its use practical in commercial systems as a part of the EBW initiator. It can be chained with another explosive booster, often a pellet of tetryl, RDX or some PBX (e.g., PBX 9407). Detonators without such booster are called initial pressing detonators (IP detonators). During initiation, the wire heats with the passing current until melting point is reached. The heating rate is high enough that the liquid metal has no time to flow away, and heats further until it vaporizes. During this phase the electrical resistance of the bridgewire assembly rises. Then an electric arc forms in the metal vapor, leading to drop of electrical resistance and sharp growth of the current, quick further heating of the ionized metal vapor, and formation of a shock wave. To achieve the melting and subsequent vaporizing of the wire in time sufficiently short to create a shock wave, a current rise rate of at least 100 amperes per microsecond is required. If the current rise rate is lower, the bridge may burn, perhaps causing deflagration of the PETN pellet, but it will not cause detonation. PETN-containing EBWs are also relatively insensitive to a static electricity discharge. Their use is limited by the thermal stability range of PETN. Slapper detonators, which can use high density hexanitrostilbene, may used in temperatures up to almost in environments ranging from vacuum to high pressures. Firing system The EBW and the slapper detonator are the safest known types of detonators, as only a very high-current fast-rise pulse can successfully trigger them. However, they require a bulky power source for the current surges required. The extremely short rise times are usually achieved by discharging a low-inductance, high-capacitance, high-voltage capacitor (e.g., oil-filled, Mylar-foil, or ceramic) through a suitable switch (spark gap, thyratron, krytron, etc.) into the bridge wire. A very rough approximation for the capacitor is a rating of 5 kilovolts and 1 microfarad, and the peak current ranges between 500 and 1000 amperes. The high voltage may be generated using a Marx generator. Low-impedance capacitors and low-impedance coaxial cables are required to achieve the necessary current rise rate. The flux compression generator is one alternative to capacitors. When fired, it creates a strong electromagnetic pulse, which is inductively coupled into one or more secondary coils connected to the bridge wires or slapper foils. A low energy density capacitor equivalent to a compression generator would be roughly the size of