countries. Following the bombing of PanAm 103 over Scotland, the International Civil Aviation Organization (ICAO) was instrumental in effecting a worldwide requirement for placing a detection taggant in plastic bonded explosives. There is a choice between four possible detection taggant chemicals which must be added to plastic explosives under the 1991 International Civil Aviation Organization's Convention on the Marking of Plastic Explosives for the Purpose of Detection. In the United States the marker is always 2,3-dimethyl-2,3-dinitrobutane, usually called DMDNB or DMNB. Dogs are very sensitive to it and can detect as little as 0.5 parts per billion in the air, as can specialised ion mobility spectrometers. Other taggants in use are ethylene glycol dinitrate, known as EGDN and used to mark Semtex, ortho-mononitrotoluene (o-MNT), and para-mononitrotoluene (p-MNT). Identification (or post detonation) taggants These have been considered for introduction in industrial explosives so that the manufacturer and batch number can be determined if they are used illegally. The taggant must survive the detonation of the product and not be contaminated by the environment afterwards. Several different technologies have been considered, but the most common are microscopic polymer/metallic particles. Taggant evidence was crucial in the 1980 conviction of James L. McFillin in Maryland for the 1979 truck bombing murder of Nathan A. Allen, Sr. A contention claimed for opposing mandated taggants is that most terrorist attacks use homemade explosives (HME) which would allegedly not be tagged. Examples given included, for instance, the 1993 World Trade Center bombing, the Oklahoma City and the Omagh bombings. Contamination of the site is also cited as a problem, since different taggants might be present at a crime scene from, for example, explosives used to obtain the building materials. Switzerland passed a law in 1980 requiring taggants in explosives manufactured there, and that the code must be changed every six months. So far it is the only country which requires identification taggants. Imported explosives must be tagged only if competing products are also manufactured in Switzerland. In the United States, the NRA opposed the mandated use of taggants in firearm propellants after tests revealed a dangerous increase in burn rates. It was claimed that a chemical incompatibility with the propellent powders would cause such an increase in pressures that many firearms would burst after using a taggant-laced powder that had been stored for as little as several months. However, these tests were performed on gunpowder with a