By
Charles S. McCowan, Jr.

RULE 1. GET THE AIR MODELERS TO AGREE ON WHAT THEY CAN. A mistake that is commonly made in air emission cases is to rely on the time honored defense, "My air modeler is better than your air modeler." The key to the effective use of air modelers is to get them to agree on what they can within their area of expertise before they disagree. A successful technique that has been employed is to ask the court to order a pre-hearing meeting of air modelers to attempt to determine if there is agreement among them on geographic areas that, in their opinion, were not affected by the incident. In such a meeting, the air modelers are encouraged to discuss and agree on specifically defined geographic areas that have not been adversely impacted by source emissions. The meeting is not intended to force the modelers to reach an agreement on the areas that have been affected or to serve as an agreement or admission that a class is appropriate, or to what extent. The sanction for the parties not agreeing to have their modeler participate in good faith in the meeting is for the party to be prevented from using that modeler. In order to achieve the purposes of the meeting, the modelers are directed by the court to develop definitions, set parameters, review their respective reports, exchange information and data; and, through discussion, attempt to determine those areas that were not affected by the incident. The purpose of the meeting is not to estimate concentrations, attempt to determine whether harmful levels of constituents were present or to address which individuals in the resulting "area in dispute" were adversely affected, or to what extent. The beneficial result is for both parties to focus on the true "area in dispute" and to eliminate claimants that are too remote for recovery. While the first blush reaction to such a procedure is that, "The plaintiffs will never agree," the reality is that plaintiffs' counsel often have "too many clients" and do not have a procedural vehicle to cull the weak cases without alienating the "good" ones. This concept provides a vehicle to achieve such a result. For instance, the modelers may be able to agree on the location and readings from relevant weather and monitoring stations, and pertinent meteorological data. In this regard, all models have three types of input: source information, meteorological information and location information, or points selected for evaluation. If the modelers are able to agree on the key inputs, without consideration to the actual location of the claimants, it is probable that they can agree on areas that were not affected. Then, when the claimant locations are plotted, it is possible that many will be eliminated, as being outside the "area in dispute" or out of an area of concern based upon the health professional's evaluation of the model's concentration level predictions within the "area in dispute." The result of the air modelers' meeting can be depicted as follows using any one of a number of commercially available computer programs:

As can be seen, the first step is to produce a working map of the entire area claimed to have been impacted. Then, based upon the results of the air modelers' meeting, certain portions of the area can be agreed as "not in dispute," or not impacted, and the remainder is the "disputed area." The next step is to begin to narrow the possible area that could have received concentrations in levels that could have a harmful effect.

RULE 2. REQUIRE THE AIR MODELER TO STICK TO AIR MODELING.

Computers are wonderful things. They can compute to infinitesimal numbers. Air modelers love computers and will use them to the extent of their capabilities, unless instructed otherwise. The resulting models will depict meaningless concentrations that, when illustrated, show a plume that extends "to China." Thus, defendants are often faced with plumes that their modeler has produced that go too far and that do not pose any health risk. Air modelers exceed their area of expertise when they determine "how far" the model should go. It is suggested that an integrated approach be used, where health professionals, such as industrial hygienists, toxicologists and physicians determine the threshold health risk limit and model only to that limit.

There are many recognized standards that industrial hygienists and generally accepted medical professionals use to determine a permissible exposure limit of either occupational workers or the general population exposed to an airborne potentially toxic material. These guidelines include the American Conference of Governmental Industrial Hygienists' Threshold Limit Values, EPA National Ambient Air Quality Standards, various industry developed community exposure guidelines, National Research Council/National Academy of Science Emergency Exposure Guidance Levels and the American Industrial Hygiene Association Emergency Planning Guidelines. It is submitted that these types of professional standards are more appropriate for measuring the potential for a harmful exposure than some governmental standards that are designed to apply to exposure of the general population over a lifetime. Modelers should be instructed that, except in unusual circumstances, there is no need to depict plumes below the recognized geographic area's background level. These background levels are generally recognized as being a regulated safe level. Yet, "background" is not necessarily the minimum "safe" level of exposure that dictates a modeling limit. Health professionals can reasonably agree and direct the modeler to not go below threshold limit values (TLV), or concentrations of substances under which it is believed that workers can be repeatedly exposed to during the workday on a day to day basis without harmful health effects. There are arguments that TLVs may not produce a "relative exposure limit" for the general population in a long term or accidental release. However, time weighted averages (TWA), which permit excursions above the TLV, provided that they are compensated by equivalent excursions below the TLV may be appropriate to determine a "relevant" exposure level. In the case of accidental releases, the TLV, which is normally averaged over an 8 hour workday and serves to protect against both acute and chronic health effects, may be inappropriate for evaluating brief emergency periods. The American Industrial Hygiene Association (AIHA) has developed Emergency Response Planning Guidelines (ERPGs) for accidental community releases. The numbers developed therein are thought to be useful in planning and response and are felt to be suitable for the protection from health effects due to short term exposures. These guidelines are classified as:

ERPG-1, which is the maximum airborne concentration below which it is believed nearly all individuals could be exposed for up to one hour without experiencing other than mild transient adverse health effects or perceiving a clearly defined objectionable odor;

ERPG-2, which is the maximum airborne concentration below which it is believed nearly all individuals could be exposed for up to one hour without experiencing or developing irreversible or other serious health effects or symptoms that could impair their ability to take protective action; and

ERPG-3, which is the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to one hour without experiencing or developing life threatening health effects.

The use of the ERPGs, for exceedances and the other available permissible exposure guidelines for longer term exposure can provide guidance to the air modeler that can produce a realistic exposure model.

STEP 3. USE THE RESULTING INFORMATION IN A MEANINGFUL WAY.

This model can then be plotted on an informational map so as to provide the defense a method to reasonably classify exposure in defined areas, rather than merely draw a circle and define it as a "zone of danger." The result will appear as follows:

The plaintiffs' understanding of the plume's location may differ from the defendant's. However, if the defendant has mobile monitors that are employed during the incident; or, if there is air monitoring information available from governmental or industry sources, a strong case can be made for the plume's actual location.

The next step of the process is to have the air modeler depict the "problem" areas in the plume. This entails calculations of locations where the exposure is "relevant to a health risk." It must be remembered that there are confounding factors, such as whether the plaintiffs' exposure took place largely indoors, which would have a filtering effect. Additionally, emission from other sources can also be important in determining the impact of a litigative source. "Background" should be the minimum concentration benchmark. In any event, it is preferable for the air modeler to determine which particular areas in the plume were the subject of exceedances for the entire period of the incident, for only a portion of the incident, or which did not exceed the background levels.

This technique also provides a manner of differentiating the claims in settlement negotiations based upon the "relevant" exposure level. Additionally, using a relatively small "box" area (.3 miles) the resulting area can be shown in a much more meaningful way than just using "circles" to show a "zone of danger:"

When all of the claimants' locations are plotted, the entire area can be overlayed with area boxes and the result will show the exaggerated nature of the claims in relation to the claimants' location and the location of the areas of the plume that exceed a "relevant" exposure level.

In the focus of the certification hearing, or settlement negotiations, "Box locations" that are outside of the "relevant" exposure level can be shown not worthy of class inclusion or settlement payments. Additionally, through the use of this technique, many times the concentrations in the plume are incredibly small compared to the "relevant exposure level."