CXS490 Carbon Dioxide Systems

History CO2 recognized as a fire extinguishing agent for many years Used in fixed systems since before World War I.

CO2 Applications Hazards and equipment satisfactorily protected include: Flammable liquid materials Electrical hazards (transformers, switches, circuit breakers,rotating equipment, and electronic equipment) Engines utilizing gasoline & other flammable liquid fuels. Ordinary combustibles (paper, wood, and textiles) Hazardous solids

Static Electricity When used to protect areas where explosive atmospheres could exist metal nozzles must be used, and entire system must be properly grounded. In addition, objects exposed to discharge from CO2 nozzles must be grounded to dissipate electrostatic charges.

Properties Carbon dioxide colorless odorless electrically nonconductive inert gas Suitable medium for extinguishing fires. Carbon dioxide gas is 1.5 times heavier than air. Liquid forms solid dry ice (“snow”) when released directly into the atmosphere. It can be easily liquified by compression and cooling.

Properties

Additional Properties Non Combustible Does not react with most substances Provides its own pressure for discharge Does not produce residues

} } Physical Properties Gas HP 850 psi LP 300 psi Liquid/Gas Triple Point Solid/Gas Gas Solid

Physical Properties At normal temperature and pressure, CO2 is a gas. Above critical temperature (87.8° F), CO2 is a gas, regardless of the pressure. Between 87.8° F and - 69° F (Triple point), carbon dioxide is partly a liquid and partly a gas. Below the triple point (- 69° F, and 75 psi), it is either a solid or a gas depending on pressure and temperature. Solid carbon dioxide is obtained below - 110° F.

Toxicity At extinguishing concentrations, CO2 has a: • suffocating effect that can produces unconsciousness and death.

Use Carbon dioxide fire-extinguishing systems are useful within limits of NFPA 12 standard in extinguishing fires involving specific hazards or equipment in the following occupancies where: an inert electrically nonconductive medium is essential or desirable cleanup of other media presents a problem they are more economical to install than other media

Use

Limitations Carbon dioxide cannot be used on chemicals containing their own supply of oxygen (such as cellulose nitrate) reactive materials (sodium, potassium, etc.) and metal hydrides. Carbon dioxide's low cooling effect limits its use for deep-seated fires. Deep-seated fires require higher concentrations to be maintained for longer periods

Components Storage High Pressure Containers: designed to store carbon dioxide at room temperature 850 psi at 70° F Pressure rises rapidly with temperature maximum temperature for storage container limited to 130° F limitation of filling density to 68 %. single hazard - discharges all agent 35, 50, 75, 100 & 120 lb or 16, 23, 34, 45 & 54 kg cylinders

Components Storage - High Pressure

Components Storage Low Pressure Containers: 1,000 lbs up to many tons Vessels maintained at 0° F, 300 psi by means of insulation and mechanical refrigeration Filling densities can be as high as 95 % Relief valves on container prevent pressure exceeding safe limits due to refrigeration failure. Multiple hazards - can be operated for a discharge time

Components Storage - Low Pressure

Components - Pipes & Fittings Piping and fittings shall be able to withstand high pressure developed in system. Carbon dioxide enters piping as a liquid. Due to friction, the pressure drops, and consequently part of liquid boils, creating a mixture of liquid and gas in piping (two phase).

Components - Pipes & Fittings Piping must be designed and dimensioned so that pressure never drops under 75 psi (triple point) to avoid formation of solid ("snow") which could block the nozzles' orifices. In practice, systems are calculated so that pressure never drops under: 150 psi for low pressure systems, and 300 psi for high pressure systems.

Components - Nozzles Must be used within listing's limits Mainly two types: low or high velocity For local application must cover entire surface involved in fire.

Hand Hose Line System Fixed supply of carbon dioxide supplying hose lines

Standpipe System & Mobile Supply Mobile supply of carbon dioxide capable of being quickly moved to position and connected to a system of fixed piping supplying fixed nozzles and /or hose lines.