Humidity MIL-STD-810 Method 507 is used to evaluate the ability of products to resist the effects of exposure to warm humid climates. This evaluation can be performed in a test facility using environmental chambers where costs or product scheduling is a consideration. The method provides test cycles for natural or induced exposures representative of a variety of global exposures.
Effects of Humidity Exposure
Temperature-humidity conditions can have a wide array of effects on equipment. It can cause accelerated oxidation of metals, increase the rate of chemical reactions, breakdown coatings, interact with dusts and other deposits to create corrosive film, and cause binding or sticking. Additionally, it can cause changes in the properties of materials that result in loss of strength, delamination, degradation of lubricants, and degradation of insulators. When allowed to condense, humidity can cause short circuits and change thermal transfer characteristics.
Limitations of Laboratory Testing
Laboratory testing cannot replicate all the effects associated in a natural environment in humid areas. The method is intended to simulate a stressful environmental condition that can reveal potential problem areas in equipment design or choice of materials. Specifically this test method does not address condensation caused by changes of pressure for airborne equipment or the synergetic effects of multiple environmental stressors.
Procedures for Humidity Testing
There are two humidity testing procedures available for Humidity in MIL-STD-810:
- Procedure I – Induced and Natural Cycles are designed to replicate natural exposures to warm humid environments. Induced cycles are designed to replicate conditions in contained environments where air circulation is limited such as storage and transit conditions.
- Procedure II – Aggravated does not replicate naturally occurring cycles of humidity but exposes the test item to extreme temperature and humidity for shorter durations (usually 10 twenty-four-hour cycles). This can be useful for ascertaining if the test item is susceptible to humidity, but the standard recommends caution in the interpretation of results.
Humidity Cycles
MIL-STD-810 in conjunction with MIL-HDBK-310 and NATO STANAG 4370 define three geographical categories for humidity that are applicable to Procedure I:
- Constant high humidity (B1) is typical of tropical areas, and seasonally, some mid-latitude locations. These locations are typically in heavily forested areas during rainy seasons where solar radiation exposure is unlikely.
- Cyclic high humidity (B2) can be found in the same locations as B1 but where forest cover is limited (such as in urban areas) and solar radiation creates a more differentiated diurnal exposure.
- Hot-Humid (B3) represents conditions that occur on a narrow coastal strip in the Red Sea and Persian Gulf. These conditions occur naturally about 10 to 15 times a year. Although this cycle is in many ways the most extreme, it is not to be used in lieu of testing in other exposures if expected in the Life Cycle Environmental Profile (LCEP).
The standard provides diurnal cyclical test schedules for all three environmental profiles for both natural and induced conditions.
Test Durations
An effective humidity test requires long periods of exposure. This can place strains on schedules and budgets, especially when multiple profiles must be run. Test duration requirements are broken down into two categories, hazardous items and nonhazardous items. Hazardous items are defined as equipment that if subject to unknown deterioration could result in damage to equipment or result in injury or death to personnel.
For humidity cycles B1 and B2 this means that for hazardous items, a minimum of ninety cycles is required to simulate natural exposures and one hundred and eighty for induced (storage and transit). For non-hazardous items the durations are half of these values. B3 cycle durations are thirty for hazardous and fifteen for non-hazardous.
As previously mentioned, Aggravated humidity, requires a minimum of ten cycles which can make it an attractive alternative if permitted by requirements or when perceived vulnerability to humidity exposure is minimal.
Test Sequence Considerations
Prolonged exposures to humidity may compromise the integrity of seals, coatings, and plastics among other components. It therefore is not advisable to use the same item for this method as for Salt Fog/Corrosive Environments, Sand and Dust, Acidic Atmosphere, or Fungus. Additionally, the standard recommends performing dynamic testing, such as shock and vibration, prior to humidity, as the cumulative effects of these tests could identify design flaws.
Detailed Environmental Test Plan Templates
CVG Strategy offers EZ Test Plan Templates for MIL-STD environmental (climatic/dynamic) and EMI/EMC test documentation. Our Detailed Environmental Test Plans (DETP)s are written as specified in MIL-STD-810 Task 405. They are available for specific applications such as Ground Mobile, Ground Stationary, and Shipboard Controlled, Shipboard Uncontrolled, and Aircraft Military.
These DETPs include appropriate methods, (such as Humidity MIL-STD-810 Method 507) addendums for product specific information, test labels for photo identification and data sheets for collection of required data. Profile (LCEP).
Our Electromagnetic Interference Test Plans are written as specified in MIL-STD-461. They contain the test methodology, addendums for product specific information, test labels for photo identification and data sheets. These plans are available for procedures listed in MIL-STD-461 and are also available for MIL-STD-1275, MIL-STD-704, and MIL-STD-1399-300.
Custom Test Plans are also available for applications not covered in the EZ Test Plan offerings. These plans can be written for any number of applications and their relevant standards.
Put CVG Strategy’s Experience to Work for You
Companies of all sizes, from start up to established product developers, face challenges in product test and evaluation. This can particularly be the case when a product is developed for a new market sector or expanding sales internationally.
Properly tested products prevent costly product recalls, product redesign, and product liability. They maintain customer satisfaction and keep your company’s reputation in good standing. Contact CVG Strategy to see how our services can assist your engineering team with Humidity MIL-STD-810 Method 507 or any other test and evaluation concern.
MIL-STD-810 Training Classes
CVG Strategy MIL-STD-810 classes will provide you with the ability to develop and conduct an environmental test program. Our two-day course not only provides you with valuable information about climatic and dynamic test methods but also includes training in the methodology to correctly apply test tailoring relevant to the test item’s expected life cycle.
This course is available online or onsite. Ample time is available for questions and comments so that participants are encouraged to keep engaged. Check here for our online Training Registration Schedule.