Inherently safe equipment

The same principles could be apphed to hazardous equipment, in that inherently safe equipment would not involve high energy systems such as pressure, vacuum, or high speed rotation . 

Reactors are designed to be inherently safe based on physical principles, supplemented by redundant equipment and special procedures. Nuclear power benefits from the appHcation of the concept of defense in depth, ie, by using fuel form, reactor vessel, building containment, and emergency backup procedures to ensure safety. 

Processes can be divided into those that are intrinsically safe, and those for which the safety has to be engineered in. An intrinsically safe process is one in which safe operation is inherent in the nature of the process a process which causes no danger, or negligible danger, under all foreseeable circumstances (all possible deviations from the design operating conditions). The term inherently safe is often preferred to intrinsically safe, to avoid confusion with the narrower use of the term intrinsically safe as applied to electrical equipment (see Section 9.3.4). 

An inherently safe plant1112 relies on chemistry and physics to prevent accidents rather than on control systems, interlocks, redundancy, and special operating procedures to prevent accidents. Inherently safer plants are tolerant of errors and are often the most cost effective. A process that does not require complex safety interlocks and elaborate procedures is simpler, easier to operate, and more reliable. Smaller equipment, operated at less severe temperatures and pressures, has lower capital and operating costs. 

This section discusses how a runaway reaction occurs and lists some of the process deviations that can lead to such a runaway. Equipment for identifying potentially hazardous process steps is reviewed, and general principles for inherently safe process design are given. 

Inherently Safe - An essential character of a process, system or equipment that makes it without or very low in hazard or risk. 

Provisions for safe and rapid isolation of piping systems and equipment Use piping, gaskets, and valves that take advantage of modern technology Use strong vessels to withstand maximum pressure of process upsets Avoid inherently unsafe equipment Use pumps suitable for hazardous service... 

Because there is always risk when equipment, instrumentation, and human activity are involved, there is no method of making a plant completely safe. However, facilities can be made inherently safer by careful examination of all aspects of design and management, using modem techniques that are now available. If we are to improve our process safety performance and our public image, inherently safe process design coupled with inherently safe process management is imperative. 

Extrinsically safe A term applied when safety is built in by adding instrumentation, controls, alarms, interlocks, equipment redundancy, safety procedures, and the like during engineering, design, constmction, or operation of a component, system, or facility. Contrasted with inherently safe. 

The risks to do with working on energized systems can be reduced by designing equipment and piping to be more inherently safe. Some ways of doing this are discussed in the following sections. 

---