuel tank for each diesel engine should be provided independently and must be adequate for 6 hours continuous running of the pump.