RTCA DO-160 – Section 13.0 – Fungus Resistance
These tests determine whether equipment material is adversely affected by fungi under conditions favorable for their development, namely, high humidity, warm atmosphere and presence of inorganic salts.
A. Fungi proximity to other materials, exposure to daily susceptible contaminants such as fluids during routine operation and maintenance, or equipment exposure to solar actinic effects – may break molecular bonds and reduce the item to sub-compositions which may be fungus nutrients.
B. This test shall not be conducted after Salt Spray or Sand and Dust. A heavy concentration of salt may effect the fungal growth, and sand and dust can provide nutrients, which could compromise the validity of this test (see Subsection 3.2, “Order of Tests”).
Typical problems caused by fungi growing on equipment are:
a. Microorganisms digest organic materials as a normal metabolic process, thus degrading the substrate, reducing the surface tension and increasing moisture penetration.
b. Enzymes and organic acids, produced during metabolism, diffuse out of the cells and onto the substrate and cause metal corrosion, glass etching, hardening of grease and other physical and chemical changes to the substrates.
c. The physical presence of microorganisms produces living bridges across components that may result in electrical failures.
d. The physical presence of fungi can also cause health problems and produce aesthetically unpleasant situations in which users will reject using the equipment.
The detrimental effects of fungal growth are summarized as follows:
a. Direct attack on materials. Nonresistant materials are susceptible to direct attack as fungus breaks these 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 material. Products of natural origin (carbon based) are most susceptible to this attack.
(a) Cellulose materials (e.g., wood, paper, natural fiber textiles, and cordage).
(b) Animal- and vegetable-based adhesives.
(c) Grease, oils, and many hydrocarbons.
(2) Synthetic materials.
(a) PVC formulations (e.g., those plasticized with fatty acid esters).
(b) Certain polyurethanes (e.g., polyesters and some polyether).
(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 acidic waste products of fungus on adjacent materials that are susceptible to direct attack come in contact with the resistant materials.
Category F: Equipment that is installed in an environment where it will be exposed to severe fungus contamination is identified as Category F and shall be subjected to the fungus resistance test. If all materials used in the construction of the equipment can be shown to be non nutrients for the growth of fungi, either through their composition or through previous testing, this test is not required. If non-nutrient material certification is utilized for this verification, this fact shall be declared on the Environmental Qualification Form (see Appendix A).