ASTM G21

Fungus Resistance

ASTM G21; MIL-STD 810; IPC-SM-840; IPC-TM-650

The Fungus Resistance test is used to determine the resistance of materials to fungi and to determine if such material is adversely affected by fungi under conditions favorable for their development, namely high humidity, warm atmosphere, and presence of inorganic salts.

Many products that operate in warm, humid environments must be tested to withstand fungal attacks since this problem can cause a myriad of operational challenges. To varying degrees, live fungi will use wood, paper, leather, hydrocarbons, PVC, polyurethanes, certain plastics and paints, as well as other materials, as fuel for growth.

Types of Fungal Attacks

  • Getting under protective covers and marring the appearance and degrading the optical capabilities of your product
  • Metabolic waste products from fungus cause corrosion or etching
  • Electrical systems can develop undesirable conducting paths
  • Fungus can block delicate moving parts
  • Introduce internal moisture affecting system performance

Fungus Testing

These test methods are used to determine the effect of fungi on the properties of synthetic polymeric materials in the form of molded and fabricated articles, tubes, rods, sheets, and film materials. The test can reveal not only that the specimen under test supplies sufficient nutrition for fungal growth but can also show, for long test durations, the effects that fungus may have on the test specimen such as changes in appearance, mechanical, and electrical properties.

One has to be careful in handling samples that are for fungus testing as the cleanliness of the specimens is important prior to testing – especially testing is being conducted on a cleaning or decontamination process. Contamination can have a negative effect on the test results since it could very easily provide nutrients to the fungus for growth. In order to minimize contamination good practices are not remove the test specimens from the packaging until it is time for inoculation and if handling is necessary gloves should be worn if the test specimens are to be handled. If the samples are mishandled or suspected of contamination prior to testing, the samples should be cleaned and testing cannot be conducted on the test specimens before 72 hours.

The spores are grown for approximately 2 -3 weeks followed by inoculation of the spore suspension (the combine spores that are selected for testing) and placed in a test chamber for 28 days or as specified. The fungus results are usually determined and recorded as a growth rating: where “0” is no growth, “1” is <10% observed growth, “2” is 10 to 30% or 100% cobwebby growth (white growth) observed growth, “3” is 30 to 60% observed growth, and a “4” is greater than 60% observed growth. If the sample appears to be absent of growth magnifications upwards of 50x should be used to verify no growth exists. There could be fungal spores on the samples that are not readily visible to the eye due to the size of the spores, localized areas of growth, or the color of the spores are similar to those of the test specimen.