Burping Tankers Spread Sulfurous Fumes

The smelly cloud of sulfurous fumes that wafted over Bellingham Saturday evening, June 3, was apparently not that unusual an occurrence. It happened due to an overpressure on the Italian oil tanker Mare Siculum, which was then anchored east of Vendovi Island, awaiting unloading at the BP Refinery at Cherry Point, northwest of the city.

Standard procedure under these conditions is to vent the built-up gases and relieve excess pressure on the tanker holds, according to US Coast Guard Lieutenant Krysta Zangle of its Foreign Vessel Branch in Seattle. “The smell of the fumes is indicative of cargo vapors being released as a result of pressure build-up within the cargo tanks,” she explained in a email. “This is a normal occurrence that ensures the safety of the tanker and our waterways.”

An inert gas containing mostly carbon dioxide is injected into the holds to reduce the amount of oxygen present there, which can otherwise lead to explosive conditions, she continued. That gas mixes with vapors released from the crude oil, typically due to overheating of the tanker deck by the sun. Pressure-relief valves automatically open to allow excess gas to escape and dissipate, in what can be called a “tanker burp.” More inert gas is then injected into the holds to keep oxygen levels below 8 percent.

“A team of Coast Guard inspectors reached the vessel on [the following] Wednesday,” added Zangle. “They found no safety concerns; in fact, all systems were operating as designed.”

In this incident, the Mare Siculum was carrying Arab extra-light crude oil with about 1 percent sulfur content, according to engineer Toby Mahar of the Northwest Clean Air Agency (NWCAA) in Mount Vernon. Thus the acrid stench that reached Bellingham that evening, was probably due to sulfur dioxide (SO₂) and mercaptan (CH₄S) gases. In the prevailing southerly winds, the plume first reached Edgemoor, situated seven to eight miles north of the tanker, followed by Fairhaven and then downtown Bellingham. Despite many 911 calls, fire department officials could not trace the source of the odor—which, it turns out, was well beyond their jurisdiction!

A similar release of sulfurous vapors occurred late Friday afternoon, June 2, leading to about two dozen complaints from the vicinity of Bow, Edison and Samish Island. Indeed, the winds had shifted from southerly to westerly just before 4 pm, which would explain why a plume from the tanker headed that way. Otherwise, it would likely have reached Bellingham, too. And a third tanker burp came on Monday, June 5, according to Mahar, but in that case nobody reported any odors or other ill effects.

The Mare Siculum reached the BP refinery late on Wednesday, June 7, ahead of schedule and began off-loading its crude oil at the BP south pier, finishing by Friday morning. Through a birding spotter scope from my home on Orcas Island, I could observe excess gases being burned off at a “vapor combustor” on the north pier. This appears to be standard operating procedure, according to an NWCAA permit I viewed. This agency has jurisdiction over toxic releases at the refinery and its piers, but not from the tankers sailing to and from it—or anchored elsewhere.

In fact, an anchored tanker like the Mare Siculum would be significantly more likely to release pent-up gases than one cruising in open waters, for it would not benefit from the cooling effect of waters flowing past its hull—unless tidal currents can provide that cooling instead. As the sun travels high overhead in summer and Salish Sea waters warm, the likelihood of burping tankers increases substantially.

Indeed, what were previously mysterious releases of sulfurous gases may well have been due to these burps, which often happen in summer. At least two such events occurred in the summer of 2013, for example, according to a Bellingham Herald article, “Strange odor coming from waterfront in Bellingham.” In one of them on September18, the odors were first reported south of Fairhaven and then flowed north, just as in the recent event. Southerly winds were blowing that evening, too. Was that event due to another burp from a tanker anchored off Vendovi?

One explanation offered in 2013 was that the odors were due to hydrogen sulfide released by decaying organic matter being exposed at low tide. That could probably account for an August 2013 event but not the one on September 18.

The NWCAA has little jurisdiction over such releases from mobile and maritime sources, which unfortunately appear to be the inevitable consequence of tankers bringing sulfurous crude oil to Puget Sound refineries. The agency can only monitor their impacts on local populations and appeal to the Coast Guard to take preventive and corrective measures. NWCAA has a number of sulfur-dioxide measuring stations in Island, Skagit and Whatcom Counties (but curiously none in Bellingham) that would be able to detect dangerous levels of this noxious gas.

In other words, we just have to live with occasional clouds of sulfurous vapors descending upon our habitats. It’s a price we pay for having oil refineries in our area.

But we all carry one of the most sensitive detectors of sulfur dioxide—and of mercaptan, the smelly gas added to odorless natural gas to warn about leaks—just above our mouths and between our eyes. So if you ever feel yourself gagging from any sulfurous vapors, just call NWCAA at 360-428-1617 or use its web site to report it. They have good, responsible professionals there who take their job seriously.