1.. MIL-STD-81OD . . . . . . . . ly July .lyc$j Downloaded from https://www.everyspec.com I-3.2 i2h0iceof related test condi.tiw. Variables”under each test ~procbdure include the test item configuration, rainfall rate, wind veloc”ity;tes~ item exposure surfaces, water.pressure, and any additional appropriate’g“uideliriesin accordance with the requirements document. .- . . . a., est Item con~. The test item should be”tested in’all the configurations-in which it can be placed-dui’ingits life cycle:’ AS ‘a”min”imum,~ the following’configurations should be considered: 2 I (1) ,,. :.. .. Protected or’not protected. ,,. . .. ,-, .,, ., In a shipping/storage container or transit c&e.
(2) (3) In its operational configuration. :, ,,. , ,: .,,: ,, .? Modified with kits for special application. (4) b. ~1 rate. The rainfall rate used in procedure 1:pay be tailored to the anticipated deployment locale and duration. An instantaneous rainfall rate equivalent to O .8o mm/min .(1.89 in./h) occurs commonly in areas,of heavy rainfall, but a”minimum rate of 10 cm/hr ‘(4in./h) is recommended, since it is nOt an uncommon occurrence and.would provide a reasonable degree of confidence in the test item. Asia, for example, is known to have high rainfall intensities. The highest recorded intensity for 1 minute occurred in Maryland and was 31.2 mm/min (1.23 in./rein).
For testing purposes,.the foliowing table’ of rainfall rates (from MIL-STD-21OB) for worldwide expected durations’of ,, exposure (~E) from 2 to 25 years is more realistic. a TABLE 506.2-I. .. ~ected rainfal1 rates for different ~osure .durat~. ,. EDE Rate (yr) (in./h) (cm/h) ,, 2 4.0 10 4.7 ,:, I 10 5.2 13 25 5.8 15 ., C. ~. Nominal’drop-size spectra exist for instantaneous rainfall rates, but, according to MIL-STD-21OB, for the long-term rainfall” rates they are meaningless, since rates are made up of many different““ instantaneous rates possessing different spectra.
For these tests, droplet sizes should not be smaller than approximately 0.5 mm in diameter,,1/”’which’ considered.to be.mist or drizzle rath6r than rain (reference e.), or larger than 4.5 mm. ,,. ,. ,.. .,. ,. .\ 1/ Observationa Show that there are no drops of less than roughly 0:5 mm diameter during intense rains (reference c): !. METHOD 506.2 19 July 1983’ ,. 506.2-4