# Your process control system is overly complicated Consider yourselves lucky we live in the modern era of the DCS/SIS systems. An anecdote from I-do-not-know-where: > A rather simplistic example of an engineered recovery system comes from the annals of the chemical company ICI Ltd. Many years ago, the company operated a rather dangerous batch reactor under manual temperature control. The reaction taking place was unstable and proceeded explosively if the temperature was allowed to rise too high. If the temperature fell too low, the reaction would not proceed at all. Since this was before the era of automatic temperature control systems, the operator was required to observe the temperature and control it within set limits by manually adjusting the flow of cooling water to a coil inside the reactor. If the temperature rose too high then he would increase the flow of cooling water and vice versa. The problem with this task was that although the task itself was undemanding, a high level of vigilance of the operator was required. However, the task was so undemanding it was found that the operator's attention was liable to wander leading to a high frequency of temperature excursions. In spite of the severe consequence of the operator failing to perform his task, it was so boring that even the most diligent of operators would tend to fall asleep. In a modern chemical plant, such a dangerous reactor would be subject to automatic temperature control with independent systems to monitor the temperature and shut the system down if the temperature approached the upper limit. > > However, at the time this plant was operated, such systems were not employed and an alternative but extremely effective method was provided to protect against high temperature in the reactor due to the loss of vigilance by the operator. The operator was provided with a one-legged stool. If the operator fell asleep he would fall off the stool an extremely effective way of restoring his attention to the task in hand. This is an early example of an engineered recovery system.