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MIL STD 810 G – Test Method 500.5 – Low Pressure (Altitude)
SCOPE
Purpose
Use low pressure (altitude) tests to determine if materiel can withstand and/or operate in a low pressure environment and/or withstand rapid pressure changes.
Application
Use this method to evaluate materiel likely to be:
stored and/or operated at high ground elevation sites.
transported or operated in pressurized or unpressurized areas of aircraft (also consider method 520 for actively-powered materiel operated at altitude).
exposed to a rapid or explosive decompression and, if so, to determine if its failure will damage the aircraft or present a hazard to personnel.
carried externally on aircraft.
Limitations
This method is not intended to be used to test materiel to be installed or operated in space vehicles, aircraft or missiles that fly at altitudes above 21,300m (70,000 ft). Recommend the test be to the maximum altitude (minimum pressure) normally reached by the appropriate mode of transportation.
Procedure IV is not intended to be used for materiel transported in a cargo bay. For example, analysis for a C-5 aircraft indicates that to go from a cabin altitude of 8,000 ft to an ambient altitude of 40000′ in 1 second would require a hole of approximately 350 square ft, or 19 ft x 19 ft. Instantaneous creation of a hole that large in the side of the airplane would be catastrophic to the airplane. Please note that the 350 square foot hole is for a 1-second depressurization. To depressurize in one tenth of a second would require a hole ten times as large.
TEST PROCESS
Procedure I – Storage/Air Transport
Step 1. Adjust the test item to its storage or transport configuration and install it in the test chamber.
Step 2. If appropriate, stabilize the test item to the required temperature (see paragraph 2.3.1) at a rate not to exceed 3°C/min (5°F/min).
Step 3. Adjust the chamber air pressure to that which corresponds to the required test altitude, at an altitude change rate as specified in the test plan.
Step 4. Maintain the conditions for a minimum of one hour unless otherwise specified in the test plan.
Step 5. Adjust the chamber air to standard ambient conditions at a rate not to exceed 3°C/min (5°F/min).
Step 6. Visually examine the test item to the extent possible and conduct an operational check. Document the results, and see paragraph 5 for further guidance.
Procedure II – Operation/Air Carriage
Step 1. With the test item in its operational configuration, install it in the chamber and adjust the chamber air pressure (and temperature, if appropriate – see paragraph 2.3.1) to that which corresponds to the required operational altitude at a rate not to exceed that specified in the test plan.
Step 2. Maintain the conditions for a minimum of one hour unless otherwise specified in the test plan.
Step 3. Conduct an operational check of the test item in accordance with the requirements documents, and document the results. If the test item does not operate satisfactorily, follow the guidance in paragraph 4.3.2 for test item failure.
Step 4. Adjust the chamber air to standard ambient conditions at a rate not to exceed 3°C/min (5°F/min).
Step 5. Visually examine the test item to the extent possible and conduct an operational check. Document the results, and see paragraph 5 for further guidance.
Procedure III – Rapid Decompression
Step 1. With the test item in the storage or transit configuration, install it in the chamber and adjust the chamber air pressure (and temperature if appropriate – see paragraph 2.3.1) at a rate not to exceed 3°C/min (5°F/min)or as otherwise specified in the test plan, to the cabin altitude (2,438m (8,000 ft)) (see paragraph 2.3.1b).
Step 2. Reduce the chamber air pressure to that which corresponds to the required test altitude of 12,192m (40,000 ft) (18.8 kPa (2.73 psi)), or as otherwise specified in the test plan for the maximum flight altitude, in not more than 15 seconds. Maintain this stabilized reduced pressure for at least 10 minutes.
Step 3. Adjust the chamber air to standard ambient conditions using a pressure change rate not greater than 10m/s, and a temperature change rate not to exceed 3°C/min (5°F/min).
Step 4. Visually examine the test item to the extent possible. Document the results. Be alert for potential safety problems (see paragraph 5).
Procedure IV – Explosive Decompression
Step 1. With the test item in the installed configuration, install it in the chamber and adjust the chamber air pressure (and temperature if appropriate–see paragraph 2.3.1) at the rate specified in the test plan to the cabin altitude of 2,438m (8,000 ft) (see paragraph 2.3.1b).
Step 2. Reduce the chamber air pressure to that which corresponds to the required test altitude of 12,192m (40,000 ft) or as otherwise specified in the test program, in not more than 0.1 seconds. Maintain this stabilized reduced pressure for at least 10 minutes.
Step 3. Adjust the chamber air to standard ambient conditions using a pressure change rate not greater than 10m/s, and a temperature change rate not to exceed 3°C/min (5°F/min).
Step 4. Visually examine the test item to the extent possible. Document the results, and be alert for potential safety problems (see paragraph 5).
NOTE: Tailoring is essential. Please, ask to your confidence laboratory for further details about tailoring of test methods.