Billings Gazette

By CLAIR JOHNSON
Of The Gazette StaffAn ExxonMobil investigative team looking into an explosion and fire at the Lockwood oil refinery Oct. 17 has finished its field work, but a cause has not yet been determined…. ([1] Full Story)

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The fire burned for a few hours and caused 685 pounds of sulfur dioxide [SO₂] to be emitted during the incident.  Montana Sulphur & Chemical Co., which treats ExxonMobil’s sulfur-bearing gases, also reported flaring sulfur dioxide in a major malfunction after the refinery fire.

Montana Sulphur & Chemical Co. said it flared 5,673 pounds of sulfur dioxide over almost three hours in the late afternoon on Oct. 18.

On account of the explosion-and-fire-related SO₂ release, air monitoring equipment measured elevated SO₂ readings of 120 ppb, short of the safe threshold for Montana of 500 ppb.  Safe limits depend on duration of exposure.  No time interval for the measurement was identified in the article.

Alberta’s one-hour guideline for sulphur dioxide emission reporting is 170 parts per billion (ppb).  The 8-hour occupational exposure limit is 2,000 ppb or 2 ppm.   ([2] Link, Source: Canadian Safety Council, Data Sheet, Occupational Safety and Health and Province of Alberta Occupational Health and Safety Act, Chemical Hazards Regulations)