Low pressure CO2 fire fighting systems
Extinguisher
Carbon dioxide is a compound made up of carbon and oxygen, its chemical formula being CO2.
At atmospheric pressures and ambient temperatures, it is a colourless, tasteless gas with a slight odour. It does not damage material it comes into contact with, does not leave any residue and has very good dielectric characteristics.
Depending upon the temperature and pressure it is put through, it can become solid, liquid or gaseous.
It is possible for it to be in the three phases contemporarily at a temperature of -5°C and as a relative pressure of 4.28 kg/cm² (condition known as the triple point).
At a temperature lower than the triple point, the carbon dioxide is solid or gaseous.
The solid carbon dioxide, at sublimation atmospheric pressures, passes directly from a solid state to a gaseous state.
At temperatures higher than the triple point, but lower than 31°C, (critical temperature) it is only in the gaseous state.
One kilo of CO2, in the liquid state and at a temperature of 20°C, develops approximately 510 litres of gas when expelled at the atmospheric pressure and ambient temperatures.
The physical characteristics of carbon dioxide are:
- Chemical formula................................................................................................ CO2
- Molecule weight.................................................................................................. 44
- Triple point......................................................................................................... -56°C 4.28 bar rel.
- Sublimation temperature at atmospheric pressure............................................. 78.9°C
- Critical temperature............................................................................................. 31°C
- Critical pressure................................................................................................... 73.96 bar rel.
- Sublimation heat at -78.9°C................................................................................ 136,89 cal/kg
- Specific weight in the gaseous phase at 0°C and at atmospheric pressure........ 1.977 kg/m³
Used for inerting purposes CO2, like other inert gases, drops down oxygen concentration avoiding the event of combustion with high velocity (explosion). In this installation, minimum quantity to be discharged in protected areas are evaluated by CO detectors, located into silos.
The extinguishing action of carbon dioxide happens by suffocating the fire, diluting the percentage of oxygen contained in the air and by the cooling action provoked by the rapid expansion of gas.
Low pressure F.F. System
In low-pressure storage systems the temperature of the contained carbon dioxide is controlled at about 0°F (-18°C) by means of insulation and refrigeration. The normal pressure is thus maintained at about 300 psi (2068 kPa). Welded pressure vessels are used for this service, and there is no special limitation as far as size is concerned. This vessel has a nominal capacity of 11500 lts. and al oveflow level contains abt.8000 Kgs. of carbon dioxide. To direct the CO2 discharge are installed on a manifold two direct valves with electric/manual actuators.
Protected areas
The L.P. CO2 System protect the follow areas:
a. rolling coolant oil storage
b. rolling coolant oil distillation
a.Rolling coolant oil storage
- Volume of protected area............................................................ 2800.71 m3
- Average tank pressure................................................................ 22 bar
- CO2 quantity required for suppression........................................ 2063.69 kg
- Area of openings ........................................................................ 20.0 m2
- CO2 quantity required for leakages............................................ 1708.56 kg
- CO2 required weight................................................................... 3772.25 kg
- CO2 total weight ........................................................................ 4000.0 kg
- CO2 tank capacity....................................................................... 11500 litres
- CO2 tank charge......................................................................... abt 8000 kg
- discharge duration...................................................................... abt 120 sec
- CO2 concentration...................................................................... 36.05%
- rapid discharge cones involved................................................... no. 35
b.Rolling coolant oil distillation
- Volume of protected area........................................................ 698.94 m3
- Average tank pressure............................................................ 22 bar
- CO2 quantity required for suppression.................................... 559.79 kg
- Area of openings ..................................................................... 5.0 m2
- CO2 quantity required for leakages......................................... 427.14 kg
- CO2 required weight................................................................ 986.93 kg
- CO2 total weight ..................................................................... 1000.0 kg
- CO2 tank capacity.................................................................... 11500 litres
- CO2 tank charge...................................................................... abt 8000 kg
- discharge duration................................................................... abt 120 sec
- CO2 concentration.................................................................... 34.45%
- rapid discharge cones involved................................................. no. 9
F.F. System description
The CO2 F.F. System system assures F.F. System of volumes by means the flooding of the protected zone and is designed and sized for flowing the protected room with the required quantity of CO2.
In standard conditions the carbon dioxide inside the tank is keep at –18° C by the cooling system located above the tank.The pressure of CO2 is set at 20,7 bar. This 8000 kg of CO2 has been provided a quantity of CO2 able to make a double complete discharge on rolling coolant oil storage. The discharge phase is controlled by the direction valves which have the electric/manual actuators.
These actuators receive the “OPEN” signal when the Detection System detect a fire alarm situation and about 120 seconds after the signal became “CLOSE”.
Signallings of F.F. System systems to remote consist of:
- CO2 tank/cylinders empty alarm signal, supplied by weighting system switches, which signals a reduction of CO2 to advise of the low level;
- system in operation alarm signal, supplied by pressure switch, After operation it is necessary to manually reset the pressure switch.