CARBON DIOXIDE (CO2) EQUIPMENT

Aboard ship, carbon dioxide fire-extinguishing equipment includes 15-pound CO2 portable extinguishers, 50-pound CO2 hose-and-reel installations, and 50-pound CO2 installed flooding systems. The carbon dioxide is contained under pressure in steel cylinders. It is released through a CO2 hose or fixed piping when the control valves are opened.

In all carbon dioxide extinguishers used by the Navy, the CO2 is held under a pressure of 850 psia at 70F. (This pressure corresponds to a gauge pressure of 835.3 psig.) Any increase in temperature increases the pressure, and any decrease in temperature decreases the pressure. Since pressure builds up rapidly as the temperature increases, remember these three precautions to prevent the danger of explosion:

. Never fill cylinders to more than 68 percent of their volume capacity. The full volume capacity of a carbon dioxide cylinder is the amount of water at maximum density (39 'F) that the cylinder will hold. l Cylinders are designed to withstand pressures up to 3,000 psi.

. Cylinders are equipped with safety release disks. The safety release disk ruptures at a pressure between 2,650 and 3,000 psi. The head of the safety nut is drilled to prevent recoil when the disk bursts. The bursting pressure depends upon the strength and thickness of the disk and the diameter of the hole in the safety nut. Therefore, replacement disks, nuts, and washers must be in accordance with the manufacturer's technical manual.

Because the pressure in a CO2 cylinder will vary with a change in temperature, you cannot determine the amount of carbon dioxide in a cylinder by reading a pressure gauge. Instead, you must weigh the cylinders periodically to determine the amount of CO2 in them. The intervals at which CO2 cylinders must be weighed are specified in the 3-M Systems. The weight of each cylinder when empty and the weight when filled to capacity are stamped on the cylinder valve or written on a tag that is attached to the cylinder. In each case, the weight refers to the weight of the cylinder alone, without the horn and hose, Therefore, it is easy to check the weight of the carbon dioxide contained in any cylinder.

All CO2 cylinders should be filled to their nominal capacity (by weight). The exception is 15-pound cylinders exposed to temperatures which may exceed 120F. These should be charged or bled down to 90 percent of nominal capacity, or 13.5 pounds. Carbon-dioxide cylinders used in fixed flooding and hose reel systems are a nominal 50-pound capacity. These cylinders can be installed in spaces at temperatures up to 135 "F with a full charge. Therefore, an undercharge or bleed down is not required.

When carbon dioxide is released from a cylinder at normal temperatures, it expands rapidly to about 450 times its stored volume. This rapid expansion causes the temperature to drop to about - 110 'F. Most of the liquid carbon dioxide is vaporized and becomes a gas, but some of it forms snow. Do NOT allow this snow to _{contact your skin.} Because of its very low temperature, carbon dioxide snow can blister the skin and produce a very painful injury.

Since CO2 is 50 percent heavier than air, it tends to settle and cover the fire. A CO2 blanket separates the air from the fire. The fire is thus smothered. If there is some wind or a draft, you should work so the carbon dioxide will be drawn or blown over the fire rather than away from it. Even though carbon dioxide reaches a very low temperature as it expands from the cylinder, it has only a very slight cooling effect on the fire. CO2 is used primarily for its smothering effect, not for its cooling effect.

Carbon dioxide is most effective when it is used in confined spaces. When you are using CO2, keep the compartment closed and secure the ventilation to prevent unnecessary dilution of the CO2. Except in an emergency, you should not open a CO2-flooded compartment for at least 15 minutes after it has been flooded. This delay is a precautionary measure to give the burned substances time to cool down so that they will not reignite when air is admitted to the compartment.

Do not attempt to use CO2 unless you know what you are doing. In high concentrations, C O2 will cause suffocation as rapidly as it will smother a fire, unless proper precautions are taken. You may enter a CO2-flooded compartment, if necessary. However, you must use an approved Navy oxygen breathing apparatus or a hose (air-line) mask. Do NOT use a gas mask. It filters the air but does not provide the necessary oxygen.

PORTABLE CO2 FIRE EXTINGUISHERS

The portable CO2 fire extinguisher that is used on Navy ships is the 15-pound unit. This unit is recharged from a carbon dioxide transfer unit using a 50-pound CO2 cylinder. These units are described below.

15-Pound CO2 Fire Extinguisher

The standard Navy portable CO2 fire extinguisher has a rated capacity (by weight) of 15 pounds of CO2. The portable extinguisher is simple to operate. You just remove the locking pin and squeeze the squeeze-grip release valve. The squeeze-grip release valve makes a tight seal when

pressure on the grip is released. Any unexpended CO2 is contained inside the cylinder indefinitely without danger of leakage.

To operate the portable 15-pound CO2 extinguisher, proceed as follows:

1. Carry the extinguisher in an upright position and approach the fire as closely as possible.

2. Remove the locking pin from the valve.

3. Grasp the horn handle. This handle is insulated to protect you against frostbite from the suddenly expanding CO2.

4. Squeeze the release lever to open the valve and release the CO2. Direct the flow of CO2 toward the base of the fire. The maximum effective range of a 15-pound CO2 extinguisher is 5 feet from the outer end of the horn. This distance is reduced if the wind is against you and increased if the wind is with you. If possible, attack the fire from the windward side to increase the range and also to protect yourself from the fire. Move the horn slowly from side to side and advance on the flames as they recede.

5. When conditions permit, close the valve. Continue to open and close the valve as the situation requires. When continuous operation is necessary or when the valve is to remain open for recharging, slip the D-yoke ring on the carrying handle over the operating handle. The operating handle should be in the depressed position when you put on the D-yoke ring. The D-yoke ring permits continuous operation as long as any CO2 remains in the extinguisher.

Once a 15-pound cylinder has been used, it should be recharged before it is returned to its stowage place. Spare portable 15-pound CO2 cylinders in storage must also be weighed at the required intervals and recharged whenever the weight has dropped to 13 1/2 pounds-that is, when there is a 10 percent loss. As previously noted, however, cylinders stowed in hot places are charged to only 90 percent of their capacity by weight, or in this case 13 1/2 pounds.