is intermittently charged with ore, fuel and flux and intermittently tapped for molten pig iron and slag; however, the chemical reaction of reducing the iron and silicon and later oxidizing the silicon is continuous. Semi-continuous processes, such as machine manufacturing of cigarettes, were called "continuous" when they appeared. Many truly continuous processes of today were originally batch operations. The Cromford mill of 1771, designed by Richard Arkwright, was the first factory to use a continuous process from raw material to finished product in a series of operations. The Fourdrinier paper machine, patented in 1799, was one of the earliest of the Industrial Revolution era continuous manufacturing processes. It produced a continuous web of paper that was formed, pressed, dried and reeled up in a roll. Previously paper had been made in individual sheets. The paper machine influenced other continuous processes such as the continuous rolling of iron and later steel. Another early continuous processes was Oliver Evans'es flour mill (ca. 1785), which was fully automated. Early chemical production and oil refining was done in batches until process control was sufficiently developed to allow remote control and automation for continuous processing. Processes began to operate continuously during the 19th century. By the early 20th century continuous processes were common. Shut-downs In addition to performing maintenance, shut downs are also when process modifications are performed. These include installing new equipment in the main process flow or tying-in or making provisions to tie-in sub-processes or equipment that can be installed while the process is operating. Shut-downs of complicated processes may take weeks or months of planning. Typically a series of meetings takes place for co-ordination and planning. These typically involve the various departments such as maintenance, power, engineering, safety and operating units. All work is done according to a carefully sequenced schedule that incorporates the various trades involved, such as pipe-fitters, millwrights, electricians, mechanics, laborers, etc., and the necessary equipment (cranes, mobile equipment, air compressors, welding machines, scaffolding, etc.) and all supplies (spare parts, steel, pipe, wiring, nuts and bolts) and provisions for power in case power will also be off as part of the outage. Often one or more outside contractors perform some of the work, especially if new equipment is installed. Safety Safety meetings are typically held before and during shutdowns. Other safety measures include providing adequate ventilation to hot areas or areas where oxygen may become depleted or toxic gases