High-Volume Storage: An Incident Involving High Volumes of Toxic and Flammable Chemicals

The chemical industry stores many chemicals at its facilities in the form of raw materials, intermediates, products, and by-products. These products and by-products are then sold to customers who store them on their sites for direct use or the manufacture of other products. The products of interest to a terrorist are chemicals that are toxic, flammable, or explosive, or a combination thereof. AsFigure 4.1

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indicates, this scenario has particular relevance to the storage of inorganic chemicals, industrial gases, and petrochemicals and fossil fuels. Examples of inorganic chemicals that are toxic and stored in large volumes include chlorine, ammonia, and hydrogen fluoride. Industrial gases that are toxic include carbon monoxide; nitrogen and argon are asphyxiants; oxygen and hydrogen are flammable. Most petrochemical and fossil fuel products, intermediates, and by-products are flammable, while a few such as hydrogen cyanide, hydrogen sulfide, and phosgene are toxic.

Scenario

Location. The fictional River City is located on a major transportation corridor, serves as an inland port, and is a centralized hub of industrial production. The city abuts a major fresh waterway that serves as a source of drinking water for millions of people in the city and downstream from it. River City's terrain is moderately hilly, and a majority of the population resides in low-lying areas, increasing the potential for a persistent toxic cloud to develop over a large residential area at a concentration hazardous to life and health. Limited evacuation routes are available to the community. River City has a population density greater than 8,000 people per square mile.

FIGURE 4.1 High-volume scenario: storage. As depicted in (a), a chemical facility is located within the midsized, fictitious River City. In the terrorist attack outlined in (b), Facility A is targeted first. The shock wave from this attack causes the destruction of Facility B. Shrapnel from Facility B hits Storage Tanks C, which then releases toxic chemicals into the river, the source of drinking water for River City and downstream communities. See text for details.

Time of Incident.The incident occurs during summer at or around mid-Night on a Saturday, Sunday, or holiday, when lower numbers and junior levels of permanent employees staff industrial facilities.

Ambient Conditions. The night is clear with a temperature of approximately 80 F. Wind speed is low (<4 miles per hour), and the wind is blowing from the chemical sources toward areas of high population density. The atmosphere is relatively stable.

Other Special Circumstances. Facility A is undergoing major maintenance and construction, so a large number of temporary contract staff is on-site, working around the clock.

They are initiating Event (Stage One). Terrorists attack Facility A, triggering one or more explosions involving large storage containers of inorganic chemicals, petrochemicals, or fuels and specialty chemicals. (Examples might be potentially explosive fertilizers, light hydrocarbons capable of generating a large vapor cloud explosion, or high-energy reactive chemicals.) Multiple initiating pathways could be proposed that would generate significant pressure waves and projectile materials from the exploded storage vessels. The pressure waves and projectiles could further impact not only Facility A but also facilities beyond its boundaries. Perpetrators provide plausible evidence to the media to demonstrate that the incident is due to terrorism.

Immediate Consequences (Stage One). The initial explosion results in 250 fatalities on-site, most of whom are contract employees; 100 people are killed off-site. One thousand people are injured on-site, and 2,000 are injured off-site. The number of fatalities and injuries on-site severely compromises the ability of the facility to implement any emergency response activities. Most windows in the nearby vicinity are broken, destroying the capability for many to shelter-in-place.

They are cascading Events (Stage Two). In the proposed scenario, the potential exists for additional consequences resulting from the initial attack. These consequences can be described as "cascading event" consequencesfor example, the initial explosion caused by the attack damages other equipment and causes further explosions or toxic releases that may be significantly more severe than the initial event. These events may not be anticipated or planned by the attacker, and in fact, the attacker may not even be aware of the potential for cascading events. The consequences described here would also obtain if the disruption of the second facility was the result of a direct attack.

Pressure waves and projectiles from the explosion at Facility A strike large storage containers or rail cars at a separate plant (Facility B). The result is a loss of containment from the storage containers at Facility B, releasing highly toxic industrial chemicals (e.g., hydrofluoric acid, chlorine, ammonia, phosgene, hydrogen sulfide, sulfur dioxide, sulfur trioxide, hydrogen cyanide, selenium hydride). These chemicals will readily evaporate to form highly concentrated vapor clouds at the temperature postulated for the incident. The resultant vapor clouds will not dissipate or mix rapidly with the surrounding atmosphere because of the low wind speed and stable atmosphere that prevails at the time of the incident. The toxic gas cloud remains relatively concentrated and close to the ground, giving maximum potential exposure to the surrounding population. Toxic chemical exposures of residents in the community are increased because of broken windows and other structural damage to nearby property caused by the initial explosion, because of the timing of the event (people are at home), and because of limited evacuation routes.

Another potential cascading event is a release of toxic liquid from a storage tank into the river. Materials with a boiling point near normal atmospheric temperaturefor example, monomethyl amine (boiling point 6 C)could form a toxic vapor cloud, yet remain partially liquid and flow into the river. The pressure wave and projectiles from the initiating explosion could impact storage vessels at a third facility, Facility C, releasing high volumes of liquid chemicals (e.g., petroleum fuels; chemicals that are persistent and bioaccumulative9

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) that flow into the river, the source of public drinking water and industrial water for River City and many downstream communities.

Immediate Consequences (Stage Two). On-site, 15 people are killed at Facility B; 1,000 are killed off-site; 20,000 people are exposed off-site, incurring injuries with a wide range of severity; business interruption occurs throughout River City. The consequence of Facility C's release grows subsequently in River City and the downstream communities as liquid chemical contamination of water supplies occurs.

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Bioaccumulative: substances that concentrate in living organisms as they breathe contaminated air, drink or live in contaminated water, or eat contaminated food rather than being eliminated through natural processes.

What are the three possible approaches to mitigating the consequences identified in this scenario?