Blowout preventer blocks, each having a channel and plate(s) to close it. The blocks are placed over a pipe through which oil or other fluid is escaping, so that the pipe is in their channels. Alongside the channel in each block are one or more plates, having diameters somewhat larger than the diameter of the channel. Explosive charges propel the plates into the channel to seal it off and stop the leak. When multiple blocks and/or multiple plates in a block are placed over a pipe, the assembly may be referred to as a “Christmas tree.” There are passages that allow the plates to move into place to block the channel. Leading edges of the plates act as male elements that engage female reciprocal ends of the passages to create a seal. Grooves and tunnels in the plates allow fluid to escape into the pipe to ensure a seal.