CHAPTER 9 BIOLOGICAL AND CHEMICAL AGENTS

Nuclear weapons are primarily designed to destroy material by blast and shock. Biological and chemical substances for military use are primarily antipersonnel agents; they are intended to produce casualties without the destruction of buildings, ships, or equipment.

This chapter is an overview of shipboard biological warfare (BW) and chemical warfare (CW) defense and countermeasures. Detailed information on this subject is available in Naval Ships' Technical Manual, chapter 470.

BIOLOGICAL WARFARE AND CHEMICAL WARFARE COUNTERMEASURES

The BW agents include a variety of microbes and C W agents include poisons. These agents produce temporary incapacitation, sickness, or death in personnel. In tactical use, these agents are generally atomized in the air as aerosols (microscopic airborne solid particles, fine sprays or mists), vapors, or gases. For practical purposes, BW and CW agents in these forms are odorless, colorless, tasteless, and invisible. However, a concentrated spray of aerosol cloud may be temporarily visible when adjacent to an exploded or spraying munition. Also, most BW and CW agents produce no pain or other sensation until physiological damage is well underway. The properties allow an attacker to gain and hold military advantages of surprise and concealment.

The BW and CW agents are entirely different in their detailed effects on the human body, in the medical treatment required, and in their speed of action. However, the Navy has found it useful to consider BW and CW as a single system of toxic warfare for defensive purposes. All BW or CW agents that require the individual to wear both the protective mask and protective clothing fall into the MC (mask and clothing) group. Other BW and CW agents, against which adequate protection is given by the mask alone, are in the MO (mask only) group.

The BW agents are not quick-acting tactical weapons. They are best used for delayed effects against convoys, advanced bases, repair facilities, shipyards, port concentration of ships, task groups at sea, and civilian populations. The CW agents, on the other hand, can be selected for either immediate or delayed action, for brief or prolonged disability, or for temporary physical or mental incapacitation. In general, CW agents are best adapted for quick antipersonnel effects. These agents can be mixed, as can BW agents, to obtain combinations of properties to complicate and confuse the defense.

WEATHER FACTORS

The use of BW or CW agents is dependent upon weather and topography. Calm and lowvelocity winds keep the agent clouds concentrated the longest as they move downwind. Gusty and high-velocity winds break up the agent clouds quickly. This makes it difficult to use the winds "to target" units downwind. Precipitation and the vertical temperature gradient in the lower atmosphere significantly affect BW or CW attacks. Heavy and extended rain or snow will gradually wash the air clean of the agents, but short and light precipitation is of little help in cleaning the air.

Normally, the air temperature decreases with an increase in altitude. This rate of temperature decrease is known as the temperature gradient. When the temperature decreases 5.5'F per 1,000 feet of altitude in dry air or 2.8F per 1,000 feet of altitude in saturated air, the gradient is neutral, and a neutral stability condition prevails. Neutral stability is prompted by overcast skies and a seasurface temperature equal to the air temperature. With a neutral gradient, BW and CW agents will hang suspended with essentially no rising or falling. When the temperature gradient is larger than the figures given above, the air becomes unstable. A sea surface that is warmer than air, the presence of a cold air mass, and bright sunlight

all contribute to atmospheric instability. Agents tend to rise continuously in unstable air. The atmosphere increases in stability as the temperature gradient decreases. In a temperature inversion, the atmosphere is extremely stable. It results from a sea-surface temperature that is cooler than the air. Mixing of the lower atmosphere in this condition is produced only by strong winds. The agents tend to move with very little vertical spread.

SHIPBOARD VENTILATION CONTROL

All Navy ships, with the exception of submarines, are continuously ventilated with weather air to some degree under all present material conditions and degrees of closure. Theory and practical tests show there is no ''gastight envelope" on any type of United States Navy ship.

Ventilation rates are expressed as rates of change (R of C). An average R of C for spaces in which little heat is generated is about 3 minutes per change. The R of C for air-conditioned spaces is about 20 to 30 minutes per change, although the air within the air-conditioned compartment is recirculated over cooling coils at a much higher rate.

In material condition Zebra, with X-ray, Yoke, and circle William fittings closed, all nonessential fans and blowers are secured. The ship is expected to be in a satisfactory condition of watertight integrity. However, it is not gastight. Air leakage in a closed-up ship is caused by the following: . Ventilation ducts without closures

. Structural leaks (such as defective welds, aluminum-to-steel joints, and stuffing boxes) . Bypass leaks through doors, hatches,

portholes, and closures due to worn gaskets . Very large leaks from violations of

condition Zebra and unauthorized opening of doors

The rate of increase, or buildup, of outside contamination in a ventilated compartment follows an exponential growth rule. When a ship enters a BW or CW zone, the concentration of contamination in the compartment air increases very rapidly at first and then more slowly as it approaches the concentration of the outside air. As soon as the ship passes out of BW or CW contaminated air, the concentration of the contaminant in the compartment air begins to decrease or decay. The rate of decay follows the same exponential rule as for buildup; there is a fast decrease at first, but it gradually decreases as the compartment contamination level approaches zero.

NOTE: One air change will produce a concentration equal to 63% of the external concentration; three air changes, 95%; and six air changes, 99.8%.

The most favorable ventilation control in a BW or CW situation is ventilation at the lowest practical rate while the ship is in the contaminated zone (interior concentration buildup phase). This is followed by the highest practical rate in clean air (interior concentration decay phase). If the ship is in the contaminated zone for six or more air changes, the compartment dosage will approach the topside dosage, but cannot exceed it.

The least favorable ventilation control in a BW or CW situation is ventilation at a high rate while the ship is in the contaminated zone, followed by a low rate as the ship enters clean air. Under these conditions, the compartment dosage may reach several times the topside dosage.

The situations described above are considered possible but difficult to achieve in practice. They presume (1) exact knowledge of the time of entering and leaving the contaminated zone or (2) the chance increase or decrease of ventilation rate just when the ship leaves the contaminated zone.

A more probable situation is that the ship transits a contaminated zone with no knowledge of the presence of a contaminant. Assuming an unchanging ventilation rate, compartment dosages will be approximately equal to topside dosages.

A thorough indoctrination, full intelligence data, and alert observation will offer you some clues to the existence of contaminated zones. These clues should be considered together with the other elements of the tactical situation. They can then be applied to the best advantage by minimizing ventilation rates during the period of suspected exposure to contaminated air and maximizing ventilation rates for a period of 6 to 12 air changes in clean air.

When there is a possibility of BW exposure, you should consider the effect of sunlight. Airborne microbes live longer when there is little or no light. Therefore, ventilation should be kept to the minimum during the hours of little or no sunlight. The safest period to increase ventilation is between midmorning and midafternoon.