This is part 10 of a series delving into the intricacies of Mil-Std-810G. 810G covers fungus growth in Method 508.6. This method comprises 11 pages plus a 1 page annex on decontaminating equipment after the tests and a 1 page annex on fungus-inert materials. The purpose of Method 508.6 is to assess the extent to which materiel will support fungal growth and how any fungal growth may affect performance or use of the materiel. The primary objectives of the fungus test are to determine:
- if the materials comprising the test object, or the assembled combination of same, will support fungal growth, and if so, of what species.
- how rapidly fungus will grow on the materiel.
- how fungus affects the materiel, its mission, and its safety for use following the growth of fungus on the material.
- if the material can be stored effectively in a field environment.
- if there are simple reversal processes, e.g., wiping off fungal growth.
Because some other tests in 810G such as salt fog, sand and dust, or humidity can change the results of a fungus test, those tests should be conducted on a sample after the fungus test is complete. It is imperative the sample be decontaminated after the fungus tests. Electronic equipment is typically manufactured using fungus-resistant material such as fiberglass, metal, plastic, etc. Materials affected by fungus such as fabrics are not typically used in electronic equipment. However, fungus growth can still have detrimental effects on electronic circuitry. The detrimental effects of fungus growth can include:
- Natural material – products such as paper, natural fibers, fabric, etc., are most susceptible as they can feed the fungus. Other organic materials such as adhesives, grease, oils, etc. and leather are susceptible.
- Synthetic materials – PVC formulations, some polyurethanes, plastics with organic fillers and paints or varnishes with susceptible constituents.
Effects of indirect attack include:
- Fungal growth on surface deposits of dust, grease, or other contaminants can cause damage to the underlying material.
- Metabolic waste products of the fungus (organic acids) can cause corrosion of metals, etching of glass, or staining or degrading of plastics and other materials.
- Fungus growth can bridge sensitive circuitry changing the electrical properties.
- Fungus can affect optical systems by adversely affecting light transmission through the system or block delicate moving parts.
The Method includes a warning note that 1) highly-specialized techniques are required for the analysis and 2) simple analysis is not sufficient and testing should be performed. Fungus growth can have a negative health impact as many people are very sensitive to mold and fungus. This is a long test, lasting 28 days as a minimum, to allow germination, break-down of carbon-containing molecules, and degradation of the material. In addition, it is recommended the test be extended to 84 days to fully evaluate the impact of fungus growth. The Method identifies five different varieties of fungus which are known to affect different materials and are distributed worldwide. Other species can be introduced as required. It is recommended to only use 5 or 6 species for testing. The more dominant species will prevail in testing and adding additional species will only add to the cost without additional degradation to the underlying material. The test requires a relatively sophisticated chamber to maintain the desired humidity and temperature as these greatly impact fungus growth. The chamber needs to be vented and filtered to release pressure changes and to filter fungus spores from the discharge. The method goes into great detail on cleaning the test items and the chamber. In addition, while the fungi used in the tests are not typically harmful to humans, some people may have or may develop allergies or other reactions so good housekeeping and handling precautions should be observed. As mentioned earlier, this is a sophisticated test and requires trained personnel and specialized laboratory equipment such as a centrifuge to properly administer the test. The fungal spores need to be prepared and tested for viability. Control strips of cotton are prepared and hung adjacent to the test specimen to be exposed as much as possible to the conditions the specimen is seeing. After the test period, the material under test is analyzed for the fungus species, extent of growth, impact on the underlying material, long range effect the growth could have on the material, and the specific nutrients supporting the growth. Chassis Plans has worked with various customers to define test procedures, as required by MIL-STD-810G, to validate our rugged rackmount computer systems and displays.