at a flow rate that was still increasing. The oil and gas fumes exploded on contact with the operating pump motors, starting a fire which led to the collapse of the Sedco 135 drilling rig riser. The collapse caused damage to the BOP stack at the seafloor. The damage to the BOP led to the release of significant quantities of oil into the Gulf. Volume and extent of spill In the initial stages of the spill, an estimated of oil per day were flowing from the well. One barrel of oil is equivalent to 159 liters (or 42 gallons) of liquid. In July 1979, the pumping of mud into the well reduced the flow to per day, and early in August the pumping of nearly 100,000 steel, iron, and lead balls into the well reduced the flow to per day. Pemex claimed that half of the released oil burned when it reached the surface, a third of it evaporated, and the rest was contained or dispersed. Mexican authorities also drilled two relief wells into the main well to lower the pressure of the blowout, however, the oil continued to flow for three months following the completion of the first relief well. In total, around were spilled throughout the roughly 10 months it took for the oil to stop leaking. Pemex contracted Conair Aviation to spray the chemical dispersant Corexit 9527 on the oil. A total of 493 aerial missions were flown, treating of oil slick. Dispersants were not used in the U.S. area of the spill because of the dispersant's inability to treat weathered oil. Eventually the on-scene coordinator (OSC) requested that Mexico stop using dispersants north of 25°N. In Texas, an emphasis was placed on coastal countermeasures protecting the bays and lagoons formed by the barrier islands. Impacts of oil on the barrier island beaches were ranked as second in importance to protecting inlets to the bays and lagoons. This was done with the placement of skimmers and booms. Efforts were concentrated on the Brazos-Santiago Pass, Port Mansfield Channel, Aransas Pass, and Cedar Bayou which during the spill was sealed with sand. Economically and environmentally sensitive barrier island beaches were cleaned daily. Laborers used rakes and shovels to clean beaches rather than heavier equipment which removed too much sand. Ultimately, of oil impacted of U.S. beaches, and over of oiled material were removed. Containment In the next nine months,