The M40 protective mask is available in three sizes, and when worn correctly, will protect the face, eyes, and respiratory tract. The M40 utilizes a single screw on filter element which involves two separate but complementary mechanisms: 1) impaction and adsorption of agent molecules onto ASC Whetlerite Carbon filtration media, and 2) static electrical attraction of particles initially failing to contact the filtration media. Proper maintenance and periodic replacement of the crucial filter elements are of the utmost priority. The filter MUST be replaced under these circumstances: the elements are immersed in water, crushed, cut, or otherwise damaged; excessive breathing resistance is encountered; the "ALL CLEAR" signal is given after exposure to a biological agent; 30 days have elapsed in the combat theater of operations (the filters must be replaced every 30 days); supply bulletins indicate lot number expiration; or when ordered by the unit commander. The filter element can only be changed in a non-contaminated environment. Two styles of optical inserts for the protective mask are available for soldiers requiring visual correction. The wire frame style is considered to be the safer of the two and is more easily fitted into the mask. A prong-type optical insert is also available. A drinking tube on the mask allows the wearer to drink while in a contaminated environment. Note that the wearer should disinfect the canteen and tube by wiping with a 5 percent hypochlorite solution before use.

The battle dress overgarment suits come in eight sizes and are currently available in both woodland and desert camouflage patterns. The suit may be worn for 24 continuous hours in a contaminated environment, but once contaminated, it must be replaced by using the MOPP-gear exchange procedure described in the Soldier's Manual of Common Tasks. The discarded BDO must be incinerated or buried. Chemical protective gloves and overboots come in various sizes and are both made from butyl rubber. They may be decontaminated and reissued. The gloves and overboots must be visually inspected and decontaminated as needed after every 12 hours of exposure in a contaminated environment. While the protective equipment will protect against biological agents, it is important to note that even standard uniform clothing of good quality affords a reasonable protection against dermal exposure of surfaces covered.

Those casualties unable to continue wearing protective equipment should be held and/or transported within casualty wraps designed to protect the patient against further chemical-biological agent exposure. Addition of a filter blower unit to provide overpressure enhances protection and provides cooling.

Collective protection by the use of either a hardened or unhardened shelter equipped with an air filtration unit providing overpressure can offer protection for personnel in the biologically contaminated environment. An airlock ensures that no contamination will be brought into the shelter. In the absence of a dedicated structure, enhanced protection can be afforded within most buildings by sealing cracks and entry ports, and providing air filtration with high efficiency particulate air (HEPA) filters within existing ventilation systems. The key problem is that these shelters can be very limited in military situations, very costly to produce and maintain, and difficult to deploy. Personnel must be decontaminated prior to entering the collective protection unit.

The most important route of exposure to biological agents is through inhalation. Biological warfare (BW) agents are dispersed as aerosols by one of two basic mechanisms: point or line source dissemination. Unlike some chemical threats, aerosols of agents disseminated by line source munitions (e.g., sprayed by low-flying aircraft or speedboats along the coast) do not leave hazardous environmental residua (although anthrax spores may persist and could pose a hazard near the dissemination line). On the other hand, aerosols generated by point-source munitions (i.e., stationary aerosol generator, bomblets, etc.) are more apt to produce ground contamination, but only in the immediate vicinity of dissemination. Point-source munitions leave an obvious signature that alerts the field commander that a biological warfare attack has occurred. Because point-source munitions always leave an agent residue, this evidence can be exploited for detection and identification purposes.

Aerosol delivery systems for biological warfare agents most commonly generate invisible clouds with particles or droplets of < 10 micrometers (m m). They can remain suspended for extensive periods. The major risk is pulmonary retention of inhaled particles. To a much lesser extent, particles may adhere to an individual or his clothing, thus the need for individual decontamination. The effective area covered varies with many factors, including wind speed, humidity, and sunlight. In the absence of an effective real-time alarm system or direct observation of an attack, the first clue would be mass casualties fitting a clinical pattern compatible with one of the biological agents. This may occur hours or days after the attack.

Toxins may cause direct pulmonary toxicity or be absorbed and cause systemic toxicity. Toxins are frequently as potent or more potent by inhalation than by any other route. A unique clinical picture may sometimes be seen which is not observed by other routes (e.g., pulmonary edema after staphylococcal enterotoxin B (SEB) exposure). Mucous membranes, including conjunctivae, are also vulnerable to many biological warfare agents. Physical protection is then quite important and the use of full-face masks equipped with small-particle filters, like the chemical protective masks, assumes a high degree of importance.

Other routes for delivery of biological agents are thought to be less important than inhalation, but are nonetheless potentially significant. Contamination of food and water supplies, either purposefully or incidentally after an aerosol biological warfare attack, represents a hazard for infection or intoxication by ingestion. Assurance that food and water supplies are free from contamination should be provided by appropriate preventive medicine authorities in the event of an attack.

Intact skin provides an excellent barrier for most biological agents. T-2 mycotoxins would be an exception because of their dermal activity. However, mucous membranes and abraded, or otherwise damaged, integument can allow for passage of some bacteria and toxins, and should be protected in the event of an attack.