Failures: active 91 single-point

Communications plays a vital role in alerting and notifying both in facility personnel and outside emergency agencies that a major incident has occurred. Communication systems should not be arranged so a single point failure exists. Of primary concern is the provision of a backup source of power and a remote backup activation and signaling post. 

Almost all biochemical reactions are catalysed by enzymes, which are found both inside and outside body cells. Enzymes are a special kind of catalyst which are proteins and which are effective in extremely small concentrations. Their mode of action remains imperfectly understood, but they make possible many chemical reactions which would not otherwise occur at the dilutions and comparatively low temperatures at which life cells operate. Many different enzymes are produced by a single variety of plant or animal species moreover, the same enzymes are usually found in many different varieties of life forms. Enzymes are essential for the normal functioning and development of the human body, and failure to produce even one of them may result in a metabolic disorder. Enzymes are generally far more efficient than ordinary catalysts and can increase reaction rates by as much as 10 -10 times or even more. They are not used up in the reaction and do not influence any equilibrium point. Enzymes lower the activation energy of a reaction but cannot make a thermodynamically unfavourable process favourable. Enzyme-catalysed reactions can give yields of nearly 100% without any by-products. 

Spring-loaded safety or relief valves that are designed for and operate under single-phase fluid conditions are not considered for active failures to close when pressure is reduced below the valve set point. However, when valves designed for single-phase flow are challenged with two-phase flow, such as a steam generator or pressuriser safety valve, the failure to reseat is considered as an active failure. 

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