CHEMICAL DECONTAMINATION

The purpose of chemical decontamination is to decontaminate successfully after an attack by any of the blister or nerve agents. The methods generally used are natural weathering, chemical action, heat, and physical removal.

Natural Weathering

Natural weathering relies on the effects of sun, wind, and rain to dissipate, evaporate, or decompose toxic chemical agents. Weathering is by far the simplest and most common method of chemical decontamination. In some instances, it offers the only practical way to neutralize chemical agents, particularly where large areas are contaminated.

Chemical Action

Decontamination by chemicaI action involves a chemical reaction between the chemical agent and the chemical decontaminant. The reaction usually produces a harmless new compound or a compound that can be removed more easily than the original agent. Calcium hypochlorite is the chemical most often used aboard ship for both chemical and biological decontamination.

Heat

Expendable objects or objects of little value may be burned if they become contaminated. This procedure should be used only as an emergency measure or to dispose of material that has been highly contaminated. If you use this method, you need a very hot fire. Intense heat is required to destroy toxic chemicals. Moderate or low heat may only volatilize the agent and spread it in aerosol form. When a large amount of highly contaminated material is being burned, downwind areas may contain a dangerous concentration of toxic vapors. Keep personnel away from such areas.

Steam may be used to decontaminate chemical agents in interior compartments of the ship. The steam hydrolyzes and evaporates chemical agents and flushes them away from the surface. The effectiveness of the steam increases with temperature-the hotter the steam, the faster the neutralizing action. Use the following procedure to steam a compartment.

1. Introduce steam at 30 to 50 psi, using the air test fittings or other outlets.

2. Be sure that the compartment is entirely secured except for an exhaust line. The exhaust line should be led topside.

3. If possible, check the exhaust temperature. When the exhaust temperature is about 200F, reduce the pressure to 20 psi. If it is not feasible to check the exhaust temperature, assume that it is high enough after 15 minutes of steaming; then reduce the steam pressure to 20 psi.

4. Continue steaming for one-half hour or longer, depending upon the size of the compartment and the degree of contamination.

5. Check the exhaust periodically with a detector kit for residual traces of contamination.

6. After the steaming, clean the compartment thoroughly.

Although steam is noncorrosive quick acting and readily available aboard ship, it does have some disadvantages. It should NEVER be used to decontaminate lewisite (L), since another poisonous compound may result. Also, the high temperatures of steam decontamination can cause damage to some compartments and to certain types of gear. The moisture content of steam may also damage some equipment.

Physical Removal

Chemical decontamination can also be carried out by physically removing the toxic agents from the contaminated surfaces. This can be done by washing or flushing the surface with water, steam, or various solvents.

Decontamination can be accomplished with the water washdown system or by hosing. The procedures are similar to those used to flush away radiological and biological agents. However, there are some disadvantages. Water, like steam, must not be used for lewisite decontamination because of the poisonous residue that may be left. Also, flushing with water is not effective against blister gases unless it is done immediately after exposure to the blister agents before the agents penetrate

any surfaces. The use of water may also release nonpoisonous but highly corrosive acids. Therefore, all surfaces must be washed thoroughly so that no reaction products remain. Hot water is much more effective than cold water for chemical decontamination. The effectiveness of water may be increased by the addition of soaps or detergents.

You may sometimes use solvents other than water to dissolve chemical agents so that they may be readily removed. These include gasoline, oils, alcohol, antifreezes, dry cleaning solvents, and so forth. Use them in accordance with appropriate safety precautions.

Alkaline solutions destroy G-agents (discussed in chapter 9) by hydrolysis. Alkaline solutions that may be used include lye, washing soda, ammonia, and baking soda. The stronger alkali solutions are more effective than the weaker ones.

Start decontamination as soon as possible after chemical attack. The priorities for decontamination vary, depending upon the type of ship and other factors. In general, you should use something similar to the following sequence of priorities.

1. Weapons equipment

2. Navigation equipment

3. Vital topside areas, such as gun mounts, the bridge, lookout stations, and areas which must necessarily be occupied by personnel

4. Vital machinery spaces

5. Topside areas from which the contamination could spread to the interior of the ship

6. Interior compartments

7. All other areas