Niche Threat? - Organic Peroxides as Terrorist Explosives

Abstract

Viewed superficially, the 2005 London bombings appeared to be a fairly standard, albeit devastating terrorist attack. However, post-blast investigations pointed to the use of a potent new weapon in the modern terrorist’s arsenal — organic peroxide explosives (OPEs). Through analysis of the London bombings and other key incidents in which these explosives have been used, this article will reveal a gradual but unequivocal increase in the manufacture and employment of OPEs in explosive attacks. In order to counter the threat posed by OPEs, it is essential to understand their unique characteristics, to recognise their implica- tions, and to devise mitigation strategies. This knowledge is not only crucial to the work of explosive ordnance device (EOD) personnel, but also to intelligence operators and capability managers. This article aims to draw together elements of terrorist methodology, security planning and explosives chemistry to define the unique threat posed by OPEs in an effort to raise awareness, promote discussion and articulate options for dealing with this threat.

The ADF is emerging from a period of intense counter-IED capability development while also coming to terms with a strategic shift of focus away from the Middle East. Given the ADF’s partnership with other government agencies in responding to such threats in a domestic context, the time is ripe for discussion of the ADF’s ability to manage the threat posed by OPEs in both a domestic and international setting.

Introduction

Terrorism and asymmetric warfare have arguably been two of the ADF’s key threats since the 9/11 attacks catapulted religious extremism to the front of the national psyche and prompted Australia’s contribution to the US occupation of Iraq. Improvised Explosive Devices (IEDs), considered the asym- metric weapon of choice, represent by far the largest source of coalition casualties in the recent Iraq and continuing Afghan campaigns. But, as a number of mass casualty domestic terrorist attacks in coalition countries have shown, this new conflict is not always conducted in an easily defined area of operations.

Counter-terrorism in Australia is a multi-agency affair, with the ADF tasked by government to be prepared to deal with contingencies beyond the resources of state or federal agencies. It is therefore important that the ADF’s explosive ordnance device (EOD) capability, as part of the whole of government counter- terrorism solution, is able to counter explosive threats as capably in central Sydney as in the Middle East. This is particularly timely considering the ADF’s current strategic refocus from the Middle East. Australia is now better prepared to respond to terrorism than ever before. Intelligence agencies were strengthened in the wake of the 9/11 attacks, boosting their ability to detect threats while still in the planning phase. The increased resources allocated to border protection operations have also reduced the likelihood of terrorists, weapons and explosives being smuggled into the country.

Yet an asymmetric threat will, by definition, adapt to new strengths in the responsive agencies. Increased border protection adds impetus to the growth of ‘home-grown’ terrorists such as those discovered in the UK and US. Similarly, making the import of explosive materials more difficult provides greater incentive for terrorists to switch to domestically sourced improvised or stolen explosives. The increased monitoring and surveillance of terrorist activities also forces them to seek resources in new, more covert ways. For these reasons it is vital to continually analyse those means by which strengthened controls can be bypassed. This article will analyse the way in which organic peroxide explosives (OPEs) can be utilised by both terrorists in Australia and insurgents in Afghanistan, and the factors which push IED manufacturers to accept the risks inherent in using such dangerous materials. Robust responses to small technical threats comprise the building blocks to achieving an effective counter-terrorism capability in Australia.

Terrorism and explosives

The development and gradual proliferation of explosives in the wider community has provided terrorists with an unprecedented means to commit large-scale terrorist attacks while avoiding capture. An explosive is a semi-stable chemical or mix of chemicals that can sustain a rapid chemical reaction without the participa- tion of external reactants such as oxygen. Such rapid reactions typically trigger the explosive’s production of vast quantities of gas and heat, resulting in a shock that causes mass damage to nearby objects through thermal burns, shock force and kinetic transfer.

Explosives are classed as tertiary, secondary and primary, based on their relative sensitivities. Reliable initiation requires a highly sensitive explosive to transform an external force (electrical, chemical, thermal or mechanical) into a shock wave strong enough to ensure the detonation of the bulk explosive. This class of materials, known as primary explosives, is the most sensitive to friction and heat, as illustrated in Table 1. This sensitivity is the reason for their use in one of the critical components of an IED — the detonator. Their sensitivity means that a flame, hot electrical filament or mechanical striker can provide enough energy to trigger an explosive chain reaction. These primary explosives are critical resources in IED manufacture as they comprise the deter- mining factor between a pop or small fire, and a devastating blast.

Terrorist use of explosives

The ability to store chemical energy in such a dense, controllable and easily acces- sible form has increased the broad employability of explosives — from mine blasting to passenger vehicle airbags. These same properties also allow terrorists to plan an attack that can be triggered variously by the victim, a remote timer or environmental conditions once a getaway has been effected. This largely removes the need to face one’s intended target, a moment when an attacker may have a last minute change of mind. The ‘remoteness’ of explosive devices increases the likelihood of escape. No other form of terrorist weapon comes close to explosives for this combination of killing power and separation for the perpetrator.

Security authorities have long recognised that protecting the population from terrorist attacks is best achieved by preventing or interdicting the device prior to its placing or detonation — often referred to being ‘left of the bomb’ (on a left-to-right timeline from formation of intent to successful attack). Precursors for easily synthesised explosives are regulated and tracked to ensure that any planned attack will rise above the surveillance threshold early enough to allow interven- tion. Critical supplies such as detonators are hazardous to manufacture due to the sensitivity of the required primary explosives. The primary explosive fill used in commercial detonators is difficult both to source discreetly and to synthesise in high purity.

Table 1. Comparison of explosive classifications.

Note: This table highlights the differences in the characteristics of each of the key types of explosive. Detonation velocity measures provide an indicator of the impact of the shock wave, while the volume of gas generated tends to govern how powerful the explosion is. Together they determine the destructive potential of an explosive. Friction sensitivity shows how much pressure needs to be applied to two sliding surfaces between which the explosive will detonate on movement.

The ever-increasing list of terrorist attacks in modern societies demonstrates, however, that these difficulties are not insurmountable. Ultimately, individual bombers and groups will reach a compromise between the risk of drawing the attention of security agencies and a desire for the enormous impact of high-powered commercial or military explosives. Any means of gaining access to explosives while avoiding detection provides terrorists with a dangerous opportunity to gain the initiative and poses a highly attractive option — even if such means entail consider- able personal risk. Personal risk appears to rank low on the list of concerns of a terrorist intent on making a large-scale attack. 

Organic peroxides

Not all organic peroxides can be used as explosives. The term ‘peroxide’ refers to a molecule within which two oxygen atoms are bonded together by a single bond. The simplest form of peroxide is hydrogen peroxide, commonly used in dilute solution as a bleaching agent and disinfectant. The peroxide oxygen-oxygen single bond is particularly weak, a characteristic which gives peroxides their inherently unstable nature.

Certain organic peroxides are able to sustain a powerful detonation, and at this point they begin to be regarded as explosives in their own right. The best known of these include triacetone triperoxide (TATP), hexamethylenetriperoxide diamine (HMTD) and methylethylketone peroxide (MEKP). It is important to distinguish between OPEs and explosives mixes containing hydrogen peroxide. Hydrogen peroxide — organic matter (HPOM) mixes — are more akin to ammonium nitrate/ fuel oil (ANFO). In a HPOM, the oxidiser is hydrogen peroxide, and the fuel can be  almost any finely ground organic material, although performance will vary based on the fuel used. A HPOM is not an OPE as molecular bonds between the hydrogen peroxides and the organic components are not required. HPOMs are significantly less friction sensitive than OPEs such as TATP and HMTD, and usually less powerful.

To understand the power of these explo- sives, it is illustrative to compare them with a standard military grade explosive such as TNT. TATP achieves a power result of 83% of TNT. HMTD is more powerful still. A notable characteristic of OPEs is their very high levels of sensitivity to mechanical impact, friction, heat and electrostatic discharge. TATP, HMTD and MEKP are all significantly more sensitive to friction than lead azide, which is one of the most common primary explosives used in military and commercial detonators. The data presented in Table 1 compares the sensitivity of OPEs with that of other common explosives. The sensitivity of TATP in particular is heightened by the tendency to sublime (slowly vaporise) at room temperature and crystallise on nearby surfaces. These characteristics make OPEs extremely dangerous to handle in any significant quantity. Paradoxically, these same dangerous characteristics are precisely those sought by a potential terrorist.

Most OPEs also have simple synthetic procedures. The synthesis of TATP is rela- tively straightforward as long as some basic precautions are taken with temperature and rate of addition. Recipes for preparing these explosives are available through a number of internet sites, not all of which are terrorist sites. Purification is also straightforward, providing pure crystalline products as depicted in Figure 1. Their sensitivity makes handling large quantities dangerous, though this can be mitigated to some extent.

Figure 1. Raw OPEs. TATP and HMTD both form white crystalline powders in their raw form, similar to this organic peroxide used in laboratory trials. Synthesis and purification methods for most OPEs are relatively simple and do not require specialist equipment.

All of this means that OPEs occupy a unique niche in the explosive world on the scale of sensitivity versus accessibility. As was noted earlier, primary explosives are crucial to the construction of an IED that can be relied upon to fully detonate. Lack of primary explosives (together with a generally poor understanding of explosives) was part of the reason the Times Square

Bomber of 2009 failed to initiate his load of  gas cylinders and fertiliser — the result was a fire rather than an explosion. The sensi- tivity of OPEs presents a potential solution to this problem. On the other side of the scale, many raw ingredients for OPEs are available at most hardware shops, and the sheer volume of these chemicals in indus- trial use make tracking the small quantities required challenging if not impossible. This unfortunate intersection of covert access, power and sensitivity places OPEs in a separate class when their security implications are considered.

OPEs as explosives

OPEs have been recognised for over 100 years, with HMTD discovered as early as 1885 and TATP in 1895. HMTD reportedly found use for a brief period in the mining industry as a primary explosive, but was soon superseded by more stable compounds. In general, however, OPEs have seen very little legitimate use due to their sensitivity. After their initial discovery, TATP and other OPEs were not researched in any great depth due to their lack of application.

The 1980s saw a resurgence of interest in these compounds, but from a more sinister source. Extremist groups such as the military wing of Hamas saw OPEs as a ready source of primary and even bulk explosive. The risks inherent in the production and handling of these explosives was outweighed by the sheer difficulty in acquiring conventional explosives, and TATP became a staple explosive for the conduct of suicide bombings and other attacks. With the rise of Al Qaeda in the late 1980s and the establishment of its associated training camps, knowledge of the production of OPEs spread, further accelerated through the growth of the internet in the late 1990s.

With information on its synthesis so readily available, it is now reasonably common for law enforcement agencies in modern Western democracies such as Australia to discover these explosives in bombing incidents. In 2008, for example, a Sydney man detonated a phone-activated TATP pipe bomb at a suburban property, killing a bystander. More recently, in October 2010, a US teenager was charged over the detonation of a TATP-filled pen-bomb which injured a fellow student. When police searched the teenager’s home, ‘significant quantities’ of TATP were found.

Figures from the AFP Australian Bomb Data Centre reveal that from 2006 to 2008 home-made explosives accounted for 9.5% of total bombing incidents in Australia. With the exclusion of bombs known to have been built with incendiaries such as fireworks, gas pressure, and Molotov cocktails (which are technically not explosives), this figure rises to 28%. While more detailed figures are classified, it is reasonable to assume that a proportion of these incidents would involve OPEs considering their ease of access and simple production. Anecdotal evidence from members of the state fire authorities supports this conclusion.

The use of TATP is not limited to schoolyard pranks and home experiments. Aside from consistent use in the Israeli-Palestinian conflict, OPEs have seen increased use in major international terrorism cases. One of the most prominent cases was the ‘shoe-bomber’, Richard Reid, a self-confessed member of Al Qaeda.

Reid attempted to detonate a bomb containing the high explosive PETN with a TATP priming charge on board Flight 63 from Paris to Miami. The attempt failed due a minor technical glitch, but had the potential to bring down the passenger airliner. It was later discovered that the shoe-bomb was by no means unique, with a second, identical bomb found in the possession of Gloucester (UK) resident Saajid Badat. Badat had also been planning to board an aircraft with the aim of near- simultaneous destruction of two US-bound airliners, but had pulled out at the last minute. Both men allegedly received their bombs from an Arab bomb-maker during a visit to Afghanistan in 2001, a claim supported by forensic analysis.

The shoe-bomb cases highlight the importance to terrorists of TATP as an acces- sible primary explosive. While PETN is a relatively sensitive secondary explosive, it is not sufficiently sensitive to be reliably detonated by a simple mechanism such as a firing pin or flame. In this instance, TATP appears to have been the trigger to initiate the powerful PETN main charge.

While the shoe-bomb plot was foiled, another example, in which the bombs remained undetected prior to detonation, demonstrates the power produced by the combination of OPEs with other HMEs. On 7 July 2005, four men (all British citizens) arrived at a London train station in two hire cars. After organising their rucksacks in the  boot of the cars, the men disappeared into the transport system. At 8.50 am, three of the men simultaneously detonated bombs hidden in their rucksacks during the height of the subway rush hour, while another was detonated over an hour later on a double- decker bus. The coordinated attack killed 52 people, injured hundreds and brought OPEs have been recognised for over 100 years, with HMTD discovered as early as 1885 and TATP in 1895. London’s public transport system and business district to a complete standstill. While the terrible cost in terms of lives lost can be calculated, the financial and psychological cost extended far beyond the physical damage of the bombs.

The official account of the 7 July attack (often referred to as the 7/7 bombing) delivered to the House of Commons provides a detailed insight into the way this group of men was able to achieve its goal of destruction. Notably, the key members of this plot were British-born citizens and had not attracted the attention of British security services up to the point of the attack. This is a remarkable achievement considering the capability of British counter-terrorism agencies with their decades of experience from operations in Northern Ireland. Two of the four bombers were found on intelligence records when reviewed after the bombing, but simply as peripheral to other ongoing investigations. All four men had evaded the attention of authorities during the planning, preparation and execution of their attack.

The British Intelligence and Security Committee Report of 2006 revealed that the bombs were constructed using OPE-based explosives. Multiple open source outlets have quoted TATP as the specific explosive used, although the 2011 Coroner’s inquest revealed that an OPE (HMTD) was utilised only in the detonator. The bulk explosive was a lower powered mix of hydrogen peroxide and organic material (a HPOM), making it less sensitive and less powerful than OPEs. The committee report suggested a figure of two to five kilograms of explosive per device. The official account stated that the fourth bomber had bought batteries at a news-stand prior to detonating his device on the bus, suggesting that the devices were electrically initiated, which was confirmed in the Coroner’s inquest. The bomb-making facility was later identified in a suburban flat in Leeds. It is not clear in the open source literature where the bombers acquired their explosive know-how. Two members of the group had travelled to Pakistan for a few weeks in the lead-up to the bombings, and authorities  believe that it is possible the men received some training during these brief visits.

The London 7/7 attack is an example of the way home-made OPEs enabled a determined group with minimal training to avoid detection by authorities while planning a highly coordinated terrorist bombing with devastating consequences. At no point in the lead-up to the attack had the purchase of chemicals or the explosives manufacturing process in the middle of suburbia triggered suspicion from authorities or the local populace. The use of HMTD in the home-made detonators ensured the reliability of the group’s IED design, with all devices functioning as planned (despite one apparently suffering battery problems). Furthermore, the power of HPOM explosives, made from easily accessible sources, was graphically and clearly demonstrated in vision of the upper deck of the London bus which had been torn open by the explosion, as illustrated in Figure 2. While OPEs may not have constituted the main explosive fill, they enabled the construction of a reliable weapon capable of achieving the primary aim of the terrorists — the infliction of mass casualties to deliver a political message.

These international examples have brought OPEs not only to the attention of authorities, but to other terrorist groups as well. Counter-terrorism raids in Australia in October 2005 were, in part, triggered by advice from intelligence agencies that had intercepted the group’s attempts to buy sizeable quantities of acetone, sulphuric acid, a large ice box and (tellingly) backpacks. At this stage, the media had reported the use of TATP in the London attacks. It was all but certain that the men were planning a copy-cat attack of the London bombing, and the quantities of chemicals involved hinted at large-scale destruction. Again, the terrorists were men who were residents of the country they planned to attack. Fortunately, in this instance, the Australian Federal Police and other agencies had sufficient evidence to launch raids before the cell had a chance to put its plans into action.

Figure 2. London 7/7 bombings. The power of home-made explosives was graphically illustrated in the bombing of this London bus on 7 July 2005. A bomb (estimated at around five kilograms) carried in a backpack destroyed the bus and killed 14 people including the bomber, injuring 110 others. All four of these devices detonated as planned, signalling the use of HMTD in the improvised detonators.

The spread of OPE use was further illustrated in the Christmas Day attack in 2009, in which a Nigerian Islamic extremist attempted to detonate a (reportedly) TATP/PETN device hidden in his underwear. The unique design involved initia- tion by injection of a liquid in a plastic syringe, making the bomb entirely free of metal so as to evade airport security. While this initiation method was distinctly different to Richard Reid’s shoe-bomb, the two main explosive ingredients were the same (PETN and TATP), as was the idea of secreting the device in clothing. Fortunately, this device failed to detonate in the same way as Reid’s. The links suggest that attacks do not even need to be successful to effectively propagate their design globally. Again in 2009, Najibullah Zazi brought quantities of TATP to New York planning to bomb the subway system, but was foiled by the FBI. Needless to say, this planned attack was also inspired by the 7/7 bombings. According to open source reporting, Zazi intended to use TATP as his explosive of choice, possibly even in the main charge.

The application of OPEs in IEDs also has the potential to affect ADF EOD elements abroad. Technical details of IEDs found in current theatres of operation remain classified, which is why this discussion has necessarily remained domesti- cally focussed and does not extend to the latest developments and threats. It is clear, however, that threat forces in ADF areas of operation such as Afghanistan tend to have reasonable levels of access to military grade explosives or detonators through theft, the availability of the explosive remnants of war, or through the black market, so the somewhat riskier explosives such as OPEs are not required to construct IEDs. Insurgent access, however, is coming under threat as coalition operations continue to strengthen the local authorities’ ability to police and control access to explosives and precursor material such as ammonium nitrate fertiliser. As access becomes more difficult, IED facilitators will need to look for new sources of explosives.

The pressures of supply and demand in the IED chain can encourage IED manufacturers to incur additional risk, These international examples have brought OPEs not only to the attention of authorities, but to other terrorist groups as well. and it would be surprising if OPEs do not begin to appear as the security situation in Afghanistan improves. Any forces remaining in theatre will need to react and evolve with the threat as the ADF’s mission accomplishment changes the technical threat confronting EOD operators.

Unique hazards, novel solutions

First responders faced with OPEs must also confront a unique set of hazards in any device or container that includes OPEs. The first challenge is to identify that OPEs are actually present in the IED. EOD operators may not be able to identify whether an IED contains an OPE detonator as the detonator itself is unlikely to be accessible. Of greater concern is the use of an OPE main charge. While such a design may be dismissed as too dangerous, the Moroccan attacks of 2003 provide just one historical example which demonstrates that personal risk is often not a major concern to terrorists. This incident, which claimed 45 lives including those of the bombers, was reportedly (at least in open sources) conducted with TATP as the bulk charge.

Leaving aside the difficulties in determining whether an IED contains an explosive fill of OPEs, dealing with the sensitivity of such an IED can test conven- tional EOD methods and equipment. The safest method of dealing with an IED is to blow it up in place using a counter-charge or triggering the IED remotely. However this is not always possible, particularly if the device has been placed next to fixed sensitive installations (flammable stores, high value infrastructure, etc). The use of ‘blow in place’ procedures also destroys much of the forensic evidence on the IED which may be crucial in identifying the bomber and the source of the explosives. This is particularly important in the domestic context, but also increasingly in military peace enforcement and stability operations. In such situations, rendering safe (also known as disablement or defusing) is the preferred option.

While there are a number of ways to render such devices safe, the principles remain consistent. The components of the IED must be separated using a method that prevents the device from functioning as designed. One common method is the use of kinetic disruptors in which high speed jets of water target strategic areas of the IED to neutralise key components. While this is a very effective method under normal conditions, it carries an unreasonable risk of triggering an OPE main charge, as the high kinetic energy transfer is liable to directly detonate an impact-sensitive explosive fill. Dissolving the explosive fill with diesel is another method EOD teams often use to deal with OPEs. However, aside from practical concerns over how to contain, store and move the litres of explosive-contaminated fuel, this method has not been subject to thorough safety testing. Despite these risks, dissolution remains one of the few viable methods to deal with such a situation and continues to be recommended in Standard Operating Procedures for bomb squads around the world. An ideal solution for the OPE hazard lies in identifying a chemical agent or One common method is the use of kinetic disruptors in which high speed jets of water target strategic areas of the IED to neutralise key components. physical process that would rapidly and safely neutralise the material in situ.

Methods that have been investigated include thermal degradation, acid degradation and metallic compound degradation. Most of these methods, however, do not work well in the field environment. Given the risk of explosion, heating is not a suitable means of safely neutralising peroxide explosives in anything other than microgram quantities. Substantial heat is also produced in the reaction of acid with OPEs, which leads to detonation of anything greater than microgram-sized quantities of peroxide. When weaker solutions are used to reduce this risk, degradation is incomplete, leaving a residual explosive risk. Some work has been undertaken to investigate the neutralising of TATP or other OPEs through other chemical reactions; however, at this point, a result suitable for field use in the EOD trade remains elusive.

While research continues, a viable, field-ready solution remains some way off. The ultimate goal is a catalyst-based solution that allows a small quantity of agent to neutralise many times its own weight of explosive, providing a portable and safe means of neutralising the explosive hazard. The technical barriers are significant, and continued research will be necessary to realise the goal of rapid field neutralisation of OPEs.

Conclusion

The aim of this article is not to imply that Australian society is at the mercy of a weapon that is at every terrorist’s disposal — the situation is not quite so dire. Nor is it assumed that this is the highest priority within all counter-IED efforts, as there are more pressing technical challenges to improve safety both for operators and the protected population. It is important to note, however, that in all the historical OPE incidents described, the explosives have detonated before authorities were aware of them, would never have functioned in the first place due to technical glitches, or had not yet become operational due to effective or fortuitous intelligence and surveillance. There have been few instances that have permitted the use of EOD techniques to render a viable OPE device safe. This leaves a delicate decision to be made in terms of the priority allocation of scarce EOD resources. Should the potential damage that may be caused by the disabling of an OPE IED be simply accepted on the basis that OPE IEDs are currently relatively rare? Or should the ADF and other agencies work to increase their ability to deal with an explosive which is likely to grow in utilisation as the security apparatus closes off alternatives?

Both options are potentially acceptable and justifiable, but cannot be debated effectively in open-source literature. The debate must be grounded in real-time and robust intelligence, considering the exact limitations of classified capabilities, and be balanced against broader counter-IED and counter-terrorism initiatives and priorities. Should a decision be taken to increase the ADF’s ability to deal with such devices, some investment in specific research, trials, and materiel will be required to boost capability. Specifically, suggested areas for development include devices to provide stand-off detection of OPEs to allow EOD operators timely warning of the precise nature of the device they face. Comprehensive field trials must be conducted to ensure the suitability and safety of currently recommended methods of dealing with OPEs such as dissolution. Continued research towards a safe, field-deployable method of complete neutralisation is essential, with extensive field trials of identified solutions a follow-up to the necessary research.

The IED threat encountered by the ADF across its operational theatres is daunting to say the least, and managing that threat comes down to an ‘art of the possible’. Providing capability against every contingency is not an option. In some instances a deliberate decision is taken to leave a contingency unguarded; at other times the gap is not identified until exposed by an incident. Promoting discussion on the nature of such threats can only enhance those decisions relating to the ADF’s capability to deal with OPE IEDs, allowing such decisions to be made, as they say, ‘left of the bomb’.