Utility systems, hazards nitrogen

On chemical plants and oil refineries, steam, nitrogen, compressed air. lubricating oil, and other utility systems are responsible for a disproportionately large number of accidents. Flammable oils are recognized as a hazard, but services are given less attention. If the modification to the lubricating system had been systematically studied before it was made, as recommended in Chapter 2, a larger vent could have been installed, or a pipe-break and funnel could have been installed at the inlet to the sump. 

Backup supplies are always useful when a utility is lost Spare equipment or multiple-train equipment may be used in order to keep the utility on line even if one part of the system shuts down. An alternative or supplement is to provide backup from a different utility system. The number of different air systems found in a plant provides an opportunity to do this. Moreover, nitrogen can be used to back up some of the air systems. All these tie-ins require careful review during hazard analyses. Usually, the backup supply is activated when the primary supply loses a certain amount of line pressure. If this is done by means of a single pressure regulator and the pressure is also low on the backup system, the flow may be opposite to that intended. It is essential to keep nitrogen out of an air supply to a confined, inhabited space (e.g., the instrument air supply to a control room), and it is essential to keep air out of nitrogen when it is used as an inert gas. 

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