MIL-STD-331D is the United States military standard containing the environmental and performance test methods for fuzes, igniters and their associated components. The standard exists because a fuze has an unusual requirement: it must remain completely inert throughout storage, transport, handling and installation, and must then function reliably at the moment of use, often after years of storage and after exposure to the full range of climatic and mechanical conditions that a round of ammunition meets. The methods are numbered and grouped, and they cover mechanical shock, vibration, acceleration, impact and rough handling, the climatic conditions of temperature, humidity, thermal cycling and salt fog, and the electromagnetic conditions to which a fuze is exposed, including the electrostatic discharge that is of particular concern for electrically initiated devices and the radio frequency fields present near transmitting equipment. Each method states the apparatus, the conditioning, the procedure and the acceptance criteria.