An Evaluation of Radiation Exposure Guidance for Military Operations: Interim Report (1997)

The previous sections describe the potential adverse health consequences of radiation exposure and outline the currently accepted methods for limiting those consequences. In light of that background, we will now consider how well the ACE Directive fulfills a similar mission specifically for soldiers.

The Army has published guidance for control of doses from routine occupational exposures and those associated with nuclear war. The ACE Directive is an encouraging step in developing control measures for other situations. We realize that the Directive was meant for a specific mission (Bosnia) and that the Army recognizes its limitations. The criticisms that follow should be viewed as constructive and in no way diminish the significant progress that the Army has made toward the control of the complete spectrum of radiation hazards on the battlefield and in operational situations other than war.

In this review we will look first at general characteristics of the ACE Directive as compared to existing radiation protection methods in the civilian sector. Then we will make several comments on specific parts of the Directive.

We begin with an assessment of the underlying philosophy of the ACE Directive. The Directive states (NATO, 1996, § 1-2.) that:

From that standpoint, the Directive captures the two central principles of radiation protection as they apply to interventions. These are justification and optimization. The Directive does not appear to use the concept of practices, for which there are specified dose limits, since none are mentioned in the Directive policy statement.

Several dose and dose rate levels in the Directive are associated with actions of one type or another. For example, a survey team is directed to turn back when one of its members encounters a dose rate of 0.003 mGy/hr (0.0003 rad/hr), and commanders are to establish dose control measures as part of operations at a cumulative dose of 5–50 mGy (0.5–5 rad) (NATO, 1996). These may be thought of as reference levels—values at which certain actions should occur.¹¹ Although it does not specifically say so, the ACE Directive assumes an underlying philosophy that corresponds closely to that of an intervention as defined by ICRP.

The analogy of military action as intervention is not perfect. ICRP sees an intervention as an action directed at the radiation source, e.g., to prevent further contamination or to put out a fire in a reactor. In the case of the Army, the object of the intervention may have nothing to do with the radiation source.

Many situations in military operations resemble practices more than interventions. For example, sending a survey team into an area of unknown radioactive contamination is clearly an intervention, and the ACE Directive is applicable. On the other hand, consider a soldier assigned to guard the entrance of a damaged nuclear plant. The dose rate at the guard station probably would have been measured as the result of a preceding intervention. Providing routine guard services would no longer be part of the intervention. At that point, exposure levels should be well known and dose to the soldier should therefore be kept not only as low as reasonably achievable but also within accepted dose limits. This activity should be controlled as a practice, not as an intervention.

Having said that, we hasten to say that a military operation is a unique situation where simple definitions of practices and interventions become complex and conditions may change quickly. In the civilian version of our scenario, the guard would finish a shift and go home. In the military situation, the plant may suddenly come under attack, resulting in the guard being unable to avoid exceeding occupational limits. Thus, the military situation that began as a practice, subject to dose limits, must now be managed as an intervention.

One could argue that all military operations, since they involve such uncertain situations, should be managed as interventions, without dose limits. However, given the substantial involvement of the military in peacekeeping and humanitarian assistance missions, it is hard to justify not providing soldiers with the level of protection that controlling exposures as a practice would provide.

For nonemergency situations, the ACE Directive does not provide guidance that would afford protection to soldiers at a level appropriate for a practice.

There are terms in the ACE Directive that the committee considers misleading. The first, and by far the most serious issue, is the term Low Level Radiation when it is applied broadly to doses in the range 50 to 700 mSv (5 to 70 rem). Low level may be an appropriate descriptor when comparing these doses to those that could result from the detonation of a nuclear device. In the broader context of radiation protection, however, low level clearly implies much lower doses. While the terminology may be perfectly clear to those involved in developing the guidance, it probably will be misunderstood by others. The Army's use of this term to describe doses that approach thresholds for acute effects easily could be misinterpreted as an intent to mislead soldiers on the seriousness of such exposures.

The committee has concerns about the terms used to describe effects of dose categories in the table in Annex A. No risk is used to describe the effect of doses less than 0.5 mGy (0.05 rad). This is inconsistent with international positions on the effects of radiation, specifically the assumption that even small radiation doses may produce some deleterious effects. Likewise, the term normal risk incorrectly implies that an exposure of 0.5 to 5 mGy (0.05 to 0.5 rad) adds no additional risk to that from natural background radiation exposure, even though such exposures are considered to contribute very small, possibly negligible, health risks.

Radiological hazard is often used in the ACE Directive to describe any radiation exposure.¹² Hazard is an ambiguous term. Given the uncertainty as to the magnitude of the health consequences at low levels, the term hazard should not be appended to radiation automatically. Rather, it should be used advisedly to identify the potential for significant health consequences.

The ACE Directive (NATO, 1996, § 1-3.a. and c.(1)) indicates that there is a prospective assessment of risk, high or low. It is unclear whether this refers to (a) intelligence assessments of the likelihood of radiation contamination or (b) the magnitude of measurable levels of radiation contamination.

In principle, the committee agrees with the Directive's requirement for ''dose rate instruments to measure alpha-and beta-emitting particles as well as gamma radiations'' (§1-3.b.). Instruments sensitive to beta and alpha radiation will be useful in conducting assessments for potential skin contamination and

internal deposition and for triggering appropriate protective actions. However, the exact wording of the requirement suggests that the instrumentation will be capable of measuring "dose rate." The committee is not aware of any instruments that can directly measure beta and alpha radiation dose rates in the field.

The ACE Directive defines a radiological hazard area as anywhere the dose rate is in excess of 0.002 mGy/hr (0.0002 rad/hr). This dose rate is approximately 20 times the background radiation dose rate found in the United States (NCRP, 1987) and one-tenth the maximum dose rate allowed for uncontrolled areas that members of the public might frequent. If a soldier were to spend a year in such an area—0.002 mGy/hr (0.0002 rad/hr)—a worst case scenario, that soldier would accrue a dose of approximately 20 mGy (2 rad). That is equal to the ICRP recommended annual dose limit for civilian radiation workers. Continuous exposure at this level would not exceed the current U.S. radiation worker annual exposure limit of 50 mSv set by the Nuclear Regulatory Commission (CFR, 1991). Given its consistency with these comparison figures, the radiation dose rate at the edge of the exclusion zone is reasonable for defining contaminated areas and instituting radiation protection actions.

The ACE Directive requires that, in deciding to allow a soldier to be put at risk of exposure to radiation, a commander will ensure that an accurate radiation dose is recorded to document that soldier's exposure (NATO, 1996). To do that, the commander must be able to determine an accurate dose for each individual soldier. The committee agrees with that requirement but finds its implementation problematic.

Available dosimeters may not be capable of providing adequate dosimetry. The IM-93 pocket dosimeter, currently fielded for individual soldiers, is not issued to all and is fragile and prone to error in rugged field use. The dosimeter planned for individual issue, the DT-236, is not sensitive below 100 mGy (10 rad). Thus, it cannot be used to differentiate between exposures in the low dose categories specified in the ACE Directive. Thermoluminescent dosimeters that can be used to monitor dose at low dose levels are available from the Army Dosimetry Center, but the equipment needed to read these devices is not normally available or issued to combat units. In summary, although individual dosimetry is appropriately required by the Directive, it may be difficult to do with currently available hardware.

The level of exposure at which dosimetry is recommended is stated in the Operational Exposure Guidance table of the ACE Directive. At 0.5 mSv (0.05 rad), the beginning of RES category labeled "1A," the commander is advised to

record individual dose readings, and initiate periodic monitoring." It is not clear what circumstances would lead to the start of individual dosimetry. If individual dosimetry has not yet begun, how is it determined that the 0.5 mSv (0.05 rem) level has been exceeded, triggering the start of periodic monitoring? We assume that there are no dose histories, since monitoring has not yet begun. Therefore, the decision to start monitoring must be based upon projected whole body doses of 0.5 mSv or more. Similarly, in civilian practice, the decision to issue individual dosimeters for monitoring can be made based on projected doses. However, the ACE Directive requirement is considerably more stringent than that commonly followed in occupational programs and the rest of the DoD (DoDI, 1996). The DoD requires monitoring of individual doses only above 5 mSv (0.5 rem), ten times the ACE Directive recommended level.

There is an inconsistency between the text (NATO, 1996, § 1-3.f.(3.)) and the table in Annex A. The text states that:

The table of Annex A, however, directs that monitoring begin at 0.5 mGy (0.05 rad). As a result of this ambiguity, it is conceivable that an individual could enter a low level contaminated zone without dosimetry. It is possible that this could result in exposure from unknown, localized hot spots that could cause doses above the monitoring threshold in Annex A.

While it is understandable that the radiation community within the military might want to retain the familiar unit of absorbed dose, the rad, and rename it the centigray, cGy, the practice is not internationally accepted. The same may be said for the unit of effective dose, the cSv, as a pseudonym for the rem.

Reported doses and particularly dose rates will probably be low. Reporting doses and survey measurements in cGy, or cGy/hr, will require the use of very small decimal numbers (e.g., the ACE Directive limit on a contaminated area of "0.0002 cGy/hr"). In handwritten transmissions of data, this could lead to errors in transcription (e.g., 0.0002 mistaken for 0.00002).

While the ACE Directive requires individual assignment of external whole body doses, there do not appear to be any requirements to identify or evaluate

internal deposition of radionuclides or to estimate the radiation dose from such depositions. Neither is there a requirement to determine the potential for internal dose hazards in the area of operations. In fact, Note 1 of the table in Annex A to the Directive (NATO, 1996) states that:

The ACE Directive recognizes the problem of internalized radioactive materials—soldiers are directed to put on their protective masks when in a radiological hazard area (NATO, 1996)—but proceeds under the assumption that no such exposures will occur. The ACE Directive assumes that the respiratory protection is 100 percent effective and is silent on situations in which protective equipment is not worn or is defective. The ACE Directive does not specify, quantitatively, at what level of radiological contamination the protective mask should be worn.

The note in the table cited above implies that protective clothing and respirators are being used whenever any radioactivity above background is detected. ACE Directive paragraph 1-3.g.(1) requires that respiratory protection be worn in a "radiological area," but the area is not defined (§1-3.c.(2)(c)) by airborne radioactive contamination levels. It is conceivable that the wearing of the protective mask could be required when the actual air concentration is well within acceptable limits. This could happen if the radiological contamination was not easily resuspended or was fixed on the surfaces of military hardware that had been partially decontaminated. On a very hot day, the wearing of the protective mask under these conditions would unnecessarily diminish the performance of the soldier, perhaps increasing risk of other nonradiation hazards, jeopardizing the mission.

In addition to knowing the total dose accumulated by an individual, it is useful to know the time history of that exposure. The ACE Directive enhancements to the Operational Exposure Guidance specify that dose reference levels are to be used with cumulative doses. However, the guidance does not specify whether doses are accumulated over an operation, a year, or a lifetime. It does not appear that individual dose records indicating prior occupational and other exposures will be available to commanders in assigning RES categories.

The ACE Directive Operational Exposure Guidance table (Annex A) subdivides the some-exposure category (RES-1, our Table 4-1) of existing OEG guidance (HQDA, 1994, NATO, 1986). Each level is accompanied by a narra-

tive description of the risk corresponding to a dose level and by a series of required control actions.

The appropriateness of the dose categories depends largely on the way in which they will be used. These categories could be very useful and appropriate in controlling individual exposures and making future assignments. Such uses assume that individual dosimetry is available with the resolution and sensitivity of better than 0.5 mGy (0.05 rad, the width of the narrowest category). Without that, it will be impossible to resolve exposures into the lower RES categories.

If the table is intended for planning interventions in heavily contaminated areas, the fine detail in the lower categories may not be useful. It is not uncommon in nuclear accident areas (e.g., Chernobyl) to find wide variation in dose rates across small distances. Individuals could easily stray into hot spots where dose rates are significantly higher (e.g., by a factor of 10) than initial survey estimates would indicate. Without real-time, self-reading,¹³ individual dosimetry, it would be unreasonable to expect to control doses for all individuals in the first two RES categories (0–0.5 mGy [0–0.05 rem] and 0.5–5 mGy [0.05–0.5 rem]).

There is no indication in the ACE Directive of how unknown doses will be handled in recording individual doses or in assigning RES categories to units. In occupational radiation protection practice, it is normal to assign an administrative dose or to estimate a dose based upon best available data.

At doses ranging, from 5 to 50 mGy (0.5–5 rad, RES Category 1B), the Operational Exposure Guidance recommends "establishing dose control measures as part of operations." If we consider that the dose limit for the public used by the USNRC until 1994 was 5 mSv, this level for beginning dose control might be appropriate. However, the current limit for public exposure is 1 mSv (ICRP, 1991a; CFR, 1991). In addition, the ACE Directive itself institutes controls of radiation exposure beginning at 0.002 mGy/hr (0.0002 rad/hr). From this it would appear that some measures of control may be appropriate below the Category 1B level.

Radiation exposure status category IC indicates that only priority tasks are to be attempted between 50 mGy (5 rad) and 100 mGy (10 rad). Priority tasks are defined as those to avert danger to persons or to prevent damage from spreading. This level is comparable to EPA (1991) guidance that allows up to 100 mSv (10 rem) for similar tasks.¹⁴ It is also within the 500-mSv limit recommended by NCRP (1993). In the next higher exposure categories—1D (100–250 mSv, 10–25 rad) and 1E (250–700 mSv, 25–70 rad)—the ACE Directive limits missions to those that are necessary to save a life. The only difference between these two categories appears to be that the lower band is described as increased

risk and the higher as significant risk. The actions associated with them are the same. In emergencies, ICRP (1991b) recommends that every effort be made to keep doses below 1,000 mSv (100 rem) to prevent serious deterministic health effects (e.g., acute radiation sickness). The exposure levels in 1D and 1E are in keeping with that guidance.

The ACE Directive (§1-3.f.(3)) requires preparation and maintenance of individual medical records. Again, implementation is in question. Current Army doctrine for maintaining records during combat operations (HQDA, 1994) specifies that only the unit's radiation exposure status is transferred with the individual soldier. On the other hand, the Department of Defense requires that during peacetime individual doses be maintained (DoDI, 1996).

The ACE Directive (§1-3.f.(3)) requires commanders to ensure that the dose a soldier receives is accurately recorded upon each radiological exposure and that the total dose is annotated in his or her individual medical record in accordance with national regulations. Also, the theater commander (§1-3.f.(4)) is charged with ensuring "that the appropriate medical and NBC Cells [consisting of specialists in nuclear, biological, and chemical matters] are tasked to receive, monitor and maintain all radiological data in accordance with national regulations [emphasis added]." For U.S. soldiers, it is not clear whether that means in accordance with Nuclear Regulatory Commission guidelines or Army regulations. The committee assumes that this refers to the Nuclear Regulatory Commission regulations. If that is the case, then internal doses must be documented along with external doses.

The ACE Directive does not specify exactly what dose-related data must be collected (e.g., internal dose, external dose, effective dose, environmental data, etc.). Ultimately, it may be necessary to link this information from its repository to an individual for purposes of compensation determinations or epidemiologic study.