501.7-22 tailoring guidance

2.1.1 Effects of High Temperature Environments

High temperatures may temporarily or permanently impair performance of materiel by changing physical properties or dimensions of the material(s) of which it is composed. The following are examples of problems that could result from high temperature exposure that may relate to the materiel being tested. 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. Parts bind from differential expansion of dissimilar materials.
• b. Lubricants become less viscous; joints lose lubrication by outward flow of lubricants.
• c. Materials change in dimension, either totally or selectively.
• d. Packing, gaskets, seals, bearings and shafts become distorted, bind, and fail causing mechanical or integrity failures.
• e. Gaskets display permanent set.
• f. Closure and sealing strips deteriorate.

MIL-STD-810H

METHOD 501.7

• g. Fixed-resistance resistors change in values.
• h. Electronic circuit stability varies with differences in temperature gradients and differential expansion of dissimilar materials.
• i. Transformers and electromechanical components overheat.
• j. Operating/release margins of relays and magnetic or thermally activated devices alter.
• k. Shortened operating lifetime.

1. Solid pellets or grains separate.

• m. High pressures created within sealed cases (projectiles, bombs, etc.).
• n. Accelerated burning of explosives or propellants.
• o. Expansion of cast explosives within their cases.
• p. Explosives melt and exude.
• q. Discoloration, cracking, or crazing of organic materials.
• r. Out-gassing of composite materials or coatings (i.e. VOCs, CO, and Phthalates).
• s. Failure of adhesives.

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 high temperature test early in the test sequence. Another approach is to apply environments to maximize the likelihood of disclosing synergetic effects. This test may be used in combination with shock and vibration tests to evaluate the effect of dynamic events (i.e., shipping, handling, and shock) on hot materials. Also, this test may contribute significantly to the results of low pressure testing of seals, e.g., see paragraphs 2.1.1d, e, and f.

2.2.1 Procedure Selection Considerations

When selecting procedures, consider:

• a. The operational purpose of the materiel.

• b. The natural exposure circumstances (ambient or induced).

• c. The test data required to determine whether the operational purpose of the materiel has been met.

• d. Procedure sequence. If both the storage and operation procedures are to be applied, perform Procedure I before Procedure II. Consider using Procedure III in lieu of Procedure II for unique cases in which materiel in its operational configuration is non-operational (awaiting use) and is exposed to solar heating, e.g., aircraft cockpits, ground vehicle passenger compartments, etc.

• e. Other significant adjacent heat sources that could affect the materiel such as motors, engines, power supplies, other electronics, or exhaust air.

• f. 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.

2.2.2 Difference Among Procedures

While all three procedures involve temperature conditioning and performance testing, they differ on the basis of the temperature load prior to and during performance tests. The storage procedure assesses the effects of high temperature storage on subsequent materiel performance. The operation procedure assesses the effects of high temperatures during performance. The tactical-standby to operational procedure evaluates the ability of materiel (usually enclosed by transparent or translucent material) that has soaked in the sun in a high temperature environment to become operational in a relatively short period of time.

• a. Procedure I - Storage. Use Procedure I to investigate how high temperatures during storage affect the materiel (integrity of materials, and safety/performance of the materiel). This test procedure includes exposing the test item to high temperatures (and low humidity where applicable) that may be encountered in the materiel's storage situation, followed by an operational test at ambient conditions. For materiel inside an enclosure that is, in turn, exposed to solar heating, consider using Method 505.7, Procedure I to determine the actual level of heating of the test materiel caused by solar loading.
• b. Procedure II - Operation. Use Procedure II to investigate how high ambient temperatures may affect materiel performance while it is operating. There are two ways to perform Procedure II:
• (1) Expose the test item to cyclic chamber conditions with the test item operating either continuously or during the period of maximum response (highest item temperature).
• (2) Expose the test item to a constant temperature and operate the test item when its temperature stabilizes. (To be used only for items situated in close proximity to heat-producing equipment or when it is necessary to verify operation of an item at a specified constant temperature.)
• c. Procedure III - Tactical-Standby to Operational. This procedure is not a substitute for solar radiation (Method 505.7). This procedure evaluates the materiel's performance at the operating temperatures after being presoaked at non-operational temperatures. Since actinic effects and directional heating are not applicable in this method, consider applying this procedure when materiel is in an enclosed environment, (e.g., aircraft and ground vehicles with closed transparent or translucent areas can develop high internal temperatures prior to equipment operation due to solar heating; enclosures such as communications shelters may require immediate operation after being exposed to solar heating). These are not items in storage or transit situation, but rather items in the operational configuration (ready-to-go as needed) that must be operational in a relatively short period of time. Usually, the "cooling" option refers to merely opening the enclosed areas and allowing the ambient air to begin cooling the interior areas so normal operation can begin.

The term “tactical” is used here to identify materiel that is not in storage, but is in a standby operational configuration, and as such is subjected to extended non-operational conditions immediately prior to operation.

MIL-STD-810H

METHOD 501.7

2.3.1 Climatic Conditions

Identify the appropriate climatic conditions for the geographic areas in which the materiel will be operated and stored. There are two climatic categories where high temperatures are typically encountered: Hot Dry and Basic Hot (Part One, Annex C, Figure C-1). Data for these areas are shown in Tables 501.7-I, -II, and -III. Determine high temperature levels with respect to:

• a. Climatic area of concern.
• b. Exposure to solar radiation: Is this exposure directly on the materiel, shipping container, protective package shelter, etc.?
• c. Analysis of the path of heat transfer from the ambient air and solar radiation to the materiel.

${ }^{1}$ The diurnal cycles for temperature and humidity are given in tables 501.7-II and -III.

2/ Induced conditions are air temperature levels to which materiel may be exposed during extreme storage or transit situations, or non-operational but in the operational configuration without containerization.

MIL-STD-810H

METHOD 501.7

• ¹ These cycles were obtained from AR 70-38, 1 August 1979 (see paragraph 6.1, reference c), and essentially conform to those in MIL-HDBK-310 and NATO STANAG 4370, AECTP 230 (paragraph 6.1, references a and b). These values represent typical conditions throughout a typical day in this climatic category. "Induced Conditions" are air temperature levels to which materiel may be exposed during storage or transit situations that are aggravated by solar loading, or during non-operating situations but in an operational configuration and not containerized.
• ² Humidity control during high temperature testing is generally not necessary. Use these values only in special cases where, for instance, it is known that high levels of temperature and low humidity may adversely affect your items.
• ³ Data were originally recorded in °F and converted to °C. Hence, table data conversion may not be consistent.

• ¹ These cycles were obtained from AR 70-38, 1 August 1979 (see paragraph 6.1, reference c), and essentially conform to those in MIL-HDBK-310 and NATO STANAG 4370, AECTP 230 (paragraph 6.1, references a and b). These values represent typical conditions throughout a typical day in this climatic category. "Induced Conditions" are air temperature levels to which materiel may be exposed during storage or transit situations that are aggravated by solar loading, or during non-operating situations but in an operational configuration and not containerized.
• 24 Humidity control during high temperature testing is generally not necessary. Use these values only in special cases where, for instance, it is known that high levels of temperature and low humidity may adversely affect your item.
• ³ Data were originally recorded in °F and converted to °C. Hence, table data conversion may not be consistent.

2.3.2 Exposure Conditions

Before determining the levels at which to set test temperatures, determine the way in which the materiel is exposed to heat in normal storage and operational circumstances. Review the Life Cycle Environmental Profile (LCEP) to help make this determination (see Part Three for additional guidance). Consider at least the following exposure conditions, and the possible alternative of using Method 505.7, Procedure I:

MIL-STD-810H

METHOD 501.7

• a. Deployment configuration.
• (1) Exposed. Of interest are the most severe conditions that materiel would experience when deployed in any climatic area of the world without the benefit of a protective cover or sheltering enclosure.
• (2) Sheltered. Of interest are the most severe conditions that materiel would experience when deployed in any climatic area of the world when under cover or inside a sheltering enclosure. The amount of ventilation available and the presence of adjacent shade can significantly affect the temperature of the air surrounding sheltered materiel. Examples of these situations are provided below. (Note: If field data are not available, the conditions for this exposure may be approximated using Part Three of this document, MIL-HDBK-310 and/or NATO STANAG 4370, AECTP 230 (paragraph 6.1, references a and b)). The outdoor ambient air temperature and humidity conditions described in these references are those measured in standard meteorological shelters at a height of 1.2 to 1.8 m (4 to 6 ft) above the ground.
• (a) Inside unventilated enclosures.
• (b) Within enclosed vehicle bodies.
• (c) Within aircraft sections having surfaces exposed to solar heating.
• (d) Inside of tents.
• (e) Under closed tarpaulins.
• (f) Located above, on, or below the surface of the Earth.
• b. Special conditions. Although high temperature testing is generally based on the average temperature of the air envelope surrounding the materiel, significant localized heating can occur because of special heating conditions. This localized heating can be well above the average surrounding air and therefore can significantly affect the evaluation of the materiel's thermal behavior and performance. When these conditions exist (as described below), include or simulate them in the high temperature test setup to the extent practical. These extreme conditions would be applied by extending the levels of the temperatures given in Tables 501.7-I and 501.7-II based on actual field measurements.
• (1) Aggravated solar. These conditions are induced but involve temperatures as high as 71 to 85 °C (160 to 185 °F), making greater allowance for the effects of solar radiation. Applicable conditions for such testing include materiel that is employed in enclosed compartments having glazed or transparent panels (aircraft cockpits, vehicle compartments, etc.); consider applying Method 505.7.
• (2) Man-made sources. Man-made heat-producing devices (motors, engines, power supplies, high-density electronic packages, etc.) may significantly raise the local air temperature near the material, either by radiation, convection, or impingement of exhaust air. This near constant temperature environment may negate the effects of the diurnal cycle.

2.3.3 Exposure Duration

Determine the duration of exposure that the materiel will experience for each of the exposure conditions identified. Exposure may be constant or cyclic, in which case, also identify the number of times that the exposure occurs.

Caution: When temperature conditioning, ensure the total test time at the most severe temperature does not exceed the life expectancy of any material (see Part One, paragraph 5.19).

2.3.3.1 Constant Temperature Exposure

For constant temperature exposure (used only for items situated in close proximity to heat-producing equipment or when it is necessary to verify operation of an item at a specified constant temperature), soak the test item until its temperature has stabilized, and maintain the test temperature at least two hours following test item stabilization.

NOTE: This is not a substitute for situations in which diurnal cycling is typical.

MIL-STD-810H

METHOD 501.7

2.3.3.2 Cyclic Temperature Exposure

For cyclic exposure, determine the test duration based on an estimate of the number of cycles required to satisfy the design requirements and the guidance below. The duration of high temperature exposure may be as significant as the temperature itself. Because Procedures I and II could expose the test items to cyclic temperatures, the number of cycles is critical. (Cycles are 24-hour periods unless otherwise specified.)

• a. Procedure I - Storage. The number of cycles for the storage test is set at a minimum of seven to coincide with the one percent frequency of occurrence of the hours of extreme temperatures during the most severe month in an average year at the most severe location. (The maximum temperature occurs for approximately one hour in each cycle.) When considering extended storage, critical materials, or materials determined to be very sensitive to high temperature, increase the number of cycles to assure the design requirements are met.
• b. Procedure II - Operation. The minimum number of cycles for the operational exposure test is three. This number is normally sufficient for the test item to reach its maximum response temperature. A maximum of seven cycles is suggested when repeated temperature response is difficult to obtain.

2.3.4 Test Item Configuration

Determine the test item configuration based on realistic configuration(s) of the materiel anticipated for storage and operation. As a minimum, consider the following configurations:

• a. In a shipping/storage container or transit case.
• b. Protected or unprotected (under canopy, enclosed, etc.).
• c. In its normal operating configuration (realistic or with restraints, such as with openings that are normally covered).
• d. Modified with kits for special applications.
• e. Stacked or palletized configurations.

2.3.5 Humidity

Generally, relative humidity (RH) control during high temperature tests is not necessary. In special cases, extremely low RH may have a significant effect on some materiel during high temperature testing. If the materiel has special characteristics that could be affected by extremely low RH, use the values for RH shown in Tables 501.7-II and -III.