A guest post by “Harrison Gilmour”*

On Wednesday, November 28, 2018 Delaware County Council released a risk assessment produced for it by G2 Integrated Solutions of the proposed Sunoco Mariner East 2 (ME2) pipeline. (See “G2 ME2-Adelphia Risk Assessment v2.1“) This pipeline, if constructed, would transport industrial quantities of hazardous, highly volatile liquids through densely populated Chester and Delaware Counties. This report confirms the risk to life and property is enormous. The report is particularly important because it is the first publicly-available report of its kind that has been commissioned by a public agency. Let’s take a closer look at some of the details.

1. Maximum flash fire zone: much larger than we knew. “Risk” is comprised of the two elements of “consequences” and “probability,” each of which can be evaluated and quantified separately. G2 calculated accident consequences for the proposed ME2 pipeline using a program called Phast, developed by DNV-GL. (DNV-GL provides services to Sunoco or its parent ETP). Using Phast, G2 developed a model that shows a maximum flash fire vulnerability zone that covers an area that is at least 8 times greater than that calculated by Quest Consultants in the Citizens Risk Assessment.

For example, this chart from page 56 of the Delaware County risk assessment shows that a delayed ignition flammable vapor cloud could extend downwind 2,075 meters, or about 6,800 feet (1.3 miles). (The box in the top right tells you G2 assumed “F” atmospheric stability, meaning a stable atmosphere, and winds of 1.5 meters per second, or about 3 mph.) Quest’s comparable calculation was 2,115 feet. Anyone outdoors in the flammable vapor cloud would be burned to death upon ignition.

G2 20-inch full bore rupture flash fire 12-1-18
This diagram from the Delaware County risk assessment titled “Late Flammable Cloud Footprint” illustrates the thermal impact resulting from a rupture of a 20-inch highly volatile liquids pipeline with ignition delayed for several minutes. The two loops show the area where the gas concentration would be in the flammable range. The inner one shows the area affected under turbulent atmospheric conditions, and the outer one shows the area affected under stable, low-wind conditions, such as often occur at night. The outer area extends 2,075 meters from the leak (about 6,800 feet, more than a mile and a quarter). According to the risk assessment, people outdoors and within this area will be fatally burned.

2. “Overpressure” fatalities and injuries: a still larger area. In the chart below (from page 58 of the report), G2 models a “late vapor cloud explosion.” That is, the Delaware County report is predicting the size of what Sunoco itself calls the “blast radius.” In this chart, G2 assumes a rupture has occurred at the zero meter mark, and a combustible vapor cloud has formed and moved downwind before finding an ignition source. (Tim Boyce, Director of Delaware County Emergency Services, recently stated that in a densely populated area, there is virtually a 100% certainty that a combustible vapor cloud will ignite).

G2 models the overpressure (the “shock wave”) that it believes will result from this explosive event. Within the red circle, drawn at 1,600 meters or about one mile, this overpressure will be greater than .3 bar. This will kill 100% of the people exposed to it, regardless of whether they are indoors or outside (see Tables 6 and 7 in the report). But that’s not all: the Delaware County report predicts that overpressure of .1 bar or higher will be experienced out to the edge of the green circle, drawn at about 2,400 meters, or 7,875 feet or an astonishing one and a half miles. Overpressures between .1 and .3 bar are sufficient to be fatal to some people exposed to them. In other words, this chart models a risk of fatality that is 100% to a distance of one mile from the center of a late vapor cloud explosion, or about 3 square miles. Some fatalities will occur out to 1.5 miles just as a result of the overpressure.

G2 20-inch full bore rupture overpressure 12-1-18
This diagram shows the extent of the overpressure (“shock wave”) from the explosion of the vapor cloud due to a rupture, delayed ignition, and explosion of a 20-inch NGL pipeline. The red, inner circle shows the area where the overpressure would be 0.3 bar—enough to kill anyone exposed to it. The outer circle shows the area where the overpressure would be 0.1 bar, causing many injuries and some deaths.

3. The probability of an accident is seriously understated in this report, and here’s why. What about the “probability” side of the risk equation? Here, G2 disregarded the fact that Sunoco proposes to operate multiple hazardous, highly volatile liquids transmission pipelines in the same right-of-way. This omission is important because, everything else being equal, two pipelines doubles the probability of a release over a single pipeline. And doubling probability also doubles risk. Three pipelines triples the risk, and so on. (This point was addressed by Quest in the Citizens Risk Assessment).

In the event of a known or suspected leak or rupture, Sunoco’s boilerplate, one-size-fits-all public awareness program directs people who are inside to go outside and walk upwind and away from the pipeline. We will review G2’s “outdoor risk” probability calculation, since that’s where Sunoco recommends you should go.

In the “risk transect” graph below, (Figure 12 in the report) G2 has graphed “Mariner East 2 Outdoor Individual Risk versus Common Risk Sources.” This graph shows how the risk is greatest right at the pipeline and tapers off as the distance from it increases.

G2 mariner risk vs common risks 12-1-18
This diagram shows the annual risk of being at various distances from an NGL pipeline. The level of risk (purple line) tapers off as the distance from the pipeline increases. What the diagram does not show is the risk if you are near more than one pipeline. The central peak would be twice as tall with two pipelines, and three times as tall with three pipelines.

However, this is for one pipeline only. Adding a second pipeline doubles the risk at zero meters (using the scientific notation of this report, it would go from 6.0E-6 to 1.2E-5). This value would be off the top of their chart, and greater than all the other risks they present (with the exception of being in a motor vehicle accident, something which is so common that most people know someone who has been fatally injured in one).

And this risk calculation only considers individual risk of fatality. It disregards the fact that most locations in Chester and Delaware Counties (for example, the Chester County Library and Glenwood Elementary School) may contain dozens or hundreds of people within what Sunoco calls the “blast radius.”

Conclusion: With a modeled blast radius of almost 1.5 miles, the results of the Delaware County risk assessment are shocking. No matter which risk assessment you consult (the new Delaware County one or the Citizens’ Risk Assessment from Quest), it is now abundantly clear that the rupture of a hazardous, highly volatile liquids transmission pipeline in Chester or Delaware County is going to be a mass casualty event.  And the odds of this happening are disturbingly high. Del-Chesco United for Pipeline Safety calls on the Chester County Commissioners and Delaware County Council to take action now based on the alarming public safety implications of this report.

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* Harrison Gilmour is a pseudonym. I prefer to use actual names when publishing a guest post, but I will honor requests for anonymity if circumstances warrant it.