MIL-STD-1901A
3 Definitions
3.1 Armed. An ignition system is armed when the output of a primary explosive, a sensitive pyrotechnic or application of a firing stimulus can produce ignition of the munition propulsion system.
a. An ignition system employing an ignition safety device with pyrotechnic train interruption (see 5.2.2) is considered armed when the interrupter(s) position (or condition) is ineffective in preventing propagation of the pyrotechnic train, given initiation of the sensitive elements of the train, at a rate equal to or exceeding 0.5 percent at a confidence level of 95 percent.
b. An ignition system employing firing energy train interruption (see 5.2.3.1) is considered armed when the interrupters' position or condition is ineffective in preventing initiation of the first element of the pyrotechnic train at a rate equal to or exceeding 0.5 percent at a confidence level of 95 percent.
c. An ignition system employing a non-interrupted pyrotechnic train and a non- interrupted firing energy train (see 5.2.3.2) is considered armed when the firing energy available for delivery to the initiator equals or exceeds the initiator's maximum no-fire stimulus.
3.2 Common mode failures. Multiple failures that result from, or are caused by, seemingly unrelated failure(s) or an adverse environment. Examples include the failure of two gates on a single digital integrated circuit due to loss of the ground to the chip or failure of two transistors due to exposure to a high temperature environment.
3.3 Enabling. The act of removing or deactivating any safety feature, which prevents arming.
3.4 Environment. A specific physical condition to which the ignition system may be exposed.
3.5 Environmental stimulus. A specific stimulus obtained from an environment.
3.6 Fail-safe design. A characteristic of an ignition system and/or part thereof, including the ignition safety device, designed to preclude ignition of the propulsion system or hazard to personnel when safety features malfunction.
3.7 Firing Energy Train. The path of all non-chemical energy leading to the first element of a non-interrupted pyrotechnic train.
3.8 Firmware. The combination of a hardware device and computer instructions or computer data that reside as read only software on the hardware device. The software cannot be readily modified under program control.
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