This executive summary describes the final report for this project.
Martin Marietta Energy Systems Contract No. 62XST730
The purpose of this project was to document widely applicable methods for characterizing the magnetic fields in a given environment, recognizing the many sources co-existing within that space. The guidelines are designed to allow the reader to follow an efficient process to (1) plan the goals and requirements of a magnetic-field study, (2) develop a study structure and protocol, and (3) document and carry out the plan. These guidelines take the reader first through the process of developing a basic study strategy, then through planning and performing the data collection. Last, the critical factors of data management, analysis reporting, and quality assurance are discussed. The guidelines are structured to allow the researcher to develop a protocol that responds to specific site and project needs.
The Research and Public Information Dissemination Program (RAPID) is based on exposure to magnetic fields and the potential health effects. Therefore, the most important focus for these magnetic-field measurement guidelines is relevance to exposure. The assumed objective of an environment-specific measurement is to characterize the environment (given a set of occupants and magnetic-field sources) so that information about the exposure of the occupants may be inferred.
Ideally, the researcher seeks to obtain complete or "perfect" information about these magnetic fields, so that personal exposure might also be modeled perfectly. However, complete data collection is not feasible. In fact, it has been made more difficult as the research field has moved to expand the list of field parameters measured, increasing the cost and complexity of performing a measurement and analyzing the data.
The guidelines address this issue by guiding the user to design a measurement protocol that will gather the most exposure-relevant information based on the locations of people in relation to the sources. We suggest that the "microenvironment" become the base unit of area in a study, with boundaries defined by the occupant's activity patterns and the field variation from the sources affecting the area. Such a stratification allows the researcher to determine which microenvironments are of most interest, and to methodically focus the measurements in those areas, in order to gather the most relevant set of data.
The first step in developing a responsive protocol for performing magnetic-field measurements in a given environment is to design the research strategy to best characterize the exposures. This step will help to limit and optimize the measurement tasks. The strategy development must take into account the study purpose, the project resources, the physical characteristics of the environment, the field parameters desired for measurement, and the instrumentation to be used in the study. The guidelines describe the study strategy development in six steps, summarized below.
Determining and documenting the study purpose. A statement of purpose should be developed and understood by the investigators and the study sponsor or client. That statement should answer the following five questions:
Documenting the study purpose will provide a basis for actions and help ensure that each task is optimized to provide the desired product.
Determining the environment classification. The guidelines next present a method for classifying the environment type, based on Standard Industrial Classification code numbers for establishments. Such classification will encourage focus on the environment's properties, stratification within databases, and comparisons with similarly classified environments previously studied.
Determining the project resources. The scope of studies will almost always be limited by project resources. The financial resources, staff availability, instrumentation availability, and any time constraints should be assessed early in the planning process.
Reviewing the physical characteristics of the environment. Preliminary information on the environment's characteristics and sources will highlight important features that should be considered in the measurement plan. These include features that may indicate what field parameters might be of interest, as well as the scope of measurements that might be necessary, based on the size and complexity of the environment.
Selecting field parameters for measurement. The dose metrics of magnetic-field exposure have not been defined. Therefore, the investigator will want to obtain information on multiple parameters. The guidelines discuss parameters that may be selected for measurement, but leave choices open to the investigator, based on the study purpose, site characteristics, and practicality of measurement. The guidelines acknowledge that performing rms magnetic flux density measurements will continue to be a focus of environment-specific measurements because this measurement is easy to perform, is readily understood by the research community and general public, and has been the focus of most previous studies.
Selecting instrumentation. The investigators should select instrumentation based on measurement and memory capabilities suited to the study goals, as well as on efficiency, reliability, convenience, and price. However, availability is usually the most prevalent factor. The guidelines discuss single-axis and three-axis rms meters and commercially available waveform capture systems, and the nature and potential functions of each class of instrument.
Developing a measurement strategy and data collection structure. Outlining a plan for data collection is the next natural step. The measurement strategy, a part of this plan, is the decision-making process by which it is ultimately determined where, when, and how magnetic-field data will be collected. The guidelines stress designing the measurements to gather only the most exposure-relevant information, and describe the use of the microenvironment to determine what information is most relevant.
The standard structure for performing magnetic-field characterization is suggested in a four-step process.
The guidelines provide examples of data-collection structures, and the possible tasks that may be involved.
Having guided the reader through the factors of a study strategy, the guidelines focus on the specific steps of performing the data collection and determining the appropriate data to consider collecting. Magnetic-field characteristics cannot be properly described by a single measurement or series of measurements. Many factors, including the physical parameters of the environment; the location and operation of sources; the activity patterns of the occupants; and the spatial, temporal, frequency, and other parameters of the magnetic fields together paint a picture that characterizes magnetic-field exposure.
Developing the data-collection protocol. Before the researcher begins to collect data collection, it is most important to produce a written data collection protocol. This helps to ensure that relevant information is collected; that magnetic-field measurements are completed most completely, efficiently, and systematically; and that disruption to the environment is minimized. The guidelines provide examples of protocol formats, each organized in a chronological sequence. Objective, easy-to-use data-collection forms are the most reliable means to obtain and confirm a complete data set from the field. Their development is a part of generating the data-collection protocol. Examples of several forms have been included in the guidelines.
The guidelines describe the specifics of data collection, following below.
Identifying magnetic-field sources. The guidelines describe methods of source identification, including visual inspection, gathering source information from an informant, performing exploratory measurements, performing field mapping, or using such tools as a clamp-on ammeter to identify sources of net current. The guidelines further detail methods for documenting the source locations, and defining the source characteristics such as source type, level of magnetic-field magnitude, and temporal characteristics.
Gathering activity-pattern data. It is assumed that the goal of activity-pattern data collection is to provide the minimal data set of information required to properly include exposure-relevancy in the magnetic-field measurement study design. The guidelines describe methods of data collection (including interviews, questionnaires, and observation techniques) and outline the ways to choose the appropriate technique based on the study parameters. Recommendations are also given as to whether a site informant or the site's occupants are most appropriate providers of activity-pattern data. The guidelines furnish tips for constructing activity-pattern questions, as well as examples of data collection tools, such as questionnaires and interview protocols.
Gathering non-magnetic field data. Other information about the environment and its sources may provide additional insight into the characteristics of magnetic-field exposure, painting a more complete picture of the environment's magnetic-field characteristics. The guidelines describe possible appropriate information, such as: site characteristics (i.e., building age); additional source information (i.e., sizes of motors); utility information (i.e., circuit loads); and occupant information (i.e., job descriptions and ages).
Planning and performing focused magnetic-field data collection. The three tasks described above provide the information required to plan further, more focused magnetic-field measurements. A magnetic-field measurement plan will aim to finalize the locations of measurements, timing of measurements, measurement sampling rates, and the inclusion of temporal measurements. The guidelines direct the reader through the necessary steps:
It is assumed that these data will comprise the substance of the report on magnetic-field data.
Guidance is provided for managing, compiling, analyzing, and reporting the collected data to the study audience. Data management methods are described, including the following:
Options for methods and tools for data analysis are discussed. The researcher should bear in mind that the choices of methods must be based on the questions the study has been designed to answer, and upon the study resources and parameters.
The project report should be a compilation of all effort expended in the study, presented in a format tailored to convey the information to the appropriate audience. Reports generally will include the following primary areas: Introduction, Methods, Results, and Discussion. The data may be conveyed in the form of descriptions, tables, graphics, and/or electronic media. The guidelines describe sample content for each report section. Three pilot study reports are included as examples of a report format.
A quality assurance plan seeks to ensure that the data collected and reported are valid and consistent. The plan should be developed during the study planning process. Quality assurance steps can and should be specified for each phase of the study. Steps described in the guidelines include the following:
The guidelines provide flexible, widely applicable methods for performing exposure-relevant magnetic-field measurements. They may be used to produce a targeted, efficient, and useful study that collects, analyzes, and reports the data appropriate for the goals of the study.