For safety reasons, blowout preventers should be inspected, tested, and refurbished regularly. (Petroleum Oil Tools, Inc.)

Blowout preventers (BOPs) are used to control blowout. The crew usually install several blowout preventers (BOP stack) on top of the well, with an annular blowout preventer at the top and at least one pipe ram and one blind ram blowout preventer below. Also, some well control techniques require both the annular and the ram blowout preventers. (Sunnda Corporation)

Rotating blowout preventers seal tightly around kellys, drill pipe, drill collars, tubing or casing and are used for drilling in areas susceptible to kicks or blowouts, for drilling under pressure, for drilling with reverse circulation and when circulating with natural gas or air. (PatentStorm LLC.)