Wednesday, January 13, 2010

Gasoline Security Comments

Yesterday I posted a blog entry about the latest DHS National Protection and Programs Directorate request for public comments on the CFATS program. That posting was pretty much a straight news-type report on the posting in today’s Federal Register. Now it’s time to take a more opinionated look at the issues involved. Long time readers of this blog can guess where this is going as I have written on the topic a number of times, most recently in November of 2009.

Flammable Release COI 

The first thing that we have to remember is why DHS included the category of flammable release chemicals of interest (COI) in the list of chemicals that triggered the Top Screen reporting process when a screening threshold quantity of the chemical was present at a chemical facility. It wasn’t because of the threat of fire at the facilities in the event of a terrorist attack; large chemical fires have only a limited, short-term off-site affect making them of limited utility as a terrorist target. No the release-flammable COI were placed on the list of DHS Chemicals of Concern (Appendix A, 6 CFR 27) because of their potential to form large vapor clouds when released from storage tanks that could be detonated to form a vapor cloud explosion (VCE).

The blast (over pressure) affects of a VCE have the potential to be catastrophically effective over a wide area which makes a VCE a wonderful terrorist weapon. Now gasoline is not one of the 300+ chemicals listed in Appendix A. The reason is that DHS chose to only include ‘individually named’ chemicals in their list. This helped keep the list of chemicals to a manageable number. To account for the large number of chemicals in commerce that are mixtures of two or more chemicals, DHS amended the language of 6 CFR 27 to include a variety of mixture rules for the various types of chemicals of interest.

The basic release-flammable mixture rule {6 CFR 27.204(a)(2)} calls for chemicals containing at least 1% of a release-flammable COI and are rated as an NFPA (National Fire Protection Association) rating of 4 (their most dangerous flammability rating) to have their entire quantity counted as the amount of the COI on hand at the facility. Refined petroleum fuels such as gasoline, kerosene and diesel are very complex mixtures of a large number of chemical compounds. These fuels may contain a number of the listed release-flammable COI found in Appendix A; most typically pentane and butane. Gasoline has a typical NFPA rating of 3 which would normally exclude it from the §204 flammable mixture rule.

There is, however, a specific exception for these petroleum based fuels found at §203(b)(1)(v), allowing for coverage of fuels with an NFPA rating as low as 1 when they are stored in above ground tanks. The reason for this is two fold; first the NFPA rating is not a perfect predictor of VCE potential, and second is the fact that internal combustion engine fuels are, by design, optimized for their vapor explosion potential inside of those engines.

There is a third reason that petroleum based fuels should be considered a special case for the purposes of the flammable mixture rule; there is a special political dimension associated with these fuels that makes them more likely targets. First, a large portion of the oil used to make these fuels world wide comes from Muslim countries in the Middle East and this makes the fuel production and distribution systems in ‘infidel’ countries prime jihadist targets. Second, there have been ample public examples where disruptions of the fuel supply system in the United States in particular have led to widespread economic disruptions due to the rapid increase in gasoline prices, producing a potential target with an added snowball effect. Finally there is a technocrat class with a petroleum engineering background that is well represented in jihadist forces.

VCE Modeling

The flammable mixtures rule and its fuel addendum do not mean that all gasoline terminals (the generic term that DHS is applying to all facilities with above ground fuel storage tanks) will become covered facilities. It simply means that those facilities with more than 10,000 lbs of on-site fuel storage would have to complete a Top Screen submission. DHS would then evaluate that Top Screen information to make a determination if the submitting facility was at high-risk for a terrorist attack. According to the discussion in the request for comments, DHS reports that only 405 of the approximately 4,000 gasoline terminals that submitted Top Screens were preliminarily tiered as high-risk facilities.

To evaluate the potential risk level for a facility based on their Top Screen DHS will use a variety of tools that estimates the potential worst case consequences of an attack. The chemical industry has heard the EPA use the term ‘worst case scenario’ for years now. There is a difference however; EPA uses the term to describe an accidental release. For example they would consider a flow rate from a storage tank through a broken hose as the ‘worst case’ release from a storage tank. DHS, on the other hand bases their ‘worst case’ on a successful terrorist attack; probably using an IED to cause a catastrophic failure of the tank resulting in a near instantaneous release of the contents. Typically, the consequences of a DHS ‘worst case’ are more severe than an EPA ‘worst case’.

To evaluate the worst case consequence of a release-flammable COI release, DHS uses the Vapor Cloud Explosion model developed by EPA. This model takes into account a number of variables that would affect the formation of a vapor cloud to determine the distance from the point of release that there would be significant overpressure (blast) affects that would damage structures and injure/kill people. DHS then looks at the number of people and the number and types of other facilities within the potential danger area of a successful VCE.

One of the key elements of this model is determining the size of the potential vapor cloud. This is determined by a complex calculation that takes into account the physical properties of the COI (vapor pressure, flammability limits, etc), the amount of the COI and the surface area over which it might spread. According to the DHS filing in yesterday’s Federal Register, the EPA model assumes that 10% of the available (ie: spilled) liquid will evaporate and form an ignitable vapor cloud. DHS has changed that to 1% for the gasoline VCE model, reflecting the different physical characteristics for gasoline.

DHS asks in their request for comments if this assumption is reasonable. Well, while I am a trained chemist I am not an expert on models or physical chemistry. But I do know that the Chemical Safety Board is collecting a ton of information on a recent gasoline VCE that occurred in Puerto Rico last year. The information from that investigation should be used to verify the reasonableness of the VCE model assumptions.

If about 1% of the spilled fuel was involved in the initial explosion, the model assumptions are reasonable. If it was closer to 10% or 0.1% then the model needs to be adjusted as appropriate. The thing to remember about models is that they are theoretical constructs. When the results of a model accurately predict actual occurrences the model is a valuable tool. If the model cannot be used to make reliable predictions of real world conditions then it is a poor tool and should be modified or discarded. Models should be validated against new data on an ongoing basis.

Gasoline and IEDs 

Currently DHS does not include flammable liquids and gasses as theft/diversion chemicals in general and certainly not gasoline or any other petroleum based fuels. The basic reason is that the use of flammable liquids to create a VCE of any political consequence (the goal of any terrorist attack) requires a large volume of the liquid and is even difficult to set up when one has the chemicals in place.

Having said that, the Army did some work in the 1970s on using gasoline as an improvised explosive for making anti-tank ditches in built-up areas. It was inspired by a news story describing an accidental discharge of gasoline into a sewer line that was then detonated by some ignition source; a two block length of sewer line exploded making a nearly uniform trench the length of the street. While the use of this type ‘explosive’ would be significantly more complicated than the ‘underwear bomb’ of recent history it would be an effective technique to use against urban or suburban targets.

Since there is only minimal security at many fuel terminals and there are usually fuel transporters located nearby, the acquisition and transportation of the needed fuel a relative easy part of the fuel-IED process. Thus, it seems reasonable that DHS should consider adding a theft/diversion listing for gasoline because of its wide spread availability and its demonstrated utility as a raw material for an effective large scale IED.

1 comment:

Anonymous said...

Good point. Flammable liquids or gases are usually not used as the primary charge/ explosive device in Improvised Explosive Devices (IED). However, they are used to intensify the destructive nature. For example, when Iraqi insurgents were utilizing the IED on an everyday basis, they would place propane tanks and/or jugs of gasoline around the IED. So let's say the insurgents had two 155 mm artillery rounds rigged as the IED, they would also place the propane tanks right next to it to create a more intense fireball, thus increasing the effects.

/* Use this with templates/template-twocol.html */