Last week I came across a situation that had a significant impact on the site’s WCS and I would bet it is more common than most sites have considered.
When determining your worst case release scenario for an RMP, most facilities can just use their largest vessel within the process; however, larger sites may have to consider their on-site staging areas for Rail Cars. Because of DHS Security Regulations, Railroads are more antsy to get rid of the rail car from their yards and into a more secure facility (e.g. onto your property). But facilities are having the railroad leave the cars just inside their fence line for safe keeping and the facility’s switch engine will come and get when the process is ready for it. Now here is the catch, these rail cars (e.g. a 90-ton Chlorine Car) may be the facilities worst case scenario AND in some even more rare situations, the facility (mostly the larger ones) may have to report TWO WCS’s for the facility. Yes, there are situations where a facility would have to report TWO (2) different worst case scenarios. Here are the things to consider:
1) EPA defines a worst-case release as: The release of the largest quantity of a regulated substance from a vessel or process line failure AND the release that results in the greatest distance to the endpoint for the regulated toxic or flammable substance. It is the second part of the definition that slips through any consideration by facilities. The 90-ton chlorine railcar may not be the largest container in the process, but because of its location (e.g. just inside the fence line) it may have to greatest distance to an endpoint. This is usually more of a concern on larger facilities, as the distance between the railcar and the process may need to be a mile or greater depending on the toxic chemical involved. Here is what EPA states in the Off-Site Consequence Analysis Manual regarding this situation…
For Program 2 or Program 3 processes, you must analyze and report on one worst-case analysis representing all toxic regulated substances present above the threshold quantity and one worst-case analysis representing all flammable regulated substances present above the threshold quantity. You may need to submit an additional worst-case analysis if a worst-case release from elsewhere at the source would potentially affect public receptors different from those affected by the initial worst-case scenario(s).
2) EPA has made it clear that tank trucks and rail cars that are not attached to their mode of power (tractor or locomotive) are to be considered in the process threshold determination. This is from EPA’s RMP Q&A’s:
The definition of stationary source does not apply to transportation, including storage incident to transportation (40 CFR Section 68.3). Are chemicals in a tank car (e.g., tanker truck or rail car) therefore exempt from threshold determination? The chemicals in the tank car are exempt only if the tank car is in transportation. EPA considers a container to be in transportation as long as it is attached to the motive power (e.g., truck or locomotive) that delivered it to the site (63 FR 643, January 6, 1998). If the tank car is detached from the motive power, and therefore no longer in transportation, the contents of the tank car must be considered in the threshold determination. (CAA Q&A Database, September 1998)
3) As stated eariler, EPA defines a WCS as the scenario that results in the greatest distance to an endpoint beyond the stationary source boundary (40 CFR §68.25(h)). EPA recognizes that there could be release scenarios in which a smaller process could generate a greater distance to an endpoint than a release from the largest vessel or pipeline (61 FR 31682; June 20, 1996). The regulatory language at 40 CFR §68.25(h) clarifies that a scenario involving a smaller quantity of regulated substance handled at a higher process temperature or pressure, as well as a scenario involving a smaller quantity located closer to the stationary source boundary may, in fact, result in the worst-case release.
So if your facility is staging transportation containers without their mode of power close to the property’s boundary, this staging area may in fact be your worst case scenario (WCS). It should at least be analyzed to eliminate it from such, but don’t be surprised if you find it’s end-point reaches further out than the actual process.
But when would a facility have to report TWO (2) WCS’s? Here is what the standard states and then I will try an explain how this can happen.
40 CFR 68.25(a)(2)(iii) Additional worst-case release scenarios for a hazard class if a worstcase release from another covered process at the stationary source potentially affects public receptors different from those potentially affected by the worstcase release scenario developed under paragraphs (a)(2)(i) or (a)(2)(ii) of this section.
Let’s say that our rail car staging area is on the very southern tip of the facility and within 50 yards of the property line. The actual physical process is on the very northern tip of the facility. The process actual runs off the 90-ton CL2 rail car. So we now have two 90-ton rail cars on two different ends of the facility, which is setting us up for having two DIFFERENT WCS’s. As stated above, we have to report BOTH WCS’s in our RMP as we will have DIFFERENT public receptors in our set up. The WCS for both rail cars will be the EXACT same distance, but these distances will cover different ground and thus impact different public receptors.
I hope this helps explain how a facility could have a WCS other than their largest vessel within the physical process and how a facility may have to report “additional” WCS.
If you have any questions about your RMP, feel free to contact me, or post them below in the discussion forum.
Bryan