Decontamination is the reduction or removal of chemical agents. Decontamination may be accomplished by removal of these agents by physical means or by chemical neutralization or detoxification. Decontamination of skin is the primary concern, but decontamination of eyes and wounds must also be done when necessary. Personal decontamination is decontamination of self; casualty decontamination refers to the decontamination of casualties; and personnel decontamination usually refers to decontamination of noncasualties.
The most important and most effective decontamination of any chemical exposure is that decontamination done within the first minute or two after exposure. This is self-decontamination, and this early action by the soldier will make the difference between survival (minimal injury) and death (severe injury). Good training can save lives.
Decontamination of casualties is an enormous task. The process requires dedication of both large numbers of personnel and large amounts of time. Even with appropriate planning and training, the requirement demands a significant contribution of resources.
Liquids and solids are the only substances that can be effectively removed from the skin. It is generally not possible or necessary to decontaminate vapor. Removal from the atmosphere containing the vapor is all that is required.
Many substances have been evaluated for their usefulness in skin decontamination.
The most common problems with potential decontaminants are irritation of the skin, toxicity, ineffectiveness, or high cost. An ideal decontaminant will rapidly and completely decontaminate all known chemical and biological warfare agents. Furthermore, a suitable skin decontaminant must have certain properties that are not requirements for decontaminants for equipment. Recognized desirable traits of a skin decontaminant include the following:
Decontamination issues have been explored since the beginning of modern chemical warfare. After years of research worldwide, simple principles that consistently produce good results still apply.
The first, without equal, is timely physical removal of the agent. To remove the substance by the best means available is the primary objective. Chemical destruction (detoxification) of the offending agent is a desirable secondary objective. Physical removal is imperative because none of the chemical means of destroying these agents do so instantaneously. While decontamination preparations such as fresh hypochlorite react rapidly with some agents (e.g., the half time for destruction of VX by hypochlorite at a pH of 10 is 1.5 minutes), the half times of destruction of other agents, such as mustard, are much longer. If a large amount of agent is present initially, a longer time is needed to completely neutralize the agent to a harmless substance.
Decontamination studies have been conducted using common household products. The goal of these studies was identification of decontaminants for civilians, as well as field expedients for the soldier. Timely use of water, soap and water, or flour, followed by wet tissue wipes, produced results equal, nearly equal, or in some instances, better than those produced by the use of Fuller's Earth, Dutch Powder, and other compounds. (Fuller's Earth and Dutch Powder are decontamination agents currently fielded by some European countries.) This is easily understood because (1) no topical decontaminant has ever shown efficacy with penetrated agent, (2) agents in large enough quantity, especially vesicants, may begin penetrating the skin before complete reactive decontamination (detoxification) takes place, and (3) early physical removal is most important.
Military personnel may be questioned for guidance by local civilian authorities or may deal with supply shortages in the field. Knowledge of the United States' doctrinal solutions may not suffice in these situations, and awareness of alternative methods of decontamination will prove very beneficial.
However, it is not so much what method is used, rather it is how and when it is used. Chemical agents should be removed as quickly and completely as possible by the best means available.
The M291 resin kit and 0.5% hypochlorite for casualty decontamination are state-of-the-art. The M291 Kit is new, whereas hypochlorite has been around since World War I. The M291 Kit is the best universal dry decontaminant for skin. Fresh 0.5% hypochlorite solution with an alkaline pH is the best available universal liquid decontaminating agent. Liquids are best for large or irregular surface areas. Hypochlorite solutions are well suited for medical treatment facilities with adequate water supplies. For hypochlorite to be the best universal liquid skin decontaminant, it has to be relatively fresh (made daily or more frequently, particularly in a warm environment where evaporation will occur) and at a concentration of 0.5% at an alkaline pH. Hypochlorite solutions are for use on skin and soft tissue wounds only. Hypochlorite should not be used in abdominal wounds, open chest wounds, on nervous tissue, or in the eye. Surgical irrigation solutions should be used in liberal amounts in the abdomen and chest. All such solutions should be removed by suction instead of sponging and wiping. Only copious amounts of water, normal saline, or eye solutions are recommended for the eye. Contaminated wounds will be discussed later.
The M291 resin kit is best for spot decontamination of skin only. It rapidly adsorbs the chemical agent with carbonaceous material, physically removing the agent from skin contact. Later, an ion exchange resin neutralizes the offending agent by chemical detoxification. Since the M291 Kit is small and dry and easily carried by the soldier, it is well suited for field use. It will be the early intervention with the use of this kit that will reduce chemical injury and save lives in most cases. Decontamination of the casualty using an M291 Kit does not obviate the need for decontamination at a field facility. The decontamination station is more conducive to thorough decontamination. Chemical agent transfer is a potential problem that can be resolved by a second deliberate decontamination. Decontamination at the medical treatment facility prevents spread of the agent to areas of the body previously uncontaminated, contamination of personnel assisting the patient, and contamination of the medical facility.
CERTIFICATION OF DECONTAMINATION
Certification of decontamination is accomplished by any of the following: processing through the decontamination facility; M8 paper; M9 tape; M256A1 sampler; or by the CAM (Chemical Agent Monitor). If proper procedure is followed, the possibility of admitting a contaminated casualty to a field medical facility is extremely small. The probability of admitting a dangerously contaminated casualty is minuscule to nonexistent. Fear is the worst enemy, not the contaminated soldier.
Three basic methods of decontamination are physical removal, chemical deactivation, and biological deactivation of the agent. Biological deactivation has not been developed to the point of being practical.
Several types of physical and chemical methods are at least potentially suitable for decontaminating equipment and material. Flushing or flooding contaminated skin or material with water or aqueous solutions can remove or dilute significant amounts of agent. Scraping with a wooden stick, i.e., a tongue depressor or Popsicle stick, can remove bulk agent by physical means. For the decontamination of clothing only, adsorbents and containment materials (to be used on outer garments before their removal and disposal) have been considered. A significant advantage of most physical methods is their nonspecificity. Since they work nearly equally well on chemical agents regardless of chemical structure, knowledge of the specific contaminating agent(s) is not required.
Flushing with Water or Aqueous Solutions. When animal skin contaminated with GB was flushed with water (a method in which physical removal predominates over hydrolysis of the agent), 10.6 times more GB was required to produce the same mortality rate as when no decontamination occurred. In another study, the use of water alone produced better results than high concentrations of hypochlorite (i.e., 5.0% or greater, which are not recommended for skin). Timely, copious flushing with water physically removes the agent and will produce good result.
Adsorbent Materials. Adsorption refers to the formation and maintenance of a condensed layer of a substance, such as a chemical agent, on the surface of a decontaminant as illustrated by the adsorption of gases by charcoal particles and by the decontaminants described in this section. Some NATO nations use adsorbent decontaminants in an attempt to reduce the quantity of chemical agent available for uptake through the skin. In emergency situations, dry powders such as soap detergents, earth, and flour, may be useful. Flour, followed by wiping with wet tissue paper, is reported to be effective against GD, VX, and HD.
M291 Resin. The current method of battlefield decontamination by the individual soldier involves the use of a carbonaceous adsorbent, a polystyrene polymeric, and ion exchange resins (M291). The resultant black resin is both reactive and adsorbent. The M291 Kit has been extensively tested and proven highly effective for skin decontamination. It consists of a wallet-like carrying pouch containing six individual decontamination packets. Each packet contains a nonwoven, fiberfill-laminated pad impregnated with the decontamination compounds. Each pad provides the individual with a single step, nontoxic/nonirritating decontamination application that can be used on the skin, including the face, and around wounds. Instructions for use are marked on the case and packets. The individual decontamination pads are impregnated with the decontamination compound, "Ambergard XE-555 Resin", which is the black, free-flowing, resin-based powder. As the pad is scrubbed over the contaminated skin, the chemicals are rapidly transferred into and trapped in the interior of the resin particles. The presence of acidic and basic groups in the resin promotes the destruction of trapped chemical agents by acid and base hydrolysis. Because the resin is black, it maps out the areas that have been decontaminated.
Three types of chemical mechanisms have been used for decontamination: water/soap wash, oxidation, and acid/base hydrolysis.
Mustard (HD) and the persistent nerve agent VX contain sulfur molecules that are readily subject to oxidation reactions. VX and the other nerve agents (GA, GB, GD, and GF) contain phosphorus groups that can be hydrolyzed. Therefore, most chemical decontaminants are designed to oxidize HD and VX and to hydrolyze nerve agents (VX and the G series).
Water/Soap Wash. Both fresh water and sea water have the capacity to remove chemical agents not only through mechanical force, but also via slow hydrolysis; however, the generally low solubility and slow rate of diffusion of chemical warfare agents in water significantly limit the agent hydrolysis rate.
The predominant effect of water and water/soap solutions is the physical removal or dilution of agents; however, slow hydrolysis does occur particularly with alkaline soaps. In the absence of hypochlorite solutions or other appropriate means of removing chemical agents, these methods are considered reasonable options.
Oxidation/Hydrolysis. The most important category of chemical decontamination reactions is oxidative chlorination. This term covers the "active chlorine" chemicals like hypochlorite. The pH of a solution is important in determining the amount of active chlorine concentration. An alkaline solution is advantageous. Hypochlorite solutions act universally against the organophosphorus and mustard agents.
Both VX and HD contain sulfur atoms that are readily subject to oxidation. Current doctrine specifies the use of a 0.5% sodium or calcium hypochlorite solution for decontamination of skin and a 5% solution for equipment.
Hydrolysis. Chemical hydrolysis reactions are of two types, acid and alkaline. Acid hydrolysis is of negligible importance for agent decontamination because the hydrolysis rate of most chemical agents is slow, and adequate acid catalysis is rarely observed. Alkaline hydrolysis is initiated by the nucleophilic attack of the hydroxide ion on the phosphorus atoms found in VX and the G agents. The hydrolysis rate is dependent on the chemical structure and reaction conditions such as pH, temperature, the kind of solvent used, and the presence of catalytic reagents. The rate increases sharply at pH values higher than 8 and increases by a factor of 4 for every 10oC rise in temperature. Several of the hydrolytic chemicals are effective in detoxifying chemical warfare agents; unfortunately, many of these (e.g., NaOH) are unacceptably damaging to the skin. Alkaline pH hypochlorite hydrolyzes VX and the G agents quite well.
All casualties entering a medical unit after experiencing a chemical attack are to be considered contaminated unless there is certification of noncontamination. The initial management of a casualty contaminated by chemical agents will require removal of MOPP and decontamination with 0.5% hypochlorite before treatment within the field treatment facility.
Initial Decontamination. During initial decontamination in the decontamination areas, bandages are removed and the wounds are flushed; the bandages are replaced only if bleeding recurs. Tourniquets are replaced with clean tourniquets and the sites of the original tourniquets decontaminated. Splints are thoroughly decontaminated, but removed only by a physician.
The new dressings are removed in the operating room and submerged in a 5% solution of hypochlorite or placed in a plastic bag and sealed.
General Considerations. Of the agents discussed, only two types, the vesicants and nerve agents, might present a hazard from wound contamination. Cyanide is quite volatile, so it is extremely unlikely that liquid cyanide will remain in a wound, and it requires a very large amount of liquid cyanide to produce vapor adequate to cause effects.
Mustard converts to a cyclic compound within minutes of absorption into a biological milieu, and the cyclic compound rapidly (minutes) reacts with blood and tissue components. These reactions will take place with the components of the wound--the blood, the necrotic tissue, and the remaining viable tissue. If the amount of bleeding and tissue damage is small, mustard will rapidly enter the surrounding viable tissue where it will quickly biotransform and attach to tissue components (and its biological behavior will be much like an intramuscular absorption of the agent).
Although nerve agents cause their toxic effects by their very rapid attachment to the enzyme acetylcholinesterase, they also quickly react with other enzymes and tissue components. As they do with mustard, the blood and necrotic tissue of the wound will "buffer" nerve agents. Nerve agent that reaches viable tissue will be rapidly absorbed, and since the toxicity of nerve agents is quite high (a lethal amount is a small drop), it is unlikely that casualties who have had much nerve agent in a wound will survive to reach medical care.
Potential risk to the surgeon from possibly contaminated wounds arises from agent on foreign bodies in the wound and from thickened agents.
Thickened Agents. Thickened agents are chemical agents that have been mixed with another substance (commonly an acrylate) to increase their persistency. They are not dissolved as quickly in biological fluids, nor are they absorbed by tissue as rapidly as other agents. VX, although not a thickened agent, is absorbed less quickly than other nerve agents and may persist in the wound longer than other nerve agents.
Thickened agents in wounds require more precautions. Casualties with thickened nerve agents in wounds are unlikely to survive to reach surgery. Thickened HD has delayed systemic toxicity and can persist in wounds even when the large fragments of cloth have been removed. Though the vapor hazard to surgical personnel is extremely low, contact hazard from thickened agents does remain and should always be assumed.
No country is currently known to stockpile thickened agents. In a chemical attack, the intelligence and chemical staffs should be able to identify thickened agents and to alert medical personnel of their use.
Off Gassing. The risk from vapor off-gassing from chemically contaminated shrapnel and cloth in wounds is very low and not significant. Further, there is no vapor release from contaminated wounds without foreign bodies. OffSgassing from a wound during surgical exploration will be negligible (or zero). No eye injury will result from off-gassing from any of the agents. A chemical-protective mask is not required for surgical personnel.
Foreign Material. The contamination of wounds with mustard or nerve agents is basically confined to the foreign material (e.g., battle dress uniform (BDU) and protective garment in the wound). The removal of this cloth from the wound effectively eliminates the hazard. There is little chemical risk associated with individual fibers left in the wound. No further decontamination of the wound for chemical agent is necessary.
Wound Contamination Assessment. The CAM can be used to assist in locating contaminated objects within a wound; however, 30 seconds are required to achieve a bar reading. The CAM detects vapor, but may not detect liquid (a thickened agent or liquid on a foreign body) deep within a wound. A single bar reading on CAM with the inlet a few millimeters from the wound surface indicates that a vapor hazard does not exist.
Hypochlorite. Diluted hypochlorite (0.5%) is an effective skin decontaminant for patient use. The solution should be made up fresh daily with a pH in the alkaline range. Plastic bottles containing 6 ounces of calcium hypochlorite are currently fielded for this purpose.
Hypochlorite solution is contraindicated for the eye. This substance may result in corneal opacities. It is also not recommended for brain and spinal cord injuries. Irrigation of the abdomen may lead to adhesions and is therefore also contraindicated. The use of hypochlorite in the thoracic cavity may be less of a problem, but the hazard is still unknown.
Wound Exploration/Debridement. Surgeons and assistants are advised to wear a pair of well-fitting (thin), butyl rubber gloves or double latex surgical gloves and to change them often until they are certain there are no foreign bodies or thickened agents in the wound. This is especially important where puncture is likely because of the presence of bone spicules or metal fragments.
The wound should be explored with surgical instruments rather than with fingers. Pieces of cloth and associated debris must not be examined closely, but quickly disposed of in a container of 5% hypochlorite. The wound can then be checked with the CAM, which may direct the surgeon to further retained material. It takes about 30 seconds to get a stable reading from the CAM. A rapid pass over the wound will not detect remaining contamination. The wound is debrided and excised as normal, maintaining a no-touch technique. Removed fragments of tissue are dropped into hypochlorite. Bulky tissue such as an amputated limb should be placed in a plastic or rubber bag (chemical proof) which is then sealed.
Hypochlorite solution (0.5%) may be instilled into deep, noncavity wounds following the removal of contaminated cloth. This solution should be removed by suction to an appropriate disposal container. Within a short time, i.e., five minutes, this contaminated solution will be neutralized and nonhazardous. Subsequent irrigation with saline or other surgical solutions should be performed.
Penetrating abdominal wounds caused by large fragments or containing large pieces of chemically contaminated cloth will be uncommon. Surgical practices should be effective for the majority of wounds in identifying and removing the focus of remaining agent within the peritoneum. When possible, the CAM may be used to assist. Saline, hydrogen peroxide, or other irrigating solutions do not necessarily decontaminate agents, but may dislodge material for recovery by aspiration with a large bore sucker. The irrigation solution should not be swabbed out manually with surgical sponges. The risk to patients and medical attendants is minuscule. However, safe practice suggests that any irrigation solution should be considered potentially contaminated. Following aspiration by suction, the suction apparatus and the solution should be disposed of in a solution of 5% hypochlorite.
Superficial wounds should be subjected to thorough wiping with 0.5% hypochlorite and subsequent irrigation with normal saline.
Instruments that have come into contact with possible contamination should be placed in 5% hypochlorite for ten minutes prior to normal cleansing and sterilization. Reusable linen should be checked with the CAM, M-8 paper, or M-9 tape for contamination. If found to be contaminated, it should be disposed of in a 5 to 10% hypochlorite solution.
Decontamination at the medical treatment facility is directed toward: (1) eliminating any agent transferred to the patient during removal of protective clothing; (2) decontaminating or containing of contaminated clothing and personal equipment; and (3) maintaining an uncontaminated treatment facility.
Current doctrine specifies the use of 0.5% hypochlorite solution or the M291 Kit for contaminated skin. These are both state-of-the-art decontamination preparations, one old, and one new.
Fabric and other foreign bodies that have been introduced into a wound have the capacity to sequester and slowly release chemical agent presenting a liquid hazard to both the patient and medical treatment personnel. There is no vapor hazard to surgical personnel. Protective masks are not necessary.
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Introduction |
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