CHAPTER 8

CARBON DIOXIDE

Learning Objective: Upon completion of this chapter, you will be able to describe, inspect, recharge, and perform maintenance on carbon dioxide

cylinders and transfer units.

Carbon dioxide is a heavy, colorless gas. The chemical symbol for carbon dioxide is CO2. You will find that most people use this symbol when referring to carbon dioxide.

C O2 doesn't burn and does not support combustion; therefore, it makes a fine fire-fighting agent. It is strongly recommended for use on electrical fires. The servicing of fire-fighting equipment is not part of the PR rate, and so this text does not cover fire extinguishers.

As a PR you deal with life raft and life recharge, and repair. preserver CO2 cylinders, which you weigh,

Carbon dioxide is ordinarily procured from local commercial sources. It is stored in standard supply cylinders that contain 50 pounds of carbon dioxide when full.

Before learning how to recharge CO

₂ cylinders, you should be familiar with the following information:

In its gas form, carbon dioxide is 1.53 times heavier than air. C O2 gas can be converted into a liquid by applying pressure to the gas. With as little as 600 psi at a temperature below 88F, the CO2 ga s can be converted into a liquid and stored in that state until it is subjected to the outside atmosphere. By opening the cylinder valve and letting the carbon dioxide escape into the atmosphere, you cause a rapid drop in pressure. As the CO2 escapes through the small opening, it forms carbon dioxide snow. This snow, when compressed into blocks or cubes, is known as dry ice. At atmospheric pressure, dry ice will remain at - 110F, directly evaporating into CO2 gas. CO2 exists as a liquid only when under pressure.

Whenever you are working with CO 2 in any of its three stages-gas, liquid, or dry ice, you should be aware that small percentages of CO2 in the air causes tiredness and perhaps headaches. Experiments have shown that a 3-percent concentration in the air doubles your breathing effort, 5 percent causes panting, 8 percent causes marked distress, and 10 percent causes unconsciousness very quickly.

Treatment of exposed personnel includes removing them from the CO2-laden atmosphere, artificial resuscitation, administering oxygen, and keeping the patient warm.

CO2 RECHARGE EQUIPMENT

Carbon dioxide recharge equipment is manufactured for the Navy by several different companies. The two most widely used units are those manufactured by the C-O-TWO Company of Newark, New Jersey (do not confuse this company with the chemical symbol CO2) and the Walter Kidde Company of Belleville, New Jersey.

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Figure 8-1.-C-O-TWO recharge or transfer unit (supplycylinder without a syphon tube).

A typical C-O-TWO recharge unit is shown in figure 8-1 and consists of a supply cylinder containing 50 pounds of CO2, a tilting rack for inverting the supply cylinder, a motor-driven pump, a rack for inverting the cylinder being recharged, a scale for determining the weight of the cylinder being recharged, and the necessary high-pressure hoses, control valves, adapters, etc., to properly hookup the equipment. The two units are covered in detail in the PR 1 & C.

Before learning the operation of any specific type of recharge equipment, you should be familiar with the following general information, which applies to all units.

Carbon dioxide recharge equipment pumps CO2 in its liquid state only, and the amount of liquid CO2 a cylinder contains varies with the temperature and pressure. For example, a standard 50-pound supply cylinder contains approximately 38 pounds of liquid CO2 and 12 pounds of gaseous CO2 at a temperature of 70F. It follows, then, that the cooler the supply cylinder and cylinder being recharged, the more efficient the operation of the transfer equipment. For this same reason, the time required to recharge an empty cylinder increases with the temperature of the cylinders.

Figure 8-2.-CO2 supply cylinder.

When recharging a cylinder, it remains cooler and may be filled faster if inverted, rather than left in an upright position. Large cylinders, which are impractical to invert, may be placed in a horizontal position for charging.

Standard commercial supply cylinders in 50-pound sizes are obtained with or without a syphon tube. When transferring from a cylinder without a syphon tube, the cylinder must be inverted. Supply cylinders with syphon tubes should be maintained in an upright position, not more than 60 degrees from vertical.