The explosive found in the Uttar Pradesh Assembly has been identified as PETN, or Pentaerythritol tetranitrate C5H8N4012, one of the most powerful high explosives used by militaries world over — it has a relative effectiveness (RE) factor of 1.66. Ammonium Nitrate, which has been used by terrorists in many bombs in India, has an RE factor of 0.42. Only 100 grams of PETN can fully destroy a medium-sized car.
The odourless white crystalline solid, with a specific gravity of 1.76, has a confined detonation velocity of over 25,000 feet/second. It is used by the military for very specific purposes: in detonators as a primer, in detonating cords as its explosive core, in booster and bursting charges of small calibre ammunition, in upper charges of detonators in land mines and shells. The US military, thus, has a restriction on the use of pure PETN except for the fuze interrupter of a weapons system.
PETN has been used by terrorists because it is potent, hard to detect and safe to handle. In 2001, Richard Reid, the “shoe bomber”, tried to set off a PETN device on an American Airlines jet to Miami. In 2010, a suicide bomber tried to assassinate a member of the Saudi royal family with a PETN-based bomb inside his body. The same year, a PETN device was found strapped to the left leg of Umar Farouk Abdulmutallab, who wanted to blow up Northwest Airlines flight 253 as it approached Detroit airport from Amsterdam.
PETN, like TNT, has extremely low vapour pressures in its purest form. Due to the addition of oils and plasticising agents which give it form and consistency, the vapour pressure goes even lower, making it difficult to be detected by a vapour explosive detector. When PETN is manufactured, a nitrogen-containing compound called a taggant (with a high vapour pressure) is added to make it more easily detectable. But if PETN has been manufactured using chemicals at home, it may not contain any taggant.
In any case, there are very few vapour explosive detectors in India — and none on the UP Assembly premises — which could have detected the PETN packet. The other alternative would be to use specially-trained sniffer dogs. Most Indian establishments, instead, have a metal detector which is not meant to catch explosives — it is only meant to detect metal which is required in every detonator, a small cylindrical device the size of a small pen cap.
A detonator, whether available commercially for quarrying or used by the military, is essential to detonate a high explosive, such as the PETN packet found in the UP Assembly. As the reports do not indicate the presence of any detonator, it is unlikely that the 150 grams of PETN would have exploded. But the presence of PETN itself is a serious security breach for a highly-protected VIP area such as the UP Assembly.