MIL-STD-810A Environmental Engineering Considerations and Laboratory Tests

Why is MIL-STD 810 Altitude Compliance Testing Important?

Method 500.7 of MIL 810 altitude testing is used on material that will likely be at high ground elevation sites or be exposed to rapid/explosive decompression. An example of this includes material that is transported or operated in or on an aircraft. The MIL-810A test method helps determine the material’s ability to withstand these low pressure environments and rapid pressure changes. Use it to determine if material failure will damage the aircraft or present a hazard to personnel.

However, there are some important limits to note when using the method. Firstly, be sure to test using the maximum altitude (minimum pressure) normally reached by the appropriate mode of transportation. Procedure IV should not be used to test material being transported in a cargo bay. And, this method of low pressure testing should not be used for material in space vehicles, aircrafts, or missiles flying at above 21,300 m.

Keystone Compliance is a fully equipped altitude testing lab with experience MIL-810 low pressure testing.  The following information contains the testing language from MIL-STD 810H altitude. However, it applies the previous version, MIL-STD 810G altitude. This page provides a summary of  MIL-810H altitude testing and MIL-810G altitude testing.

How to select Method 500.7 of MIL-810H Low Pressure Testing?

When considering this method first review required documents to determine what kind of pressure environment the material will be exposed to during its life-cycle. If it will be exposed to a low pressure environment the LCEP may require method 500.7 in conjunction with other MIL-STD-810 test methods. Other tests methods may include high temperature, low temperature, or vibration testing. All testing should be performed in a low pressure testing lab.

Another thing to consider is what problems typically arise when materials are exposed to low pressure environments. Beyond thermal effects, consider the potential problems listed below to determine if this test method is appropriate. This list is not all-inclusive and there may be overlap.

  • Failure of hermetic seals.
  • Deformation, rupture or explosion of sealed containers.
  • Changes in physical and chemical properties of low-density materials.
  • Gases or fluids leaking from gasket-sealed enclosures.
  • Evaporation of lubricants.
  • Reduced heat transfer causing  materials to overheat. 
  • Erratic starting and operation of the engine.
  • Erratic operation or malfunction of material resulting from arcing or corona. 

When Should MIL-810 Low Pressure Testing Be Performed in Relation to Other Tests?

The anticipated life cycle sequence of events can be used as a general sequence guide. Generally this method of testing occurs early in the life cycle, because it has limited damage potential. However, there are several instances in which other tests should be performed before the low pressure test. 

Some tests could significantly contribute to the effects of low pressure on the material. 

For example, low temperature and high temperature testing may affect seals. Dynamic tests may affect the structural integrity of the test item. And testing that causes aging of non-metallic components may reduce their strength.

How to Select the Correct Procedure For This Method?

MIL-STD 801 low pressure testing includes four different test procedures. These are Storage (Procedure I), Operation (Procedure II),  Rapid Decompression (Procedure III), and Explosive Decompression (Procedure IV). Determine which of the test procedures or combination of procedures is best based on the test data requirements.

Anticipate the most severe exposure of the material during its life-cycle and select the procedure that represents that. Take into account the shaker test data required to determine if the operational purpose of the material has been met. Consider the material configuration, and the operational requirements of the material in the procedure selection process. Also, understand the procedure sequence, and whether the cargo compartment is pressurized.

How Do each of the Four Procedures Differ?

Procedure I is best for materials that are transported or stored at high ground elevations. It is also good for material that is transported by air in its shipping/storage configuration. Determine if this procedure is appropriate by evaluating the known effects of low pressure on material and the LCEP.

Procedure II, may be preceded by Procedure I. However, if there are no low pressure storage, rapid, or explosive decompression requirements, this procedure can stand alone. Procedure II helps evaluate the performance of the material under low pressure conditions.

Procedure III may be preceded by Procedure I and/or Procedure II. It is used to determine if a rapid decrease in pressure could cause a dangerous material reaction. Such a reaction could harm nearby personnel or the transportation vehicle. 

Procedure IV may also be preceded by Procedure I and/or Procedure II. It is similar to Procedure III, but it involves an “instantaneous” decrease in the pressure of the surrounding environment. This procedure is better for items like sealed cockpit equipment, the failure of which could endanger cockpit personnel. The appropriateness of this procedure for large cargo items must be carefully evaluated. 

Situations may arise where the altitude change (climb/descent rate) is unspecified or unknown. Military transport aircrafts typically have an average altitude change rate of 7.6 m/s in a full military power takeoff. Use the value of 10 m/s for ground tests unless otherwise specified. Other than decompression tests, or when justified by deployment platforms, an altitude change should not exceed 10 m/s. 

Are You Looking for a Lab that Provides Altitude Testing Services?

Keystone Compliance has been is one of the best altitude labs in the country. We employ expert test engineers and properly equip our altitude laboratory in order to provide low pressure certifications. Contact us to learn why so many manufacturers rely on Keystone Compliance to meet their compliance testing needs.

There have been several versions of low pressure testing procedures in MIL-STD-810 altitude testing. Below is a list of each version and the appropriate method number:

Versions

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