A colleague has indicated to me that Triacetone Triperoxide (TATP) is another type of explosive that should be considered as a high threat, like PETN. It is my understanding that TATP can be manufactured from commonly available materials. This explosive has been used in the Middle East, especially by suicide bombers in Israel. TATP is one of the most sensitive explosives known, being extremely sensitive to impact, temperature change and friction.
TATP can be easily prepared in a basement lab using commercially available starting materials obtained from, e.g., hardware stores, pharmacies, and stores selling cosmetics. TATP is a fairly easy explosive to make, as far as explosives manufacturing goes. It is my understanding that all it takes is acetone, hydrogen peroxide (3% medicinal peroxide is not concentrated enough), and a strong acid like hydrochloric or sulfuric acid.
Notable terrorism incidents utilizing TATP include Richard Reid who targeted American Airlines Flight 63 with a bomb concealed in his shoe with a TATP detonator, along with PETN. The explosive may have been used as the explosive in the July 2005 London bombings. On September 4, 2007, homemade TATP was found during the arrest of eight suspected Al-Qaeda collaborators in Denmark.
The apparent ease of making the explosive is demonstrated by a report (contained in wikipedia) which indicates a 13-year-old student in Hong Kong was injured on March 28, 2009 when he tried to light some TATP powder provided by another 14-year-old boy. Police found six more bottles of TATP from his apartment. Police believe those bottles of TATP were homemade by the 14-year-old boy for curiosity’s sake. Including the injured boy, 3 teenagers were later arrested on explosives possession charges. Of course, this is also a good example of how unstable and sensitive the explosive is when handled.