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The interactions between the design and application of instrumentation and safety are many and diverse. The correct utilization of instrumentation for monitoring and control reduces risk. An obvious example is a fire detection and control system, but even a simple cistern control which prevents a water tank from overflowing affects overall safety. Any instrumentation which contributes to maintaining the designed status of an installation can arguably affect safety. However, instrumentation can increase the danger in an installation, usually by being incorrectly designed or used. The principal direct risks from electrical instrumentation are electrocution and the possibility of causing a fire or explosion by interaction between the electricity and flammable materials, which range from various insulating materials used on cables to the more sensitive oxygen-enriched hydrogen atmosphere of a badly ventilated battery charging room. Some aspects of the safety of lasers and the risks from radiation are dealt with elsewhere in this reference book, Part 3, Chapters 21, 22, and 24. Toxic materials should also be considered (see Substances Hazardous to Health in the References). These risks pale into insignificance when compared with the full range of possibilities of misapplying instrumentation to a process plant, but nevertheless, in an overall safety analysis all risks must be minimized. It is important to recognize that nowhere is absolute safety achievable, and that the aim is to achieve a socially acceptable level of safety. Quite what level has to be achieved is not well defined; it is perhaps sufficient to say that people are even more reluctant to be killed at work than elsewhere, and hence the level of safety must be higher than is generally accepted. For example, the risk level accepted by a young man riding a motorcycle for pleasure would not be acceptable to a process operator in a petrochemical plant. There are similar problems in determining how much financial expenditure is justified in achieving safety
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