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Weapons of Mass Destruction (WMD)

Chapter 6

Collective Protection

Collective protection is required to provide a safe environment for soldiers to carry out tactical functions, such as medical care, command, control, and communications, without being restricted by wearing NBC protective clothing. Collective-protection equipment (CPE) is integrated into some weapon systems to increase their effectiveness in an NBC environment. Planning for collective protection should be an integral part of plans for the AirLand Battlefield. Commanders must examine and accurately plan for the additional manpower and logistics needed to operate in a collective-protection mode. Collective protection does not replace MOPP gear; it only allows the commander to reduce MOPP levels while in a contaminated environment. Collective protection can provide relief from MOPP4 for eating, rest, and hygiene. Understanding entry/exit procedures will greatly impact on the effective use of collective-protection systems.

Types of Collective Protection

CPE provides protection to a group of individuals under NBC conditions that permits relaxation of individual NBC protection. Under NBC conditions, CPE allows soldiers to function effectively. CPE comes to a unit as either a component of a piece of equipment or as a TOE asset. This includes equipment such as the M51 shelter and the M20 SCPE. Used together, these systems enhance a unit's capability to perform its mission in an NBC environment. There are four basic types of CPE: vent ventilated-facepiece, overpressure, hybrid, and total systems (Table 6-1). See Table 6-2 for the advantages and disadvantages of each system.

Ventilated-Facepiece System

Ventilated-facepiece systems supply filtered air to the protective mask canisters (both the M25A1 and M42 masks) of combat vehicle crew members and the M24 and M43 aircrew protective masks. The systems are assigned as GPFUS and are rated by their airflow capacity, in cubic feet per minute. The currently fielded systems are given in Table 6-3. Except for the M13A I GPFU, the components of these systems are similar.

The filtered, pressurized air supplied to individuals extends the MOPP gear's capabilities. It reduces breathing resistance through masks, and it aids in sweat evaporation. In addition, it can provide warm air to facepieces in cold weather.

Overpressure System

An overpressure system is an enclosure of pressurized; purified air. Gas and particulate filters remove any NBC contamination from the air. The system does not protect against gamma radiation or neutrons. The air pressure precludes leakage of contaminated air into the enclosure. Personnel enter and exit through a protective entrance. This entrance is an air lock, and it prevents contamination from entering the enclosure. Overpressure systems for fixed sites are discussed in detail in FM 3-4-1.

M51 Shelter System

The M51 shelter is a trailer-mounted system (Figure 6-1). It features an overpressure and environmental control system. The shelter is predominately used by battalion aid stations and other medical units. It can also be used as a temporary rest and relief shelter.

M20 Simplified Collective-Protection Equipment

The SCPE provides a clean-air shelter for use against chemical and biological warfare agents and radioactive particles (Figure 6-2). It is lightweight and mobile, and it allows unit commanders to convert existing structures into protected command, control, and operations centers. Just as the M51, the SCPE can be used as a temporary rest and relief shelter (for example, as a break area for personnel working in heavy maintenance and supply operations) or as a command and control center. It provides a contamination-free environment in which 10 soldiers can work, eat, or rest without the encumbrance of the IPE. The M20 can be erected without the liner using only the protective entrance and blower compartment. Places such as a bank vault or warehouse freezer are examples of where an M20 without liner can be placed. Any cracks or holes will need to be sealed in the doorway. A bib section is available that will fit between the protective entrance and the frame of any door, and when taped down, seals the entrance from outside contamination. Entry and exit restrictions remain the same. For guidance on maintenance and parts of the SCPE see TM 3-4240-288-12&P.

Modular Collective-Protection Equipment

Modular CPE provides positive pressure NBC protection to a variety of vans and shelters. The system includes a variety of equipment, consisting of GPFUs, protective entrances, and various installation kits (Figure 6-3). An example of MCPE application to weapon systems includes mounting on a wheeled or tracked vehicle, on the M292 expandable van, or on a series of vans linked together (Figure 6-4).

Hybrid System

The hybrid system provides protection for personnel in combat vehicles, vans, and shelters. The system combines positive pressure and Ventilated race mask inside the enclosure with the option of using the positive pressure, the ventilated face mask, or both. The system can be used during closed-hatch, positive pressure operations or open-hatch, ventilated face mask operations (Figure 6-5). During open-hatch operations, the positive pressure reduces the amount of vapor contamination that enters. If contamination enters, the system helps purge the interior of toxic vapors. See Figure 6-6 for components of the hybrid system.

Total System

A hybrid system combines with some form of environmental control to make a total system (Figure 6-7). This system reduces heat-stress casualties; however, it increases the logistical burden, primarily because of maintenance. The M1A1 Abrams main battle tank has a total system. During closed-hatch operations the system provides a positive pressure and crew cooling. During open-hatch operations the system will provide cool, filtered air to the ventilated facepiece and cooling vest. Before initiating open-hatch operations, soldiers must be masked before exiting the M1A1 tank to prevent any possibility of chemical agent exposure. Additionally, the system provides modest overpressure that significantly reduces the amount of contamination infiltrating the crew compartment. Consequently, the time required to purge contamination is reduced.

Associated Equipment

Collective-protection associated equipment includes cooling and alarm systems and protective entrances.

Cooling Systems

Cooling reduces heat stress in soldiers operating in extremely hot and/or humid conditions. MOPP gear significantly increases the potential for heat stress, making cooling systems desirable. The two basic types are crew compartment and individual. Crew compartment cooling provides air conditioning to the compartment. Individual cooling is more effective when used while MOPP gear is worn. The choice of cooling system depends on the vehicle type and primary mission. The next generation of combat vehicles will provide individual and compartment cooling systems.

Collective-Protection Alarm Systems

Unit TOE chemical detection equipment and warning assets provide area warning to unit positions. These assets will also provide warning to occupants of collective-protection systems. Dedicated alarms are particularly useful for systems that must operate alone and away from supporting units. Unless an alarm is provided, carry out full entry and/or exit procedures whenever anyone enters and/or exits. Even if an alarm is available, occupants must conduct internal monitoring. This can be less frequent than when there is a known external hazard.

Protective Entrances

A protective entrance provides an interface between the contaminated environment and the protected enclosure. It enables shelter users to remove contaminated clothing and perform decontamination procedures, providing a relatively clean environment before entry into the shelter.

In a contaminated environment, overpressure systems not having a protective entrance (air lock) must minimize contamination entering the enclosure. They must establish drills and procedures for this purpose. These systems are usually on smaller, S250-type shelter systems and combat vehicles. An example is a main battle tank. Weight and space constraints make an air lock unfeasible. A system without an air lock consists of a clean shelter area only. During a liquid or vapor chemical attack, the system must remain closed, and soldiers must not enter or exit. Opening the doors allows contamination inside, and the crew must assume a higher MOPP level until the interior is purged or decontaminated.

The disadvantages of systems without an air lock emphasize the need for an air lock in a contaminated environment. An air lock prevents contamination from entering the enclosure. The air lock is pressurized, and contamination is eliminated through the use of filtered air. Air pressure in the entrance is slightly less than that in the protective enclosure, but slightly more than outside pressure. Air passing through the air lock purges contaminants that might enter during entry or exit of personnel or equipment. This air comes from the protective enclosure, the filter unit, or both. Different protective entrance configurations create variations of the overpressure category. These variations are those with a single air lock and those with a two-stage air lock.

Single air lock. In most cases, vans and shelters modified for collective protection use a single-compartment protective entrance. An example is the M12 protective entrance (Figure 6-8). This variation consists of the clean shelter area and an air lock (Figure 6-9). Before entering the air lock from a contaminated area, personnel must remove their MOPP gear except gloves and mask. Minor exposure to chemical agent vapor is possible between overgarment removal and entrance into the air lock. Clothing tends to absorb any chemical agent vapor in the atmosphere during this brief exposure. The amount of agent absorbed depends on agent concentration in the atmosphere, length of exposure, type of agent, type of clothing exposed, and climatic conditions. The air purge in the air lock flushes out the contaminated air brought in. It also reduces the amount of absorbed agent on clothing before the soldier enters the protective shelter. After a soldier and/or piece of equipment enters the protective shelter, monitoring ensures hazardous levels of agent were not carried inside.

Two-stage air lock. Adding a contamination control area (CCA) to a single air-lock system creates a two-stage air lock (Figure 6-9). Entering soldiers remove MOPP gear in the CCA. This affords better control of the liquid and vapor hazards of entry and exit.

Integral Protective Entrances

Integral protective entrances are designed to offer improved accessibility, more convenient storage and transport, and reduced setup time. There are two types of integral protective entrances: internal and external. Integral protective entrances are smaller than the detachable protective entrances and require less airflow during the purge cycle. The integral protective entrance and the shelter door are provided as a single bolt assembly. Integral protective entrances are currently designed for the S250 and S280 shelters.

Internal integral protective entrance. Deployed internally, the integral protective entrance can remain in its functional configuration and need not be stowed for transport. Since it is contained within the shelter, it is much less vulnerable on the battlefield (Figure 6-10).

External integral protective entrance. The external integral protective entrance is used for shelters that cannot sacrifice the internal space (Figure 6-11). The self-supporting integral protective entrance must be stowed for transport.

Field-Expedient Collective Protection

The unventilated shelter is the only type of field-expedient collective protection. Such a shelter has very little value because of the lengthy set-up time and rapid depletion of usable oxygen.

A wide variety of structures may be made into unventilated shelters. Such variety makes specific instructions difficult. Generally, the effectiveness depends largely on the tightness of the seal. The shelter must be airtight, and all openings must remain sealed as long as the hazard exists. Because sealing creates a stagnant air supply inside the shelter, occupancy is limited to a relatively short period.

Collective-Protection Planning

Providing for collective protection should bean integral part of plans for the AirLand Battlefield. A protective environment allows soldiers to carry out technical functions without the burden of MOPP gear. Also, soldiers need a protective environment where they can seek relief from MOPP gear. In addition, logistics, manpower, and other considerations enter into the planning for collective protection.

Collective-Protection Uses

Avoiding or displacing from contaminated terrain is desirable. Neither is always possible. It may be necessary to cross, occupy, or remain in contaminated terrain. Otherwise, the enemy could channel our movement and deny us key terrain features that could give our forces a tactical advantage. Every unit is equipped, trained, and conditioned to fight under contaminated conditions when the mission requires. However, individual efficiency and morale may decrease with time, and at some point, relief from wearing MOPP gear is necessary. The best relief method is rotating contaminated soldiers to a known clean area. Even in the worst situations, clean areas exist. Rotation is the least costly in terms of manpower and logistical support. However, the tactical situation may preclude displacement or rotation to clean areas. These situations require collective protection.

Collective-protection systems, like MOPP, are flexible. Flexibility allows the commander to maintain a balance between mission capability and NBC survivability. The commander must consider the threat, mission, tactical environment, and type of collective protection. In assessing a specific situation, the commander must decide if the reduced MOPP levels and relief are worth the additional logistics and manpower burden. For fixed-site collective-protection planning, see FM 3-4-1.


Commanders must plan for supplies, maintenance including filter replacement, and transportation to support collective-protection systems.


Adequate supply planning is a key element in effective use of collective-protection systems. These systems are not supply intensive; however, operation of such systems requires a continuous resupply of consumable and expendable items. Included are items that provide a means of contamination avoidance such as rain gear, ponchos, and plastic bags. These will keep liquid contamination away from the overgarment. Survival under NBC conditions could depend on these items. Therefore, it is not a question of merely maintaining special purpose collective-protection supplies. It is a matter of obtaining needed quantities of existing supplies.

Arrange to have supplies to support extended operations of a shelter kept inside the shelter if possible. Plan for the needed supplies, and stockpile them before an attack. As a minimum, these supplies should include protective clothing, expedient contamination avoidance items, decon kits, detector kits, and filters. These will allow shelter users to conduct an exchange. Provide adequate food and water if the shelter will operate for long periods within the contaminated area. If the shelter requires fuel, ensure it is requisitioned and stored. If the system has an external power supply, store fuel outside and away from the shelter. Plan for supplies to maintain operation of personnel in the shelter. These supplies include pens, paper, batteries, and parts.


In most cases, maintenance of collective-protection systems is minimal at organizational levels. Most systems have little or no operators' maintenance other than before-, during-, and after-operation checks and services. Operators may need to reset circuit breakers or perform system start-up procedures. At the unit level, maintenance is usuall

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