2.1 Selecting the Fungus Method
After examining requirements documents and applying the tailoring process in Part One of this Standard to determine where fungal growth is anticipated in the life cycle of materiel, use the following to confirm the need for this Method and to place it in sequence with other methods.
MIL-STD-810H
METHOD 508.8
2.1.1 Effects of Fungus Growth
Fungal growth impairs the functioning or use of materiel by changing its physical properties.
2.1.1.1 Detrimental Effects
The detrimental effects of fungal growth are summarized as follows:
- a. Direct Attack on Materials. Nonresistant materials are susceptible to direct attack as the fungus breaks the materials down and uses them as nutrients. This results in deterioration affecting the physical properties of the material. Examples of nonresistant materials are:
- (1) Natural Materials. Products of natural origin are most susceptible to this attack.
- (a) Cellulosic materials (e.g., wood, paper, natural fiber textiles, and cordage).
- (b) Animal- and vegetable-based adhesives.
- (c) Grease, oils, and many hydrocarbons.
- (d) Leather.
- (2) Synthetic Materials.
- (a) PVC formulations (e.g., those plasticized with fatty acid esters).
- (b) Certain polyurethanes (e.g., polyesters and some polyethers).
- (c) Plastics that contain organic fillers of laminating materials.
- (d) Paints and varnishes that contain susceptible constituents.
- b. Indirect Attack on Materials. Damage to fungus-resistant materials results from indirect attack when:
- (1) Fungal growth on surface deposits of dust, grease, perspiration, and other contaminants (that find their way onto materiel during manufacture or accumulate during service) causes damage to the underlying material, even though that material may be resistant to direct attack.
- (2) Metabolic waste products (i.e., organic acids) excreted by fungus cause corrosion of metals, etching of glass, or staining or degrading of plastics and other materials.
- (3) The products of fungus on adjacent materials that are susceptible to direct attack come in contact with the resistant materials.
2.1.1.2 Physical Interference
Physical interference can occur as follows:
- a. Electrical or Electronic Systems. Damage to electrical or electronic systems may result from either direct or indirect attack. Fungi can form undesirable electrical conducting paths across insulating materials, for example, or may adversely affect the electrical characteristics of critically adjusted electronic circuits.
- b. Optical Systems. Damage to optical systems results primarily from indirect attack. The fungus can adversely affect light transmission through the optical system, block delicate moving parts, etched glass, and change non-wetting surfaces to wetting surfaces with resulting loss in performance.
2.1.1.3 Health and Aesthetic Factors
Fungus on materiel can cause physiological problems (e.g., allergies) or be so aesthetically unpleasant that the users will be reluctant to use the materiel.
2.1.2 Sequence Among Other Test Methods
- a. General. Use the anticipated life cycle sequence of events as a general sequence guide (see Part One, paragraph 5.5).
- b. Unique to This Method. Because of the potentially unrepresentative combination of environmental effects, it is generally inappropriate to conduct this test on the same test sample previously subjected to salt fog, sand and dust, or humidity tests. However, if it is necessary, perform the fungus test before salt fog, or sand and
dust tests. A heavy concentration of salt may affect the germinating fungus growth and sand and dust can provide nutrients, thus leading to a false indication of the bio-susceptibility of the test item. Be sure to decontaminate the test item prior to other testing (see Annex A).
2.2 Selecting Procedure Variations
This Method has one procedure. Since the combination of temperature and humidity is critical to microbial growth, it is essential that these be maintained as specified in the procedure. However, other possible variations are described below.
2.2.1 Test Duration
Twenty-eight days is the minimum test period to allow for fungus germination, breakdown of carbon-containing molecules, and degradation of material. Since indirect effects and physical interference are not likely to occur in the relatively short time frame of the fungus test, consider extension of the exposure period to 84 days if a greater degree of certainty (less risk) is required in determining the existence or effect of fungus growth.
2.2.2 Choice of Fungus
The fungi used for this test are listed in Table 508.8-I. These organisms were selected because of their ability to degrade materials, their worldwide distribution, their stability, and their Biological Safety Level 1 classification. These organisms have, where possible, been identified with respect to the materials to which they are known to attack. Substitution of the species is not recommended.
- a. Because the test item may not be sterile before testing, other microorganisms may be present on the surfaces. When the test item is inoculated with the test fungi, both these and the other organisms will compete for available nutrients. It is not surprising to see organisms other than the test fungi growing on the test item at the end of the test. Hence, the need for trained personnel, e.g., mycologists, microbiologists, etc., to identify such situations.
- b. The spores chosen were identified as being prolific throughout the world and should remain as the base species for this test. The more dominant species will prevail in testing, therefore adding more species will likely only increase test costs without an increase in deterioration to material. You may add, but not substitute, additional species of fungus to those required in this test Method. However, if additional fungi are used (suggest only 1 or 2 other species), base their selection on prior knowledge of specific material deterioration. Consult trained personnel, e.g., mycologists, microbiologists, etc., to identify such situations.