Search for

No matches. Check your spelling and try again, or try altering your search terms for better results.


Jun 22, 2006 | 03:48 GMT

12 mins read

The Chemical Threat to Subways: Dispelling the Clouds

Chief Security Officer, Stratfor
Fred Burton
Chief Security Officer, Stratfor

Recent reports outlining what Time magazine has called the "untold story" of a canceled al Qaeda plot against the New York subway system have excited considerable media hype and public consternation. The account is part of Ron Suskind's new book, The One Percent Doctrine, that was excerpted in the June 26 edition of Time. According to Suskind, al Qaeda developed a "revolutionary new WMD device" that would generate cyanide gas, and these weapons — which he refers to as "mubtakkar" devices — were to have been planted on subways by operatives who were in place and preparing to act in early 2003. The plot, however, reportedly was called off by al Qaeda's No. 2 leader, Ayman al-Zawahiri. The account of the plot, as outlined by Suskind, raises several issues. First, is there a credible terrorist threat to passenger rail systems in the United States? Second, is there a viable risk that an attack using a mubtakkar device or hydrogen cyanide gas could be carried out? And third, how might such an attack serve the interests of jihadists? Some of these questions are easy to answer. It long has been our view that the passenger rail system tops the list of soft targets in the United States, and we continue to believe that an attack of some sort will be carried out. And it certainly is possible chemical gases or mubtakkar devices could be used — with some effect — in such an attack. However, any description of such devices as a "revolutionary" new threat (or even a particularly deadly one) would be overstating the case. Because of this, it would be highly unlikely that a strategically significant organization with an interest in conducting "spectacular strikes" would opt to use such a weapon. That is not the same as saying that no one could be killed or injured — but the use of a mubtakkar as described by Suskind in a terrorist strike would likely show more about the perpetrator's weaknesses than his strengths.

Threats to Transportation

Even in light of the security measures taken following the 9/11 attacks, there remain in the United States a great many "soft targets" that are difficult, if not impossible, to completely defend from a terrorist attack. The nation's passenger rail system tops this list. Due to the sheer numbers of people who use the system and the number of stations it encompasses, the security measures necessary to eliminate the possibility of a terrorist strike would all but bring the passenger rail system to a grinding halt. The risks are particularly relevant in the rail corridor running from Washington, D.C., to New York City. Counterterrorism officials refer to this region as "the X," or target zone, given the symbolic value of both cities and the heavy usage of the rail system there. On average, local transit authorities say, 4.9 million passengers use New York City's trains and subways every weekday, as do 700,000 passengers in Washington. From a terrorist's perspective, subway and commuter trains provide a dense concentration of potential victims, neatly packaged in a small metal box. When that box is placed inside a concrete tunnel, the confined space can amplify the blast effects of an improvised explosive device (IED). Moreover, there are chances of follow-on casualties as the tunnel fills with smoke and fire; confusion and panic among the passengers is frequently compounded, and people can be trampled or injured by smoke inhalation. Thus, subway and commuter-rail cars not only are vulnerable to terrorist attacks, but from the attacker's perspective, can present a more desirable target than average crowds in other settings. Obviously, there have been successful attacks against passenger rail systems in recent years. In addition to the strikes in London and Madrid, there have been several thwarted plots touching on the New York subway system. Among these were the July 1997 plot involving Ghazi Ibrahim Abu Mezer and Lafi Khalil, who were arrested in the early hours of the day on which they had planned to execute their attack, and the 2004 plot involving Shahawar Matin Siraj and James Elshafay. As shown by the attacks in London and Madrid (and perhaps most vividly by the botched July 21 attack in London last year), grassroots jihadist cells have both the reach and means to strike at passenger rail lines. And because such attacks result in considerable mayhem and press coverage, they could provide a model that aspiring jihadists attempt to follow. In addition to the potential threats from grassroots jihadists, it is known that operatives affiliated with the core al Qaeda leadership have gathered targeting intelligence concerning the New York and Washington, D.C., rail systems. We cannot completely rule out the possibility that "al Qaeda prime" might attempt to put that research into use at some point; as we have noted on several occasions, al Qaeda has a history of returning to specific targets or target categories over time. At the very least, a hit on a train in the heart of Manhattan, or near the Pentagon or Capitol South stations in D.C., would be highly symbolic — as would an attack against the Amtrack Metroliner traveling between Washington's Union Station and New York City's Penn Station. Symbolism is one consideration as al Qaeda attempts to speak simultaneously to audiences in the Muslim world and in the West. But for any successful terrorist organization, attack techniques and their efficacy also must be considered.

Cyanide Devices

In light of this, it is worth examining the odds of a hydrogen cyanide device being used, and the consequences that could follow. Certainly, al Qaeda has demonstrated that it possesses the rudimentary knowledge to produce a device that generates hydrogen cyanide gas. In testimony at his 2001 trial for the "millennium bomb plot," Ahmed Ressam described training he had received at al Qaeda's Deronta facility in Afghanistan for building a hydrogen cyanide device. Ressam said members of the group had practiced their skills, using the gas to kill a dog that was confined in a small box. Videos found by U.S. troops after the invasion of Afghanistan supported Ressam's testimony — as did confiscated al Qaeda training manuals that contained recipes for biological toxins and chemical agents, including hydrogen cyanide gas. There have been other examples as well. In February 2002, Italian authorities arrested several Moroccan men — who allegedly were planning to attack the U.S. Embassy in Rome — who were found with about nine pounds of potassium ferrocyanide. And years prior to that, Abdel Basit said he had considered a cyanide gas plot targeting the World Trade Center towers, before settling instead on a truck bomb as the vehicle for his 1993 attack. From this history, it appears that some jihadists have a fixation on chemical attacks, using agents like hydrogen cyanide, much as others have been fixated on operations involving planes. That said, there is nothing particularly "revolutionary" about the use of cyanide in a weapon. Hydrogen cyanide gas has been used as a chemical weapon since World War I, and the concept of manufacturing binary chemical weapons also has been around for decades. In fact, Aum Shinrikyo attempted at least three attacks using improvised binary hydrogen cyanide gas devices against subway systems in 1995. (We say "at least three" because Aum conducted several other chemical attacks in early 1995; in some of those, the chemical agent used was never identified.) A review of the confirmed Aum cyanide attacks is useful, however, in understanding the implications of the jihadist plot outlined by Suskind. In the first attack, on May 5, 1995, Aum members placed sodium cyanide and sulfuric acid in separate vinyl bags, planted the devices in a subway restroom and lit them on fire in an effort to rupture the bags — thus combining the ingredients and creating a cloud of hydrogen cyanide gas. Because of the fire, however, the devices were found before they could function fully. Only four people were injured — and those only slightly, complaining of respiratory troubles and throat irritations. On July 4 and 5, 1995, Aum again deployed devices using vinyl bags to hold acid and sodium cyanide. These "new and improved" devices were to be activated by means of a timer connected to a small motor. The motor had a rotating blade, intended to shred the bags and combine the ingredients. The July attacks both failed, however, because the devices malfunctioned, and there were no injuries to speak of. The device that Suskind has labeled a "mubtakkar" is similar in theory to those used by Aum Shinrikyo. Generally speaking, the mubtakkar consists of five components: 1. A container, such as a paint can (to hold other components of the device), perforated to allow gas to escape 2. Acid 3. Cyanide salts, such as sodium cyanide or potassium cyanide 4. Soda bottles, positioned amid the cyanide salts, to contain the acid 5. A blasting cap to shatter the bottles and release the acid, allowing it to mix with the cyanide Clearly, the device is not very complicated, and the requisite materials are easy to obtain; thus, someone with little or no training could build one of these devices. In fact, in April 2003, someone did, and it was seized by U.S. federal agents in east Texas. The suspect who was arrested was not a jihadist, but an anti-government extremist named William Krar. According to investigators, Krar found the blueprint for his device on the Internet. The more important point, however, is that the construction of a so-called mubtakkar is more or less intuitive and relies upon a simple and well-recognized chemical reaction. In all three cases, the design of the devices employed the principle of keeping the volatile ingredients separate and then, by use of a delay mechanism, allowing them to mix and generate hydrogen cyanide gas.

Applying a Threat Matrix

While hydrogen cyanide gas is deadly in high concentrations, it is a volatile gas and dissipates quickly. Because of this, deadly concentrations are often hard to achieve in a real-world setting. It follows, then, that however easy a mubtakkar device might be to build, its use would not be likely to generate massive casualties. And that means it probably would not be the weapon of choice for an organized group with a reputation to consider and protect, such as al Qaeda — unless, of course, the central organization was indeed desperate and disrupted. Given the ease with which more loosely organized groups or cells might build and use such a device, however, a few points are worth noting. Initiating a device like the mubtakkar with a detonator would create a significant bang and create a thick cloud of caustic smoke. Government tests have shown that such a device generates cyanogen chloride, hydrogen cyanide, and possibly chlorine. The cyanogen chloride would irritate people's eyes, throats and lungs before the hydrogen cyanide could build up to lethal concentration. With those physical symptoms, victims would be apt to evacuate the area in search of fresh air. Depending on details of the location, they might be able to escape before inhaling lethal doses. Even if the device were activated in an enclosed area, such as a subway car, they could buy time by staying low to the ground, since hydrogen cyanide gas is lighter than air. The release of caustic smoke in a subway car would cause a panic, and it would be difficult to see or breathe; however, a smoke hood and small flashlight can be life-saving devices in such events. There also is a risk of psychosomatic injury — people erroneously believing they have been injured — so keeping calm is critical. (In cases where psychosomatic injuries have occurred, "victims" sometimes pass out — which leaves them vulnerable to smoke, fire and trampling — or deadly gas fumes.) A more important point, however, is that hydrogen cyanide gas — used as a chemical weapon — is not as effective as other toxic substances, such as the nerve agent sarin. And even sarin (which was used in Aum Shinrikyo's March 20, 1995, strikes against the Tokyo subway system) can be less than devastating. In that attack, Aum members on five different subway trains punctured 11 plastic bags filled with sarin, killing 12 people. The more conventional bombing attacks in Madrid and London, by way of comparison, killed 191 and 54 people respectively. Given this history, then, it is little wonder that (if Suskind's information is correct) the al Qaeda leadership would call off an attack involving hydrogen cyanide gas. Weapons of this sort certainly may be part of the al Qaeda arsenal (and perhaps of jihadist mythology), but in practical terms they do not represent a revolution of any sort in terrorist tactics — nor, quite frankly, are they even as deadly as a more conventional bomb of comparable size. Judging from the historical examples, one clearly has a much better chance of escaping from a rail car containing a mubtakkar device than one containing a 20-pound Madrid-style backpack bomb. Whether al Qaeda leaders were or are aware of these tactical considerations is an interesting question. Why a plot involving such a weapon proceeded nearly to the completion phase — and what other considerations the leadership might have had in mind when the plan was called off — are, to our minds, far more intriguing still.

Connected Content


Article Search

Copyright © Stratfor Enterprises, LLC. All rights reserved.

Stratfor Worldview


To empower members to confidently understand and navigate a continuously changing and complex global environment.

Google Play