to worker illness or death. Workplace assessment methods Although there are many aspects to occupational hygiene work the most known and sought after is in determining or estimating potential or actual exposures to hazards. For many chemicals and physical hazards, occupational exposure limits have been derived using toxicological, epidemiological and medical data allowing hygienists to reduce the risks of health effects by implementing the "Hierarchy of Hazard Controls". Several methods can be applied in assessing the workplace or environment for exposure to a known or suspected hazard. Occupational hygienists do not rely on the accuracy of the equipment or method used but in knowing with certainty and precision the limits of the equipment or method being used and the error or variance given by using that particular equipment or method. Well known methods for performing occupational exposure assessments can be found in "A Strategy for Assessing and Managing Occupational Exposures, Third Edition Edited by Joselito S. Ignacio and William H. Bullock". The main steps outlined for assessing and managing occupational exposures: Basic Characterization (identify agents, hazards, people potentially exposed and existing exposure controls) Exposure Assessment (select occupational exposure limits, hazard bands, relevant toxicological data to determine if exposures are "acceptable", "unacceptable" or "uncertain") Exposure Controls (for "unacceptable" or "uncertain" exposures) Further Information Gathering (for "uncertain" exposures) Hazard Communication (for all exposures) Reassessment (as needed) / Management of Change Basic characterization, hazard identification and walk-through surveys The first step in understanding health risks related to exposures requires the collection of "basic characterization" information from available sources. A traditional method applied by occupational hygienists to initially survey a workplace or environment is used to determine both the types and possible exposures from hazards (e.g. noise, chemicals, radiation). The walk-through survey can be targeted or limited to particular hazards such as silica dust, or noise, to focus attention on control of all hazards to workers. A full walk-through survey is frequently used to provide information on establishing a framework for future investigations, prioritizing hazards, determining the requirements for measurement and establishing some immediate control of potential exposures. The Health Hazard Evaluation Program from the National Institute for Occupational Safety and Health is an example of an industrial hygiene walk-through survey. Other sources of basic characterization information include worker interviews, observing exposure tasks, material safety data sheets, workforce scheduling, production data, equipment and maintenance schedules to identify potential exposure agents and people possibly exposed.