Properties of Carbon Dioxide: Storage and Discharge
Carbon dioxide (CO₂) is stored and discharged under specific conditions to ensure safety and effectiveness in fire suppression. Its storage methods and discharge properties are critical in maintaining its effectiveness as a fire-extinguishing agent.
Storage of Liquid Carbon Dioxide
Liquid carbon dioxide can be stored in high-pressure cylinders or low-pressure refrigerated containers. High-pressure cylinders have a storage temperature that varies with the surrounding environment, while low-pressure systems are designed to maintain a storage temperature of approximately 0°F (-18°C).
High-pressure cylinders typically range from 5 lb (2.27 kg) to 120 lb (54.4 kg) in capacity, whereas low-pressure storage units have capacities ranging from 750 lb (340 kg) to a massive 60 tons (54,431 kg) per unit.
High-pressure cylinders are equipped with siphon tubes that draw liquid CO₂ from the bottom of the cylinder. The contents are then discharged through a control valve to the fire zone. When the discharge valve opens, the entire content is typically released.
Discharge Properties
The discharge of liquid carbon dioxide has a white, cloudy appearance due to the formation of a water fog as the air is cooled below its dew point. This fog results from both the cooling of the air and the fine dry ice particles produced. The water fog can persist for a time after the dry ice particles have sublimed.
Even after the fog dissipates, dangerous concentrations of CO₂ may remain in the area, making proper ventilation crucial during and after discharge.
Static Electricity Concerns
During the discharge process, dry ice particles can accumulate static electricity. Additionally, static charge can build up on ungrounded discharge nozzles. To avoid the risk of electric shocks or unwanted static discharges—especially in explosive environments—all discharge nozzles must be grounded.
Vapor Density of CO₂
Carbon dioxide vapor is much denser than air. Its density is one and a half times greater than air at the same temperature. As CO₂ vapor discharges to the atmosphere, it can approach temperatures as low as -110°F (-79°C), making it denser than the surrounding air. This greater density allows CO₂ to replace the oxygen above burning surfaces, maintaining a smothering atmosphere and effectively suppressing the fire.
Physiological Effects of Carbon Dioxide
Carbon dioxide is a natural component of Earth's atmosphere, typically present at 0.04%. It is also a normal by-product of cellular respiration in both humans and animals. In the human body, CO₂ plays a crucial role in regulating breathing, ensuring a sufficient supply of oxygen to the system.
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