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total raw gas concentration in air and estimate the percentage of trace contaminants based on analytical data. Alternately, continuous use of more sophisticated personnel or area sampling could be required. Any monitoring or sampling plan should be able to demonstrate an approach with a justifiable rationale, and should be scrutinized for statistical validity. The necessity for such monitoring or additional sampling should be determined by an experienced and qualified professional based on the types of hazards and risks present and the extent of exposure for the work to be performed. 9. Records Maintenance Accurate, reproducible, and verifiable records are essential for an effective overall health and safety program. They also provide protection against liability and preclude situations where compliance cannot be demonstrated. Records should include medical assessment--and respirator use approvals, certification of fit test, respirator eyeglass insert information, respirator maintenance records, and gas characterization information. D_ HAZARD ASSESSMENT AND IDENTIFICATION A necessary step in the implementation of respiratory and bodily protection is the identification of the hazards to be protected against. Extreme caution is warranted in dealing with situations where LFG is detected within the explosive range. Other kinds of special hazards are listed under the section of this document titled "Safety Procedures for Well Drilling and Construction". In the case of LFG, hazard assessment and identification should include a complete site-specific characterization of the gas. Initial characterization may be performed by gas chromatograph/mass spectrometer_ Once chemicals are tentatively identified qualitatively, more specific quantitative data can be obtained using a more specific analytical detector for the classes of chemicals in question. The analytical method selected should be capable, at a minimum, of identifying those compounds of concern at concentration levels at or below any action levels set for those compounds (i.e_, one half the TLV or PEL)_ Identification is difficult due to the heterogeneous nature of landfills and the dynamic nature of the biological decomposition process occurring within the landfill. Hence LFG composition varies from site to site, as well as throughout any site. An appropriate initial characterization, however, can serve to generally predict chemicals that are present and their relative concentrations. When characterization is performed, care must be exercised in interpreting results, taking into consideration the specific limitations of the analytical methods and hardware used. In addition to the fixed gases (CH,, 02, N2, and CO,), trace contaminants are present .n LFG_ There are literally hundreds to thousands of chemicals in LFG, most of which 1:8