2.1 Selecting the Low Temperature Method
After examining requirements documents and applying the tailoring process in Part One of this Standard to determine where low temperatures are foreseen in the life cycle of the materiel, use the following to confirm the need for this Method and to place it in sequence with other methods.
2.1.1 Effects of Low Temperature Environments
Low temperatures have adverse effects on almost all basic material. As a result, exposure of materiel to low temperatures may either temporarily or permanently impair the operation of the materiel by changing the physical properties of the material(s) of which it is composed. Consider low temperature tests whenever the materiel will be exposed to temperatures below standard ambient, and consider the following typical problems to help determine if this Method is appropriate for the materiel being tested. This list is not intended to be all-inclusive.
- a. Hardening and embrittlement of materials.
- b. Binding of parts from differential contraction of dissimilar materials and the different rates of expansion of different parts in response to temperature transients.
- c. Loss of lubrication and lubricant flow due to increased viscosity. In addition, fuels may gel at low temperature.
- d. Changes in electronic components (resistors, capacitors, etc.).
- e. Changes in performance of transformers and electromechanical components.
- f. Stiffening of shock mounts.
- g. Cracking of explosive solid pellets or grains, such as ammonium nitrate.
- h. Cracking and crazing, change in impact strength, and reduced strength.
- i. Static fatigue of restrained glass.
- j. Effects due to condensation and freezing of water in or on the materiel.
- k. Decrease in dexterity, hearing, and vision of personnel wearing protective clothing.
- Change of burning rates.
MIL-STD-810H
METHOD 502.7
2.1.2 Sequence Among Other 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. There are at least two philosophies related to test sequence. One approach is to conserve test item life by applying what are perceived to be the least damaging environments first. For this approach, generally apply the low temperature test early in the test sequence. Another approach is to apply environments to maximize the likelihood of disclosing synergetic effects. This test may also be used in combination with shock and vibration tests to evaluate the effect of dynamic events (i.e., shipping, handling, and shock) on cold materials. Also, this test may significantly alter the performance of seals during the low pressure testing of Method 500.6.
2.2 Selecting Procedures
This Method includes three test procedures, Procedure I (Storage), Procedure II (Operation), and Procedure III (Manipulation). Based on the test data requirements, determine which test procedure, combination, or sequence of procedures is applicable. In most cases, all three procedures will apply.
NOTE: The materiel's anticipated Life Cycle Environmental Profile (LCEP) may reveal other low temperature scenarios that are not specifically addressed in the procedures. Tailor the procedures as necessary to capture the LCEP variations, but do not reduce the basic test requirements reflected in the below procedures. (See paragraph 2.3 below.) NOTE: Consider the potential synergistic effects of temperature, humidity and altitude, and the use of Method 520.5 in addition to this method. However, Method 520 is NOT a substitute for Method 502.
2.2.1 Procedure Selection Considerations
When selecting procedures, consider:
- a. The operational purpose of the materiel. From the requirements documents, determine the functions to be performed by the materiel in a low temperature environment and any limiting conditions, such as storage.
- b. The natural exposure circumstances.
- c. The test data required to determine whether the operational purpose of the materiel has been met.
- (1) The expected temperature at the deployment location.
- (2) The expected duration at the deployment location.
- (3) The test item configuration.
- d. Procedure sequence.
- (1) If the materiel is not intended to be stored at low temperature or manipulated before use, Procedure II is conducted as a standalone test.
- (2) Combining of Procedures I and II when using constant temperature. When attempting to combine procedures it is preferable to conduct Procedure II followed by Procedure I and then a repeat of Procedure II. Testing should be conducted in series with no return to ambient conditions until test completion. If manipulation test is required, Procedure III can precede one or both operational tests.
2.2.2 Difference Among Procedures
While all procedures involve low temperatures, they differ on the basis of the timing and nature of performance tests.
- a. Procedure I - Storage. Use Procedure I to investigate how low temperatures during storage affect materiel safety during and after storage, and performance after storage.
- b. Procedure II - Operation. Use Procedure II to investigate how well the materiel operates in low temperature environments. For the purpose of this document, operation is defined as excitation of the materiel with a minimum of contact by personnel. It does not exclude handling (manipulation).
MIL-STD-810H METHOD 502.7
- c. Procedure III - Manipulation. Use Procedure III to investigate the ease with which the materiel can be set up or assembled, operated, and disassembled by personnel wearing heavy, cold-weather clothing. In addition, this could also include maintenance procedures.
2.3 Determine Test Levels and Conditions
Having selected this Method and relevant procedures (based on the test item's requirements documents and the tailoring process), complete the tailoring process by identifying appropriate parameter levels and applicable test conditions and techniques for these procedures. Base these selections on the requirements documents, the Life Cycle Environmental Profile (LCEP), and information provided with this procedure. Consider the following when selecting test levels.
2.3.1 Climatic Conditions
Select the specific test temperatures, preferably from the requirements documents. If this information is not available, determine the test temperature(s) based on the world areas in which the materiel will be used, plus any additional considerations. Although the natural low temperature environment is normally cyclic, the effect of solar loading is minimal, if not absent, so in most instances it is acceptable to use a constant low temperature test. Only in those instances where design assessment suggests that exposure to varying low temperatures may be important are the appropriate cold cycles from MIL-HDBK-310, AR 70-38, or STANAG 4370, AECTP 230 (paragraph 6.1, references a, b, and c) recommended. The information below provides guidance for choosing the test temperatures for selected regions (climatic categories), for worldwide use without extended storage (two years or longer), and for worldwide use with extended storage periods.
- a. Selected regions. Table 502.7-I in this Method, and Figure C-3 and Table C-I in Part One, Annex C, Part One of this Standard can be used to determine the test temperature when the test item is to be used within specific regions only. Except for severe cold, that is based on a 20 percent frequency of occurrence, air temperature criteria shown in Table 502.7-I are based on a one percent frequency of occurrence of the hours during an average year at the most severe location within the geographical area encompassed by the climatic region. The values shown in Table 502.7-I represent the range of the diurnal cycles. The diurnal cycles can be found in Part Three, Tables 9 and 11. For this Method, the lowest value in each range is usually considered.
- b. Worldwide use. When the materiel is to be stored or operated worldwide, temperature selection must not only include consideration of the absolute cold, but also of the frequency of a given cold condition. Unless frequency is considered, it is possible to create an unrealistic overtest condition. In terms of frequency, the frequency-of-occurrence values shown in Table 502.7.I refer to the percent of total hours, in the most extreme month and area in the world, during which the given cold temperature is equaled or exceeded. For example, the 20 percent frequency of occurrence of a temperature of -51 °C (-60 °F) means that during an average year, a temperature of -51 °C (-60 °F) or lower may be expected to occur 20 percent of the hours during the most extreme month in the cold area of the world. A 20 percent frequency of occurrence is used for most applications with normal development cost considerations. However, to satisfy specific applications or test requirements, other more extreme values may be appropriate. (See Table 502.7-II.)
NOTE: Antarctica is excluded from consideration by international treaty restrictions.
MIL-STD-810H
METHOD 502.7
| DESIGN TYPE | LOCATION | TEMPERATURE1 | |
|---|---|---|---|
| Ambient Air | Induced Environment (Storage & Transit) | ||
| °C (°F) | °C (°F) | ||
| Basic Cold (C1) | Most of Europe; Northern contiguous US; Coastal Canada; High-latitude coasts (e.g., southern coast of Alaska); High elevations in lower latitudes | -21 to -32 (-5 to -25) | -25 to -33 (-13 to -28) |
| Cold (C2) | Canada, Alaska (excluding the interior); Greenland (excluding the "cold pole"); Northern Scandinavia; Northern Asia (some areas), High Elevations (Northern and Southern Hemispheres); Alps; Himalayas; Andes | -37 to -46 (-35 to -50) | -37 to -46 (-35 to -50) |
| Severe Cold (C3) | Interior of Alaska; Yukon (Canada); Interior of Northern Canadian Islands; Greenland ice cap; Northern Asia | -51 (-60) | -51 (-60) |
¹These cycles were derived from AR 70-38, 1 August 1979, and essentially conform to those in MIL-HDBK-310 and NATO STANAG 4370, AECTP 230 (except for category C0). These values represent typical conditions. Induced conditions are extreme levels to which materiel may be exposed during storage or transit situations. Do not use these levels carte blanche, but tailor them to the anticipated storage or transit situation.
NOTE: See Part Three Tables IX and XI for low-temperature diurnal temperatures.
| Low Temperature | Frequency of Occurrence |
|---|---|
| -51 °C1 (-60 °F) | 20 percent |
| -54 °C (-65 °F) | 10 percent |
| -57 °C (-71 °F) | 5 percent |
| -61 °C (-78 °F) | 1 percent |
¹Corresponds to the "Severe Cold" condition.
- c. Worldwide use with extended storage periods. If materiel is to be stored for extended periods (years) without shelter or protection in areas that experience extreme low temperatures such as the "cold pole" of northeast Siberia or central Greenland, there is an increased chance that the materiel may experience much lower temperatures (approaching -65 °C (-85 °F)). Such prolonged exposure to extreme low temperatures can affect the safety of items such as munitions, life support equipment, etc.
MIL-STD-810H
METHOD 502.7
2.3.2 Exposure Duration
The duration of exposure to low temperature may be a factor in materiel safety, integrity and performance.
- a. Nonhazardous or non-safety-related (non-life-support type) materiel. Most materiel in this category (in a non-operating mode), with the possible exception of rubber and plastics, will not experience deterioration following temperature stabilization of the materiel at low temperatures. Following temperature stabilization of the test item, use a storage period of four hours for this materiel if no other value is available.
- b. Explosives, munitions, rubber and plastics, etc. These items may continue to deteriorate following temperature stabilization; consequently, it is necessary to test them at low temperatures for long periods of time. Use a minimum storage period of 72 hours following temperature stabilization of the test item.
- c. Restrained glass. Glass, ceramics, and glass-type products (such as those used in optical systems, laser systems, and electronic systems) that require mounting or restraining in specific positions may experience static fatigue. A more extended period of low temperature may be required to induce this phenomenon. Use a minimum storage period of 24 hours following temperature stabilization of the test item. In some cases, glass will only reveal static fatigue to low temperature after previously being subjected to other environments.
2.3.3 Test Item Configuration
The configuration of the materiel is an important factor in how it may be affected by temperature. Therefore, use the anticipated configuration of the materiel during storage or use during the test. As a minimum, consider the following configurations:
- a. In a shipping/storage container or transit case.
- b. Protected or unprotected.
- c. Deployed (realistically or with restraints, such as with openings that are normally covered).
- d. Modified with kits for special applications.
2.3.4 Additional Guidelines
Review the materiel specifications and requirements documents. Apply any additional guidelines necessary. Part Three of this document includes further information on the low temperature environment (e.g., paragraphs 2.2, 2.3, 4.2.6, and 4.3).