Semtex is a general-purpose plastic explosive containing RDX and PETN. It is used in commercial blasting, demolition, and in certain military applications. Semtex became notoriously popular with terrorists because it was, until recently, extremely difficult to detect, as in the case of Pan Am Flight 103.
For its original military use it was manufactured under the name B 1. It has been manufactured under its current name since 1964, labeled as SEMTEX 1A, since 1967 as SEMTEX H and since 1987 as SEMTEX 10.
The composition of the two most common variants differ according to their use. The 1A (or 10) variant is used for blasting, and is based mostly on crystalline PETN. The version 1AP and 2P are formed as hexagonal booster charges; a special assembly of PETN and wax inside the charge assures high reliability for detonating cord or detonator. The H (or SE) variant is intended for explosion hardening.
Semtex was invented in the late 1950s by Stanislav Brebera, a chemist at VCHZ Synthesia, Czechoslovakia. The explosive is named after Semtín, a suburb of Pardubice in the Czech Republic where the mixture was first manufactured starting in 1964. The plant was later renamed to become Explosia a.s., a subsidiary of Synthesia.
Semtex was very similar to other plastic explosives, especially C-4, in that it was easily malleable; but it was usable over a greater temperature range than other plastic explosives, as it stays plastic between −40 and +60 °C; it is also waterproof. There are also visual differences: whereas C-4 is off-white in colour, Semtex is red or brick-orange.
The new explosive was widely exported, notably to the government of North Vietnam, which received 14 tons during the Vietnam War. However, the main consumer was Libya; about 700 tons of Semtex were exported to Libya between 1975 and 1981 by Omnipol. It has also been used by Islamic militants in the Middle East and by the Provisional Irish Republican Army (IRA) and the Irish National Liberation Army in Northern Ireland.
Exports fell after the name became closely associated with terrorist blasts. Export of Semtex was progressively tightened and since 2002 all of Explosia's sales have been controlled by a government ministry. As of 2001 , approximately only 10 tons of Semtex were produced annually, almost all for domestic use.
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