As discussion heats up about a proposed 22.7-million-gallon propane tank in Searsport, a number of questions have been raised by residents ranging from the safety of the terminal to the potential effects of a large gas storage tank on tourism, whether the new taxes and jobs will be worth it and what the effect will be on local roads.

In an effort to distill some of the major ideas, VillageSoup looked at two of the more talked about concerns — safety and visual impact.

Worst-case scenario

Online videos of propane explosions are easy to find — everything from people shooting backyard barbecue tanks with high-caliber rifles to footage of major industrial accidents. The Discovery Channel’s “MythBusters” show tested the veracity of a scene from a James Bond movie where Bond evades pursuers by shooting a propane tank causing it to explode. In real life, the professional debunkers found, it didn’t work.

When propane does explode, the effect is dramatic enough to make it the go-to fuel for movie producers and other purveyors of theatrical shock and awe. So while the bullet in the James Bond movie might not have blown up the tank in real life, the explosion in the film was most likely made with real propane.

Closer to home, there’s the controlled burn of a kitchen range or backyard grill.

But if lighting a range — essentially a leaking tank — or shooting a propane tank with a bullet doesn’t cause it to explode, what does?

Hang around the propane safety water cooler long enough and the acronym BLEVE (short for boiling liquid expanding vapor explosion, and pronounced like “Chevy”) invariably comes up. A BLEVE happens when liquid propane or natural gas is subjected to extreme heat, often as the result of another tank or pipeline that has ruptured and caught fire. The fuel in the undamaged tank expands as the temperature increases and releases pressure through a safety vent.

The trouble comes when a wall of the tank that has emptied and is no longer being cooled from inside is exposed to intense heat, which leads to a rupture, releasing a large amount of propane quickly and causing an explosion.

BLEVEs are the basis for the some of the more apocalyptic visions of tank opponents, including the one-mile-fireball theory and the idea of an “incineration zone.” Historically, the largest LPG disasters have involved much smaller quantities of fuel than has been proposed for Searsport, so there is no direct precedent for a worst-case scenario involving a BLEVE at a facility the size of the proposed DCP Midstream LPG tank.

One of the largest historical LPG accidents in terms of fatalities involved a series of BLEVEs that destroyed the PEMEX LPG terminal in San Juan Ixhuatepec, Mexico in 1984. The accident killed between 400 and 500 people and injured between 2,000 and 7,200 by one account.

The PEMEX terminal had a collective capacity of roughly 3 million gallons of a propane and butane mixture, spread among 54 tanks. Reports from the time indicated that a substantial amount of the heavier-than-air mixture leaked before it caught fire. The first BLEVEs happened within five minutes. A large area of the town was destroyed by the explosions and fires that followed.

An exhaustive study by the Paul Scherrer Institute, a Swiss research center, of energy-related accidents between 1969 and 1996 ranked the PEMEX terminal explosion the tenth worst in terms of fatalities — burst dams and nuclear power plant accidents easily topped the fatalities list — and worst in terms of injuries.

The same report found that immediate fatality rates were typically higher in LPG accidents than in accidents involving other energy sources.

Other LPG accidents have caused major spectacles, property damage or disruptions but few fatalities.

A 1979 train derailment in Mississauga, Ontario, outside Toronto, involving a propane explosion prompted the evacuation of 200,000 people. It was reportedly the largest peacetime evacuation prior to Hurricane Katrina in 2005. The evacuation, however, was primarily due to a chlorine gas leak secondary to the propane explosion.

In 2008, the Toronto area was hit with another sensational propane accident when tanks at the Sunrise Propane terminal, having a total capacity of 4,000 gallons, exploded. Newspapers reported that the cause was an “illegal tank-to-tank transfer.” Residents mistook the blast for everything from a plane crash to a nuclear bomb. Two people died; one of them a firefighter who suffered a heart attack.

At 22.7 million gallons, the proposed DCP Midstream terminal in Searsport would be among the larger propane storage facilities in the country. The company also operates a 20-million-gallon facility in Virginia.

Sea-3, a subsidiary of Transammonia (and according to the company’s website, the largest importer and distributor of propane in the Northeastern United States) has a slightly larger tank — 26 million gallons — in Tampa, Fla. Searsport tank opponents have pointed out that the Sea-3 tank, which is located on a peninsula in a heavily industrial area, is further removed from the residential population than the Searsport tank would be.

While LPG is not as widely used in the United States as in other parts of the world, there is some historical precedent for large-capacity tanks here. A pair of 12-million-gallon propane storage tanks in Elk Grove, a suburb of Sacramento, Calif., were built 40 years ago, and have provided a propane distribution point for the San Joaquin Valley almost without incident. In 2000, FBI agents arrested two local militiamen who were allegedly planning to blow up the tanks in an effort to catalyze hate groups around Y2K hysteria with a goal of overthrowing the U.S. government.

The plot was foiled. But over the years residential areas of Elk Grove have inched closer to the once-industrial zone, fueling renewed concerns about the safety of the tanks.

Though large-scale propane accidents have the potential to be catastrophic, statistically, they barely register as hazards.

According to a 1981 study by the U.S. Department of Energy (“LPG Land Transportation and Storage Safety”) cited in literature from the National Propane Gas Association, an person’s odds of being killed by an accident related to LPG are 1 in 37 million, about the same odds of a person on the ground being killed by an airplane crash.

Presumably these odds increase for people who live near an LPG terminal, though whether they would rise to the level of a fatal lightning strike (1 in 3.75 million), a fatal car crash (1 in 4,700) or something else is not addressed in the cited statistics.

Data collected in two major studies of energy-related accidents, the Paul Scherrer Institute study and an analysis by Benjamin Sovacool of energy-related accidents between 1907 and 2007, show some broad trends. Petroleum industry-related accidents in the Paul Scherrer Institute study, for example, increased with oil consumption, peaking in the mid-1980s, then declined over the next 10 years. But both studies suggest that individual accidents follow no predictable pattern.

As a final note, VillageSoup asked François Amar of the University of Maine’s Chemistry Department to illuminate a worst-case scenario. Namely, what would happen if the whole thing blew up?

Amar professed no specialized knowledge of propane accidents, but offered what he called a “Freshman chemistry-type calculation” to determine the amount of energy in 22.7 million gallons of propane. The figure he came up with: 2,300 terajoules.

“That’s a lot of energy,” he said.

Amar left it to VillageSoup to put the terajoules figure into perspective. To frame it in terms of a frequent benchmark of explosive power, 2,300 terajoules is the equivalent of 549,713 tons of TNT.

“Part of the fear that people have is what happens if all that energy were liberated in an instant, which of course can’t happen in a chemical reaction,” Amar said. “It can burn explosively but it wouldn’t be in an instant. The oxygen has to get there so it happens over time.”

Big tank or little tank

The proposed LPG tank would invariably interrupt some of the views of forested areas of Searsport and obscure sightlines to the water, which are staples of the Midcoast tourism economy and a factor in local property values. Compared to other local view blockers, the inert geometry of the proposed tank is unlikely to be seen as an elegant extension of its surroundings in the way of, say, the Penobscot Narrows Bridge. Nor will it be a visible beehive of human productivity — like, say, Front Street Shipyard in Belfast.

But leaving aside the subjective nature of what constitutes an eyesore, how visible would the tank be?

In a full-page ad in the Nov. 19-20 edition of the Bangor Daily News, DCP Midstream President William Waldheim said that the tank would be recessed in the ground but didn’t indicate by how much. An accompanying photo illustration, showing what the tank would look like from Penobscot Bay in comparison with the nearby Irving tanks at Mack Point, appeared to downplay the visual impact.

According to a spokesperson for Irving Oil, the nearby tanks are between 45 and 50 feet tall and have diameters ranging from 100 to 160 feet.

While performing an accurate measurement against a photograph is problematic, a rough estimate based on the Irving tanks pictured in the same photo suggests that the proposed DCP tank could rise to as much as double the height that it appeared in the ad and be twice as wide.

Asked about the visualization study, DCP Midstream Spokeswoman Roz Elliott disputed this interpretation, saying the depiction in the ad was done by an expert, based on a number of criteria, and was accurate at the time it was published. She added that the tank is currently expected to be recessed 17 feet below ground level at the lowest point, taking into account the slope of the land, and that as a result would likely appear lower than the visualization in the ad.

Local opponents have compared the height of the tank to tree heights and the height of the average building in Searsport — the latter is 34 feet, according to one account by Astrig Tanguay of the group “Thanks but no Tank” — as evidence that the DCP tank would be grossly out of scale with its surroundings.

An exaggerated version of this idea appeared in series of comic strips by Meredith Ares circulated at an anti-tank rally in Searsport on Nov. 19 showing a massive cylindrical tank looming over the bay. Another panel suggested the tank could be seen from space. Unlike the DCP rendering, which presumes to show the tank in its correct scale, the comics were exaggerated for satiric effect. The point of view, however, was clear. If it’s too big, it might as well be a mile high.

Unlike the cylinder in the cartoon, the DCP tank would be rounded at the top. The shape is structural, but the sloping shoulders would also make the tank appear slightly less imposing. According to figures from the Maine Department of Environmental Protection, the peak of the tank would be 138 feet above the ground, but the vertical walls would be approximately 102 feet high.

A viewshed analysis by MDEP, which used a U.S. Geological Survey digital elevation model, concluded that the proposed project “will not have an unreasonable adverse effect on the scenic character of the surrounding area.”

Local residents and business owners have presented a different view. An image shown at a recent presentation by “Thanks but no Tank” superimposed a tiny Angler’s Restaurant in front of the tank. The drawing, which was done to scale, was not intended to show the two structures as they would appear on site, but was apt given that the tank, according to restaurant owner Buddy Hall, would be located several hundred feet behind the restaurant.

Opponents have questioned the diligence of a Maine Department of Environmental Protection approval of the project with regard to visual impact.

Some of this criticism derives from a line in the report stating, “… the project would not be visible to a viewer who is standing among trees in a forested area.” The seemingly self-evident truism has been used as a laugh line among opponents who have taken it out of context. Because trees typically block views in forested areas, the statement recognizes that views from these areas would not be impacted. This assumption informed one of several parameters used for calculating the sightlines.

The report cites the fact that Mack Point is already an industrial area to support its conclusion that the proposed DCP terminal would have “a minor visual impact on the landscape.” While Mack Point is clearly an industrial area, the surrounding area is not, and the proposed DCP tank would be substantially larger and more visible than any existing structure there.

Original documents related to the DCP Midstream proposal, including documents on safety and viewshed issues, are available for viewing at the Searsport town office. According to Town Manager James Gillway, dozens of residents have gone through the binders of supporting materials.