Oil drill operations rely on the use of derricks for their production. An oil derrick is used to dig a hole for an oil well, then to push the drill pipe deep into the earth. A mud mixture is sprayed from the drill bit to push material from the cuttings up out of the hole and cool the drill equipment, as well as to keep the bore hole stable. Then a well pipe replaces the drill pipe, so oil can be pumped out, using valves to allow the oil to move up the bore hole without sliding back down. Many workers at oil and gas drilling sites share duties to keep wells operating efficiently and safely. Derrick operators and rotary drill operators keep the mud, made of water, clay, air, and chemicals, flowing, so drills run smoothly. These workers listen to drills to ensure the vibrations are normal and may collect samples of material from the hole to monitor output. Derrick and drill operators place derricks in the correct location and keep them running around the clock, monitoring gauges, repairing equipment, and checking for problems. Drill operators also train drill crews on procedures and safety measures. Wellhead pumpers operate pumps that force oil and gas out of wells and into storage tanks and pipelines. They also monitor other production equipment and ensure that materials are being pumped at the correct pressure, density and concentration. Service unit operators work in oil and gas drilling, as well as mining operations, to troubleshoot drilling issues and resolve them. They use equipment to increase oil flow from producing wells, or to remove stuck pipes, tools, or other obstructions from drilling wells and mining exploration operations. These workers are employed by the oil and gas industry at construction sites and drilling rigs. They may work on offshore oil platforms drilling the ocean floor, or in remote locations in the far north or Middle East, which may require living onsite for long periods. Work may be seasonal, and shifts are often around the clock. Extreme weather conditions and dealing with heights is also part of the job. Machinery is noisy, and safety rules are critical. Wellhead pumpers typically need a high school diploma, while derrick operators, rotary drill operators, and service unit operators typically have no specific education requirements.