Review and Use of Laboratory Results

Laboratory procedures are imperfect, and errors in using the procedures and in calculating and reporting the results are common. Reviewing the results received from a laboratory to see if they make sense is important. This exercise is relatively straightforward for combustion characteristics because much is known about the combustion characteristics of solid waste and its component materials (see Section 10.3). Identification of erroneous laboratory results is more difficult for metals and toxic organic substances.

The following guidelines apply in an evaluation of reasonableness of laboratory results for combustion characteristics on a dry basis:

Dry-basis results for the paper, yard waste, plastics, wood, and disposable diapers categories should be close to those shown in Tables 10.3.4 and 10.3.5. Greater variability must be accepted in individual results for food waste, textiles/rubber/leather, fines, and other combustibles because of the chemical variety of these categories.

The result for carbon must always be at least six times the result for hydrogen. No oxygen result should be significantly higher than 50%. For plant-based materials and mixed food waste, oxygen results should not be significantly less than 30% on an ash-free basis.

Among the paper categories, only those with high proportions of glossy paper, such as magazines and advertising mail, should have ash values significantly greater than 10%. Nitrogen should be below 1% for all categories except grass clippings, other yard waste, food waste, textiles/rubber/leather, fines, and other organics (see Table 10.3.4).

Chlorine should be below 1% for all categories except for PVC bottles, other plastic, textiles/rubber/leather, and other organics. Sulfur should be below 1% for all categories except other organics.

The laboratory should be willing to check its calculations and repeat the test if the calculations are not the source of the problem.

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