CARBON DIOXIDE (CO2) AS FIRE EXTINGUISHING MEDIA

 

CARBON DIOXIDE (CO2) AS FIRE EXTINGUISHING MEDIA

Carbon dioxide is an effective fire extinguishing agent that responds quickly to Class B (flammable and combustible liquids like solvents, paints, greases, oils etc), Class C (flammable gases) and Electrical fires. These are also used on Class A fires (solid carbonaceous material) under limited conditions.  The main advantage of using Carbon dioxide as fire extinguishing media is that it is non-corrosive, non-conductive and leaves no residue after usage. The Carbon dioxide gas is stored in a high-pressure liquid state in the extinguishers.

Carbon dioxide which is approximately one and half times heavier than air is a 

·       Colourless

·       Odourless 

·       Electrically non-conductive gas

 

Carbon dioxide when directed at fire displaces the oxygen present to a point where it will not support combustion. This is called the smothering effect, also Carbon dioxide produces a cooling effect due to the expansion of gas when it comes out of the cylinder. This gas gets dissipated after the intended use into the atmosphere without leaving any trace of contamination to the equipment and will not harm any component of that equipment. 

Carbon dioxide gas is used as

o   Extinguisher type: These are again subdivided into 

§  Portable: They come with either

·       Mild Steel body – with 2 and 3 kg capacity

·       Aluminium body – with 2, 3 and 4.5 kg capacity

§  Trolley mounted

·       Mild steel body – with 4.5,6.5,9 and 22.5 kg capacity. 

o   Gas flooding system type:

§  Total flooding systems

§  Local application

§  High-pressure systems

§  Low-pressure systems

Carbon dioxide extinguishers are capable of operation between -30°C to +55°C, and the minimum discharge time varies with the capacity of the fire extinguisher which normally ranges from 8 seconds to 30 seconds and they have a concave base

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MARKINGS ON CARBON DIOXIDE FIRE EXTINGUISHER

All Carbon dioxide extinguishers are marked with the following information 

·       Manufacturer’s name or trade-mark

·       Method of operation in prominent letters

·       The words ‘CARBON DIOX1DE TYPE’ written in prominent letters.

·       Capacity

·       Year of manufacture of extinguisher 

·       Date of refilling and Source, 

·       Year of manufacture of the cylinder and its test pressure. 

 

On the neck of the cylinder Empty weight of the extinguisher and Filled weight of the extinguisher to know the capacity

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CHECKS OF CARBON DIOXIDE FIRE EXTINGUISHER

The manufacturing of the cylinder is done under controlled conditions and ensured that the cylinder is checked for surface defects and proper thickness of the metal body.  These are to ensure safety during cylinder operation during firefighting. The extinguisher is filled with liquefiable Carbon dioxide to the filling ratio of not more than 0.667  +/-  0.033 per cent.

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FLOODING SYSTEMS

Some areas like transformers, battery rooms, flammable liquid storage, spray painting rooms and other unmanned closed rooms are provided with flooding systems, The QUANTITY of Carbon dioxide for effective fire extinguishing is calculated based on the enclosure area and material type. A minimum of 60 seconds discharge time is kept which is enough for most of the fires to extinguish completely.

There are 4 types of CARBON DIOXIDE systems

1.     TOTAL FLOODING SYSTEMS: These are divided into two categories based on the types of fire it extinguishes

a.     Surface fires: These are extinguished when a suitable quantity is introduced into the required hazardous space when needed, to provide enough extinguishing concentration

b.     Deep-seated fires: These fires are extinguished by maintaining the concentration for a sufficient period to allow smouldering and the material to cool so that reignition will not happen

 

2.     LOCAL APPLICATION SYSTEMS: If a particular area is to be blanketed or a particular volume to be protected in the event of a fire. Then Local Application system is preferred

  

3.     HIGH-PRESSURE SYSTEMS:  These are suitable in places like engine rooms, auxiliary rooms, cargo holds, etc. In this system, Carbon dioxide cylinders are connected via a common manifold through which they led through distribution valves to the required protected spaces.  In this system, the Carbon dioxide extinguishing agent is distributed in correct quantities and within the prescribed time. The release is activated either mechanically/electrical or pneumatically. The storage pressure is 850 PSI at 27°C

 

4.     LOW-PRESSURE SYSTEMS:  These are suitable in places where large machinery is used. The advantage of this system is that a single tank is used in place of many cylinders. The entire set up of Carbon dioxide tank, refrigerators, valves, control unit with accessories is manufactured as a single unit.  The storage pressure is maintained at 300 PSI at -18°C

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SAFETY WHILE USING CARBON DIOXIDE

·       SAFETY OF PERSONNEL: The discharge of carbon dioxide immediately reduces the oxygen concentration and creates serious hazards like asphyxiation and visibility issues. The evacuation of personnel as per the emergency plan should also include safe evacuation of personnel during carbon dioxide discharge. The concentration and volume will be high in flooding systems rather than a first aid fire extinguisher, hence more care should be taken at these locations.

 

·       SAFETY IN CONFINED SPACES: The provision of a carbon dioxide discharge system into the confined space is an additional risk that can happen in the event of any leakage of carbon dioxide gas into the confined space while working (or) use of carbon dioxide fire extinguishers in confined space also adds up more risk, due to characteristics of confined space like lack of escape routes, improper ventilation and other movement restrictions causing the evacuation of personnel more difficult. Hence a work permit system to be ensured before carrying out any work in a confined space as this will allow for carbon dioxide system isolation and lock/tag till work is completed also emergency plan based on this risk should be assessed and controls to be kept in place.

 

·       SAFETY IN PROTECTED AREAS:  The entry of personnel into protected areas should be done only when the carbon dioxide flooding system is changed to manual mode with a lock-off valve.

 

·      SAFETY WITH ELECTRICITY: The carbon dioxide system components should be distantly placed (clearance) from live electrical parts with clearance increased proportionally with the increase in KV. The discharge of liquid carbon dioxide produces electrostatic discharges which can create a spark. Hence in explosive atmospheres proper bonding and earthing to be ensured.

Article by PJ Mohan

Sr.Faculty, NIFS