Under the rules of the Automobile Club de l'Ouest (ACO) only five mechanics are permitted to work on the car. One man is permitted to fuel the car; all fuelling must be completed before any other service occurs. The other four mechanics on pit lane at any given time are typically two tyre changers and two tyre carriers, each of whom handles his task on only one side of the car. Automatic pneumatic jacks are used, integrated into the car itself. At all times the car's engine must be shut off during the stop, and may start only when the stop has concluded. IMSA allows only four mechanics to service a car during a pit stop. One crew member will refuel the car while the other three are responsible for changing tyres and operating the pneumatic jacks. A fifth crew-member must serve as the team's designated firefighter and must stand ready in the pit stall with a fire extinguisher while the car is being refuelled. A sixth crew-member may assist in a driver change. Neither the firefighter or driver's assistant may perform any additional service to the car. Unlike the ACO, IMSA does not force crews to wait for fuelling to complete before changing tyres, and does not require the car's engine be shut off during the stop. In endurance racing, driver changes are mandatory; the shortest endurance races are scheduled for four hours, one hour longer than the longest nonstop time permitted behind the wheel. During a pit stop with a driver change, the new driver and a driver change assistant are permitted into the pit lane. The assistant, who may not do any mechanical work on the car, is tasked with helping the current driver out of the car, removing or swapping driver seat inserts, helping the new driver into the car, and helping the new driver tightly fasten his safety harness and connect his various helmet connections to the car's systems, including the two-way team radio and the drink bottle used to stave off dehydration. A routine pit stop with no scheduled maintenance and no driver change generally lasts from thirty to forty seconds. With a driver change included, that time increases by about ten seconds. Should there be significant scheduled maintenance, such as changing brake pads, the stop can easily last well over a minute. Unlike most other forms of racing, the practice of "double-stinting" or