Utility systems, hazards

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. 

The waste streams created by utility systems tend, on the whole, to be less environmentally harmful than process waste. Unfortunately, complacency would be misplaced. Even though utility waste tends to be less harmful than process waste, the quantities of utility waste tend to be larger than process waste. This sheer volume can then result in greater environmental impact than process waste. Gaseous combustion products contribute in various ways to the greenhouse effect, acid rain and can produce a direct health hazard because of the formation of smog. The aqueous waste generated by utility systems can also be a major problem if it is contaminated. 

A Class 2 fist might include equipment that typically does not contain highly-hazardous chemicals, but may under abnormal conditions contain such chemicals. It may also include utility systems such as cooling tower operations, compressed air or refrigeration systems whose failure could create significant upsets. 

A chemical wash introduces the potential hazard of chemical leakage into utility systems and/or into lines connected to the column. Special attention must be given to adequate blinding. In one instance (7), caustic used for washing backflowed into a steam line while steam was being vented to atmosphere, causing a wide area to be sprayed with caustic. 

Software System Hazard Analysis This type of analysis is conducted similar to a hardware system hazard analysis (SHA), analyzing software functional processing steps to determine whether they may have any particular hazardous effect on the system. The analysis utilizes a hazard-risk index to illustrate the severity of each potential failure. The main advantage to this method is in its ability to positively identify safety-critical hardware and software functions as well as consider the effect of the human element in system software operations. The results of the software SHA, which identifies single-point failures or errors within a system, can often be used to assist in the development of a software fault tree analysis or, to some degree, a system FMEA. However, as with the other various SWHA techniques briefly described above, this method is also time-consuming and costly to perform. 

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. 

When utility lines are connected to process lines or equipment, there is a danger of backflow of process material into the utility system and a danger of overpressurization of one system by the other. All connections of this kind require careful study during design and hazard analysis. Many plants review similar connections as a group and develop standard details. This standardization can include formal requirements for the number of layers of protection for each group. 

HAZOP analysis utilizes use key guidewords and system diagrams (design representations) to identify system hazards. Adjectives (guide words) such as more, no, and less, are combined with process/system conditions such a speed, flow, and pressure, in the hazard identification process. HAZOP analysis looks for hazards resulting from identified potential deviations in design operational intent. A HAZOP analysis is performed by a team of multidisciplinary experts in a brainstorming session under the leadership of a HAZOP team leader. 

Hazard Identification— This step involves identifying system hazards through as many means as possible. The primary method for identifying hazards is via HA, utilizing information from system hazard sources, checklists, experience, lessons learned, past mishaps, and so on. A major focus should be on SCFs. 

Utility systems can create many difficult-to-predict hazards because they connect many different sections of a process. Issues to do with utility-related hazards are discussed later. 

Utility systems such as water for injection (WFl). clean steam, clean-in-placc (CIP) solutions and sterile process air must be similarly proven. Also the building system itself has to be validated. Many bioprocess operations which contain potentially hazardous materials are operated in closely-controlled negative pressure enclosures with filtration of exhaust ventilating air. Sterile and particularly parenteral products arc processed in clean rooms which are maintained at positive pressure with filtered incoming air. Validation of building control systems and of personnel changing facilities and systems of work are necessary to meet CMP requirements. Manuals for formal test procedures are required to validate these activities. 

Several utility systems and networks are now outdated and lack proper seismic design and protection. For example, there are parts of the water and wastewater systems in several cities built more than a century ago. Hence, their material properties and strength are seriously affected from aging effects and are consequently more vulnerable and exposed to earthquake risk. Currently, most of urban infrastructures are not designed to sustain severe seismic hazard and complex systemic threats, and it is difficult to anticipate what may be the complex socioeconomic losses due to potential strong earthquakes. 

Eail-Safe Design features which provide for the maintenance of safe operating conditions in the event of a malfunction of control devices or an interruption of an energy source (e.g., direction of failure of a control valve on loss of signal). A system is fail-safe if failure of a component, signal, or utility that would create a hazard initiates an action that maintains the system in a safe condition. 

System designers often think dampers bloek airflow and are suitable to prevent baek drafts in idle towers. This is not the ease. Airfoil dampers simply hamper fan housing efficiency- they do not block airflow. Air Inlet Screens are always part of blow through, counterflow towers to protect people from rotating equipment. Some designs can be a hazard when accessible from the underside and require the specifier to call out additional screening. They can be a worthwhile accessory when there are nearby trees even when not required for safety reasons. Air inlet screens should be eliminated on towers utilizing inlet ductwork. Inlet ductwork may also make it necessary to block extraneous air entry such as from the underside when towers are elevated. 

The mere fact that voltage, current, or even both, are at low levels does not guarantee a circuit to be intrinsically safe, even though intrinsically safe circuits do utilize relatively low voltage and current levels. Intrinsically safe systems employ electrical barriers to assure that the system remains intrinsically safe. The barriers limit the voltage and current combinations so as not to present an ignition hazard should a malfunction develop. Typically, devices upstream of barriers are not intrinsically safe and are installed in control rooms or other unclassified locations. All devices and wiring on the downstream side of the barriers are intrinsically safe and can be installed in classified areas. 

Adequate water supplies for fire protection arc vital. Otlier utility services, such as electricity, must be reliable and well maintained during emergencies. Plants depending on outside electricity should liave two separate feeder circuits whenever possible, and possible failures of tlrese utilities should be evaluated before construction. When one system fails, tlie other system must provide suitable switching or shutdown to prevent serious hazards. 

A house is a complex system of interacting parts that contribute to overall performance including comfort, energy use, health, maintenance, and longevity. For example, a common air distribution system utilizes supply ducts running through the attic and return ducts tied directly to the air handler inside the home. If the ductwork is not properly sealed and there are combustion appliances in the home, this configuration can lead to health and fire hazards because the... 

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