A health advisory was issued Tuesday because of flaring at the Shell refinery in Martinez, but it was canceled an hour later.

Randy Sawyer of Contra Costa Health Services said a vessel at the refinery became “overpressurized,” which activated a safety mechanism that releases pressure through flaring, which creates black smoke that contains sulfur dioxide and other combustible products.

The health advisory was issued at 1:31 p.m. and lifted about 2:45 p.m.

Contra Costa Health Services downgraded the incident from Level 2 to Level 0. Last week’s fire at the Chevron refinery in Richmond was a Level 3 incident — the highest level in the classification system. Tuesday’s incident followed a fire and brief health advisory Monday at the Shell plant.