CO2 extinguishing
To extinguish certain fires, the use of CO2 as an extinguishing gas is still preferable.
Carbon dioxide, commonly called carbonic acid or CO2, is gaseous under atmospheric conditions. CO2 gas is colorless, odorless and electrically non-conductive.
Its properties make it particularly suitable as an extinguishing agent: precisely because it is an almost chemically neutral gas, it does not cause damage when extinguishing and does not affect materials. After a discharge, the CO2 simply disappears from rooms that are not located in a basement through natural ventilation.
CO2 is cheap and there are many filling stations.
CO2 is stored in high-pressure steel bottles, usually in quantities of 30 and 50 kg per bottle. At 20°C the pressure in the bottle is approximately 58 bar (5.8 MP) and the carbon dioxide is mainly present in liquid form in the bottle.
Extinguishing effect
The fire is extinguished by replacing part of the air in the room with CO2, thus quickly reducing the oxygen concentration. At this low oxygen concentration, a fire can no longer be maintained.
Evaporation and heating of the CO2 removes heat from the environment and the resulting cooling contributes to extinguishing the fire and prevents re-ignition.
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Areas of application
CO2 can be used to extinguish in two ways:
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By introducing an amount of CO2 into a 'closed' volume, depending on the nature of the risk - "extinguishing by saturation".
This method of extinguishing is used if the products or materials that can cause a fire are spread in a rather limited volume.
One may then be faced with a surface fire, such as can occur with flammable liquids. Examples of this are storage areas for solvents, rooms with petrol or diesel engines, paint spray booths.
Fires in which substances can glow, or 'deep-lying fires' can also be extinguished with CO2. The properties of CO2 are used here to prevent re-ignition or to prevent the fire from spreading further so that it can be easily fought with other means. Here the time during which this concentration is maintained is of great importance. It is therefore necessary that the protected space remains properly closed. Examples of this are: cable tunnels, rooms with power generators, rooms with electrical switchgear.
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By enclosing or covering a free-standing risk for at least 30 seconds: this is called local protection.
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of a surface: impregneading baths, deep fryers,
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of a body: engines, alternators, etc. that are installed in a space that is too large for saturation extinguishing.
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Precautions
There is a danger associated with extinguishing fires with CO2, especially when it concerns 'saturation' within a room where people may be present. Not only does the low oxygen concentration make breathing difficult and the sudden cooling creates a dense fog, the presence of a high CO2 concentration in itself is a threat.
To avoid accidents, the extinguishing system must be prevented from operating as long as there are people in the room or extinguishing must be preceded by a clear evacuation alarm. Then are required:
- a non-electric retarder and a pneumatic evacuation siren
- a blocking device that can temporarily prevent the outflow of CO2. Potential-free auxiliary contacts must indicate to the extinguishing panel that the extinguishing option has been temporarily disabled.
Permanent monitoring of the condition of the installation
Because a pressure measurement indicates the vapor pressure of CO2, it is not suitable for indicating whether a bottle has retained its original weight of CO2. This can only be determined by checking the weight of the bottles or the amount of CO2. Permanent weight or content control is often chosen and some regulations also require this. For permanent content control, we now apply an electronic measurement of the electrical capacity of the CO2 in the cylinders.
Directional valves
Various risks located in close proximity can be protected with a single supply of extinguishing agent, which, by using directional valves, can extinguish one of these risks.